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Hydrogeology of Wales: Quaternary aquifers - the Upper Lugg catchment

2015-07-28T20:06:53Z

Gareth Farr: replace EAw with NRW

{{HofW}}
The River Lugg flows from the hills to the north-west of Llangunllo, south-east to Presteigne and out of Powys towards Byton in Herefordshire. Gravel deposits floor the valley between Monaulty to the north-west and Byton in the east, below which the valley narrows sharply. The largest area of gravels lies in the broad, level valley floor to the east of Presteigne. The underlying bedrock rises steeply at the edges of the gravels. The bedrock geology is predominantly of Silurian age with isolated faulted inliers and outliers of Proterozoic and Devonian strata respectively.

The main aquifer in the Upper Lugg is the river gravel ([[Hydrogeology of Wales: References|'''ESI, 2006''']]). At Pilleth these are over 20 m thick and are highly transmissive (>1000 m2d-1). The gravels are overlain by 2 to 3 m of clay which has a low vertical permeability which allows a shallow, upper ‘perched’ groundwater system to develop in permeable cover above the clay. The water table in this shallow system is controlled by a combination of ditches and field drains in order to improve the quality of the land for agricultural purposes.

At Glan Llugwy Bridge (Monaulty) and the public supply abstraction boreholes at Pilleth [SO 260 678] the gravels are at least 23 m thick and none of the boreholes penetrate bedrock. The aquifer comprises loose, medium- to coarse-grained grey sand and fine to coarse gravel with occasional cobbles. Silt and clay horizons occur below 7 m depth. The gravels are overlain by a continuous 2 to 3.5 m-thick layer of silty, sandy clay (varying in colour between blue/grey and orange/brown). Drillers’ logs for the observation boreholes at Rock Bridge [SO 2914 6558] and Letchmoor Farm [SO 3455 6447] show that the gravels continue with a similar thickness downstream from Pilleth. The driller’s log for the Natural Resources Wales observation borehole at Evenjobb [SO 2615 6179] shows 10 m of drift overlying the Silurian Wenlock Formation; 8 m of which is 'clayey gravel'. Average annual rainfall is just over 1000 mm and effective precipitation is about 530 mm. Details of the licensed abstractions in the Upper Lugg are given in the '''Licensed abstractions table'''.

<center>
{| class="wikitable" width="750pt"
|+ Details of the licensed abstractions in the Upper Lugg (see '''Figure 4.2''' for locations of key abstractions).
|-
| Licence number
| NGR
| Annual quantity (m3)
| Daily quantity (m3)
| Surface (s) or groundwater (g)
| Use
|-
| 19/55/8/0030
| SO 316 644
| 41 596
| 114
| g
| Industrial services
|-
| 19/55/8/0030
| SO 316 644
| 72 377
| 198
| g
| Industrial services
|-
| 19/55/8/0134
| SO 170584
| 6636
| 188
| g
| General agriculture
|-
| 19/55/8/0142
| SO 238 633
| 2785
| 8
| g
| General agriculture
|-
| 19/55/8/0179
| SO 253 676
| 1 409 260
| 3819
| g
| Public water supply
|-
| 19/55/8/0046
| SO 192 624
| 141 426
| 386
| g or s
| Public water supply
|-
| 19/55/8/0125
| SO 363 641
| 414 823
| 1137
| g
| Public water supply
|-
| 19/55/8/0193
| SO 269 604
| 9092
| 318
| g or s
| Spray irrigation
|-
| 19/55/8/0210
| SO 225 628
| 7300
| 20
| g or s
| Water bottling
|-
|
|
| 2 105 295
| 6198
|
|
|}

The 19/55/8/0046 abstraction, a source for New Radnor, is currently unused (G. Hyett pers. comm.).
</center>

Dŵr Cymru has carried out a programme of testing at Pilleth ([[Hydrogeology of Wales: References|'''Celtic Water Management, 2005''']]). The specific capacity data indicate that the transmissivity of the aquifer is >1000 m2d-1. Dŵr Cymru monitors groundwater levels in ten observation boreholes. Eight of these boreholes are completed as multiple monitoring points with an upper and a lower screened section within the main gravel horizons. '''Figure P859282''' shows that groundwater levels at most of these sites do not generally fluctuate by more than 0.5 m. However, during periods of peak river flows, sharp increases in groundwater level occur, increasing the full range at most of the sites to around 1 to 1.5 m. The behaviour of the hydrographs reflects the nature of the environment of the gravel aquifer, i.e. a low permeability clay cover restricting local recharge and creating confined conditions, but with connection to the River Lugg at the margins of the aquifer allowing sudden changes in river stage to manifest themselves in the observed groundwater levels.
[[Image:P859282.jpg|thumb|center|500px|Groundwater levels monitored by Dŵr Cymru in the gravel aquifer near Pilleth (after ESI, 2006). P859282.]]

Natural Resources Wales monitors groundwater levels in the gravel aquifers in the Upper Lugg catchment at Glan Llugwy, Evenjobb and Rock Bridge. Hydrographs of the available data at these sites are shown on '''Figure P859283'''. Data from one of the Pilleth observation boreholes is shown for comparison. The Glan Llugwy and Rock Bridge hydrographs show fairly sharp responses to the onset of winter recharge. This reflects an unconfined aquifer in which recharge is relatively unimpeded and in which the one or two metres rise in the position of the water table causes a perceptible change in transmissivity (i.e. one or two metres is a significant proportion of the saturated thickness of the aquifer).
[[Image:P859283.jpg|thumb|center|500px|Groundwater levels in Environment Agency observation boreholes in the Upper Lugg catchment (after ESI, 2006). P859283.]]

Groundwater levels in the gravel aquifer in the vicinity of Pilleth are around 0.5 to 1 m below river stage and, this may contribute to losses in river flow in this reach. However, the gravel aquifer in this area is covered by a clay layer of at least 2 m thickness and a shallow ‘perched’ groundwater system is present above this that is discharging to surface water at the same time. There is a marsh downstream at Combe Moor just south of Byton which represents the main discharge area for groundwater from the gravels, just upstream of the point at which the gravels pinch out at Byton.

Dŵr Cymru was granted a licence to abstract up to 3.812 Mld-1 from four boreholes at Pilleth in 1974. The water is used to supply Presteigne (and a significant proportion of this will return to the river at Presteigne STW) and the remainder is exported from the catchment to Knighton.

The gravel aquifers of the Upper Lugg are discrete and it is likely that the hydrogeological setting in each subcatchment is subtly different. Available data only allow the conceptual model of the area around Pilleth Pumping Water Station to be described in detail ('''Figure P859284''').
[[Image:P859284.jpg|thumb|center|500px|Schematic conceptual model of the hydrogeology of the Upper Lugg catchment (after ESI, 2006). P859284.]]

The gravel aquifer is confined below this clay layer and shows the subdued response of groundwater levels to the onset of winter recharge. However, the aquifer is responsive to changes in stage in the River Lugg which indicates that the river, which is located at the edge of the valley floor at Pilleth, is likely to be in good hydraulic connection with the gravels.

The groundwater levels in the gravel aquifer are generally below the river stage in the vicinity of Pilleth – presumably as a consequence of groundwater abstraction and, as a result, the river leaks into the gravels. The peak cumulative loss is around 4 Mld-1 (most of this occurring as the river first crosses onto these gravels) although there is subsequently a gain of around 1.5 Mld-1 further downstream.

The contribution of the bedrock aquifer to the groundwater system in the gravels is uncertain. There is a perception that there is relatively little overland flow on the steep valley sides and this could indicate that much of the effective precipitation on the hills is recharged and subsequently enters the rivers via the gravels. However, the lack of overland flow could, to some extent, be a consequence of land drainage creating storage and intercepting flow.

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[Category:Hydrogeology of Wales| 029]]

Hydrogeology of Wales: Quaternary aquifers - the Upper Lugg catchment

2015-07-28T20:01:02Z

Gareth Farr:

{{HofW}}
The River Lugg flows from the hills to the north-west of Llangunllo, south-east to Presteigne and out of Powys towards Byton in Herefordshire. Gravel deposits floor the valley between Monaulty to the north-west and Byton in the east, below which the valley narrows sharply. The largest area of gravels lies in the broad, level valley floor to the east of Presteigne. The underlying bedrock rises steeply at the edges of the gravels. The bedrock geology is predominantly of Silurian age with isolated faulted inliers and outliers of Proterozoic and Devonian strata respectively.

The main aquifer in the Upper Lugg is the river gravel ([[Hydrogeology of Wales: References|'''ESI, 2006''']]). At Pilleth these are over 20 m thick and are highly transmissive (>1000 m2d-1). The gravels are overlain by 2 to 3 m of clay which has a low vertical permeability which allows a shallow, upper ‘perched’ groundwater system to develop in permeable cover above the clay. The water table in this shallow system is controlled by a combination of ditches and field drains in order to improve the quality of the land for agricultural purposes.

At Glan Llugwy Bridge (Monaulty) and the public supply abstraction boreholes at Pilleth [SO 260 678] the gravels are at least 23 m thick and none of the boreholes penetrate bedrock. The aquifer comprises loose, medium- to coarse-grained grey sand and fine to coarse gravel with occasional cobbles. Silt and clay horizons occur below 7 m depth. The gravels are overlain by a continuous 2 to 3.5 m-thick layer of silty, sandy clay (varying in colour between blue/grey and orange/brown). Drillers’ logs for the observation boreholes at Rock Bridge [SO 2914 6558] and Letchmoor Farm [SO 3455 6447] show that the gravels continue with a similar thickness downstream from Pilleth. The driller’s log for the Environment Agency Wales observation borehole at Evenjobb [SO 2615 6179] shows 10 m of drift overlying the Silurian Wenlock Formation; 8 m of which is 'clayey gravel'. Average annual rainfall is just over 1000 mm and effective precipitation is about 530 mm. Details of the licensed abstractions in the Upper Lugg are given in the '''Licensed abstractions table'''.

<center>
{| class="wikitable" width="750pt"
|+ Details of the licensed abstractions in the Upper Lugg (see '''Figure 4.2''' for locations of key abstractions).
|-
| Licence number
| NGR
| Annual quantity (m3)
| Daily quantity (m3)
| Surface (s) or groundwater (g)
| Use
|-
| 19/55/8/0030
| SO 316 644
| 41 596
| 114
| g
| Industrial services
|-
| 19/55/8/0030
| SO 316 644
| 72 377
| 198
| g
| Industrial services
|-
| 19/55/8/0134
| SO 170584
| 6636
| 188
| g
| General agriculture
|-
| 19/55/8/0142
| SO 238 633
| 2785
| 8
| g
| General agriculture
|-
| 19/55/8/0179
| SO 253 676
| 1 409 260
| 3819
| g
| Public water supply
|-
| 19/55/8/0046
| SO 192 624
| 141 426
| 386
| g or s
| Public water supply
|-
| 19/55/8/0125
| SO 363 641
| 414 823
| 1137
| g
| Public water supply
|-
| 19/55/8/0193
| SO 269 604
| 9092
| 318
| g or s
| Spray irrigation
|-
| 19/55/8/0210
| SO 225 628
| 7300
| 20
| g or s
| Water bottling
|-
|
|
| 2 105 295
| 6198
|
|
|}

The 19/55/8/0046 abstraction, a source for New Radnor, is currently unused (G. Hyett pers. comm.).
</center>

Dŵr Cymru has carried out a programme of testing at Pilleth ([[Hydrogeology of Wales: References|'''Celtic Water Management, 2005''']]). The specific capacity data indicate that the transmissivity of the aquifer is >1000 m2d-1. Dŵr Cymru monitors groundwater levels in ten observation boreholes. Eight of these boreholes are completed as multiple monitoring points with an upper and a lower screened section within the main gravel horizons. '''Figure P859282''' shows that groundwater levels at most of these sites do not generally fluctuate by more than 0.5 m. However, during periods of peak river flows, sharp increases in groundwater level occur, increasing the full range at most of the sites to around 1 to 1.5 m. The behaviour of the hydrographs reflects the nature of the environment of the gravel aquifer, i.e. a low permeability clay cover restricting local recharge and creating confined conditions, but with connection to the River Lugg at the margins of the aquifer allowing sudden changes in river stage to manifest themselves in the observed groundwater levels.
[[Image:P859282.jpg|thumb|center|500px|Groundwater levels monitored by Dŵr Cymru in the gravel aquifer near Pilleth (after ESI, 2006). P859282.]]

Natural Resources Wales monitors groundwater levels in the gravel aquifers in the Upper Lugg catchment at Glan Llugwy, Evenjobb and Rock Bridge. Hydrographs of the available data at these sites are shown on '''Figure P859283'''. Data from one of the Pilleth observation boreholes is shown for comparison. The Glan Llugwy and Rock Bridge hydrographs show fairly sharp responses to the onset of winter recharge. This reflects an unconfined aquifer in which recharge is relatively unimpeded and in which the one or two metres rise in the position of the water table causes a perceptible change in transmissivity (i.e. one or two metres is a significant proportion of the saturated thickness of the aquifer).
[[Image:P859283.jpg|thumb|center|500px|Groundwater levels in Environment Agency observation boreholes in the Upper Lugg catchment (after ESI, 2006). P859283.]]

Groundwater levels in the gravel aquifer in the vicinity of Pilleth are around 0.5 to 1 m below river stage and, this may contribute to losses in river flow in this reach. However, the gravel aquifer in this area is covered by a clay layer of at least 2 m thickness and a shallow ‘perched’ groundwater system is present above this that is discharging to surface water at the same time. There is a marsh downstream at Combe Moor just south of Byton which represents the main discharge area for groundwater from the gravels, just upstream of the point at which the gravels pinch out at Byton.

Dŵr Cymru was granted a licence to abstract up to 3.812 Mld-1 from four boreholes at Pilleth in 1974. The water is used to supply Presteigne (and a significant proportion of this will return to the river at Presteigne STW) and the remainder is exported from the catchment to Knighton.

The gravel aquifers of the Upper Lugg are discrete and it is likely that the hydrogeological setting in each subcatchment is subtly different. Available data only allow the conceptual model of the area around Pilleth Pumping Water Station to be described in detail ('''Figure P859284''').
[[Image:P859284.jpg|thumb|center|500px|Schematic conceptual model of the hydrogeology of the Upper Lugg catchment (after ESI, 2006). P859284.]]

The gravel aquifer is confined below this clay layer and shows the subdued response of groundwater levels to the onset of winter recharge. However, the aquifer is responsive to changes in stage in the River Lugg which indicates that the river, which is located at the edge of the valley floor at Pilleth, is likely to be in good hydraulic connection with the gravels.

The groundwater levels in the gravel aquifer are generally below the river stage in the vicinity of Pilleth – presumably as a consequence of groundwater abstraction and, as a result, the river leaks into the gravels. The peak cumulative loss is around 4 Mld-1 (most of this occurring as the river first crosses onto these gravels) although there is subsequently a gain of around 1.5 Mld-1 further downstream.

The contribution of the bedrock aquifer to the groundwater system in the gravels is uncertain. There is a perception that there is relatively little overland flow on the steep valley sides and this could indicate that much of the effective precipitation on the hills is recharged and subsequently enters the rivers via the gravels. However, the lack of overland flow could, to some extent, be a consequence of land drainage creating storage and intercepting flow.

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[Category:Hydrogeology of Wales| 029]]

Hydrogeology of Wales: Carboniferous aquifers - the Carboniferous Limestone aquifer

2015-07-28T19:58:39Z

Gareth Farr:

{{HofW}}
The physical hydrogeology of the Carboniferous Limestone in Wales was first described by [[Hydrogeology of Wales: References|'''Richards (1959)''']] and in south Wales was later summarised by [[Hydrogeology of Wales: References|'''Allen et al. (1997)''']], and north Wales by [[Hydrogeology of Wales: References|'''Morris et al. (2000)''']]. The Carboniferous Limestone aquifers, the Clwyd Limestone Group in north Wales and the Pembroke Limestone Group in south Wales are used for public and private supply. A number of individual studies have been carried out in recent years on various aspects of groundwater occurrence and protection, particularly in south Wales. In addition there are some notable reports on speleological investigations which provide insight into the hydraulics of the karst aquifer. However, understanding of the regional flow mechanisms is patchy although considerable detail is available on a site specific basis.

[[Image:P802429.jpg|thumb|300px|Karstic Avon Group strata at Mynydd Llangattog. P802429.]]

Postdepositional faulting and folding took place in the Variscan Orogeny, and in north Wales coincident ore and gangue mineralisation occurred along some discontinuities. Solution channels may have begun to form along fractures as early as the Mesozoic, but the wetter climes of the Pleistocene produced most of the swallow holes and caverns, some collapsed as at Gwernymynydd in Flintshire, with many later infilled with rubble and detritus in the late- and post-glacial periods. Rapid solution of the limestone ('''Plate P802429''') occurs mainly in the zone of active circulation which is in contact with the atmosphere, i.e. at the water table, or above the level of passages and caverns into which the phreatic water drains. Fossil karstic horizons, now submerged beneath the water table, may reflect past changes in base level (see box below: Development of Karst in the Carboniferous Limestone).

Speleogenesis is the origin and development of [http://en.wikipedia.org/wiki/Cave caves], the primary process that determines the evolution of karst features. The development of caves through [http://en.wikipedia.org/wiki/Limestone limestone] is caused by water circulation with [http://en.wikipedia.org/wiki/Carbon_dioxide carbon dioxide] dissolved within it, producing [http://en.wikipedia.org/wiki/Carbonic_acid carbonic acid] which permits the [http://en.wikipedia.org/wiki/Dissociation_%28chemistry%29 dissociation] of the [http://en.wikipedia.org/wiki/Calcium_carbonate calcium carbonate] in the limestone. Available CO2 in rainwater can enable up to 33 mg l-1 CaCO3 to be taken into solution, increasing to 250 mg l-1 wherever the rainwater has percolated through soil or peat to gain an enhanced CO2 content. [[Hydrogeology of Wales: References|'''Ball and Jones (1990)''']] argue that the solution of the limestone is inadequate to explain the tight stratigraphical positioning of solution tubes in the north crop, situated at the northern periphery of the coal field, and that shallow aerobic dissolution requires a bacterial catalyst to promote the reaction. That the purer oolitic horizons are generally left intact whereas the more impure sulphate-rich beds are the target of dissolution suggests a role for sulphur-loving bacteria, although mechanical attrition is also an important process in cave formation.

In addition, dolomitisation of some of the limestone in the periphery of the South Wales Coalfield effects a reduction in overall volume and the creation of vugs and fractures. Although these may be calcite or silica infilled they generally lead to an overall increase in permeability ([[Hydrogeology of Wales: References|'''Thomas et al., 1983''']]).

=== North Wales ===

In Anglesey the Clwyd Limestone Group aquifer is located in limestones that were deposited in faulted basins and have been extensively dolomitised and silicified. Flow occurs through open joints and karstic zones although mudstone horizons have inhibited the downward percolation of acidic rainwater and karstification is better developed elsewhere in north Wales. Transmissivities from test pumping at four sites reported values from 0.15 to 1.8 m2 d-1 with yields of about 1 l s-1.

The Clwyd Limestone Group in north Wales crops out to the north of the Vale of Clwyd and in a narrow strip south towards Wrexham, and south of the Vale of Clwyd towards Colwyn Bay and Great Ormes Head, Llandudno ('''Figure P859272'''). There are basal units of grey and brown limestone and an upper unit of sandy limestone, but the majority of the sequence (c. 500 m thick) comprises white limestone. The limestone has been subject to brittle fracture and enlargement of secondary features by karstic dissolution. The limestone has a low intergranular permeability but substantial groundwater flow is possible through enlarged fissures. In the Clwyd catchment the limestone crops out without significant till cover and acts as a valuable indirect recharge source to the Triassic sandstones in the Clwyd basin, particularly in the area to the south of Ruthin (see [[Hydrogeology of Wales: Permo-Triassic and Jurassic aquifers | Permo-Triassic and Jurassic aquifers]]).
[[Image:P859272.jpg|thumb|center|550px|The distribution of Carboniferous strata in North Wales. P859272.]]

Groundwater flows through the limestone in the Clwyd catchment via fractures and available karst features in a north-easterly direction to discharge to the sea. Swallow holes are common in the main Clwyd Limestone Group outcrop to the east of the Vale of Clwyd. Ffynnon Asaph [SJ 0752 7893] which flows at 4.3 Ml d-1 traditionally supplied the town of Prestatyn. Local metal mining in the limestone has exposed a number of cave and conduit systems, some of which have had a direct effect on mine dewatering.

In the Halkyn Mountain area, around Caerwys, between Cilcain and Llanferres and in the Gwernymynydd district, fossil swallow holes containing sands, clays and weathered cherts have been exposed during mining.

Other surface waters with low flows subject to loss into the limestone include the Afon Clywedog, a tributary of the Dee to the west of Wrexham, and the Afon Alyn which is dry on average for 170 days per year between Loggerheads and Rhydymwyn some 4 km above Mold ([[Hydrogeology of Wales: References|'''National Rivers Authority, 1993''']]). The Afon Alyn otherwise often disappears into a swallow hole north of Plas-yr-esgob [SJ 188 644] and re-emerges into the dry river bed just above the confluence with the Cilcain stream [SJ 187 652], below which it can be intermittently dry as far as Hesp Alyn [SJ 188 653]. The Ogof Hesp Alyn cave system has only been discovered in recent years ([[Hydrogeology of Wales: References|'''Appleton, 1974''']]) and its description illustrates the complex processes of capture, solution and attrition that combine to create such underground features. The Afon Alyn water loss is not a new phenomenon, and legend has it that a giant, when set on fire by St Cynhafal, jumped into the river to extinguish the flames whereupon the river, which was turned to steam, ceased to flow, and has only flowed intermittently ever since.

Caverns also occur west of the Vale of Clwyd at Cefn and Plas Henton and to the east at Ffynnon Beuno and Bae Gwyn. The elevation of these cave systems relative to today’s base level suggests that they all originated in the Pleistocene when sea level was about 15 m higher than it is today.

Attempts to prevent water from the River Alyn from entering the Halkyn Mine via swallow holes during the 1930s were largely unsuccessful ([[Hydrogeology of Wales: References|'''Water Resources Board, 1973''']]). A number of drainage schemes were implemented to protect the mines and their drainage used to supply industry:

:* the Halkyn Tunnel, 8 km in length across Halkyn Mountain
:* Government (War) Drainage Scheme – pumping from Taylor’s Shaft, North Hendre at 300 l s-1 into the Halkyn Tunnel
:* Milwr Sea Tunnel which was designed to lower the water table in the limestone across the Halkyn Mountain area. The minimum yield is about 55 000 m3 d-1 representing run-off from the surrounding hills onto the limestone as well as lost river water.

Borehole yields are highly variable and unpredictable, with good supplies only obtained if water-filled fractures with access to recharge are intersected. For example, a borehole drilled in Anglesey into a mixed sedimentary sequence in Carboniferous strata at Llanbedrgoch [SH 493 803] to a depth of 65 m yielded only 2.5 l s-1 over a two-hour pumping day. Two previous drilling attempts in the same vicinity at Llanbedgroch, however, had failed to find any trace of water. [[Hydrogeology of Wales: References|'''Robins and McKenzie (2005)''']] showed that the density of occurrence of wells on Anglesey in the Clwyd Limestone Group was 1.3 km-2 and of springs was 1.6 km-2. Yields are typically small with many springs being little more than minor seepages.

Groundwater chemistry on Anglesey is consistently of the Ca-HCO3 type, with a small subset tending towards Na, Mg and Cl dominance. The groundwater is oxic (Eh >127 mV) has near neutral pH, Ca ranging from 60 to 130 mg l-1 and NO3 typically < 25 mg l-1 ([[Hydrogeology of Wales: References|'''Banks et al., 2008''']]).

=== South Wales ===

In Carmarthenshire, the basal Avon Group, with thin shaly and muddy limestones, are overlain by karstic massive crystalline, fossiliferous to dolomitised limestones up to 100 to 150 m thick. These are overlain by the Oystermouth Formation (formerly the Upper Limestone Shales). The limestone has a low primary porosity. Transmissivity is between 10 and 20 m2 d-1 and storage coefficients of between 4 and 9 x 10-4 have been obtained from a small number of borehole pumping tests. Boreholes at Trapp yield 144 m3 d-1 to 240 m3 d-1. The source of the Loughor, located on a faulted contact of limestone and Marros Group grits, flows at 60 to 1000 l s-1 with a connection to caves 7 km away.

The Pembroke Limestone Group outcrop is thin both north and east of the coalfield, and to the south of the coalfield it has been eroded into a broad platform in the Vale of Glamorgan, the Gower and parts of Pembrokeshire. The strata are characterised by a basal shaly mudstone, followed by thick massive dolomitic, oolitic and bioclastic limestones and an upper mixed sequence of shale and muddy limestone. Chert may be abundant within the main limestone. In Pembrokeshire, the Pembroke Limestone Group aquifer discharges into the Bosherton ponds via spring systems at Frainslake and Bosherton. Groundwater is abstracted at Pendine for use in public supply.

Various attempts have been made to establish the water balance over all or part of the limestone outcrops. Work by [[Hydrogeology of Wales: References|'''Aspinwall and Co (1993)''']] focussed on the Vale of Glamorgan and the capture zones of the Schwyll Spring [SS 888 771] and the Pwllwy Borehole and springs [SS 992 766] noting that the water balance calculations showed that a large part of the recharge could not be accounted for and was presumably lost as offshore submarine springs. Schwyll and Pwllwy near Bridgend are believed respectively to derive from a variety of sinks on the rivers Ogmore, Ewenny, Alun and Methyr Mawr up to 7 km away ([[Hydrogeology of Wales: References|'''Hobbs, 2000''']]), whereas the Pwllwy has a more local catchment. Although rarely used for public supply, Welsh Water retains an abstraction license for 7.955 Mm3 a-1 from the Schwyll Spring sources, although they are not currently in use and [[Hydrogeology of Wales: References|'''Hobbs (1993)''']] estimated the total yield of the spring at 12.3 Mm3 a-1 derived partly from influent rivers, the Ogmore and to a lesser extent the Ewenny, and partly from groundwater. These springs periodically had to be disconnected from supply during very wet weather when the outflow became turbid. The springs can also suffer from reversed hydraulic head during periods of exceptional high spring tides when dirty surface water can ingress some of the spring heads. [[Hydrogeology of Wales: References|'''Aldous (1988a)''']] used detailed site specific knowledge to attempt to delineate flowpaths and likely transport fields for contaminant movement in the aquifer. [[Hydrogeology of Wales: References|'''Hobbs (1993)''']] identified a number of sinks and risings in the area:

:: Merthyr Mawr sinks [SS 8901 7763] on the western bank of the Ogmore river and rise at two springs which flow into the Merthyr Mawr Mill Leat [SS 88657763]

:: Pitcot Pool [SS 8955 7443] is spring fed

:: Jacobs Well [SS 9121 7480] a series of springs alongside the Afon Alun

:: Byeastwood Springs [SS 9298 8099 and SS 9258 8060] flow eventually into the River Ewenny

:: Hoel-las stream sink [SS 9288 8267], now concealed beneath the M4 motorway, and smaller sinks to the east take water draining off the Coal Measures

:: Tymaen sink [SS 8943 7705]

:: Ewenny Fach sink [SS 9542 7990] a sink in the bed of the River Ewenny

[[Image:P802428.jpg|thumb|200px|One of many springs flowing from boggy ground at the junction of the basal Namurian grit and the underlying Avon Group near Trefil, north of Tredegar . P802428.]]
In the area of the Schwyll Spring and Pwllwy Borehole and springs the Pembroke Limestone Group is over 500 m thick comprising a southward thickening alternating bioclastic and oolitic limestone 700 to 800 m thick. This is underlain by the basal Avon Group shales which are about 100 m thick. Aquifer transmissivities range between 4 and 130 m2 d-1, and hydraulic conductivity range between 0.1 and 5 m d-1. The effective porosity of the upper 8 to 10 m of the aquifer ranges between 6 and 8 per cent, reducing to 0.5-2 per cent below this. Among other sources, boreholes drawing from the concealed Pembroke Limestone Group at Bridgend contribute to public supply.

Near Llandybie at Pant-y-Llyn on the north-western limb of the coalfield is a small turlough, the only known active turlough in Wales. Pant-y-Llyn [SN 60167] is a small depression in the limestone which fills with water rising from the Pembroke Limestone Group along its faulted boundary with the Devonian Brownstones, usually in the autumn, and drains to estavelles in the late spring ([[Hydrogeology of Wales: References|'''Campbell et al., 1992)''']]. In flood it is some 160 by 60 m in area and up to 4 m deep.

Swallow holes are common over much of the limestone outcrop and also occur beneath a thin cover of the basal beds of the Marros Group grits. Particularly large examples with collapsed caverns occur at Mynydd y Glog north of Hirwaun, whereas linear developments of swallow holes occur along lines of weakness at Ystradfellte and east of Trefil. Numerous examples are present on the Twrch Sandstone Formation (formerly the Basal Grit) on the Llangattwg and Llangynidir mountains, some blocked by fine detritus to form small ponds such as Pwll Mawr which is situated on the interfluve between the Neath and the Tawe valleys.

There are numerous closely spaced swallow holes on the north crop, some of which are nothing more than open fractures. There are some 80 000 dolines on the north crop alone ([[Hydrogeology of Wales: References|'''Crowther, 1989''']]), and collectively these provide drainage to the limestone outcrop. The swallow water tends to flow southwards down dip and beneath the cover of the Bishopton Mudstone Formation. In wet conditions it rises up through the shale to emerge above Blaen-Rhymney, and much like a Chalk bourne, creates river flow where normally the bed is dry. A similar, but less ephemeral discharge near Blaen-Sirhowy was once used for public supply. There are also a few springs on the northern scarp slope. In addition there are a number of caverns beneath the north crop especially around the headwaters of the rivers Tawe and Neath.

Some caves reflect past sea levels; Little Hoyle and Hoyle’s Mouth near Tenby are about 15 m above sea level reflecting the Pleistocene sea level. The Bacon, Minchin and Paviland caves in Gower were also formed during the Pleistocene when the sea level was elevated relative to the present level.

There are numerous examples of sinks and risings (see '''Active karst systems table '''and '''Plate P802428'''). The headwaters of the Neath, including the Hepste, Mellte and Nedd-Fechan all come off the Devonian sandstone and disappear into sinks in the limestone. At the head of the Swansea valley the Llynfell flows out of the Dan-yr-Ogof cave whilst nearby the River Giedd disappears into a swallow hole. There are show caves in the Tawe Valley at the mouth of the Dan Yr Ogof cave system. The caves drain the Sink y Giedd [SN 810 179] and Waun Fignen-felen [SN 826 177] with a combined discharge of between 0.15 and 0.30 m3 s-1 depending on weather conditions ([[Hydrogeology of Wales: References|'''Coase and Judson, 1977''']]). Average flow rates of 0.14 and 0.13 km hr-1 respectively have been demonstrated with dye testing (see '''dye tests table '''). A number of dolines (e.g. the ‘Crater’) and other hollows overlie the cave system, but the remnant dry valleys occasionally flow during exceptionally wet weather.

<center>
{| class="wikitable"
|+ Selected active karst systems within the north crop (from east to west), see [[Hydrogeology of Wales: References|'''Gascoine (1989''']]).
|-
| Area
| Grid Square
| Comments
|-
| Afon Lwyd
| SO 20
| A series of sinks and caves leading to four resurgences. Pontnewynydd Risings typically issue at 6 Ml d-1.
|-
| Llangattwg
| SO 21
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Mynydd Llangynidr
| SO 21
| The main resurgence is Fynnon Shon Sheffrey [SO 1265 1188]. Dye tracing has proved the relationship between various sinks and risings ('''Figure 5.2''').
|-
| The Rhymney Valley
| SO 01
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Taff Fechan and Taff Fawr
| SO 01
| Includes Nant y Glais caves and resurgences, otherwise connections proven by dye tracing.
|-
| Cwm Cadlan and Penderyn
| SN 90
| Llygad Cynon is source of the Afon Cynon. An adjacent borehole [SN 9524 0774] reported an ‘underground lake’ at 55 m and is pumped at 5 Ml d‑1.
|-
| Afon Hepste
| SN 90
| Upper Hepste Main Sink [SN 9541 1208] discharges back to the river at Hepste Main Resurgence [SN 9360 0973] in under 24 hours.
|-
| Afon Mellte
| SN 91
| The main Mellte Sink [SN 9315 1332] has proven connections to five resurgences. Contributions also from smaller sinks.
|-
| Nedd Fechan
| SN 91
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Glyntawe and the Black Mountain
| SN 81
| Two main cave systems behind main resurgences at Glyntawe
|-
| The Twrch valley
| SN 71
| Fault-controlled resurgences.
|-
| Black Mountain – western area
| SN 61
| 7 km from main sink to resurgence proven by dye tracing.
|}
</center> <center>
{| class="wikitable"
|+ Relationship between dye tests from Waun Fignen-felen and Sink y Giedd, after [[Hydrogeology of Wales: References|'''Coase and Judson (1977)''']].
|-
|
| From Waen Fignen Felen
| From Sink y Giedd
|-
| Distance from sink to resurgence (km)
| 3.5
| 4.7
|-
| Time for dye to reach resurgence (hours)
| 25
| 36
|-
| Average flow rate (km hour-1)
| 0.14
| 0.13
|-
| Elevation of sink above resurgence (m)
| 248
| 218
|}
</center>

Other celebrated groups of caves include the Nant y Glais caves to the south of the Vaynor Moors on the north crop: Ogof Robin Goch [SO 0392 1076], Ogof y Ci [SO 0403 1051], Ogof Dŵr Dwfn [SO 0415 1022], Ogof Rhyd Sych [SO 0416 1021], Ogof Pysgodyn Gwyn [SO 0416 1016] and Ogof Jonny Bach [SO 0420 1000]. The Nant y Glais river disappears underground altogether as it traverses the cave system except in exceptionally wet weather when flow also occurs through a narrow gorge at surface ([[Hydrogeology of Wales: References|'''Ford, 1989''']]).

[[Hydrogeology of Wales: References|'''Gascoine (1989''']]) reviewed other cave systems within the north crop. Many of the sinks are situated at the feather edge of the Marros Group where it is only a few metres thick above the limestone ('''Figure P859273'''), whilst others provide connections from the Avon Group shales and the main limestone. One of the longer and more complex cave systems is Ogof Draenen [SO 2467 1176] at the eastern edge of the north crop. Numerous dolines and stream sinks are present in the area and speleological investigation recognises numerous underfit streams in large passages. [[Hydrogeology of Wales: References|'''Maurice and Guilford (2011)''']] have identified a watershed within the system whereby flow occurs both to the north to Clydach Gorge and to the south to the Afon Lwyd. The latter is in a different topographical catchment some 8 km distant and tracer testing indicates velocities of 4 km d-1.
[[Image:P859273.jpg|thumb|center|600px|Sketch map of the Pembroke Limestone group outcrop along the North Crop (after Gasgoine, 1989). P859273.]]

A wide range of borehole yields have been established depending on the hydraulic contact with productive fractures. Drilling is always speculative as targeting useful fractures is not easy. The average yield from Carboniferous Limestone Supergroup boreholes across the UK was shown by [[Hydrogeology of Wales: References|'''Monkhouse (1977)''']] to be just 4 l s-1, but there is no record of the numbers of boreholes that were abandoned as dry, while other boreholes may have a significantly higher yield.

Although fractures and karstification rapidly decreases under the cover of the Marros Group there is some evidence of deep groundwater circulation beneath the coalfield. Taff’s Well [ST 1193 8364] discharges groundwater at about 1 l s-1 from the South Wales Coal Measures Group with a temperature of 21.6 oC, the only thermal spring in Wales ([[Hydrogeology of Wales: References|'''Farr and Bottrell, 2013''']] . Previous measurements reported a variety of temperatures all less than 20 oC but these were subject to mixing with water from the River Taff which is now prevented by new flood works. Simple inspection of the geothermal gradient and of the discharge water chemistry suggests a deep flow path, probably in the Pembroke Limestone Group, which is believed to travel to a depth of about 700 m ([[Hydrogeology of Wales: References|'''Squirrell and Downing, 1969'''; '''Thomas et al., 1983''']]). Dissolved inert gas analysis indicates that the water infiltrated the ground some 500 m higher in elevation than Taff’s Well, suggesting a recharge source somewhere along the north crop ([[Hydrogeology of Wales: References|'''Burgess et al., 1980''']]; [[Hydrogeology of Wales: References|'''Edmunds, 1986''']]). The water is between 5000 and 10 000 years old based on δ18O and δ2H age indicators ([[Hydrogeology of Wales: References|'''Farr and Bottrell, 2013''']]).

A major spring was encountered in the concealed limestone in 1879 during the excavation of the Severn Railway Tunnel. Here a spring discharge of 1000 l s-1 was encountered, the Great Spring, which has been pumped to surface ever since ([[Hydrogeology of Wales: References|'''Drew et al., 1970''']]). Of good quality, it has been used for a variety of purposes including supply to a paper mill and brewery however its only current use is for public supply.

Water quality in the limestone is typified by slightly alkaline pH up to 7.6, and alkalinity concentrations (as CaCO3) ranging upwards to 230 mg l-1. The lower values reflect immature waters that have not attained Ca saturation. In north Wales, local mineralisation in the limestones promotes the solution of metals but at barely detectable concentrations. There are distinct tidal influences on some low-lying coastal areas of south Wales (including the Schwyll Spring) and a marine mixing zone in selected fractures is indicated by enhanced concentrations of Na and Cl at some sources.

A number of detailed site-specific investigations have been carried out on the limestone aquifer in south Wales which provide insight into its hydraulic processes. One such study was carried out between Porthcawl and Port Talbot looking at the environmental impact of extending local quarries in the Pembroke Limestone Group on a wetland area within adjacent superficial deposits ([[Hydrogeology of Wales: References|'''Cheney et al., 2000''']]). This work drew on extensive monitoring and analysis carried out previously in the area but was unable to develop a robust groundwater flow model due to data scarcity and the complex nature of flow in a karstic system. In addition 95 per cent of the water balance was unaccountable, suspected to drain to submarine springs in the Bristol Channel.

Groundwater is typically of the Ca-HCO3 type, with HCO3 typically in the range 90 to 550 mg l-1, the weakest mineralisation occurring along the north crop. The pH is almost always alkaline with values up to 8.2. Cl concentrations are generally low (<50 mg l-1) except on the coast near Porthcawl at Rest Bay where some private sources suffer from saline intrusion ([[Hydrogeology of Wales: References|'''Jones, 2007''']]) and in parts of the Gower Peninsula where sea spray may be the cause of elevated Na and Cl concentrations. The same pattern emerges in Pembrokeshire where Ca-HCO3 type is dominant with subordinate Na/Mg-Cl type but here it is possibly caused by ion exchange in waters that are older than in the limestone around the South Wales Coalfield ([[Hydrogeology of Wales: References|'''Fahrner et al., 2008''']]).

{| cellspacing="0" cellpadding="5" border="1"
| <center>'''Development of Karst in the Avon Group'''</center>

The development of the karst features found today in the Avon Group in south Wales reflects a continuing process which commenced almost as soon as the rocks were laid down. The most active zone of karstification is the vadose zone where unsaturated water can move freely through bedding planes and other discontinuities, but the phreatic zone may also be active when groundwater chemistry changes due to long-term effects of mixing. There were three intensive phases of karstic development: the Lower Carboniferous, the late Triassic and the Palaeogene through to the Quaternary.

The Lower Carboniferous palaeokarstic surfaces developed as the limestone initially rose out of the sea. Clay and mudstone beds, representing fossil soils, overlie the hummocky erosion surface, with discrete fissures in the limestone infilled with the soil material below. This is characteristic of both south Wales ([[Hydrogeology of Wales: References|'''Wilson et al., 1990''']]) and north Wales ([[Hydrogeology of Wales: References|'''Davies, 1991''']]) where relief varies between only a few centimetres to a few metres.

Uplift during the late Carboniferous Variscan Orogeny initiated a protracted period of erosion which lasted through to the Jurassic Period. By Late Triassic times a network of fissures and caverns had been created, some of which had already been partly infilled with rubble and clay. Mineralised hydrothermal waters may have added to the process leading to the deposition of galena and barites on fissure walls. [[Hydrogeology of Wales: References|'''Wilson et al. (1990)''']] recognised three types of karst feature in south Wales: dilated joints, irregular shaped cavities developed along bedding plains, and subvertical cylindrical pipes.

During the Palaeogene and Quaternary periods, large periodic fluctuations in sea level caused fluctuations also in the location of the vadose zone, and new and some pre-existing conduit features were developed, many now below the present-day water table. Three types of feature were created: dolines (collapsed caverns), linear fissures and large cavities. These features are commonly backfilled with silt and rubble debris. [[Hydrogeology of Wales: References|'''Gunn (1992)''']] asserted that the larger features could only develop where they were fed by a river or stream sink, and the Dan yr Ogof system was once fed by the River Haffes which has since been captured and redirected.

Reactivation of karst conduit systems has been recorded at a number of sites. At Stormy Down Quarry [SS 845 800] discharging into a doline reactivated the karst system such that extensive remedial action was required in the vicinity during the construction of the M4 motorway ([[Hydrogeology of Wales: References|'''Aldous, 1988b''']]).
|}

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[Category:Hydrogeology of Wales| 017]]

Hydrogeology of Wales: Carboniferous aquifers - the Carboniferous Limestone aquifer

2015-07-28T19:57:03Z

Gareth Farr: remove margam steel works from Severn Tunnel supply as incorrect.

{{HofW}}
The physical hydrogeology of the Carboniferous Limestone in Wales was first described by [[Hydrogeology of Wales: References|'''Richards (1959)''']] and in south Wales was later summarised by [[Hydrogeology of Wales: References|'''Allen et al. (1997)''']], and north Wales by [[Hydrogeology of Wales: References|'''Morris et al. (2000)''']]. The Carboniferous Limestone aquifers, the Clwyd Limestone Group in north Wales and the Pembroke Limestone Group in south Wales are used for public and private supply. A number of individual studies have been carried out in recent years on various aspects of groundwater occurrence and protection, particularly in south Wales. In addition there are some notable reports on speleological investigations which provide insight into the hydraulics of the karst aquifer. However, understanding of the regional flow mechanisms is patchy although considerable detail is available on a site specific basis.

[[Image:P802429.jpg|thumb|300px|Karstic Avon Group strata at Mynydd Llangattog. P802429.]]

Postdepositional faulting and folding took place in the Variscan Orogeny, and in north Wales coincident ore and gangue mineralisation occurred along some discontinuities. Solution channels may have begun to form along fractures as early as the Mesozoic, but the wetter climes of the Pleistocene produced most of the swallow holes and caverns, some collapsed as at Gwernymynydd in Flintshire, with many later infilled with rubble and detritus in the late- and post-glacial periods. Rapid solution of the limestone ('''Plate P802429''') occurs mainly in the zone of active circulation which is in contact with the atmosphere, i.e. at the water table, or above the level of passages and caverns into which the phreatic water drains. Fossil karstic horizons, now submerged beneath the water table, may reflect past changes in base level (see box below: Development of Karst in the Carboniferous Limestone).

Speleogenesis is the origin and development of [http://en.wikipedia.org/wiki/Cave caves], the primary process that determines the evolution of karst features. The development of caves through [http://en.wikipedia.org/wiki/Limestone limestone] is caused by water circulation with [http://en.wikipedia.org/wiki/Carbon_dioxide carbon dioxide] dissolved within it, producing [http://en.wikipedia.org/wiki/Carbonic_acid carbonic acid] which permits the [http://en.wikipedia.org/wiki/Dissociation_%28chemistry%29 dissociation] of the [http://en.wikipedia.org/wiki/Calcium_carbonate calcium carbonate] in the limestone. Available CO2 in rainwater can enable up to 33 mg l-1 CaCO3 to be taken into solution, increasing to 250 mg l-1 wherever the rainwater has percolated through soil or peat to gain an enhanced CO2 content. [[Hydrogeology of Wales: References|'''Ball and Jones (1990)''']] argue that the solution of the limestone is inadequate to explain the tight stratigraphical positioning of solution tubes in the north crop, situated at the northern periphery of the coal field, and that shallow aerobic dissolution requires a bacterial catalyst to promote the reaction. That the purer oolitic horizons are generally left intact whereas the more impure sulphate-rich beds are the target of dissolution suggests a role for sulphur-loving bacteria, although mechanical attrition is also an important process in cave formation.

In addition, dolomitisation of some of the limestone in the periphery of the South Wales Coalfield effects a reduction in overall volume and the creation of vugs and fractures. Although these may be calcite or silica infilled they generally lead to an overall increase in permeability ([[Hydrogeology of Wales: References|'''Thomas et al., 1983''']]).

=== North Wales ===

In Anglesey the Clwyd Limestone Group aquifer is located in limestones that were deposited in faulted basins and have been extensively dolomitised and silicified. Flow occurs through open joints and karstic zones although mudstone horizons have inhibited the downward percolation of acidic rainwater and karstification is better developed elsewhere in north Wales. Transmissivities from test pumping at four sites reported values from 0.15 to 1.8 m2 d-1 with yields of about 1 l s-1.

The Clwyd Limestone Group in north Wales crops out to the north of the Vale of Clwyd and in a narrow strip south towards Wrexham, and south of the Vale of Clwyd towards Colwyn Bay and Great Ormes Head, Llandudno ('''Figure P859272'''). There are basal units of grey and brown limestone and an upper unit of sandy limestone, but the majority of the sequence (c. 500 m thick) comprises white limestone. The limestone has been subject to brittle fracture and enlargement of secondary features by karstic dissolution. The limestone has a low intergranular permeability but substantial groundwater flow is possible through enlarged fissures. In the Clwyd catchment the limestone crops out without significant till cover and acts as a valuable indirect recharge source to the Triassic sandstones in the Clwyd basin, particularly in the area to the south of Ruthin (see [[Hydrogeology of Wales: Permo-Triassic and Jurassic aquifers | Permo-Triassic and Jurassic aquifers]]).
[[Image:P859272.jpg|thumb|center|550px|The distribution of Carboniferous strata in North Wales. P859272.]]

Groundwater flows through the limestone in the Clwyd catchment via fractures and available karst features in a north-easterly direction to discharge to the sea. Swallow holes are common in the main Clwyd Limestone Group outcrop to the east of the Vale of Clwyd. Ffynnon Asaph [SJ 0752 7893] which flows at 4.3 Ml d-1 traditionally supplied the town of Prestatyn. Local metal mining in the limestone has exposed a number of cave and conduit systems, some of which have had a direct effect on mine dewatering.

In the Halkyn Mountain area, around Caerwys, between Cilcain and Llanferres and in the Gwernymynydd district, fossil swallow holes containing sands, clays and weathered cherts have been exposed during mining.

Other surface waters with low flows subject to loss into the limestone include the Afon Clywedog, a tributary of the Dee to the west of Wrexham, and the Afon Alyn which is dry on average for 170 days per year between Loggerheads and Rhydymwyn some 4 km above Mold ([[Hydrogeology of Wales: References|'''National Rivers Authority, 1993''']]). The Afon Alyn otherwise often disappears into a swallow hole north of Plas-yr-esgob [SJ 188 644] and re-emerges into the dry river bed just above the confluence with the Cilcain stream [SJ 187 652], below which it can be intermittently dry as far as Hesp Alyn [SJ 188 653]. The Ogof Hesp Alyn cave system has only been discovered in recent years ([[Hydrogeology of Wales: References|'''Appleton, 1974''']]) and its description illustrates the complex processes of capture, solution and attrition that combine to create such underground features. The Afon Alyn water loss is not a new phenomenon, and legend has it that a giant, when set on fire by St Cynhafal, jumped into the river to extinguish the flames whereupon the river, which was turned to steam, ceased to flow, and has only flowed intermittently ever since.

Caverns also occur west of the Vale of Clwyd at Cefn and Plas Henton and to the east at Ffynnon Beuno and Bae Gwyn. The elevation of these cave systems relative to today’s base level suggests that they all originated in the Pleistocene when sea level was about 15 m higher than it is today.

Attempts to prevent water from the River Alyn from entering the Halkyn Mine via swallow holes during the 1930s were largely unsuccessful ([[Hydrogeology of Wales: References|'''Water Resources Board, 1973''']]). A number of drainage schemes were implemented to protect the mines and their drainage used to supply industry:

:* the Halkyn Tunnel, 8 km in length across Halkyn Mountain
:* Government (War) Drainage Scheme – pumping from Taylor’s Shaft, North Hendre at 300 l s-1 into the Halkyn Tunnel
:* Milwr Sea Tunnel which was designed to lower the water table in the limestone across the Halkyn Mountain area. The minimum yield is about 55 000 m3 d-1 representing run-off from the surrounding hills onto the limestone as well as lost river water.

Borehole yields are highly variable and unpredictable, with good supplies only obtained if water-filled fractures with access to recharge are intersected. For example, a borehole drilled in Anglesey into a mixed sedimentary sequence in Carboniferous strata at Llanbedrgoch [SH 493 803] to a depth of 65 m yielded only 2.5 l s-1 over a two-hour pumping day. Two previous drilling attempts in the same vicinity at Llanbedgroch, however, had failed to find any trace of water. [[Hydrogeology of Wales: References|'''Robins and McKenzie (2005)''']] showed that the density of occurrence of wells on Anglesey in the Clwyd Limestone Group was 1.3 km-2 and of springs was 1.6 km-2. Yields are typically small with many springs being little more than minor seepages.

Groundwater chemistry on Anglesey is consistently of the Ca-HCO3 type, with a small subset tending towards Na, Mg and Cl dominance. The groundwater is oxic (Eh >127 mV) has near neutral pH, Ca ranging from 60 to 130 mg l-1 and NO3 typically < 25 mg l-1 ([[Hydrogeology of Wales: References|'''Banks et al., 2008''']]).

=== South Wales ===

In Carmarthenshire, the basal Avon Group, with thin shaly and muddy limestones, are overlain by karstic massive crystalline, fossiliferous to dolomitised limestones up to 100 to 150 m thick. These are overlain by the Oystermouth Formation (formerly the Upper Limestone Shales). The limestone has a low primary porosity. Transmissivity is between 10 and 20 m2 d-1 and storage coefficients of between 4 and 9 x 10-4 have been obtained from a small number of borehole pumping tests. Boreholes at Trapp yield 144 m3 d-1 to 240 m3 d-1. The source of the Loughor, located on a faulted contact of limestone and Marros Group grits, flows at 60 to 1000 l s-1 with a connection to caves 7 km away.

The Pembroke Limestone Group outcrop is thin both north and east of the coalfield, and to the south of the coalfield it has been eroded into a broad platform in the Vale of Glamorgan, the Gower and parts of Pembrokeshire. The strata are characterised by a basal shaly mudstone, followed by thick massive dolomitic, oolitic and bioclastic limestones and an upper mixed sequence of shale and muddy limestone. Chert may be abundant within the main limestone. In Pembrokeshire, the Pembroke Limestone Group aquifer discharges into the Bosherton ponds via spring systems at Frainslake and Bosherton. Groundwater is abstracted at Pendine for use in public supply.

Various attempts have been made to establish the water balance over all or part of the limestone outcrops. Work by [[Hydrogeology of Wales: References|'''Aspinwall and Co (1993)''']] focussed on the Vale of Glamorgan and the capture zones of the Schwyll Spring [SS 888 771] and the Pwllwy Borehole and springs [SS 992 766] noting that the water balance calculations showed that a large part of the recharge could not be accounted for and was presumably lost as offshore submarine springs. Schwyll and Pwllwy near Bridgend are believed respectively to derive from a variety of sinks on the rivers Ogmore, Ewenny, Alun and Methyr Mawr up to 7 km away ([[Hydrogeology of Wales: References|'''Hobbs, 2000''']]), whereas the Pwllwy has a more local catchment. Although rarely used for public supply, Welsh Water retains an abstraction license for 7.955 Mm3 a-1 from the Schwyll Spring sources, although they are not currently in use and [[Hydrogeology of Wales: References|'''Hobbs (1993)''']] estimated the total yield of the spring at 12.3 Mm3 a-1 derived partly from influent rivers, the Ogmore and to a lesser extent the Ewenny, and partly from groundwater. These springs periodically had to be disconnected from supply during very wet weather when the outflow became turbid. The springs can also suffer from reversed hydraulic head during periods of exceptional high spring tides when dirty surface water can ingress some of the spring heads. [[Hydrogeology of Wales: References|'''Aldous (1988a)''']] used detailed site specific knowledge to attempt to delineate flowpaths and likely transport fields for contaminant movement in the aquifer. [[Hydrogeology of Wales: References|'''Hobbs (1993)''']] identified a number of sinks and risings in the area:

:: Merthyr Mawr sinks [SS 8901 7763] on the western bank of the Ogmore river and rise at two springs which flow into the Merthyr Mawr Mill Leat [SS 88657763]

:: Pitcot Pool [SS 8955 7443] is spring fed

:: Jacobs Well [SS 9121 7480] a series of springs alongside the Afon Alun

:: Byeastwood Springs [SS 9298 8099 and SS 9258 8060] flow eventually into the River Ewenny

:: Hoel-las stream sink [SS 9288 8267], now concealed beneath the M4 motorway, and smaller sinks to the east take water draining off the Coal Measures

:: Tymaen sink [SS 8943 7705]

:: Ewenny Fach sink [SS 9542 7990] a sink in the bed of the River Ewenny

[[Image:P802428.jpg|thumb|200px|One of many springs flowing from boggy ground at the junction of the basal Namurian grit and the underlying Avon Group near Trefil, north of Tredegar . P802428.]]
In the area of the Schwyll Spring and Pwllwy Borehole and springs the Pembroke Limestone Group is over 500 m thick comprising a southward thickening alternating bioclastic and oolitic limestone 700 to 800 m thick. This is underlain by the basal Avon Group shales which are about 100 m thick. Aquifer transmissivities range between 4 and 130 m2 d-1, and hydraulic conductivity range between 0.1 and 5 m d-1. The effective porosity of the upper 8 to 10 m of the aquifer ranges between 6 and 8 per cent, reducing to 0.5-2 per cent below this. Among other sources, boreholes drawing from the concealed Pembroke Limestone Group at Bridgend contribute to public supply.

Near Llandybie at Pant-y-Llyn on the north-western limb of the coalfield is a small turlough, the only known active turlough in Wales. Pant-y-Llyn [SN 60167] is a small depression in the limestone which fills with water rising from the Pembroke Limestone Group along its faulted boundary with the Devonian Brownstones, usually in the autumn, and drains to estavelles in the late spring ([[Hydrogeology of Wales: References|'''Campbell et al., 1992)''']]. In flood it is some 160 by 60 m in area and up to 4 m deep.

Swallow holes are common over much of the limestone outcrop and also occur beneath a thin cover of the basal beds of the Marros Group grits. Particularly large examples with collapsed caverns occur at Mynydd y Glog north of Hirwaun, whereas linear developments of swallow holes occur along lines of weakness at Ystradfellte and east of Trefil. Numerous examples are present on the Twrch Sandstone Formation (formerly the Basal Grit) on the Llangattwg and Llangynidir mountains, some blocked by fine detritus to form small ponds such as Pwll Mawr which is situated on the interfluve between the Neath and the Tawe valleys.

There are numerous closely spaced swallow holes on the north crop, some of which are nothing more than open fractures. There are some 80 000 dolines on the north crop alone ([[Hydrogeology of Wales: References|'''Crowther, 1989''']]), and collectively these provide drainage to the limestone outcrop. The swallow water tends to flow southwards down dip and beneath the cover of the Bishopton Mudstone Formation. In wet conditions it rises up through the shale to emerge above Blaen-Rhymney, and much like a Chalk bourne, creates river flow where normally the bed is dry. A similar, but less ephemeral discharge near Blaen-Sirhowy was once used for public supply. There are also a few springs on the northern scarp slope. In addition there are a number of caverns beneath the north crop especially around the headwaters of the rivers Tawe and Neath.

Some caves reflect past sea levels; Little Hoyle and Hoyle’s Mouth near Tenby are about 15 m above sea level reflecting the Pleistocene sea level. The Bacon, Minchin and Paviland caves in Gower were also formed during the Pleistocene when the sea level was elevated relative to the present level.

There are numerous examples of sinks and risings (see '''Active karst systems table '''and '''Plate P802428'''). The headwaters of the Neath, including the Hepste, Mellte and Nedd-Fechan all come off the Devonian sandstone and disappear into sinks in the limestone. At the head of the Swansea valley the Llynfell flows out of the Dan-yr-Ogof cave whilst nearby the River Giedd disappears into a swallow hole. There are show caves in the Tawe Valley at the mouth of the Dan Yr Ogof cave system. The caves drain the Sink y Giedd [SN 810 179] and Waun Fignen-felen [SN 826 177] with a combined discharge of between 0.15 and 0.30 m3 s-1 depending on weather conditions ([[Hydrogeology of Wales: References|'''Coase and Judson, 1977''']]). Average flow rates of 0.14 and 0.13 km hr-1 respectively have been demonstrated with dye testing (see '''dye tests table '''). A number of dolines (e.g. the ‘Crater’) and other hollows overlie the cave system, but the remnant dry valleys occasionally flow during exceptionally wet weather.

<center>
{| class="wikitable"
|+ Selected active karst systems within the north crop (from east to west), see [[Hydrogeology of Wales: References|'''Gascoine (1989''']]).
|-
| Area
| Grid Square
| Comments
|-
| Afon Lwyd
| SO 20
| A series of sinks and caves leading to four resurgences. Pontnewynydd Risings typically issue at 6 Ml d-1.
|-
| Llangattwg
| SO 21
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Mynydd Llangynidr
| SO 21
| The main resurgence is Fynnon Shon Sheffrey [SO 1265 1188]. Dye tracing has proved the relationship between various sinks and risings ('''Figure 5.2''').
|-
| The Rhymney Valley
| SO 01
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Taff Fechan and Taff Fawr
| SO 01
| Includes Nant y Glais caves and resurgences, otherwise connections proven by dye tracing.
|-
| Cwm Cadlan and Penderyn
| SN 90
| Llygad Cynon is source of the Afon Cynon. An adjacent borehole [SN 9524 0774] reported an ‘underground lake’ at 55 m and is pumped at 5 Ml d‑1.
|-
| Afon Hepste
| SN 90
| Upper Hepste Main Sink [SN 9541 1208] discharges back to the river at Hepste Main Resurgence [SN 9360 0973] in under 24 hours.
|-
| Afon Mellte
| SN 91
| The main Mellte Sink [SN 9315 1332] has proven connections to five resurgences. Contributions also from smaller sinks.
|-
| Nedd Fechan
| SN 91
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Glyntawe and the Black Mountain
| SN 81
| Two main cave systems behind main resurgences at Glyntawe
|-
| The Twrch valley
| SN 71
| Fault-controlled resurgences.
|-
| Black Mountain – western area
| SN 61
| 7 km from main sink to resurgence proven by dye tracing.
|}
</center> <center>
{| class="wikitable"
|+ Relationship between dye tests from Waun Fignen-felen and Sink y Giedd, after [[Hydrogeology of Wales: References|'''Coase and Judson (1977)''']].
|-
|
| From Waen Fignen Felen
| From Sink y Giedd
|-
| Distance from sink to resurgence (km)
| 3.5
| 4.7
|-
| Time for dye to reach resurgence (hours)
| 25
| 36
|-
| Average flow rate (km hour-1)
| 0.14
| 0.13
|-
| Elevation of sink above resurgence (m)
| 248
| 218
|}
</center>

Other celebrated groups of caves include the Nant y Glais caves to the south of the Vaynor Moors on the north crop: Ogof Robin Goch [SO 0392 1076], Ogof y Ci [SO 0403 1051], Ogof Dŵr Dwfn [SO 0415 1022], Ogof Rhyd Sych [SO 0416 1021], Ogof Pysgodyn Gwyn [SO 0416 1016] and Ogof Jonny Bach [SO 0420 1000]. The Nant y Glais river disappears underground altogether as it traverses the cave system except in exceptionally wet weather when flow also occurs through a narrow gorge at surface ([[Hydrogeology of Wales: References|'''Ford, 1989''']]).

[[Hydrogeology of Wales: References|'''Gascoine (1989''']]) reviewed other cave systems within the north crop. Many of the sinks are situated at the feather edge of the Marros Group where it is only a few metres thick above the limestone ('''Figure P859273'''), whilst others provide connections from the Avon Group shales and the main limestone. One of the longer and more complex cave systems is Ogof Draenen [SO 2467 1176] at the eastern edge of the north crop. Numerous dolines and stream sinks are present in the area and speleological investigation recognises numerous underfit streams in large passages. [[Hydrogeology of Wales: References|'''Maurice and Guilford (2011)''']] have identified a watershed within the system whereby flow occurs both to the north to Clydach Gorge and to the south to the Afon Lwyd. The latter is in a different topographical catchment some 8 km distant and tracer testing indicates velocities of 4 km d-1.
[[Image:P859273.jpg|thumb|center|600px|Sketch map of the Pembroke Limestone group outcrop along the North Crop (after Gasgoine, 1989). P859273.]]

A wide range of borehole yields have been established depending on the hydraulic contact with productive fractures. Drilling is always speculative as targeting useful fractures is not easy. The average yield from Carboniferous Limestone Supergroup boreholes across the UK was shown by [[Hydrogeology of Wales: References|'''Monkhouse (1977)''']] to be just 4 l s-1, but there is no record of the numbers of boreholes that were abandoned as dry, while other boreholes may have a significantly higher yield.

Although fractures and karstification rapidly decreases under the cover of the Marros Group there is some evidence of deep groundwater circulation beneath the coalfield. Taff’s Well [ST 1193 8364] discharges groundwater at about 1 l s-1 from the South Wales Coal Measures Group with a temperature of 21.6 oC, the only thermal spring in Wales ([[Hydrogeology of Wales: References|'''Farr and Bottrell, 2013''']] . Previous measurements reported a variety of temperatures all less than 20 oC but these were subject to mixing with water from the River Taff which is now prevented by new flood works. Simple inspection of the geothermal gradient and of the discharge water chemistry suggests a deep flow path, probably in the Pembroke Limestone Group, which is believed to travel to a depth of about 700 m ([[Hydrogeology of Wales: References|'''Squirrell and Downing, 1969'''; '''Thomas et al., 1983''']]). Dissolved inert gas analysis indicates that the water infiltrated the ground some 500 m higher in elevation than Taff’s Well, suggesting a recharge source somewhere along the north crop ([[Hydrogeology of Wales: References|'''Burgess et al., 1980''']]; [[Hydrogeology of Wales: References|'''Edmunds, 1986''']]). The water is between 5000 and 10 000 years old based on δ18O and δ2H age indicators ([[Hydrogeology of Wales: References|'''Farr and Bottrell, 2013''']].

A major spring was encountered in the concealed limestone in 1879 during the excavation of the Severn Railway Tunnel. Here a spring discharge of 1000 l s-1 was encountered, the Great Spring, which has been pumped to surface ever since ([[Hydrogeology of Wales: References|'''Drew et al., 1970''']]). Of good quality, it has been used for a variety of purposes including supply to a paper mill and brewery however its only current use is for public supply.

Water quality in the limestone is typified by slightly alkaline pH up to 7.6, and alkalinity concentrations (as CaCO3) ranging upwards to 230 mg l-1. The lower values reflect immature waters that have not attained Ca saturation. In north Wales, local mineralisation in the limestones promotes the solution of metals but at barely detectable concentrations. There are distinct tidal influences on some low-lying coastal areas of south Wales (including the Schwyll Spring) and a marine mixing zone in selected fractures is indicated by enhanced concentrations of Na and Cl at some sources.

A number of detailed site-specific investigations have been carried out on the limestone aquifer in south Wales which provide insight into its hydraulic processes. One such study was carried out between Porthcawl and Port Talbot looking at the environmental impact of extending local quarries in the Pembroke Limestone Group on a wetland area within adjacent superficial deposits ([[Hydrogeology of Wales: References|'''Cheney et al., 2000''']]). This work drew on extensive monitoring and analysis carried out previously in the area but was unable to develop a robust groundwater flow model due to data scarcity and the complex nature of flow in a karstic system. In addition 95 per cent of the water balance was unaccountable, suspected to drain to submarine springs in the Bristol Channel.

Groundwater is typically of the Ca-HCO3 type, with HCO3 typically in the range 90 to 550 mg l-1, the weakest mineralisation occurring along the north crop. The pH is almost always alkaline with values up to 8.2. Cl concentrations are generally low (<50 mg l-1) except on the coast near Porthcawl at Rest Bay where some private sources suffer from saline intrusion ([[Hydrogeology of Wales: References|'''Jones, 2007''']]) and in parts of the Gower Peninsula where sea spray may be the cause of elevated Na and Cl concentrations. The same pattern emerges in Pembrokeshire where Ca-HCO3 type is dominant with subordinate Na/Mg-Cl type but here it is possibly caused by ion exchange in waters that are older than in the limestone around the South Wales Coalfield ([[Hydrogeology of Wales: References|'''Fahrner et al., 2008''']]).

{| cellspacing="0" cellpadding="5" border="1"
| <center>'''Development of Karst in the Avon Group'''</center>

The development of the karst features found today in the Avon Group in south Wales reflects a continuing process which commenced almost as soon as the rocks were laid down. The most active zone of karstification is the vadose zone where unsaturated water can move freely through bedding planes and other discontinuities, but the phreatic zone may also be active when groundwater chemistry changes due to long-term effects of mixing. There were three intensive phases of karstic development: the Lower Carboniferous, the late Triassic and the Palaeogene through to the Quaternary.

The Lower Carboniferous palaeokarstic surfaces developed as the limestone initially rose out of the sea. Clay and mudstone beds, representing fossil soils, overlie the hummocky erosion surface, with discrete fissures in the limestone infilled with the soil material below. This is characteristic of both south Wales ([[Hydrogeology of Wales: References|'''Wilson et al., 1990''']]) and north Wales ([[Hydrogeology of Wales: References|'''Davies, 1991''']]) where relief varies between only a few centimetres to a few metres.

Uplift during the late Carboniferous Variscan Orogeny initiated a protracted period of erosion which lasted through to the Jurassic Period. By Late Triassic times a network of fissures and caverns had been created, some of which had already been partly infilled with rubble and clay. Mineralised hydrothermal waters may have added to the process leading to the deposition of galena and barites on fissure walls. [[Hydrogeology of Wales: References|'''Wilson et al. (1990)''']] recognised three types of karst feature in south Wales: dilated joints, irregular shaped cavities developed along bedding plains, and subvertical cylindrical pipes.

During the Palaeogene and Quaternary periods, large periodic fluctuations in sea level caused fluctuations also in the location of the vadose zone, and new and some pre-existing conduit features were developed, many now below the present-day water table. Three types of feature were created: dolines (collapsed caverns), linear fissures and large cavities. These features are commonly backfilled with silt and rubble debris. [[Hydrogeology of Wales: References|'''Gunn (1992)''']] asserted that the larger features could only develop where they were fed by a river or stream sink, and the Dan yr Ogof system was once fed by the River Haffes which has since been captured and redirected.

Reactivation of karst conduit systems has been recorded at a number of sites. At Stormy Down Quarry [SS 845 800] discharging into a doline reactivated the karst system such that extensive remedial action was required in the vicinity during the construction of the M4 motorway ([[Hydrogeology of Wales: References|'''Aldous, 1988b''']]).
|}

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[Category:Hydrogeology of Wales| 017]]

Hydrogeology of Wales: Management and regulation of groundwater - management tools and future issues

2015-07-28T19:52:45Z

Gareth Farr:

{{HofW}}
To complement the abstraction licensing and permitting regimes that control activities which can pollute and derogate groundwater, the regulators have developed a number of assessment tools. These allow a risk based approach focussing on aquifers which are exploited for public water supply, have known problems with over-abstraction, have been identified at ‘poor’ status under the Water Framework Directive or where information is needed to respond to future pressures such as climate change. Some of the key tools include:

: River Basin Management Plans – to identify measures to achieve Water Framework Directive requirements for all water bodies. These water bodies have been compiled into specific river basin districts (RBD), three of which cover Wales: Dee, Severn and Western Wales.

[[Image:P859289.jpg|thumb|220px|Location of the present-day groundwater level and quality monitoring networks. P859289.]]

[[Image:P859288.jpg|thumb|220px|Map of Principal and Secondary aquifers in Wales. P859288.]]

: Aquifer designations - either Principal or Secondary Aquifers. These reflect the importance of the aquifer as both a resource and its role in supporting surface water flow and wetland ecosystems. Principal aquifers in Wales consist of bedrock aquifers which can supply water on a strategic scale. The principal aquifers are the Carboniferous Limestone aquifers across south Wales and area of north Wales, and the Permo-Triassic Sandstone in north east Wales ('''Figure P859288'''). Secondary Aquifers include a wide range of rock types or drift deposits with an equally wide range of water permeability and storage.

: Source Protection Zones - to protect abstractions used for public water supply and other forms of distribution to the public, such as mineral and bottled water plants, breweries or commercial food and drink production. These zones show the areas of groundwater within which there is particular sensitivity to pollution risks due to the proximity of a potable source. There are currently 76 Source Protection Zones in Wales, ranging from small catchments around water bottling sources to large zones covering areas of heavily fractured and karstic Carboniferous Limestone used for public supply, where pollutant travel times to the source are likely to be rapid. Whereas protection zones around smaller sources can be delineated with analytical or numerical modeling techniques, in areas of karstic, non-Darcian flow they are best defined by tracer testing and field examination.

: Nitrate Vulnerable Zones - delineated in areas of agricultural nitrate pollution to meet the requirement of the EU Nitrate Directive (91/676/EEC). Where groundwater quality data demonstrates increasing nitrate trends above the trigger of 11.3 mg-N l-1, the drinking water standard, further investigation, for example of land management practices, is applied to refine the catchment areas. The zones are reviewed every 4 years and currently cover around 4% of the land area (cf. 70% in England) and are currently delineated only in parts of the Vale of Clwyd and Dee and Wye Valleys.

: Groundwater level and quality monitoring networks - to comply with European and National legislation and meet internal and external needs from groundwater level and groundwater quality monitoring networks. Groundwater levels are monitored at 140 sites and groundwater quality at 250 sites across Wales ([[Hydrogeology of Wales: References|'''Jones and Farr, 2015''']]) ('''Figure P859289''').

Population growth coupled with a changing climate is likely to increase the demand for water, and water companies may have to reinstate historic groundwater abstractions or investigate new groundwater sources which will requirement active management. Land uses and land management practices may also alter in response to changing climate which may impact infiltration or increase the risks of groundwater pollution.

Over the last decade the Water Framework Directive has been the driver for much positive work on groundwater, including the development of statutory monitoring networks, delineation of groundwater bodies and identifying where groundwater quality and resources are being impacted. This has built on the pollution prevention and remediation work promoted by the 1980 Groundwater Directive which was aimed largely at controlling discharges of certain (hazardous) substances to groundwater. The immediate future of groundwater management in Wales is likely to focus on addressing the impacts of diffuse pollution and abandoned metal mines.

Work is ongoing in Wales to prioritise which of the Groundwater dependant terrestrial ecosystems are most vulnerable to diffuse pollution or abstraction pressure, and to develop a programme to investigate specific impacts and develop remedial measures.

{| Class="wikitable" width="750pt"
|+ Industrial and commercial waste produced in Wales (tonnes x 103) – data compiled by Environment Agency Wales
| Waste type
| Industry
| Commerce
| Total
| % of total for all England and Wales
|-
| Inert
| 129
| 9
| 138
| 5.8
|-
| Paper and card
| 150
| 106
| 256
| 4.9
|-
| Food
| 105
| 18
| 123
| 4.8
|-
| General industrial and commercial
| 572
| 853
| 1425
| 5.0
|-
| Other general and biodegradable
| 370
| 80
| 450
| 5.1
|-
| Metals
| 393
| 22
| 415
| 8.7
|-
| Contaminated general
| 198
| 33
| 231
| 5.8
|-
| Mineral wastes and residues
| 2654
| 1
| 2655
| 20.7*
|-
| Chemical and other
| 418
| 19
| 437
| 7.4
|-
| Total
| 4989
| 1141
| 6130
| 8.2
|}

<nowiki>*</nowiki>This percentage reflects the high level of activity in the minerals sector in Wales.

{| class="wikitable" width="750pt"
|+ Chemical properties of types of mine and spoil discharges (after Rees et al., 2002)
| Source
| pH
| Net alkalinity CaCO3 (mg l-1)
| Type
|-
| Flooded workings
| <5 – 8
| 0 to >500
| Ca-Mg-SO4/HCO3
|-
| Spoil tip
| <5
| -2500 to 0
| Ca-Mg-SO4
|-
| Free draining workings
| 5 – 7
| +80 to +180
| Ca-Mg-SO4
|-
| Flooded and free draining workings
| >5 <8
| -350 to +200
| Ca-Mg-SO4
|-
| Pumped mine discharge
| 6.5 – 7.5
| +500 to +1000
| Na-HCO3/SO4
|}

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[category:Hydrogeology of Wales| 037]]

Hydrogeology of Wales: Management and regulation of groundwater - management tools and future issues

2015-07-28T19:52:11Z

Gareth Farr: add Jones and Farr ref for monitoring networks

{{HofW}}
To complement the abstraction licensing and permitting regimes that control activities which can pollute and derogate groundwater, the regulators have developed a number of assessment tools. These allow a risk based approach focussing on aquifers which are exploited for public water supply, have known problems with over-abstraction, have been identified at ‘poor’ status under the Water Framework Directive or where information is needed to respond to future pressures such as climate change. Some of the key tools include:

: River Basin Management Plans – to identify measures to achieve Water Framework Directive requirements for all water bodies. These water bodies have been compiled into specific river basin districts (RBD), three of which cover Wales: Dee, Severn and Western Wales.

[[Image:P859289.jpg|thumb|220px|Location of the present-day groundwater level and quality monitoring networks. P859289.]]

[[Image:P859288.jpg|thumb|220px|Map of Principal and Secondary aquifers in Wales. P859288.]]

: Aquifer designations - either Principal or Secondary Aquifers. These reflect the importance of the aquifer as both a resource and its role in supporting surface water flow and wetland ecosystems. Principal aquifers in Wales consist of bedrock aquifers which can supply water on a strategic scale. The principal aquifers are the Carboniferous Limestone aquifers across south Wales and area of north Wales, and the Permo-Triassic Sandstone in north east Wales ('''Figure P859288'''). Secondary Aquifers include a wide range of rock types or drift deposits with an equally wide range of water permeability and storage.

: Source Protection Zones - to protect abstractions used for public water supply and other forms of distribution to the public, such as mineral and bottled water plants, breweries or commercial food and drink production. These zones show the areas of groundwater within which there is particular sensitivity to pollution risks due to the proximity of a potable source. There are currently 76 Source Protection Zones in Wales, ranging from small catchments around water bottling sources to large zones covering areas of heavily fractured and karstic Carboniferous Limestone used for public supply, where pollutant travel times to the source are likely to be rapid. Whereas protection zones around smaller sources can be delineated with analytical or numerical modeling techniques, in areas of karstic, non-Darcian flow they are best defined by tracer testing and field examination.

: Nitrate Vulnerable Zones - delineated in areas of agricultural nitrate pollution to meet the requirement of the EU Nitrate Directive (91/676/EEC). Where groundwater quality data demonstrates increasing nitrate trends above the trigger of 11.3 mg-N l-1, the drinking water standard, further investigation, for example of land management practices, is applied to refine the catchment areas. The zones are reviewed every 4 years and currently cover around 4% of the land area (cf. 70% in England) and are currently delineated only in parts of the Vale of Clwyd and Dee and Wye Valleys.

: Groundwater level and quality monitoring networks - to comply with European and National legislation and meet internal and external needs from groundwater level and groundwater quality monitoring networks. Groundwater levels are monitored at 140 sites and groundwater quality at 250 sites across Wales ([[Hydrogeology of Wales: References|'''Jones and Farr, 2015''']]('''Figure P859289''').

Population growth coupled with a changing climate is likely to increase the demand for water, and water companies may have to reinstate historic groundwater abstractions or investigate new groundwater sources which will requirement active management. Land uses and land management practices may also alter in response to changing climate which may impact infiltration or increase the risks of groundwater pollution.

Over the last decade the Water Framework Directive has been the driver for much positive work on groundwater, including the development of statutory monitoring networks, delineation of groundwater bodies and identifying where groundwater quality and resources are being impacted. This has built on the pollution prevention and remediation work promoted by the 1980 Groundwater Directive which was aimed largely at controlling discharges of certain (hazardous) substances to groundwater. The immediate future of groundwater management in Wales is likely to focus on addressing the impacts of diffuse pollution and abandoned metal mines.

Work is ongoing in Wales to prioritise which of the Groundwater dependant terrestrial ecosystems are most vulnerable to diffuse pollution or abstraction pressure, and to develop a programme to investigate specific impacts and develop remedial measures.

{| Class="wikitable" width="750pt"
|+ Industrial and commercial waste produced in Wales (tonnes x 103) – data compiled by Environment Agency Wales
| Waste type
| Industry
| Commerce
| Total
| % of total for all England and Wales
|-
| Inert
| 129
| 9
| 138
| 5.8
|-
| Paper and card
| 150
| 106
| 256
| 4.9
|-
| Food
| 105
| 18
| 123
| 4.8
|-
| General industrial and commercial
| 572
| 853
| 1425
| 5.0
|-
| Other general and biodegradable
| 370
| 80
| 450
| 5.1
|-
| Metals
| 393
| 22
| 415
| 8.7
|-
| Contaminated general
| 198
| 33
| 231
| 5.8
|-
| Mineral wastes and residues
| 2654
| 1
| 2655
| 20.7*
|-
| Chemical and other
| 418
| 19
| 437
| 7.4
|-
| Total
| 4989
| 1141
| 6130
| 8.2
|}

<nowiki>*</nowiki>This percentage reflects the high level of activity in the minerals sector in Wales.

{| class="wikitable" width="750pt"
|+ Chemical properties of types of mine and spoil discharges (after Rees et al., 2002)
| Source
| pH
| Net alkalinity CaCO3 (mg l-1)
| Type
|-
| Flooded workings
| <5 – 8
| 0 to >500
| Ca-Mg-SO4/HCO3
|-
| Spoil tip
| <5
| -2500 to 0
| Ca-Mg-SO4
|-
| Free draining workings
| 5 – 7
| +80 to +180
| Ca-Mg-SO4
|-
| Flooded and free draining workings
| >5 <8
| -350 to +200
| Ca-Mg-SO4
|-
| Pumped mine discharge
| 6.5 – 7.5
| +500 to +1000
| Na-HCO3/SO4
|}

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[category:Hydrogeology of Wales| 037]]

Hydrogeology of Wales: References

2015-07-28T19:49:27Z

Gareth Farr: add Jones & Farr, 2015 reference

{{HofW}}
''PUBLISHED''

'''Allen, D J, Brewerton, L J, Coleby, L M, Gibbs, B R, Lewis, M A, MacDonald, A M, and Wagstaff, S J. 1997.''' ''The physical properties of major aquifers in England and Wales''. Environment Agency R&D Publication, No.8.

'''Appleton, P. 1974.''' Subterranean courses of the River Alyn, including Ogof Hesp Alyn, North Wales. ''Transactions of the British Cave Research Association'', Vol. 1, 29−42.

'''Ball, T K, and Jones, J C. 1990.''' Speleogenesis in the limestone outcrop north of the South Wales Coalfield: the role of micro-organisms in the oxidation of sulphides and hydrocarbons. ''Cave Science'', Vol. 17, 1, 3−8.

'''Banks, D, and Robins, N S. 2002.''' ''An introduction to groundwater in crystalline bedrock''. Norges geologiske undersøkelse, Trondheim.

'''Bassett, D A. 1969.''' The study of groundwater, with particular reference to Wales and the Welsh Border. ''Transactions of the Cardiff Naturalists’ Society'', Vol. 94, 62−87.

'''Bassett, M G , Deisler, V K , and Nichol, D , (editors) 2005.''' Urban Geology in Wales: 2. ''National Museum of Wales Geological Series, No. 24,'' Cardiff. 262pp.

'''BGS, 1986.''' ''Hydrogeological map of South Wales, Scale 1: 125 000''. (Keyworth, Nottingham: British Geological Survey.)

'''BGS, 1989.''' ''Hydrogeological map of Clwyd and the Cheshire Basin, Scale 1: 100 000''. (Keyworth, Nottingham: British Geological Survey.)

'''BGS, 2000'''. ''Regional geochemistry of Wales and part of west central England: stream sediment and soil''. (Keyworth, Nottingham: British Geological Survey.)

'''Brabham, P J. 2004.''' The Rhondda Valleys: using GIS to visualise the rise and fall of coal mining and its industrial heritage. 193-206 in ''Urban Geology in Wales'', (Cardiff: National Museum of Wales.)

'''Campbell, S, Gunn, J, and Hardwick, P. 1992.''' Pant-y-Llyn – the first Welsh turlough? ''Earth Science Conservation'', Vol. 31, 3-7.

'''CEH/BGS, 2003.''' ''Hydrometric register and statistics 1996-2000.'' (Wallingford, Oxford: Centre for Ecology and Hydrology/British Geological Survey.)

'''Coase, A, and Judson, D. 1977.''' Dan yr Ogof and its associated caves. ''Transactions of the British Cave Research Association'', Vol. 4, 1/2, 247-344.

'''Crowther, J. 1989'''. Karst geomorphology of South Wales. 20-39 in ''Limestones and Caves of Wales,'' T D Ford (editor), (Cambridge: Cambridge University Press.)

'''Davies, J R.''' 1991. Karstification and pedogenisis on a late Dinantion carbonate platform, Anglesey, North Wales. ''Proceedings of the Yorkshire Geological Society'', Vol, 48, 297-321.

'''Davis, P'''. 2003. ''Sacred Springs: In search of the Holy Wells and Spas of Wales''. (Abergavenny: Blorenge Books.)

'''Davy, A J, Hiscock, K M, Jones, M L M, Low, R, Robins, N S, and Stratford, C. 2010.''' ''Ecohydrological guidelines for wet dune habitats''. Environment Agency Report Wet Dune Habitats, No. 2.

'''Drew, D P, Newson, M D, and Smith, D I. 1970.''' Water tracing of the Severn Tunnel Great Spring. ''Proceedings of the University of Bristol Speleological Society'', Vol. 12, 203-212.

'''EC, 1991.''' European Community Nitrates Directive, (91/676/EEC).

'''EC, 2000.''' European Community Water Framework Directive, (2000/60/EC).

'''Edmunds, W M. 1986.''' Geochemistry of geothermal waters in the UK. In ''Geothermal energy – the potential in the United Kingdom''. Downing, R A, and Gray, D A (editors). (London: HMSO)

'''Edmunds, W M, Robins, N S, and Shand, P. 1998.''' The saline waters of Llandrindod and Builth, Central Wales. ''Journal of the Geological Society of London'', Vol, 155, 627-637.

'''Environment Agency, 2008.''' ''Underground, Under threat: The state of groundwater in England and Wales''. (Bristol: Environment Agency.)

'''Environment Agency, 2009.''' ''Water for people and the environment: Water Resource Strategy for Wales''. (Bristol: Environment Agency.)

'''Farr, G and Bottrell, S.H. 2013.''' The hydrogeology and hydrochemistry of the thermal waters at Taffs Well, South Wales, UK. ''Cave and Karst Science Transactions of the British Cave Research Association.'' 40 (1). 5-12.

'''Ford, T D. 1989.''' The caves of Nant y Glais, Vaynor. 153-154 in ''Limestones and Caves of Wales.'' T D Ford (editor). (Cambridge: Cambridge University Press.)

'''Gascoine, W. 1989.''' The hydrology of the limestone outcrop north of the coalfield. 40-55 in ''Limestones and Caves of Wales'' T D Ford (editor). (Cambridge: Cambridge University Press.)

'''Gibbons, W.''' 1983. The Moinian ‘Penmynydd Zone of metamorphism’ in Llyn, North Wales. ''Geological Journal'', Vol. 18, 21-41.

'''Greenly, E. 1919.''' The Geology of Anglesey. ''Memoirs of the geological Survey of England and Wales''.

'''Gunn, J. 1992.''' Hydrogeological contrasts between British Carboniferous Limestone aquifers. 25-42 in ''Hydrogeology of selected Karst regions'', International Association of Hydrogeologists International Contributions to Hydrogeology, No. 13.

'''Haria, A H, and Shand, P. 2004.''' Evidence for deep subsurface flow routing in forested upland Wales: implications for contaminant transport and stream flow generation. ''Hydrology and Earth Systems Sciences'', Vol. 8, 3, 344-344.

'''Heathcote, J A, Lewis, R T, and Sutton, J S. 2003.''' Groundwater modelling for the Cardiff Bay Barrage, UK – prediction, implementation of engineering works and validation of model. ''Quarterly Journal of Engineering Geology and Hydrogeology'', Vol. 36, 2, 159-172.

'''Hiscock, K, and Paci, A. 2000'''. Groundwater resources in the Quaternary deposits and Lower Palaeozoic bedrock of the Rheidol catchment, west Wales. 141-155 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Hobbs, S L. 1993'''. The hydrogeology of the Schwyll Spring catchment Area, South Wales. ''Proceedings of the Bristol Speleological Society'', Vol. 19, 3, 313-335.

'''Hobbs, S L. 2000.''' Influent rivers: a pollution threat to Schwyll Spring, South Wales? 113-121 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Ineson, J. 1967.''' Groundwater conditions in the Coal measures of the South Wales Coalfield. ''Water Supply Papers of the Geological Survey of Great Britain,''Hydrogeological Report No. 3.

'''Jones, D. A and Farr, G. 2015.''' Natural Resources Wales's monitoring networks for groundwater level and quality: the story so far. ''In: Bevins, Richard E.; Nichol, Douglas; Solera, Sergio A., (eds.) Urban geology in Wales. 4. Cardiff, UK, National Museum of Wales, 217-225. National Museums of Wales Geological Series, 27.''

'''Jones, F. 1992'''. ''The Holy Wells of Wales''. (Cardiff: University of Wales Press.)

'''Jones, H K, Morris,B L, Cheney, C S, Brewerton, L J, Merrin, P D, Lewis, M A, MacDonald, A M, Coleby, L M, Talbot, J C, MacKenzie, A A, Bird, M J, Cunnigham, J, and Robinson, V K. 2000''' The physical properties of minor aquifers in England and Wales. ''British Geological Survey Technical Report,'' WD/00/4. ''Environment Agency R & D Publication,'' No. 68.

'''Jones, N, Walters, M, and Frost, P , 2004'''. Mountains and orefields: metal mining landscapes of mid and north-east Wales. ''Council for British Archaeology Research Report,'' No. 142.

'''Kirchner, J W, Feng, X H, and Neal, C. 2001'''. Catchment-scale advection and dispersion as a mechanism for fractal scaling in stream tracer concentrations. ''Journal of Hydrology'', Vol. 254, 82-101.

'''Lambert, A O. 1981.''' The River Clwyd Augmentation/Abstraction Scheme. ''Journal of the Institution of Water Engineers and Scientists'', Vol. 35, 125-134.

'''Lambert, A O, English, K B, Skinner, A, Fleet, M, and Wilkinson, W B. 1973.''' ''Groundwater resources of the Vale of Clwyd''. ''Water Resources Board, Reading'', Publication No. 20.

'''Lovelock, P E R. 1977.''' Aquifer properties of the Permo-Triassic sandstones of the United Kingdom. ''Bulletin of the Geological Survey of Great Britain'', No. 56, 50.

'''Maurice, L, and Guilford, T. 2011.''' The hydrogeology of Ogof Draenen: new insights into a complex multi-catchment karst system from tracer testing. ''Cave and Karst Science'', Vol. 38, 1, 23-30.

'''NRA, 1993'''. ''Low Flows and Water resources, facts on the top 40 low-flow rivers in England and Wales''. (Bristol: National Rivers Authority.)

'''Neal, C, Robson, A J, Shand, P, Edmunds, W M, Dixon, A J, Buckley, D K, Hill, S, Harrow, M, Neal, M, Wilkinson, J, and Reynolds, B. 1997'''. The occurrence of groundwater in the Lower Palaeozoic rocks of Central Wales. ''Hydrology and Earth Systems Sciences'', Vol. 1, 3-18.

'''Nichol, D , Bassett, M G, and Deisler, V K (editors). 2004.''' Urban Geology in Wales. ''National Museum of Wales, Cardiff. Geological Series'', No. 23

'''Ranwell, D S. 1959.''' Newborough Warren Anglesey. I. The dune system and dune slack habitat. ''Journal of Ecology'', Vol. 47, 571-601.

'''Rees, S B, Bowell, R J, and Wiseman, I. 2002.''' Influence of mine hydrogeology on mine water discharge chemistry. 379-390 in Younger, P L, and Robins, N S (editors). ''Mine water hydrogeology and geochemistry''. Geological Society of London Special Publications, No. 198.

'''Robins, N S. 1999.''' Groundwater occurrence in the Lower Palaeozoic and Precambrian rocks of the UK: implications for source protection. ''Journal of the Chartered Institution of Water and Environmental Management'', Vol. 13, 6, 447-453.

'''Robins, N S. 2005.''' Fracture flow and preferential groundwater flow paths in hard rocks - illustrations from Precambrian and Lower Palaeozoic strata in Wales.'' 25th Anniversary Groundwater Seminar, International Association of Hydrogeologists'', Tullamore, April 2005.

'''Robins, N S. 2009'''. Regional hydrogeological assessment of Wales. 141-150 in ''Urban Geology in Wales: 3''. Bassett,M G, Boulton, H, and Nichol, D (editors). National Museum of Wales, Cardiff, Geological Series, No. 29.

'''Robins, N S, and McKenzie, A A. 2005.''' Groundwater occurrence and the distribution of wells and springs in Precambrian and Palaeozoic rocks, north-west Anglesey. ''Quarterly Journal of Engineering Geology and Hydrogeology'', Vol. 38, 1, 83-88.

'''Robins, N S, Shand, P, and Merrin, P D. 2000.''' Shallow groundwater in drift and Lower Palaeozoic bedrock: the Afon Teifi valley in west Wales. 123-131 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Robins, N S, Davies, J, Cheney, C, and Tribe, E L. 2005.''' Groundwater in a water-rich environment: Wales, a land of plenty. ''Journal of the Chartered Institution of Water & Environmental Management'', Vol. 19, 1, 62-67.

'''Robins, N S, Davies, J, and Dumpleton, S. 2008.''' Groundwater flow in the South Wales Coalfield – historical data informing 3D modelling. ''Quarterly Journal of Engineering Geology and Hydrogeology''. Vol. 41, 4, 477-486.

'''Shand, P, Edmunds, W M, Wagstaff, S, Flavin, R, and Jones, H K. 1999'''. Hydrogeochemical processes determining water quality in upland Britain. '' British Geological Survey, Hydrogeological Report,''.

'''Shand, P, Darbyshire, D P F, Gooddy, D C, Darling, W G, Neal C, Haria, A H, and Dixon, A J. 2001.''' The application of Sr isotopes to catchment studes: the Plynlimon upland catchment of Central Wales. ''Water-Rock Interaction'', Vol. 10, 1577-1580.

'''Shapiro, A M. 1993.''' The influence of heterogeneity in estimates of regional hydraulic properties in fractured crystalline rock. ''Memoirs of the 24th Congress of the International association of Hydrogeologists'', Oslo, 125-129.

'''Squirrell, H C, and Downing, R A. 1969.''' Geology of the South Wales Coalfield, Part 1. The country around Newport (Mon). ''Memoirs of the Geological Survey of Great Britain''.

'''Stratford, C, Ratcliffe, J, Hughes, A G, Roberts, J, and Robins, N S. 2007.''' Complex interaction between shallow groundwater and changing woodland, surface water, grazing and other influences in partly wooded duneland in Anglesey, Wales 2007.''' '''Proceedings CD XXXV Congress International Association of Hydrogeologists ''Groundwater and Ecosystems'', Lisbon, 17-21 September 2007.

'''Stratford, C, Robins, N S, and Hollingham,M. 2009.''' An assessment of the interactions between hydrology, land use and climate change at two coastal dune systems in Wales, UK. Proceedings of the Second Multidisciplinary Conference on Hydrology and Ecology, Vienna, April 2009 (CD).

'''Stratford, T. 1995.''' ''Caves of South Wales: A Caver’s Guide Book.'' (Leicester: Cordee.)

**'''Thomas, L P.''' 1974. The Westphalian (Coal Measures) in South Wales. IN: T R Owen (Editor)

'''Warren, P T, Price, D, Nutt, M J C, and Smith, E G. 1984'''. Geology of the country around Rhyl and Denbigh. ''Memoir of the British Geological Survey'', Sheets 95 and 107 and parts of sheets 94 and 106 (England and Wales).

'''Waters, C N, Price, S J, Davies, J, Tye, A M, Brown, S E, and Schofield, D I. 2005.''' Urban geology of Swansea-Neath-Port Talbot. 7-22 in ''Urban Geology in Wales 2''. Bassett, M G, Deisler, V K, and Nichol, D (editors). ''National Museum of Wales, Cardiff, Geological Series'', No 24.

'''Watson, J W, and Sissons, J B (editors). 1965.''' ''The British Isles a systematic geography''. (London: Thomas Nelson & Sons.)

'''Webb, M M. 2000.''' The water resources of Bardsey, North Wales. 239-246 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors). ''Geological Society of London Special Publications'', Vol. 182.

'''WRB, 1973.''' Groundwater resources of the Vale of Clwyd. ''Water Resources Board, Reading''. Publication No. 20,

'''Younger, P L, Jenkins, D A, Rees, S B, Robinson, J, Jarvis, A P, Ralph, J, Johnston, D N, and Coulton, R H. 2004.''' Mine waters in Wales: pollution, risk management and remediation. 138-154 in ''Urban Geology in Wales''. Nichol,D, Bassett, M G, and Deisler, V K (editors). National Museum of Wales, Cardiff, Geological Series, No. 23.

''UNPUBLISHED''

'''Aldous, P J. 1988a'''. Groundwater transport and pollutant pathways in Carboniferous Limestone Aquifers. The Cardiff-Cowbridge Block: Final report. WRc Technical Report CO 1820/M/1/EV 8663.

'''Aldous, P J. 1988b.''' Investigation of the geology, hydrogeology and environmental impact of a proposed landfill at Stormy Down – tracer studies. WRc Technical Report CO 1990/M/EV 8716.

'''Aspinwall & Co. 1993.''' Vale of Glamorgan Carboniferous Limestone study. Report for National Rivers Authority, Aspinwall & Co., Shrewsbury.

'''Banks, D, Farr, G, Inman, P, and Low, R. 2007.''' Groundwater quality and supply survey for the Precambrian Gwna Group Anglesey. Environment Agency, Bristol, Technical Report.

'''Banks, D, Boland, M, Farr, G, Inman, P, and Low, R. 2008.''' Groundwater quality and supply survey for the Carboniferous Limestone, Anglesey. Environment Agency, Bristol, Technical Report.

'''Burgess, W G, Edmunds, W M, Andrews J N, Kay R L F, and Lee, D J. 1980.''' The hydrogeology and hydrochemistry of the thermal waters in the bath-Bristol basin. Institute of Geological Sciences Technical Report (Investigation of the Geothermal Potential of the UK series).

'''Celtic Water Management, 2005.''' Pumping 2004 & 2005: Yield & Sand Ingress Test Pumping. Technical Report Celtic Water Management, Cardigan, for Dwr Cymru.

'''Cheney, C S, Davies, J R, Hughes, A G, Darling, W G, and Macdonald, D M J. 2000.''' An assessment of the possible effects of dewatering proposed extensions to quarries in the South Cornelly area, South Wales, ''British Geological Survey Technical Report'', WD/00/21.

'''CWPU, 1978.''' Groundwater resources in the coalfields of England and Wales – the South Wales Coalfield. Central Water Planning Unit Technical Note.

'''Entec, 1996.''' Cardiff Bay Barrage groundwater characterisation. Technical report Entec Ltd, Shrewsbury.

'''Entec 2009.''' Source protection zone for Lovesgrove boreholes. Technical report Entec Ltd, Shrewsbury, for Environment Agency Wales.

'''ESI, Ltd. 2003.''' Vale of Clwyd aquifer study Phase 1. Technical report ESI Ltd, Shrewsbury, for Environment Agency Wales.

'''ESI, Ltd. 2006.''' The hydrogeology of three catchments of the River Wye. Technical report ESI Ltd, Shrewsbury, for Environment Agency Wales.

'''Fahrner, S, Gomme, J, Farr, G, and Mann, A. Undated.''' Groundwater quality review: Clwyd Permo-Triassic sandstone. Environment Agency, Bristol, Technical Report.

'''Fahrner, S, Gomme, J, Davies, B, and Farr, G. 2008.''' Groundwater quality review: The Carboniferous Limestone of the Pembrokeshire Carboniferous Limestone groundwater monitoring unit. Environment Agency, Bristol, Technical Report.

'''Glendining, S J. 1981.''' Hydrogeological reconnaissance study: Dyfi Valley, Wales. Institute of Geological Sciences Technical Report, ENPU 81-2.

'''Griffiths, K J, Shand, P,and Ingram, J. 2002.''' Baseline report series 2: The Permo-Triassic sandstones of west Cheshire and the Wirral. ''British Geological Survey Technical Report'', CR/02/109.

'''Howard Humphreys, 1984'''. The Olwen borehole, Lampeter. Howard Humphreys & Partners, London.

'''Jones, D A. 2007.''' Hydrogeological investigation of a Carboniferous Limestone aquifer near Rest Bay. Unpublished MSc Thesis, University of Cardiff.

'''Jones, P S. 1993.''' Ecological and hydrological studies of dune slack vegetation at Kenfig National Nature Reserve, Mid-Glamorgan. Unpublished PhD Thesis, University of Cardiff.

'''Lewis, B J, Leighfield, K G, and Cox, S J. 2000.''' The South Wales Coalfield (including the Pembrokeshire Coalfield): A review of mine water recovery. Report Wardell Armstrong for the Coal Authority, job No. NL02906.

'''Monkhouse, R A. 1977.''' Yields of public wells in the more important aquifers of England and Wales. Central Water Planning Unit Technical Report 1977/11.

'''Monkhouse, R A. 1982.''' A note on groundwater in Wales. ''Institute of Geological Sciences Technical Report,'' WD/82/3.

'''Moreau, M, Shand, P, Wilton, N, Brown, S, and Allen, D. 2004.''' Baseline Report Series 12. The Devonian sandstone aquifer of South Wales and Herefordshire. ''British Geological Survey Commissioned Report,'' CR/04/185.

'''Rae, G W. 1978a.''' Mine drainage from coalfields in England and Wales, a summary of its distribution and relationship to water resources. Central Water Planning Unit Technical Note.

'''Rae, G W. 1978b.''' Groundwater resources in the coalfields of England and Wales – the South Wales Coalfield. Draft Central Water Planning Unit Technical Note.

'''Richards, H J. 1959.''' Draft report on the hydrogeology of the Carboniferous Limestone of Wales. ''Geological Survey Technical Report'', WD/59/3

'''Robertson, A S. 1974.''' Flow measurements made by IGS in boreholes EP4, EP5, EP7 and EP9 at the Dinorwic Site Llanberis 5-9 March 1974. ''Institute of Geological Sciences Technical Report'', WD/ST/74/9.

'''Shand, P, Edmunds, W M, Wagstaff, S, and Flavin, R. 1995.''' The application of hydrogeochemical data and maps for environmental interpretation in upland Britain. ''British Geological Survey Technical Report'', WD/94/57.

'''Shand, P, Abesser, C, Farr, G, Wilton, N, Lapworth, D J, Gooddy, D C, Haria, A, and Hargreaves, R. 2005'''. Baseline Report Series 17, The Ordovician and Silurian metasedimentary aquifers of central and south west Wales. ''British Geological Survey Commissioned Report'', CR/05/34.

'''Shand, P, Edmunds, W M, Lawrence, A R, Smedley, P R, and Burke, S. 2007'''. The natural (baseline) quality of groundwater in England and Wales. ''British Geological Survey Research Report,'' RR/07/06.

'''Thomas, L P, Evans, R B, and Downing, R A. 1983'''. The geothermal potential of the Devonian and Carboniferous rocks of South Wales. ''Institute of Geological Sciences Technical Report'' (Investigation of the Geothermal Potential of the UK series).

'''Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009.''' A lithostratigraphical framework for the Carboniferous successions of southern Great Britain (onshore). ''British Geological Survey Research Report'', RR/09/01.

'''Welsh Office Agriculture Department. 1986.''' Letter dated 19 March 1986 from Regional Soil Scientist. BGS Wellmaster record SH45/3.

'''Wilson, D; Davies, J R; Fletcher, C J N; and Smith, M. 1990.''' Geology of the South Wales Coalfield, Part VI, the country around Bridgend. ''Memoir of the British Geological Survey'', Sheets 261 and 262.

'''Wilson, D; Waters, C; and Rollin, K E. 2002'''. A geological and geophysical desk study of the Vale of Clwyd. ''British Geological Survey Commissioned Report'', CR/02/177.

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[category:Hydrogeology of Wales | 045]]

Hydrogeology of Wales: Management and regulation of groundwater - management tools and future issues

2015-07-28T19:45:18Z

Gareth Farr: capital letters for Principal and Secondary aqufiers

{{HofW}}
To complement the abstraction licensing and permitting regimes that control activities which can pollute and derogate groundwater, the regulators have developed a number of assessment tools. These allow a risk based approach focussing on aquifers which are exploited for public water supply, have known problems with over-abstraction, have been identified at ‘poor’ status under the Water Framework Directive or where information is needed to respond to future pressures such as climate change. Some of the key tools include:

: River Basin Management Plans – to identify measures to achieve Water Framework Directive requirements for all water bodies. These water bodies have been compiled into specific river basin districts (RBD), three of which cover Wales: Dee, Severn and Western Wales.

[[Image:P859289.jpg|thumb|220px|Location of the present-day groundwater level and quality monitoring networks. P859289.]]

[[Image:P859288.jpg|thumb|220px|Map of Principal and Secondary aquifers in Wales. P859288.]]

: Aquifer designations - either Principal or Secondary Aquifers. These reflect the importance of the aquifer as both a resource and its role in supporting surface water flow and wetland ecosystems. Principal aquifers in Wales consist of bedrock aquifers which can supply water on a strategic scale. The principal aquifers are the Carboniferous Limestone aquifers across south Wales and area of north Wales, and the Permo-Triassic Sandstone in north east Wales ('''Figure P859288'''). Secondary Aquifers include a wide range of rock types or drift deposits with an equally wide range of water permeability and storage.

: Source Protection Zones - to protect abstractions used for public water supply and other forms of distribution to the public, such as mineral and bottled water plants, breweries or commercial food and drink production. These zones show the areas of groundwater within which there is particular sensitivity to pollution risks due to the proximity of a potable source. There are currently 76 Source Protection Zones in Wales, ranging from small catchments around water bottling sources to large zones covering areas of heavily fractured and karstic Carboniferous Limestone used for public supply, where pollutant travel times to the source are likely to be rapid. Whereas protection zones around smaller sources can be delineated with analytical or numerical modeling techniques, in areas of karstic, non-Darcian flow they are best defined by tracer testing and field examination.

: Nitrate Vulnerable Zones - delineated in areas of agricultural nitrate pollution to meet the requirement of the EU Nitrate Directive (91/676/EEC). Where groundwater quality data demonstrates increasing nitrate trends above the trigger of 11.3 mg-N l-1, the drinking water standard, further investigation, for example of land management practices, is applied to refine the catchment areas. The zones are reviewed every 4 years and currently cover around 4% of the land area (cf. 70% in England) and are currently delineated only in parts of the Vale of Clwyd and Dee and Wye Valleys.

: Groundwater level and quality monitoring networks - to comply with European and National legislation and meet internal and external needs from groundwater level and groundwater quality monitoring networks. Groundwater levels are monitored at 140 sites and groundwater quality at 250 sites across Wales ('''Figure P859289''').

Population growth coupled with a changing climate is likely to increase the demand for water, and water companies may have to reinstate historic groundwater abstractions or investigate new groundwater sources which will requirement active management. Land uses and land management practices may also alter in response to changing climate which may impact infiltration or increase the risks of groundwater pollution.

Over the last decade the Water Framework Directive has been the driver for much positive work on groundwater, including the development of statutory monitoring networks, delineation of groundwater bodies and identifying where groundwater quality and resources are being impacted. This has built on the pollution prevention and remediation work promoted by the 1980 Groundwater Directive which was aimed largely at controlling discharges of certain (hazardous) substances to groundwater. The immediate future of groundwater management in Wales is likely to focus on addressing the impacts of diffuse pollution and abandoned metal mines.

Work is ongoing in Wales to prioritise which of the Groundwater dependant terrestrial ecosystems are most vulnerable to diffuse pollution or abstraction pressure, and to develop a programme to investigate specific impacts and develop remedial measures.

{| Class="wikitable" width="750pt"
|+ Industrial and commercial waste produced in Wales (tonnes x 103) – data compiled by Environment Agency Wales
| Waste type
| Industry
| Commerce
| Total
| % of total for all England and Wales
|-
| Inert
| 129
| 9
| 138
| 5.8
|-
| Paper and card
| 150
| 106
| 256
| 4.9
|-
| Food
| 105
| 18
| 123
| 4.8
|-
| General industrial and commercial
| 572
| 853
| 1425
| 5.0
|-
| Other general and biodegradable
| 370
| 80
| 450
| 5.1
|-
| Metals
| 393
| 22
| 415
| 8.7
|-
| Contaminated general
| 198
| 33
| 231
| 5.8
|-
| Mineral wastes and residues
| 2654
| 1
| 2655
| 20.7*
|-
| Chemical and other
| 418
| 19
| 437
| 7.4
|-
| Total
| 4989
| 1141
| 6130
| 8.2
|}

<nowiki>*</nowiki>This percentage reflects the high level of activity in the minerals sector in Wales.

{| class="wikitable" width="750pt"
|+ Chemical properties of types of mine and spoil discharges (after Rees et al., 2002)
| Source
| pH
| Net alkalinity CaCO3 (mg l-1)
| Type
|-
| Flooded workings
| <5 – 8
| 0 to >500
| Ca-Mg-SO4/HCO3
|-
| Spoil tip
| <5
| -2500 to 0
| Ca-Mg-SO4
|-
| Free draining workings
| 5 – 7
| +80 to +180
| Ca-Mg-SO4
|-
| Flooded and free draining workings
| >5 <8
| -350 to +200
| Ca-Mg-SO4
|-
| Pumped mine discharge
| 6.5 – 7.5
| +500 to +1000
| Na-HCO3/SO4
|}

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[category:Hydrogeology of Wales| 037]]

Hydrogeology of Wales: Acknowledgements

2015-07-28T19:41:41Z

Gareth Farr: replace EA with NRW

{{HofW}}
Groundwater investigation in Wales has tended to be piecemeal with project reports and technical papers issued from time to time. The only holistic review of groundwater in Wales was written by [[Hydrogeology of Wales: References|'''Bassett (1969)''']] although various regional compilations, such as the two available hydrogeological maps ([[Hydrogeology of Wales: References|'''BGS, 1986; 1989''']]), have updated Bassett’s work. More recently the regulator, Environment Agency Wales, has published catchment-scale reports and has commissioned a range of in depth studies, while others have worked at project-level providing insight into aspects of a variety of groundwater occurrence problems peculiar to Wales.

This report attempts to provide an updated review of the occurrence of groundwater throughout Wales. It is part of a series of regional- and aquifer-scale reports issued by the British Geological Survey, the Groundwater Programme Research Report series. An introductory chapter is followed by chapters on each lithostratigraphical system. These describe the outline geology and hydrogeology and highlight the availability of groundwater, its quality and any issues pertaining to the hydrogeology of the units within each system. In addition a concluding chapter describes the past and present regulatory framework in Wales and the modern-day management tools used by Natural Resources Wales with illustrations of some of the problems that need to be addressed.

The report draws on data available in the public domain, both published and unpublished. The reference list provides a valuable record of all these sources. In addition datasets held by both the British Geological Survey and Natural Resources Wales have been consulted along with data held by Dŵr Cymru Welsh Water and Cardiff University.

Although the report was compiled by Nick Robins and Jeff Davies, an important contribution was also prepared by David Jones Natural Resources Wales and Gareth Farr (previously of Environment Agency Wales) who drafted the bulk of the chapter on management and regulation. The principal authors are also grateful to Kay Roberts and Beth Davies and others at Natural Resources Wales for valuable peer review comments on the manuscript. Peter Neve is thanked for comments on hydrogeology in north east Wales. David Schofield and Colin Waters provided geological advice including validation of stratigraphical terminology.

Others who have provided data or helped in the preparation of this report include: the late David Headworth at Environment Agency Wales; Ian Brown at Dŵr Cymru Welsh Water; Glyn Hyett of Celtic Water Management Ltd. Cardigan; Emma Paris, Tim Jones and Charlie Harris at Cardiff University; Ron Fuge, University of Wales, Aberystwyth; Paul Younger, University of Strathclyde, formerly University of Newcastle-upon-Tyne; Ab Grootjans at University of Groningen, Netherlands; John Ratcliffe and colleagues at the Countryside Council for Wales; Charlie Stratford and Laurence Jones at the Centre for Ecology and Hydrology.

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[Category:Hydrogeology of Wales| 0001]]

Hydrogeology of Wales: Management and regulation of groundwater

2015-07-28T19:39:57Z

Gareth Farr: add text on formation of Natural Resources Wales

{{HofW}}
[[Image:P859287.jpg|thumb|300px|The abstraction licence exempt are (as at 2012). P859287.]]

==Background==

Groundwater sources have been important drinking-water supplies to communities across Wales for many centuries. The location of settlements with easy access to groundwater resources is no coincidence and historic springs can be seen at the centre of towns and villages.

Prior to the implementation of the ''Water Resource Act, 1963'' groundwater and surface water sources were typically managed by local water boards and district councils, which totalled over twenty in Wales in the early 20th century. This localised approach did allow co-ordination of resources even on a catchment scale. The ''Water Resources Act, 1963'' recognised the importance of water resource planning and also introduced the abstraction licensing system. Water resources in Wales were managed by the Wye, Usk, Glamorgan, South-west Wales, Gwynedd, Dee and Clwyd and Severn river authorities. Due to the low-yielding nature of the aquifers across west, mid and north-west Wales these areas were subsequently designated in the late 1960s via Statutory Instrument, as exempt from groundwater abstraction licensing ('''Figure P859287''').

The subsequent ''Water Act, 1973'' abolished the Water Resource Board and river authorities and combined their functions into regional water authorities, defined by catchment boundaries and responsible for the supply of drinking water, sewerage, water quality and pollution prevention. Regulation of groundwater in Wales was the responsibility of the Welsh National Water Development Authority (renamed Welsh Water Authority in 1977) and the Severn Trent Water Authority.

The ''Water Act, 1989'' enacted the privatisation of the regional water authorities, creating water supply and sewage treatment utility companies. Their regulatory functions passed to a new organisation, the National Rivers Authority, the detailed functions of which were set out in the ''Water Resource Act, 1991''. The Welsh Water Authority became Dŵr Cymru Welsh Water and is the principal supplier of drinking water and sewerage. Severn Trent provides the same function in the Severn Valley corridor in mid-Wales, with Dee Valley Water providing drinking water within the River Dee corridor in north-east Wales.

The''Environment Act, 1995''resulted in the formation of a statutory body, Environment Agency Wales, responsible for the management and protection of groundwater in Wales. On the 1st April 2013 a new regulatory body called Natural Resources Wales for formed combining the roles of Environment Agency Wales, Countryside Council for Wales and the Forestry Commission Wales.

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[Category:Hydrogeology of Wales| 033]]

Hydrogeology of Wales: Carboniferous aquifers - the Carboniferous Limestone aquifer

2015-07-28T19:34:11Z

Gareth Farr: add Farr&Bottrell 2013

{{HofW}}
The physical hydrogeology of the Carboniferous Limestone in Wales was first described by [[Hydrogeology of Wales: References|'''Richards (1959)''']] and in south Wales was later summarised by [[Hydrogeology of Wales: References|'''Allen et al. (1997)''']], and north Wales by [[Hydrogeology of Wales: References|'''Morris et al. (2000)''']]. The Carboniferous Limestone aquifers, the Clwyd Limestone Group in north Wales and the Pembroke Limestone Group in south Wales are used for public and private supply. A number of individual studies have been carried out in recent years on various aspects of groundwater occurrence and protection, particularly in south Wales. In addition there are some notable reports on speleological investigations which provide insight into the hydraulics of the karst aquifer. However, understanding of the regional flow mechanisms is patchy although considerable detail is available on a site specific basis.

[[Image:P802429.jpg|thumb|300px|Karstic Avon Group strata at Mynydd Llangattog. P802429.]]

Postdepositional faulting and folding took place in the Variscan Orogeny, and in north Wales coincident ore and gangue mineralisation occurred along some discontinuities. Solution channels may have begun to form along fractures as early as the Mesozoic, but the wetter climes of the Pleistocene produced most of the swallow holes and caverns, some collapsed as at Gwernymynydd in Flintshire, with many later infilled with rubble and detritus in the late- and post-glacial periods. Rapid solution of the limestone ('''Plate P802429''') occurs mainly in the zone of active circulation which is in contact with the atmosphere, i.e. at the water table, or above the level of passages and caverns into which the phreatic water drains. Fossil karstic horizons, now submerged beneath the water table, may reflect past changes in base level (see box below: Development of Karst in the Carboniferous Limestone).

Speleogenesis is the origin and development of [http://en.wikipedia.org/wiki/Cave caves], the primary process that determines the evolution of karst features. The development of caves through [http://en.wikipedia.org/wiki/Limestone limestone] is caused by water circulation with [http://en.wikipedia.org/wiki/Carbon_dioxide carbon dioxide] dissolved within it, producing [http://en.wikipedia.org/wiki/Carbonic_acid carbonic acid] which permits the [http://en.wikipedia.org/wiki/Dissociation_%28chemistry%29 dissociation] of the [http://en.wikipedia.org/wiki/Calcium_carbonate calcium carbonate] in the limestone. Available CO2 in rainwater can enable up to 33 mg l-1 CaCO3 to be taken into solution, increasing to 250 mg l-1 wherever the rainwater has percolated through soil or peat to gain an enhanced CO2 content. [[Hydrogeology of Wales: References|'''Ball and Jones (1990)''']] argue that the solution of the limestone is inadequate to explain the tight stratigraphical positioning of solution tubes in the north crop, situated at the northern periphery of the coal field, and that shallow aerobic dissolution requires a bacterial catalyst to promote the reaction. That the purer oolitic horizons are generally left intact whereas the more impure sulphate-rich beds are the target of dissolution suggests a role for sulphur-loving bacteria, although mechanical attrition is also an important process in cave formation.

In addition, dolomitisation of some of the limestone in the periphery of the South Wales Coalfield effects a reduction in overall volume and the creation of vugs and fractures. Although these may be calcite or silica infilled they generally lead to an overall increase in permeability ([[Hydrogeology of Wales: References|'''Thomas et al., 1983''']]).

=== North Wales ===

In Anglesey the Clwyd Limestone Group aquifer is located in limestones that were deposited in faulted basins and have been extensively dolomitised and silicified. Flow occurs through open joints and karstic zones although mudstone horizons have inhibited the downward percolation of acidic rainwater and karstification is better developed elsewhere in north Wales. Transmissivities from test pumping at four sites reported values from 0.15 to 1.8 m2 d-1 with yields of about 1 l s-1.

The Clwyd Limestone Group in north Wales crops out to the north of the Vale of Clwyd and in a narrow strip south towards Wrexham, and south of the Vale of Clwyd towards Colwyn Bay and Great Ormes Head, Llandudno ('''Figure P859272'''). There are basal units of grey and brown limestone and an upper unit of sandy limestone, but the majority of the sequence (c. 500 m thick) comprises white limestone. The limestone has been subject to brittle fracture and enlargement of secondary features by karstic dissolution. The limestone has a low intergranular permeability but substantial groundwater flow is possible through enlarged fissures. In the Clwyd catchment the limestone crops out without significant till cover and acts as a valuable indirect recharge source to the Triassic sandstones in the Clwyd basin, particularly in the area to the south of Ruthin (see [[Hydrogeology of Wales: Permo-Triassic and Jurassic aquifers | Permo-Triassic and Jurassic aquifers]]).
[[Image:P859272.jpg|thumb|center|550px|The distribution of Carboniferous strata in North Wales. P859272.]]

Groundwater flows through the limestone in the Clwyd catchment via fractures and available karst features in a north-easterly direction to discharge to the sea. Swallow holes are common in the main Clwyd Limestone Group outcrop to the east of the Vale of Clwyd. Ffynnon Asaph [SJ 0752 7893] which flows at 4.3 Ml d-1 traditionally supplied the town of Prestatyn. Local metal mining in the limestone has exposed a number of cave and conduit systems, some of which have had a direct effect on mine dewatering.

In the Halkyn Mountain area, around Caerwys, between Cilcain and Llanferres and in the Gwernymynydd district, fossil swallow holes containing sands, clays and weathered cherts have been exposed during mining.

Other surface waters with low flows subject to loss into the limestone include the Afon Clywedog, a tributary of the Dee to the west of Wrexham, and the Afon Alyn which is dry on average for 170 days per year between Loggerheads and Rhydymwyn some 4 km above Mold ([[Hydrogeology of Wales: References|'''National Rivers Authority, 1993''']]). The Afon Alyn otherwise often disappears into a swallow hole north of Plas-yr-esgob [SJ 188 644] and re-emerges into the dry river bed just above the confluence with the Cilcain stream [SJ 187 652], below which it can be intermittently dry as far as Hesp Alyn [SJ 188 653]. The Ogof Hesp Alyn cave system has only been discovered in recent years ([[Hydrogeology of Wales: References|'''Appleton, 1974''']]) and its description illustrates the complex processes of capture, solution and attrition that combine to create such underground features. The Afon Alyn water loss is not a new phenomenon, and legend has it that a giant, when set on fire by St Cynhafal, jumped into the river to extinguish the flames whereupon the river, which was turned to steam, ceased to flow, and has only flowed intermittently ever since.

Caverns also occur west of the Vale of Clwyd at Cefn and Plas Henton and to the east at Ffynnon Beuno and Bae Gwyn. The elevation of these cave systems relative to today’s base level suggests that they all originated in the Pleistocene when sea level was about 15 m higher than it is today.

Attempts to prevent water from the River Alyn from entering the Halkyn Mine via swallow holes during the 1930s were largely unsuccessful ([[Hydrogeology of Wales: References|'''Water Resources Board, 1973''']]). A number of drainage schemes were implemented to protect the mines and their drainage used to supply industry:

:* the Halkyn Tunnel, 8 km in length across Halkyn Mountain
:* Government (War) Drainage Scheme – pumping from Taylor’s Shaft, North Hendre at 300 l s-1 into the Halkyn Tunnel
:* Milwr Sea Tunnel which was designed to lower the water table in the limestone across the Halkyn Mountain area. The minimum yield is about 55 000 m3 d-1 representing run-off from the surrounding hills onto the limestone as well as lost river water.

Borehole yields are highly variable and unpredictable, with good supplies only obtained if water-filled fractures with access to recharge are intersected. For example, a borehole drilled in Anglesey into a mixed sedimentary sequence in Carboniferous strata at Llanbedrgoch [SH 493 803] to a depth of 65 m yielded only 2.5 l s-1 over a two-hour pumping day. Two previous drilling attempts in the same vicinity at Llanbedgroch, however, had failed to find any trace of water. [[Hydrogeology of Wales: References|'''Robins and McKenzie (2005)''']] showed that the density of occurrence of wells on Anglesey in the Clwyd Limestone Group was 1.3 km-2 and of springs was 1.6 km-2. Yields are typically small with many springs being little more than minor seepages.

Groundwater chemistry on Anglesey is consistently of the Ca-HCO3 type, with a small subset tending towards Na, Mg and Cl dominance. The groundwater is oxic (Eh >127 mV) has near neutral pH, Ca ranging from 60 to 130 mg l-1 and NO3 typically < 25 mg l-1 ([[Hydrogeology of Wales: References|'''Banks et al., 2008''']]).

=== South Wales ===

In Carmarthenshire, the basal Avon Group, with thin shaly and muddy limestones, are overlain by karstic massive crystalline, fossiliferous to dolomitised limestones up to 100 to 150 m thick. These are overlain by the Oystermouth Formation (formerly the Upper Limestone Shales). The limestone has a low primary porosity. Transmissivity is between 10 and 20 m2 d-1 and storage coefficients of between 4 and 9 x 10-4 have been obtained from a small number of borehole pumping tests. Boreholes at Trapp yield 144 m3 d-1 to 240 m3 d-1. The source of the Loughor, located on a faulted contact of limestone and Marros Group grits, flows at 60 to 1000 l s-1 with a connection to caves 7 km away.

The Pembroke Limestone Group outcrop is thin both north and east of the coalfield, and to the south of the coalfield it has been eroded into a broad platform in the Vale of Glamorgan, the Gower and parts of Pembrokeshire. The strata are characterised by a basal shaly mudstone, followed by thick massive dolomitic, oolitic and bioclastic limestones and an upper mixed sequence of shale and muddy limestone. Chert may be abundant within the main limestone. In Pembrokeshire, the Pembroke Limestone Group aquifer discharges into the Bosherton ponds via spring systems at Frainslake and Bosherton. Groundwater is abstracted at Pendine for use in public supply.

Various attempts have been made to establish the water balance over all or part of the limestone outcrops. Work by [[Hydrogeology of Wales: References|'''Aspinwall and Co (1993)''']] focussed on the Vale of Glamorgan and the capture zones of the Schwyll Spring [SS 888 771] and the Pwllwy Borehole and springs [SS 992 766] noting that the water balance calculations showed that a large part of the recharge could not be accounted for and was presumably lost as offshore submarine springs. Schwyll and Pwllwy near Bridgend are believed respectively to derive from a variety of sinks on the rivers Ogmore, Ewenny, Alun and Methyr Mawr up to 7 km away ([[Hydrogeology of Wales: References|'''Hobbs, 2000''']]), whereas the Pwllwy has a more local catchment. Although rarely used for public supply, Welsh Water retains an abstraction license for 7.955 Mm3 a-1 from the Schwyll Spring sources, although they are not currently in use and [[Hydrogeology of Wales: References|'''Hobbs (1993)''']] estimated the total yield of the spring at 12.3 Mm3 a-1 derived partly from influent rivers, the Ogmore and to a lesser extent the Ewenny, and partly from groundwater. These springs periodically had to be disconnected from supply during very wet weather when the outflow became turbid. The springs can also suffer from reversed hydraulic head during periods of exceptional high spring tides when dirty surface water can ingress some of the spring heads. [[Hydrogeology of Wales: References|'''Aldous (1988a)''']] used detailed site specific knowledge to attempt to delineate flowpaths and likely transport fields for contaminant movement in the aquifer. [[Hydrogeology of Wales: References|'''Hobbs (1993)''']] identified a number of sinks and risings in the area:

:: Merthyr Mawr sinks [SS 8901 7763] on the western bank of the Ogmore river and rise at two springs which flow into the Mythyr Mawr Mill Leat [SS 88657763]

:: Pitcot Pool [SS 8955 7443] is spring fed

:: Jacobs Well [SS 9121 7480] a series of springs alongside the Afon Alun

:: Byeastwood Springs [SS 9298 8099 and SS 9258 8060] flow eventually into the River Ewenny

:: Hoel-las stream sink [SS 9288 8267], now concealed beneath the M4 motorway, and smaller sinks to the east take water draining off the Coal Measures

:: Tymaen sink [SS 8943 7705]

:: Ewenny Fach sink [SS 9542 7990] a sink in the bed of the River Ewenny

[[Image:P802428.jpg|thumb|200px|One of many springs flowing from boggy ground at the junction of the basal Namurian grit and the underlying Avon Group near Trefil, north of Tredegar . P802428.]]
In the area of the Schwyll Spring and Pwllwy Borehole and springs the Pembroke Limestone Group is over 500 m thick comprising a southward thickening alternating bioclastic and oolitic limestone 700 to 800 m thick. This is underlain by the basal Avon Group shales which are about 100 m thick. Aquifer transmissivities range between 4 and 130 m2 d-1, and hydraulic conductivity range between 0.1 and 5 m d-1. The effective porosity of the upper 8 to 10 m of the aquifer ranges between 6 and 8 per cent, reducing to 0.5-2 per cent below this. Among other sources, boreholes drawing from the concealed Pembroke Limestone Group at Bridgend contribute to public supply.

Near Llandybie at Pant-y-Llyn on the north-western limb of the coalfield is a small turlough, the only known active turlough in Wales. Pant-y-Llyn [SN 60167] is a small depression in the limestone which fills with water rising from the Pembroke Limestone Group along its faulted boundary with the Devonian Brownstones, usually in the autumn, and drains to estavelles in the late spring ([[Hydrogeology of Wales: References|'''Campbell et al., 1992)''']]. In flood it is some 160 by 60 m in area and up to 4 m deep.

Swallow holes are common over much of the limestone outcrop and also occur beneath a thin cover of the basal beds of the Marros Group grits. Particularly large examples with collapsed caverns occur at Mynydd y Glog north of Hirwaun, whereas linear developments of swallow holes occur along lines of weakness at Ystradfellte and east of Trefil. Numerous examples are present on the Twrch Sandstone Formation (formerly the Basal Grit) on the Llangattwg and Llangynidir mountains, some blocked by fine detritus to form small ponds such as Pwll Mawr which is situated on the interfluve between the Neath and the Tawe valleys.

There are numerous closely spaced swallow holes on the north crop, some of which are nothing more than open fractures. There are some 80 000 dolines on the north crop alone ([[Hydrogeology of Wales: References|'''Crowther, 1989''']]), and collectively these provide drainage to the limestone outcrop. The swallow water tends to flow southwards down dip and beneath the cover of the Bishopton Mudstone Formation. In wet conditions it rises up through the shale to emerge above Blaen-Rhymney, and much like a Chalk bourne, creates river flow where normally the bed is dry. A similar, but less ephemeral discharge near Blaen-Sirhowy was once used for public supply. There are also a few springs on the northern scarp slope. In addition there are a number of caverns beneath the north crop especially around the headwaters of the rivers Tawe and Neath.

Some caves reflect past sea levels; Little Hoyle and Hoyle’s Mouth near Tenby are about 15 m above sea level reflecting the Pleistocene sea level. The Bacon, Minchin and Paviland caves in Gower were also formed during the Pleistocene when the sea level was elevated relative to the present level.

There are numerous examples of sinks and risings (see '''Active karst systems table '''and '''Plate P802428'''). The headwaters of the Neath, including the Hepste, Mellte and Nedd-Fechan all come off the Devonian sandstone and disappear into sinks in the limestone. At the head of the Swansea valley the Llynfell flows out of the Dan-yr-Ogof cave whilst nearby the River Giedd disappears into a swallow hole. There are show caves in the Tawe Valley at the mouth of the Dan Yr Ogof cave system. The caves drain the Sink y Giedd [SN 810 179] and Waun Fignen-felen [SN 826 177] with a combined discharge of between 0.15 and 0.30 m3 s-1 depending on weather conditions ([[Hydrogeology of Wales: References|'''Coase and Judson, 1977''']]). Average flow rates of 0.14 and 0.13 km hr-1 respectively have been demonstrated with dye testing (see '''dye tests table '''). A number of dolines (e.g. the ‘Crater’) and other hollows overlie the cave system, but the remnant dry valleys occasionally flow during exceptionally wet weather.

<center>
{| class="wikitable"
|+ Selected active karst systems within the north crop (from east to west), see [[Hydrogeology of Wales: References|'''Gascoine (1989''']]).
|-
| Area
| Grid Square
| Comments
|-
| Afon Lwyd
| SO 20
| A series of sinks and caves leading to four resurgences. Pontnewynydd Risings typically issue at 6 Ml d-1.
|-
| Llangattwg
| SO 21
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Mynydd Llangynidr
| SO 21
| The main resurgence is Fynnon Shon Sheffrey [SO 1265 1188]. Dye tracing has proved the relationship between various sinks and risings ('''Figure 5.2''').
|-
| The Rhymney Valley
| SO 01
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Taff Fechan and Taff Fawr
| SO 01
| Includes Nant y Glais caves and resurgences, otherwise connections proven by dye tracing.
|-
| Cwm Cadlan and Penderyn
| SN 90
| Llygad Cynon is source of the Afon Cynon. An adjacent borehole [SN 9524 0774] reported an ‘underground lake’ at 55 m and is pumped at 5 Ml d‑1.
|-
| Afon Hepste
| SN 90
| Upper Hepste Main Sink [SN 9541 1208] discharges back to the river at Hepste Main Resurgence [SN 9360 0973] in under 24 hours.
|-
| Afon Mellte
| SN 91
| The main Mellte Sink [SN 9315 1332] has proven connections to five resurgences. Contributions also from smaller sinks.
|-
| Nedd Fechan
| SN 91
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Glyntawe and the Black Mountain
| SN 81
| Two main cave systems behind main resurgences at Glyntawe
|-
| The Twrch valley
| SN 71
| Fault-controlled resurgences.
|-
| Black Mountain – western area
| SN 61
| 7 km from main sink to resurgence proven by dye tracing.
|}
</center> <center>
{| class="wikitable"
|+ Relationship between dye tests from Waun Fignen-felen and Sink y Giedd, after [[Hydrogeology of Wales: References|'''Coase and Judson (1977)''']].
|-
|
| From Waen Fignen Felen
| From Sink y Giedd
|-
| Distance from sink to resurgence (km)
| 3.5
| 4.7
|-
| Time for dye to reach resurgence (hours)
| 25
| 36
|-
| Average flow rate (km hour-1)
| 0.14
| 0.13
|-
| Elevation of sink above resurgence (m)
| 248
| 218
|}
</center>

Other celebrated groups of caves include the Nant y Glais caves to the south of the Vaynor Moors on the north crop: Ogof Robin Goch [SO 0392 1076], Ogof y Ci [SO 0403 1051], Ogof Dŵr Dwfn [SO 0415 1022], Ogof Rhyd Sych [SO 0416 1021], Ogof Pysgodyn Gwyn [SO 0416 1016] and Ogof Jonny Bach [SO 0420 1000]. The Nant y Glais river disappears underground altogether as it traverses the cave system except in exceptionally wet weather when flow also occurs through a narrow gorge at surface ([[Hydrogeology of Wales: References|'''Ford, 1989''']]).

[[Hydrogeology of Wales: References|'''Gascoine (1989''']]) reviewed other cave systems within the north crop. Many of the sinks are situated at the feather edge of the Marros Group where it is only a few metres thick above the limestone ('''Figure P859273'''), whilst others provide connections from the Avon Group shales and the main limestone. One of the longer and more complex cave systems is Ogof Draenen [SO 2467 1176] at the eastern edge of the north crop. Numerous dolines and stream sinks are present in the area and speleological investigation recognises numerous underfit streams in large passages. [[Hydrogeology of Wales: References|'''Maurice and Guilford (2011)''']] have identified a watershed within the system whereby flow occurs both to the north to Clydach Gorge and to the south to the Afon Lwyd. The latter is in a different topographical catchment some 8 km distant and tracer testing indicates velocities of 4 km d-1.
[[Image:P859273.jpg|thumb|center|600px|Sketch map of the Pembroke Limestone group outcrop along the North Crop (after Gasgoine, 1989). P859273.]]

A wide range of borehole yields have been established depending on the hydraulic contact with productive fractures. Drilling is always speculative as targeting useful fractures is not easy. The average yield from Carboniferous Limestone Supergroup boreholes across the UK was shown by [[Hydrogeology of Wales: References|'''Monkhouse (1977)''']] to be just 4 l s-1, but there is no record of the numbers of boreholes that were abandoned as dry, while other boreholes may have a significantly higher yield.

Although fractures and karstification rapidly decreases under the cover of the Marros Group there is some evidence of deep groundwater circulation beneath the coalfield. Taff’s Well [ST 1193 8364] discharges groundwater at about 1 l s-1 from the South Wales Coal Measures Group with a temperature of 21.6 oC, the only thermal spring in Wales ([[Hydrogeology of Wales: References|'''Farr and Bottrell, 2013''']] . Previous measurements reported a variety of temperatures all less than 20 oC but these were subject to mixing with water from the River Taff which is now prevented by new flood works. Simple inspection of the geothermal gradient and of the discharge water chemistry suggests a deep flow path, probably in the Pembroke Limestone Group, which is believed to travel to a depth of about 700 m ([[Hydrogeology of Wales: References|'''Squirrell and Downing, 1969'''; '''Thomas et al., 1983''']]). Dissolved inert gas analysis indicates that the water infiltrated the ground some 500 m higher in elevation than Taff’s Well, suggesting a recharge source somewhere along the north crop ([[Hydrogeology of Wales: References|'''Burgess et al., 1980''']]; [[Hydrogeology of Wales: References|'''Edmunds, 1986''']]). The water is between 5000 and 10 000 years old based on δ18O and δ2H age indicators ([[Hydrogeology of Wales: References|'''Farr and Bottrell, 2013''']].

A major spring was encountered in the concealed limestone in 1879 during the digging of the Severn Railway Tunnel. Here a spring discharge of 1000 l s-1 was encountered, the Great Spring, which has been pumped to surface ever since ([[Hydrogeology of Wales: References|'''Drew et al., 1970''']]). Of good quality, it has been used for a variety of purposes including supply to the nearby Margam Steel Works, the Caerwent military establishment, a paper mill and latterly for public supply.

Water quality in the limestones is typified by slightly alkaline pH up to 7.6, and alkalinity concentrations (as CaCO3) ranging upwards to 230 mg l-1. The lower values reflect immature waters that have not attained Ca saturation. In north Wales, local mineralisation in the limestones promotes the solution of metals but at barely detectable concentrations. There are distinct tidal influences on some low-lying coastal areas of south Wales (including the Schwyll Spring) and a marine mixing zone in selected fractures is indicated by enhanced concentrations of Na and Cl at some sources.

A number of detailed site-specific investigations have been carried out on the limestone aquifer in south Wales which provide insight into its hydraulic processes. One such study was carried out between Porthcawl and Port Talbot looking at the environmental impact of extending local quarries in the Pembroke Limestone Group on a wetland area within adjacent superficial deposits ([[Hydrogeology of Wales: References|'''Cheney et al., 2000''']]). This work drew on extensive monitoring and analysis carried out previously in the area but was unable to develop a robust groundwater flow model due to data scarcity and the complex nature of flow in a karstic system. In addition 95 per cent of the water balance was unaccountable, suspected to drain to submarine springs in the Bristol Channel.

Groundwater is typically of the Ca-HCO3 type, with HCO3 typically in the range 90 to 550 mg l-1, the weakest mineralisation occurring along the north crop. The pH is almost always alkaline with values up to 8.2. Cl concentrations are generally low (<50 mg l-1) except on the coast near Porthcawl at Rest Bay where some private sources suffer from saline intrusion ([[Hydrogeology of Wales: References|'''Jones, 2007''']]) and in parts of the Gower Peninsula where sea spray may be the cause of elevated Na and Cl concentrations. The same pattern emerges in Pembrokeshire where Ca-HCO3 type is dominant with subordinate Na/Mg-Cl type but here it is possibly caused by ion exchange in waters that are older than in the limestone around the South Wales Coalfield ([[Hydrogeology of Wales: References|'''Fahrner et al., 2008''']]).

{| cellspacing="0" cellpadding="5" border="1"
| <center>'''Development of Karst in the Avon Group'''</center>

The development of the karst features found today in the Avon Group in south Wales reflects a continuing process which commenced almost as soon as the rocks were laid down. The most active zone of karstification is the vadose zone where unsaturated water can move freely through bedding planes and other discontinuities, but the phreatic zone may also be active when groundwater chemistry changes due to long-term effects of mixing. There were three intensive phases of karstic development: the Lower Carboniferous, the late Triassic and the Palaeogene through to the Quaternary.

The Lower Carboniferous palaeokarstic surfaces developed as the limestone initially rose out of the sea. Clay and mudstone beds, representing fossil soils, overlie the hummocky erosion surface, with discrete fissures in the limestone infilled with the soil material below. This is characteristic of both south Wales ([[Hydrogeology of Wales: References|'''Wilson et al., 1990''']]) and north Wales ([[Hydrogeology of Wales: References|'''Davies, 1991''']]) where relief varies between only a few centimetres to a few metres.

Uplift during the late Carboniferous Variscan Orogeny initiated a protracted period of erosion which lasted through to the Jurassic Period. By Late Triassic times a network of fissures and caverns had been created, some of which had already been partly infilled with rubble and clay. Mineralised hydrothermal waters may have added to the process leading to the deposition of galena and barites on fissure walls. [[Hydrogeology of Wales: References|'''Wilson et al. (1990)''']] recognised three types of karst feature in south Wales: dilated joints, irregular shaped cavities developed along bedding plains, and subvertical cylindrical pipes.

During the Palaeogene and Quaternary periods, large periodic fluctuations in sea level caused fluctuations also in the location of the vadose zone, and new and some pre-existing conduit features were developed, many now below the present-day water table. Three types of feature were created: dolines (collapsed caverns), linear fissures and large cavities. These features are commonly backfilled with silt and rubble debris. [[Hydrogeology of Wales: References|'''Gunn (1992)''']] asserted that the larger features could only develop where they were fed by a river or stream sink, and the Dan yr Ogof system was once fed by the River Haffes which has since been captured and redirected.

Reactivation of karst conduit systems has been recorded at a number of sites. At Stormy Down Quarry [SS 845 800] discharging into a doline reactivated the karst system such that extensive remedial action was required in the vicinity during the construction of the M4 motorway ([[Hydrogeology of Wales: References|'''Aldous, 1988b''']]).
|}

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[Category:Hydrogeology of Wales| 017]]

Hydrogeology of Wales: Carboniferous aquifers - the Carboniferous Limestone aquifer

2015-07-28T19:31:44Z

Gareth Farr: add Farr&Bottrell 2013 ref to taffs well section

{{HofW}}
The physical hydrogeology of the Carboniferous Limestone in Wales was first described by [[Hydrogeology of Wales: References|'''Richards (1959)''']] and in south Wales was later summarised by [[Hydrogeology of Wales: References|'''Allen et al. (1997)''']], and north Wales by [[Hydrogeology of Wales: References|'''Morris et al. (2000)''']]. The Carboniferous Limestone aquifers, the Clwyd Limestone Group in north Wales and the Pembroke Limestone Group in south Wales are used for public and private supply. A number of individual studies have been carried out in recent years on various aspects of groundwater occurrence and protection, particularly in south Wales. In addition there are some notable reports on speleological investigations which provide insight into the hydraulics of the karst aquifer. However, understanding of the regional flow mechanisms is patchy although considerable detail is available on a site specific basis.

[[Image:P802429.jpg|thumb|300px|Karstic Avon Group strata at Mynydd Llangattog. P802429.]]

Postdepositional faulting and folding took place in the Variscan Orogeny, and in north Wales coincident ore and gangue mineralisation occurred along some discontinuities. Solution channels may have begun to form along fractures as early as the Mesozoic, but the wetter climes of the Pleistocene produced most of the swallow holes and caverns, some collapsed as at Gwernymynydd in Flintshire, with many later infilled with rubble and detritus in the late- and post-glacial periods. Rapid solution of the limestone ('''Plate P802429''') occurs mainly in the zone of active circulation which is in contact with the atmosphere, i.e. at the water table, or above the level of passages and caverns into which the phreatic water drains. Fossil karstic horizons, now submerged beneath the water table, may reflect past changes in base level (see box below: Development of Karst in the Carboniferous Limestone).

Speleogenesis is the origin and development of [http://en.wikipedia.org/wiki/Cave caves], the primary process that determines the evolution of karst features. The development of caves through [http://en.wikipedia.org/wiki/Limestone limestone] is caused by water circulation with [http://en.wikipedia.org/wiki/Carbon_dioxide carbon dioxide] dissolved within it, producing [http://en.wikipedia.org/wiki/Carbonic_acid carbonic acid] which permits the [http://en.wikipedia.org/wiki/Dissociation_%28chemistry%29 dissociation] of the [http://en.wikipedia.org/wiki/Calcium_carbonate calcium carbonate] in the limestone. Available CO2 in rainwater can enable up to 33 mg l-1 CaCO3 to be taken into solution, increasing to 250 mg l-1 wherever the rainwater has percolated through soil or peat to gain an enhanced CO2 content. [[Hydrogeology of Wales: References|'''Ball and Jones (1990)''']] argue that the solution of the limestone is inadequate to explain the tight stratigraphical positioning of solution tubes in the north crop, situated at the northern periphery of the coal field, and that shallow aerobic dissolution requires a bacterial catalyst to promote the reaction. That the purer oolitic horizons are generally left intact whereas the more impure sulphate-rich beds are the target of dissolution suggests a role for sulphur-loving bacteria, although mechanical attrition is also an important process in cave formation.

In addition, dolomitisation of some of the limestone in the periphery of the South Wales Coalfield effects a reduction in overall volume and the creation of vugs and fractures. Although these may be calcite or silica infilled they generally lead to an overall increase in permeability ([[Hydrogeology of Wales: References|'''Thomas et al., 1983''']]).

=== North Wales ===

In Anglesey the Clwyd Limestone Group aquifer is located in limestones that were deposited in faulted basins and have been extensively dolomitised and silicified. Flow occurs through open joints and karstic zones although mudstone horizons have inhibited the downward percolation of acidic rainwater and karstification is better developed elsewhere in north Wales. Transmissivities from test pumping at four sites reported values from 0.15 to 1.8 m2 d-1 with yields of about 1 l s-1.

The Clwyd Limestone Group in north Wales crops out to the north of the Vale of Clwyd and in a narrow strip south towards Wrexham, and south of the Vale of Clwyd towards Colwyn Bay and Great Ormes Head, Llandudno ('''Figure P859272'''). There are basal units of grey and brown limestone and an upper unit of sandy limestone, but the majority of the sequence (c. 500 m thick) comprises white limestone. The limestone has been subject to brittle fracture and enlargement of secondary features by karstic dissolution. The limestone has a low intergranular permeability but substantial groundwater flow is possible through enlarged fissures. In the Clwyd catchment the limestone crops out without significant till cover and acts as a valuable indirect recharge source to the Triassic sandstones in the Clwyd basin, particularly in the area to the south of Ruthin (see [[Hydrogeology of Wales: Permo-Triassic and Jurassic aquifers | Permo-Triassic and Jurassic aquifers]]).
[[Image:P859272.jpg|thumb|center|550px|The distribution of Carboniferous strata in North Wales. P859272.]]

Groundwater flows through the limestone in the Clwyd catchment via fractures and available karst features in a north-easterly direction to discharge to the sea. Swallow holes are common in the main Clwyd Limestone Group outcrop to the east of the Vale of Clwyd. Ffynnon Asaph [SJ 0752 7893] which flows at 4.3 Ml d-1 traditionally supplied the town of Prestatyn. Local metal mining in the limestone has exposed a number of cave and conduit systems, some of which have had a direct effect on mine dewatering.

In the Halkyn Mountain area, around Caerwys, between Cilcain and Llanferres and in the Gwernymynydd district, fossil swallow holes containing sands, clays and weathered cherts have been exposed during mining.

Other surface waters with low flows subject to loss into the limestone include the Afon Clywedog, a tributary of the Dee to the west of Wrexham, and the Afon Alyn which is dry on average for 170 days per year between Loggerheads and Rhydymwyn some 4 km above Mold ([[Hydrogeology of Wales: References|'''National Rivers Authority, 1993''']]). The Afon Alyn otherwise often disappears into a swallow hole north of Plas-yr-esgob [SJ 188 644] and re-emerges into the dry river bed just above the confluence with the Cilcain stream [SJ 187 652], below which it can be intermittently dry as far as Hesp Alyn [SJ 188 653]. The Ogof Hesp Alyn cave system has only been discovered in recent years ([[Hydrogeology of Wales: References|'''Appleton, 1974''']]) and its description illustrates the complex processes of capture, solution and attrition that combine to create such underground features. The Afon Alyn water loss is not a new phenomenon, and legend has it that a giant, when set on fire by St Cynhafal, jumped into the river to extinguish the flames whereupon the river, which was turned to steam, ceased to flow, and has only flowed intermittently ever since.

Caverns also occur west of the Vale of Clwyd at Cefn and Plas Henton and to the east at Ffynnon Beuno and Bae Gwyn. The elevation of these cave systems relative to today’s base level suggests that they all originated in the Pleistocene when sea level was about 15 m higher than it is today.

Attempts to prevent water from the River Alyn from entering the Halkyn Mine via swallow holes during the 1930s were largely unsuccessful ([[Hydrogeology of Wales: References|'''Water Resources Board, 1973''']]). A number of drainage schemes were implemented to protect the mines and their drainage used to supply industry:

:* the Halkyn Tunnel, 8 km in length across Halkyn Mountain
:* Government (War) Drainage Scheme – pumping from Taylor’s Shaft, North Hendre at 300 l s-1 into the Halkyn Tunnel
:* Milwr Sea Tunnel which was designed to lower the water table in the limestone across the Halkyn Mountain area. The minimum yield is about 55 000 m3 d-1 representing run-off from the surrounding hills onto the limestone as well as lost river water.

Borehole yields are highly variable and unpredictable, with good supplies only obtained if water-filled fractures with access to recharge are intersected. For example, a borehole drilled in Anglesey into a mixed sedimentary sequence in Carboniferous strata at Llanbedrgoch [SH 493 803] to a depth of 65 m yielded only 2.5 l s-1 over a two-hour pumping day. Two previous drilling attempts in the same vicinity at Llanbedgroch, however, had failed to find any trace of water. [[Hydrogeology of Wales: References|'''Robins and McKenzie (2005)''']] showed that the density of occurrence of wells on Anglesey in the Clwyd Limestone Group was 1.3 km-2 and of springs was 1.6 km-2. Yields are typically small with many springs being little more than minor seepages.

Groundwater chemistry on Anglesey is consistently of the Ca-HCO3 type, with a small subset tending towards Na, Mg and Cl dominance. The groundwater is oxic (Eh >127 mV) has near neutral pH, Ca ranging from 60 to 130 mg l-1 and NO3 typically < 25 mg l-1 ([[Hydrogeology of Wales: References|'''Banks et al., 2008''']]).

=== South Wales ===

In Carmarthenshire, the basal Avon Group, with thin shaly and muddy limestones, are overlain by karstic massive crystalline, fossiliferous to dolomitised limestones up to 100 to 150 m thick. These are overlain by the Oystermouth Formation (formerly the Upper Limestone Shales). The limestone has a low primary porosity. Transmissivity is between 10 and 20 m2 d-1 and storage coefficients of between 4 and 9 x 10-4 have been obtained from a small number of borehole pumping tests. Boreholes at Trapp yield 144 m3 d-1 to 240 m3 d-1. The source of the Loughor, located on a faulted contact of limestone and Marros Group grits, flows at 60 to 1000 l s-1 with a connection to caves 7 km away.

The Pembroke Limestone Group outcrop is thin both north and east of the coalfield, and to the south of the coalfield it has been eroded into a broad platform in the Vale of Glamorgan, the Gower and parts of Pembrokeshire. The strata are characterised by a basal shaly mudstone, followed by thick massive dolomitic, oolitic and bioclastic limestones and an upper mixed sequence of shale and muddy limestone. Chert may be abundant within the main limestone. In Pembrokeshire, the Pembroke Limestone Group aquifer discharges into the Bosherton ponds via spring systems at Frainslake and Bosherton. Groundwater is abstracted at Pendine for use in public supply.

Various attempts have been made to establish the water balance over all or part of the limestone outcrops. Work by [[Hydrogeology of Wales: References|'''Aspinwall and Co (1993)''']] focussed on the Vale of Glamorgan and the capture zones of the Schwyll Spring [SS 888 771] and the Pwllwy Borehole and springs [SS 992 766] noting that the water balance calculations showed that a large part of the recharge could not be accounted for and was presumably lost as offshore submarine springs. Schwyll and Pwllwy near Bridgend are believed respectively to derive from a variety of sinks on the rivers Ogmore, Ewenny, Alun and Methyr Mawr up to 7 km away ([[Hydrogeology of Wales: References|'''Hobbs, 2000''']]), whereas the Pwllwy has a more local catchment. Although rarely used for public supply, Welsh Water retains an abstraction license for 7.955 Mm3 a-1 from the Schwyll Spring sources, although they are not currently in use and [[Hydrogeology of Wales: References|'''Hobbs (1993)''']] estimated the total yield of the spring at 12.3 Mm3 a-1 derived partly from influent rivers, the Ogmore and to a lesser extent the Ewenny, and partly from groundwater. These springs periodically had to be disconnected from supply during very wet weather when the outflow became turbid. The springs can also suffer from reversed hydraulic head during periods of exceptional high spring tides when dirty surface water can ingress some of the spring heads. [[Hydrogeology of Wales: References|'''Aldous (1988a)''']] used detailed site specific knowledge to attempt to delineate flowpaths and likely transport fields for contaminant movement in the aquifer. [[Hydrogeology of Wales: References|'''Hobbs (1993)''']] identified a number of sinks and risings in the area:

:: Merthyr Mawr sinks [SS 8901 7763] on the western bank of the Ogmore river and rise at two springs which flow into the Mythyr Mawr Mill Leat [SS 88657763]

:: Pitcot Pool [SS 8955 7443] is spring fed

:: Jacobs Well [SS 9121 7480] a series of springs alongside the Afon Alun

:: Byeastwood Springs [SS 9298 8099 and SS 9258 8060] flow eventually into the River Ewenny

:: Hoel-las stream sink [SS 9288 8267], now concealed beneath the M4 motorway, and smaller sinks to the east take water draining off the Coal Measures

:: Tymaen sink [SS 8943 7705]

:: Ewenny Fach sink [SS 9542 7990] a sink in the bed of the River Ewenny

[[Image:P802428.jpg|thumb|200px|One of many springs flowing from boggy ground at the junction of the basal Namurian grit and the underlying Avon Group near Trefil, north of Tredegar . P802428.]]
In the area of the Schwyll Spring and Pwllwy Borehole and springs the Pembroke Limestone Group is over 500 m thick comprising a southward thickening alternating bioclastic and oolitic limestone 700 to 800 m thick. This is underlain by the basal Avon Group shales which are about 100 m thick. Aquifer transmissivities range between 4 and 130 m2 d-1, and hydraulic conductivity range between 0.1 and 5 m d-1. The effective porosity of the upper 8 to 10 m of the aquifer ranges between 6 and 8 per cent, reducing to 0.5-2 per cent below this. Among other sources, boreholes drawing from the concealed Pembroke Limestone Group at Bridgend contribute to public supply.

Near Llandybie at Pant-y-Llyn on the north-western limb of the coalfield is a small turlough, the only known active turlough in Wales. Pant-y-Llyn [SN 60167] is a small depression in the limestone which fills with water rising from the Pembroke Limestone Group along its faulted boundary with the Devonian Brownstones, usually in the autumn, and drains to estavelles in the late spring ([[Hydrogeology of Wales: References|'''Campbell et al., 1992)''']]. In flood it is some 160 by 60 m in area and up to 4 m deep.

Swallow holes are common over much of the limestone outcrop and also occur beneath a thin cover of the basal beds of the Marros Group grits. Particularly large examples with collapsed caverns occur at Mynydd y Glog north of Hirwaun, whereas linear developments of swallow holes occur along lines of weakness at Ystradfellte and east of Trefil. Numerous examples are present on the Twrch Sandstone Formation (formerly the Basal Grit) on the Llangattwg and Llangynidir mountains, some blocked by fine detritus to form small ponds such as Pwll Mawr which is situated on the interfluve between the Neath and the Tawe valleys.

There are numerous closely spaced swallow holes on the north crop, some of which are nothing more than open fractures. There are some 80 000 dolines on the north crop alone ([[Hydrogeology of Wales: References|'''Crowther, 1989''']]), and collectively these provide drainage to the limestone outcrop. The swallow water tends to flow southwards down dip and beneath the cover of the Bishopton Mudstone Formation. In wet conditions it rises up through the shale to emerge above Blaen-Rhymney, and much like a Chalk bourne, creates river flow where normally the bed is dry. A similar, but less ephemeral discharge near Blaen-Sirhowy was once used for public supply. There are also a few springs on the northern scarp slope. In addition there are a number of caverns beneath the north crop especially around the headwaters of the rivers Tawe and Neath.

Some caves reflect past sea levels; Little Hoyle and Hoyle’s Mouth near Tenby are about 15 m above sea level reflecting the Pleistocene sea level. The Bacon, Minchin and Paviland caves in Gower were also formed during the Pleistocene when the sea level was elevated relative to the present level.

There are numerous examples of sinks and risings (see '''Active karst systems table '''and '''Plate P802428'''). The headwaters of the Neath, including the Hepste, Mellte and Nedd-Fechan all come off the Devonian sandstone and disappear into sinks in the limestone. At the head of the Swansea valley the Llynfell flows out of the Dan-yr-Ogof cave whilst nearby the River Giedd disappears into a swallow hole. There are show caves in the Tawe Valley at the mouth of the Dan Yr Ogof cave system. The caves drain the Sink y Giedd [SN 810 179] and Waun Fignen-felen [SN 826 177] with a combined discharge of between 0.15 and 0.30 m3 s-1 depending on weather conditions ([[Hydrogeology of Wales: References|'''Coase and Judson, 1977''']]). Average flow rates of 0.14 and 0.13 km hr-1 respectively have been demonstrated with dye testing (see '''dye tests table '''). A number of dolines (e.g. the ‘Crater’) and other hollows overlie the cave system, but the remnant dry valleys occasionally flow during exceptionally wet weather.

<center>
{| class="wikitable"
|+ Selected active karst systems within the north crop (from east to west), see [[Hydrogeology of Wales: References|'''Gascoine (1989''']]).
|-
| Area
| Grid Square
| Comments
|-
| Afon Lwyd
| SO 20
| A series of sinks and caves leading to four resurgences. Pontnewynydd Risings typically issue at 6 Ml d-1.
|-
| Llangattwg
| SO 21
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Mynydd Llangynidr
| SO 21
| The main resurgence is Fynnon Shon Sheffrey [SO 1265 1188]. Dye tracing has proved the relationship between various sinks and risings ('''Figure 5.2''').
|-
| The Rhymney Valley
| SO 01
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Taff Fechan and Taff Fawr
| SO 01
| Includes Nant y Glais caves and resurgences, otherwise connections proven by dye tracing.
|-
| Cwm Cadlan and Penderyn
| SN 90
| Llygad Cynon is source of the Afon Cynon. An adjacent borehole [SN 9524 0774] reported an ‘underground lake’ at 55 m and is pumped at 5 Ml d‑1.
|-
| Afon Hepste
| SN 90
| Upper Hepste Main Sink [SN 9541 1208] discharges back to the river at Hepste Main Resurgence [SN 9360 0973] in under 24 hours.
|-
| Afon Mellte
| SN 91
| The main Mellte Sink [SN 9315 1332] has proven connections to five resurgences. Contributions also from smaller sinks.
|-
| Nedd Fechan
| SN 91
| Dye tracing has proved relationship between a series of sinks and risings.
|-
| Glyntawe and the Black Mountain
| SN 81
| Two main cave systems behind main resurgences at Glyntawe
|-
| The Twrch valley
| SN 71
| Fault-controlled resurgences.
|-
| Black Mountain – western area
| SN 61
| 7 km from main sink to resurgence proven by dye tracing.
|}
</center> <center>
{| class="wikitable"
|+ Relationship between dye tests from Waun Fignen-felen and Sink y Giedd, after [[Hydrogeology of Wales: References|'''Coase and Judson (1977)''']].
|-
|
| From Waen Fignen Felen
| From Sink y Giedd
|-
| Distance from sink to resurgence (km)
| 3.5
| 4.7
|-
| Time for dye to reach resurgence (hours)
| 25
| 36
|-
| Average flow rate (km hour-1)
| 0.14
| 0.13
|-
| Elevation of sink above resurgence (m)
| 248
| 218
|}
</center>

Other celebrated groups of caves include the Nant y Glais caves to the south of the Vaynor Moors on the north crop: Ogof Robin Goch [SO 0392 1076], Ogof y Ci [SO 0403 1051], Ogof Dŵr Dwfn [SO 0415 1022], Ogof Rhyd Sych [SO 0416 1021], Ogof Pysgodyn Gwyn [SO 0416 1016] and Ogof Jonny Bach [SO 0420 1000]. The Nant y Glais river disappears underground altogether as it traverses the cave system except in exceptionally wet weather when flow also occurs through a narrow gorge at surface ([[Hydrogeology of Wales: References|'''Ford, 1989''']]).

[[Hydrogeology of Wales: References|'''Gascoine (1989''']]) reviewed other cave systems within the north crop. Many of the sinks are situated at the feather edge of the Marros Group where it is only a few metres thick above the limestone ('''Figure P859273'''), whilst others provide connections from the Avon Group shales and the main limestone. One of the longer and more complex cave systems is Ogof Draenen [SO 2467 1176] at the eastern edge of the north crop. Numerous dolines and stream sinks are present in the area and speleological investigation recognises numerous underfit streams in large passages. [[Hydrogeology of Wales: References|'''Maurice and Guilford (2011)''']] have identified a watershed within the system whereby flow occurs both to the north to Clydach Gorge and to the south to the Afon Lwyd. The latter is in a different topographical catchment some 8 km distant and tracer testing indicates velocities of 4 km d-1.
[[Image:P859273.jpg|thumb|center|600px|Sketch map of the Pembroke Limestone group outcrop along the North Crop (after Gasgoine, 1989). P859273.]]

A wide range of borehole yields have been established depending on the hydraulic contact with productive fractures. Drilling is always speculative as targeting useful fractures is not easy. The average yield from Carboniferous Limestone Supergroup boreholes across the UK was shown by [[Hydrogeology of Wales: References|'''Monkhouse (1977)''']] to be just 4 l s-1, but there is no record of the numbers of boreholes that were abandoned as dry, while other boreholes may have a significantly higher yield.

Although fractures and karstification rapidly decreases under the cover of the Marros Group there is some evidence of deep groundwater circulation beneath the coalfield. Taff’s Well [ST 1193 8364] discharges groundwater at about 1 l s-1 from the South Wales Coal Measures Group with a temperature of 21.6 oC, the only thermal spring in Wales ([[Hydrogeology of Wales: References|'''Farr and Bottrell, 2013''']] . Previous measurements reported a variety of temperatures all less than 20 oC but these were subject to mixing with water from the River Taff which is now prevented by new flood works. Simple inspection of the geothermal gradient and of the discharge water chemistry suggests a deep flow path, probably in the Pembroke Limestone Group, which is believed to travel to a depth of about 700 m ([[Hydrogeology of Wales: References|'''Squirrell and Downing, 1969'''; '''Thomas et al., 1983''']]). Dissolved inert gas analysis indicates that the water infiltrated the ground some 500 m higher in elevation than Taff’s Well, suggesting a recharge source somewhere along the north crop ([[Hydrogeology of Wales: References|'''Burgess et al., 1980''']]; [[Hydrogeology of Wales: References|'''Edmunds, 1986''']]). Farr (pers. comm.) suggests the water is between 5000 and 10 000 years old based on δ18O and δ2H age indicators.

A major spring was encountered in the concealed limestone in 1879 during the digging of the Severn Railway Tunnel. Here a spring discharge of 1000 l s-1 was encountered, the Great Spring, which has been pumped to surface ever since ([[Hydrogeology of Wales: References|'''Drew et al., 1970''']]). Of good quality, it has been used for a variety of purposes including supply to the nearby Margam Steel Works, the Caerwent military establishment, a paper mill and latterly for public supply.

Water quality in the limestones is typified by slightly alkaline pH up to 7.6, and alkalinity concentrations (as CaCO3) ranging upwards to 230 mg l-1. The lower values reflect immature waters that have not attained Ca saturation. In north Wales, local mineralisation in the limestones promotes the solution of metals but at barely detectable concentrations. There are distinct tidal influences on some low-lying coastal areas of south Wales (including the Schwyll Spring) and a marine mixing zone in selected fractures is indicated by enhanced concentrations of Na and Cl at some sources.

A number of detailed site-specific investigations have been carried out on the limestone aquifer in south Wales which provide insight into its hydraulic processes. One such study was carried out between Porthcawl and Port Talbot looking at the environmental impact of extending local quarries in the Pembroke Limestone Group on a wetland area within adjacent superficial deposits ([[Hydrogeology of Wales: References|'''Cheney et al., 2000''']]). This work drew on extensive monitoring and analysis carried out previously in the area but was unable to develop a robust groundwater flow model due to data scarcity and the complex nature of flow in a karstic system. In addition 95 per cent of the water balance was unaccountable, suspected to drain to submarine springs in the Bristol Channel.

Groundwater is typically of the Ca-HCO3 type, with HCO3 typically in the range 90 to 550 mg l-1, the weakest mineralisation occurring along the north crop. The pH is almost always alkaline with values up to 8.2. Cl concentrations are generally low (<50 mg l-1) except on the coast near Porthcawl at Rest Bay where some private sources suffer from saline intrusion ([[Hydrogeology of Wales: References|'''Jones, 2007''']]) and in parts of the Gower Peninsula where sea spray may be the cause of elevated Na and Cl concentrations. The same pattern emerges in Pembrokeshire where Ca-HCO3 type is dominant with subordinate Na/Mg-Cl type but here it is possibly caused by ion exchange in waters that are older than in the limestone around the South Wales Coalfield ([[Hydrogeology of Wales: References|'''Fahrner et al., 2008''']]).

{| cellspacing="0" cellpadding="5" border="1"
| <center>'''Development of Karst in the Avon Group'''</center>

The development of the karst features found today in the Avon Group in south Wales reflects a continuing process which commenced almost as soon as the rocks were laid down. The most active zone of karstification is the vadose zone where unsaturated water can move freely through bedding planes and other discontinuities, but the phreatic zone may also be active when groundwater chemistry changes due to long-term effects of mixing. There were three intensive phases of karstic development: the Lower Carboniferous, the late Triassic and the Palaeogene through to the Quaternary.

The Lower Carboniferous palaeokarstic surfaces developed as the limestone initially rose out of the sea. Clay and mudstone beds, representing fossil soils, overlie the hummocky erosion surface, with discrete fissures in the limestone infilled with the soil material below. This is characteristic of both south Wales ([[Hydrogeology of Wales: References|'''Wilson et al., 1990''']]) and north Wales ([[Hydrogeology of Wales: References|'''Davies, 1991''']]) where relief varies between only a few centimetres to a few metres.

Uplift during the late Carboniferous Variscan Orogeny initiated a protracted period of erosion which lasted through to the Jurassic Period. By Late Triassic times a network of fissures and caverns had been created, some of which had already been partly infilled with rubble and clay. Mineralised hydrothermal waters may have added to the process leading to the deposition of galena and barites on fissure walls. [[Hydrogeology of Wales: References|'''Wilson et al. (1990)''']] recognised three types of karst feature in south Wales: dilated joints, irregular shaped cavities developed along bedding plains, and subvertical cylindrical pipes.

During the Palaeogene and Quaternary periods, large periodic fluctuations in sea level caused fluctuations also in the location of the vadose zone, and new and some pre-existing conduit features were developed, many now below the present-day water table. Three types of feature were created: dolines (collapsed caverns), linear fissures and large cavities. These features are commonly backfilled with silt and rubble debris. [[Hydrogeology of Wales: References|'''Gunn (1992)''']] asserted that the larger features could only develop where they were fed by a river or stream sink, and the Dan yr Ogof system was once fed by the River Haffes which has since been captured and redirected.

Reactivation of karst conduit systems has been recorded at a number of sites. At Stormy Down Quarry [SS 845 800] discharging into a doline reactivated the karst system such that extensive remedial action was required in the vicinity during the construction of the M4 motorway ([[Hydrogeology of Wales: References|'''Aldous, 1988b''']]).
|}

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[Category:Hydrogeology of Wales| 017]]

Hydrogeology of Wales: References

2015-07-28T19:28:38Z

Gareth Farr:

{{HofW}}
''PUBLISHED''

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'''Hiscock, K, and Paci, A. 2000'''. Groundwater resources in the Quaternary deposits and Lower Palaeozoic bedrock of the Rheidol catchment, west Wales. 141-155 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Hobbs, S L. 1993'''. The hydrogeology of the Schwyll Spring catchment Area, South Wales. ''Proceedings of the Bristol Speleological Society'', Vol. 19, 3, 313-335.

'''Hobbs, S L. 2000.''' Influent rivers: a pollution threat to Schwyll Spring, South Wales? 113-121 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Ineson, J. 1967.''' Groundwater conditions in the Coal measures of the South Wales Coalfield. ''Water Supply Papers of the Geological Survey of Great Britain,''Hydrogeological Report No. 3.

'''Jones, F. 1992'''. ''The Holy Wells of Wales''. (Cardiff: University of Wales Press.)

'''Jones, H K, Morris,B L, Cheney, C S, Brewerton, L J, Merrin, P D, Lewis, M A, MacDonald, A M, Coleby, L M, Talbot, J C, MacKenzie, A A, Bird, M J, Cunnigham, J, and Robinson, V K. 2000''' The physical properties of minor aquifers in England and Wales. ''British Geological Survey Technical Report,'' WD/00/4. ''Environment Agency R & D Publication,'' No. 68.

'''Jones, N, Walters, M, and Frost, P , 2004'''. Mountains and orefields: metal mining landscapes of mid and north-east Wales. ''Council for British Archaeology Research Report,'' No. 142.

'''Kirchner, J W, Feng, X H, and Neal, C. 2001'''. Catchment-scale advection and dispersion as a mechanism for fractal scaling in stream tracer concentrations. ''Journal of Hydrology'', Vol. 254, 82-101.

'''Lambert, A O. 1981.''' The River Clwyd Augmentation/Abstraction Scheme. ''Journal of the Institution of Water Engineers and Scientists'', Vol. 35, 125-134.

'''Lambert, A O, English, K B, Skinner, A, Fleet, M, and Wilkinson, W B. 1973.''' ''Groundwater resources of the Vale of Clwyd''. ''Water Resources Board, Reading'', Publication No. 20.

'''Lovelock, P E R. 1977.''' Aquifer properties of the Permo-Triassic sandstones of the United Kingdom. ''Bulletin of the Geological Survey of Great Britain'', No. 56, 50.

'''Maurice, L, and Guilford, T. 2011.''' The hydrogeology of Ogof Draenen: new insights into a complex multi-catchment karst system from tracer testing. ''Cave and Karst Science'', Vol. 38, 1, 23-30.

'''NRA, 1993'''. ''Low Flows and Water resources, facts on the top 40 low-flow rivers in England and Wales''. (Bristol: National Rivers Authority.)

'''Neal, C, Robson, A J, Shand, P, Edmunds, W M, Dixon, A J, Buckley, D K, Hill, S, Harrow, M, Neal, M, Wilkinson, J, and Reynolds, B. 1997'''. The occurrence of groundwater in the Lower Palaeozoic rocks of Central Wales. ''Hydrology and Earth Systems Sciences'', Vol. 1, 3-18.

'''Nichol, D , Bassett, M G, and Deisler, V K (editors). 2004.''' Urban Geology in Wales. ''National Museum of Wales, Cardiff. Geological Series'', No. 23

'''Ranwell, D S. 1959.''' Newborough Warren Anglesey. I. The dune system and dune slack habitat. ''Journal of Ecology'', Vol. 47, 571-601.

'''Rees, S B, Bowell, R J, and Wiseman, I. 2002.''' Influence of mine hydrogeology on mine water discharge chemistry. 379-390 in Younger, P L, and Robins, N S (editors). ''Mine water hydrogeology and geochemistry''. Geological Society of London Special Publications, No. 198.

'''Robins, N S. 1999.''' Groundwater occurrence in the Lower Palaeozoic and Precambrian rocks of the UK: implications for source protection. ''Journal of the Chartered Institution of Water and Environmental Management'', Vol. 13, 6, 447-453.

'''Robins, N S. 2005.''' Fracture flow and preferential groundwater flow paths in hard rocks - illustrations from Precambrian and Lower Palaeozoic strata in Wales.'' 25th Anniversary Groundwater Seminar, International Association of Hydrogeologists'', Tullamore, April 2005.

'''Robins, N S. 2009'''. Regional hydrogeological assessment of Wales. 141-150 in ''Urban Geology in Wales: 3''. Bassett,M G, Boulton, H, and Nichol, D (editors). National Museum of Wales, Cardiff, Geological Series, No. 29.

'''Robins, N S, and McKenzie, A A. 2005.''' Groundwater occurrence and the distribution of wells and springs in Precambrian and Palaeozoic rocks, north-west Anglesey. ''Quarterly Journal of Engineering Geology and Hydrogeology'', Vol. 38, 1, 83-88.

'''Robins, N S, Shand, P, and Merrin, P D. 2000.''' Shallow groundwater in drift and Lower Palaeozoic bedrock: the Afon Teifi valley in west Wales. 123-131 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Robins, N S, Davies, J, Cheney, C, and Tribe, E L. 2005.''' Groundwater in a water-rich environment: Wales, a land of plenty. ''Journal of the Chartered Institution of Water & Environmental Management'', Vol. 19, 1, 62-67.

'''Robins, N S, Davies, J, and Dumpleton, S. 2008.''' Groundwater flow in the South Wales Coalfield – historical data informing 3D modelling. ''Quarterly Journal of Engineering Geology and Hydrogeology''. Vol. 41, 4, 477-486.

'''Shand, P, Edmunds, W M, Wagstaff, S, Flavin, R, and Jones, H K. 1999'''. Hydrogeochemical processes determining water quality in upland Britain. '' British Geological Survey, Hydrogeological Report,''.

'''Shand, P, Darbyshire, D P F, Gooddy, D C, Darling, W G, Neal C, Haria, A H, and Dixon, A J. 2001.''' The application of Sr isotopes to catchment studes: the Plynlimon upland catchment of Central Wales. ''Water-Rock Interaction'', Vol. 10, 1577-1580.

'''Shapiro, A M. 1993.''' The influence of heterogeneity in estimates of regional hydraulic properties in fractured crystalline rock. ''Memoirs of the 24th Congress of the International association of Hydrogeologists'', Oslo, 125-129.

'''Squirrell, H C, and Downing, R A. 1969.''' Geology of the South Wales Coalfield, Part 1. The country around Newport (Mon). ''Memoirs of the Geological Survey of Great Britain''.

'''Stratford, C, Ratcliffe, J, Hughes, A G, Roberts, J, and Robins, N S. 2007.''' Complex interaction between shallow groundwater and changing woodland, surface water, grazing and other influences in partly wooded duneland in Anglesey, Wales 2007.''' '''Proceedings CD XXXV Congress International Association of Hydrogeologists ''Groundwater and Ecosystems'', Lisbon, 17-21 September 2007.

'''Stratford, C, Robins, N S, and Hollingham,M. 2009.''' An assessment of the interactions between hydrology, land use and climate change at two coastal dune systems in Wales, UK. Proceedings of the Second Multidisciplinary Conference on Hydrology and Ecology, Vienna, April 2009 (CD).

'''Stratford, T. 1995.''' ''Caves of South Wales: A Caver’s Guide Book.'' (Leicester: Cordee.)

**'''Thomas, L P.''' 1974. The Westphalian (Coal Measures) in South Wales. IN: T R Owen (Editor)

'''Warren, P T, Price, D, Nutt, M J C, and Smith, E G. 1984'''. Geology of the country around Rhyl and Denbigh. ''Memoir of the British Geological Survey'', Sheets 95 and 107 and parts of sheets 94 and 106 (England and Wales).

'''Waters, C N, Price, S J, Davies, J, Tye, A M, Brown, S E, and Schofield, D I. 2005.''' Urban geology of Swansea-Neath-Port Talbot. 7-22 in ''Urban Geology in Wales 2''. Bassett, M G, Deisler, V K, and Nichol, D (editors). ''National Museum of Wales, Cardiff, Geological Series'', No 24.

'''Watson, J W, and Sissons, J B (editors). 1965.''' ''The British Isles a systematic geography''. (London: Thomas Nelson & Sons.)

'''Webb, M M. 2000.''' The water resources of Bardsey, North Wales. 239-246 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors). ''Geological Society of London Special Publications'', Vol. 182.

'''WRB, 1973.''' Groundwater resources of the Vale of Clwyd. ''Water Resources Board, Reading''. Publication No. 20,

'''Younger, P L, Jenkins, D A, Rees, S B, Robinson, J, Jarvis, A P, Ralph, J, Johnston, D N, and Coulton, R H. 2004.''' Mine waters in Wales: pollution, risk management and remediation. 138-154 in ''Urban Geology in Wales''. Nichol,D, Bassett, M G, and Deisler, V K (editors). National Museum of Wales, Cardiff, Geological Series, No. 23.

''UNPUBLISHED''

'''Aldous, P J. 1988a'''. Groundwater transport and pollutant pathways in Carboniferous Limestone Aquifers. The Cardiff-Cowbridge Block: Final report. WRc Technical Report CO 1820/M/1/EV 8663.

'''Aldous, P J. 1988b.''' Investigation of the geology, hydrogeology and environmental impact of a proposed landfill at Stormy Down – tracer studies. WRc Technical Report CO 1990/M/EV 8716.

'''Aspinwall & Co. 1993.''' Vale of Glamorgan Carboniferous Limestone study. Report for National Rivers Authority, Aspinwall & Co., Shrewsbury.

'''Banks, D, Farr, G, Inman, P, and Low, R. 2007.''' Groundwater quality and supply survey for the Precambrian Gwna Group Anglesey. Environment Agency, Bristol, Technical Report.

'''Banks, D, Boland, M, Farr, G, Inman, P, and Low, R. 2008.''' Groundwater quality and supply survey for the Carboniferous Limestone, Anglesey. Environment Agency, Bristol, Technical Report.

'''Burgess, W G, Edmunds, W M, Andrews J N, Kay R L F, and Lee, D J. 1980.''' The hydrogeology and hydrochemistry of the thermal waters in the bath-Bristol basin. Institute of Geological Sciences Technical Report (Investigation of the Geothermal Potential of the UK series).

'''Celtic Water Management, 2005.''' Pumping 2004 & 2005: Yield & Sand Ingress Test Pumping. Technical Report Celtic Water Management, Cardigan, for Dwr Cymru.

'''Cheney, C S, Davies, J R, Hughes, A G, Darling, W G, and Macdonald, D M J. 2000.''' An assessment of the possible effects of dewatering proposed extensions to quarries in the South Cornelly area, South Wales, ''British Geological Survey Technical Report'', WD/00/21.

'''CWPU, 1978.''' Groundwater resources in the coalfields of England and Wales – the South Wales Coalfield. Central Water Planning Unit Technical Note.

'''Entec, 1996.''' Cardiff Bay Barrage groundwater characterisation. Technical report Entec Ltd, Shrewsbury.

'''Entec 2009.''' Source protection zone for Lovesgrove boreholes. Technical report Entec Ltd, Shrewsbury, for Environment Agency Wales.

'''ESI, Ltd. 2003.''' Vale of Clwyd aquifer study Phase 1. Technical report ESI Ltd, Shrewsbury, for Environment Agency Wales.

'''ESI, Ltd. 2006.''' The hydrogeology of three catchments of the River Wye. Technical report ESI Ltd, Shrewsbury, for Environment Agency Wales.

'''Fahrner, S, Gomme, J, Farr, G, and Mann, A. Undated.''' Groundwater quality review: Clwyd Permo-Triassic sandstone. Environment Agency, Bristol, Technical Report.

'''Fahrner, S, Gomme, J, Davies, B, and Farr, G. 2008.''' Groundwater quality review: The Carboniferous Limestone of the Pembrokeshire Carboniferous Limestone groundwater monitoring unit. Environment Agency, Bristol, Technical Report.

'''Glendining, S J. 1981.''' Hydrogeological reconnaissance study: Dyfi Valley, Wales. Institute of Geological Sciences Technical Report, ENPU 81-2.

'''Griffiths, K J, Shand, P,and Ingram, J. 2002.''' Baseline report series 2: The Permo-Triassic sandstones of west Cheshire and the Wirral. ''British Geological Survey Technical Report'', CR/02/109.

'''Howard Humphreys, 1984'''. The Olwen borehole, Lampeter. Howard Humphreys & Partners, London.

'''Jones, D A. 2007.''' Hydrogeological investigation of a Carboniferous Limestone aquifer near Rest Bay. Unpublished MSc Thesis, University of Cardiff.

'''Jones, P S. 1993.''' Ecological and hydrological studies of dune slack vegetation at Kenfig National Nature Reserve, Mid-Glamorgan. Unpublished PhD Thesis, University of Cardiff.

'''Lewis, B J, Leighfield, K G, and Cox, S J. 2000.''' The South Wales Coalfield (including the Pembrokeshire Coalfield): A review of mine water recovery. Report Wardell Armstrong for the Coal Authority, job No. NL02906.

'''Monkhouse, R A. 1977.''' Yields of public wells in the more important aquifers of England and Wales. Central Water Planning Unit Technical Report 1977/11.

'''Monkhouse, R A. 1982.''' A note on groundwater in Wales. ''Institute of Geological Sciences Technical Report,'' WD/82/3.

'''Moreau, M, Shand, P, Wilton, N, Brown, S, and Allen, D. 2004.''' Baseline Report Series 12. The Devonian sandstone aquifer of South Wales and Herefordshire. ''British Geological Survey Commissioned Report,'' CR/04/185.

'''Rae, G W. 1978a.''' Mine drainage from coalfields in England and Wales, a summary of its distribution and relationship to water resources. Central Water Planning Unit Technical Note.

'''Rae, G W. 1978b.''' Groundwater resources in the coalfields of England and Wales – the South Wales Coalfield. Draft Central Water Planning Unit Technical Note.

'''Richards, H J. 1959.''' Draft report on the hydrogeology of the Carboniferous Limestone of Wales. ''Geological Survey Technical Report'', WD/59/3

'''Robertson, A S. 1974.''' Flow measurements made by IGS in boreholes EP4, EP5, EP7 and EP9 at the Dinorwic Site Llanberis 5-9 March 1974. ''Institute of Geological Sciences Technical Report'', WD/ST/74/9.

'''Shand, P, Edmunds, W M, Wagstaff, S, and Flavin, R. 1995.''' The application of hydrogeochemical data and maps for environmental interpretation in upland Britain. ''British Geological Survey Technical Report'', WD/94/57.

'''Shand, P, Abesser, C, Farr, G, Wilton, N, Lapworth, D J, Gooddy, D C, Haria, A, and Hargreaves, R. 2005'''. Baseline Report Series 17, The Ordovician and Silurian metasedimentary aquifers of central and south west Wales. ''British Geological Survey Commissioned Report'', CR/05/34.

'''Shand, P, Edmunds, W M, Lawrence, A R, Smedley, P R, and Burke, S. 2007'''. The natural (baseline) quality of groundwater in England and Wales. ''British Geological Survey Research Report,'' RR/07/06.

'''Thomas, L P, Evans, R B, and Downing, R A. 1983'''. The geothermal potential of the Devonian and Carboniferous rocks of South Wales. ''Institute of Geological Sciences Technical Report'' (Investigation of the Geothermal Potential of the UK series).

'''Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009.''' A lithostratigraphical framework for the Carboniferous successions of southern Great Britain (onshore). ''British Geological Survey Research Report'', RR/09/01.

'''Welsh Office Agriculture Department. 1986.''' Letter dated 19 March 1986 from Regional Soil Scientist. BGS Wellmaster record SH45/3.

'''Wilson, D; Davies, J R; Fletcher, C J N; and Smith, M. 1990.''' Geology of the South Wales Coalfield, Part VI, the country around Bridgend. ''Memoir of the British Geological Survey'', Sheets 261 and 262.

'''Wilson, D; Waters, C; and Rollin, K E. 2002'''. A geological and geophysical desk study of the Vale of Clwyd. ''British Geological Survey Commissioned Report'', CR/02/177.

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[category:Hydrogeology of Wales | 045]]

Hydrogeology of Wales: References

2015-07-28T19:28:08Z

Gareth Farr:

{{HofW}}
''PUBLISHED''

'''Allen, D J, Brewerton, L J, Coleby, L M, Gibbs, B R, Lewis, M A, MacDonald, A M, and Wagstaff, S J. 1997.''' ''The physical properties of major aquifers in England and Wales''. Environment Agency R&D Publication, No.8.

'''Appleton, P. 1974.''' Subterranean courses of the River Alyn, including Ogof Hesp Alyn, North Wales. ''Transactions of the British Cave Research Association'', Vol. 1, 29−42.

'''Ball, T K, and Jones, J C. 1990.''' Speleogenesis in the limestone outcrop north of the South Wales Coalfield: the role of micro-organisms in the oxidation of sulphides and hydrocarbons. ''Cave Science'', Vol. 17, 1, 3−8.

'''Banks, D, and Robins, N S. 2002.''' ''An introduction to groundwater in crystalline bedrock''. Norges geologiske undersøkelse, Trondheim.

'''Bassett, D A. 1969.''' The study of groundwater, with particular reference to Wales and the Welsh Border. ''Transactions of the Cardiff Naturalists’ Society'', Vol. 94, 62−87.

'''Bassett, M G , Deisler, V K , and Nichol, D , (editors) 2005.''' Urban Geology in Wales: 2. ''National Museum of Wales Geological Series, No. 24,'' Cardiff. 262pp.

'''BGS, 1986.''' ''Hydrogeological map of South Wales, Scale 1: 125 000''. (Keyworth, Nottingham: British Geological Survey.)

'''BGS, 1989.''' ''Hydrogeological map of Clwyd and the Cheshire Basin, Scale 1: 100 000''. (Keyworth, Nottingham: British Geological Survey.)

'''BGS, 2000'''. ''Regional geochemistry of Wales and part of west central England: stream sediment and soil''. (Keyworth, Nottingham: British Geological Survey.)

'''Brabham, P J. 2004.''' The Rhondda Valleys: using GIS to visualise the rise and fall of coal mining and its industrial heritage. 193-206 in ''Urban Geology in Wales'', (Cardiff: National Museum of Wales.)

'''Campbell, S, Gunn, J, and Hardwick, P. 1992.''' Pant-y-Llyn – the first Welsh turlough? ''Earth Science Conservation'', Vol. 31, 3-7.

'''CEH/BGS, 2003.''' ''Hydrometric register and statistics 1996-2000.'' (Wallingford, Oxford: Centre for Ecology and Hydrology/British Geological Survey.)

'''Coase, A, and Judson, D. 1977.''' Dan yr Ogof and its associated caves. ''Transactions of the British Cave Research Association'', Vol. 4, 1/2, 247-344.

'''Crowther, J. 1989'''. Karst geomorphology of South Wales. 20-39 in ''Limestones and Caves of Wales,'' T D Ford (editor), (Cambridge: Cambridge University Press.)

'''Davies, J R.''' 1991. Karstification and pedogenisis on a late Dinantion carbonate platform, Anglesey, North Wales. ''Proceedings of the Yorkshire Geological Society'', Vol, 48, 297-321.

'''Davis, P'''. 2003. ''Sacred Springs: In search of the Holy Wells and Spas of Wales''. (Abergavenny: Blorenge Books.)

'''Davy, A J, Hiscock, K M, Jones, M L M, Low, R, Robins, N S, and Stratford, C. 2010.''' ''Ecohydrological guidelines for wet dune habitats''. Environment Agency Report Wet Dune Habitats, No. 2.

'''Drew, D P, Newson, M D, and Smith, D I. 1970.''' Water tracing of the Severn Tunnel Great Spring. ''Proceedings of the University of Bristol Speleological Society'', Vol. 12, 203-212.

'''EC, 1991.''' European Community Nitrates Directive, (91/676/EEC).

'''EC, 2000.''' European Community Water Framework Directive, (2000/60/EC).

'''Edmunds, W M. 1986.''' Geochemistry of geothermal waters in the UK. In ''Geothermal energy – the potential in the United Kingdom''. Downing, R A, and Gray, D A (editors). (London: HMSO)

'''Edmunds, W M, Robins, N S, and Shand, P. 1998.''' The saline waters of Llandrindod and Builth, Central Wales. ''Journal of the Geological Society of London'', Vol, 155, 627-637.

'''Environment Agency, 2008.''' ''Underground, Under threat: The state of groundwater in England and Wales''. (Bristol: Environment Agency.)

'''Environment Agency, 2009.''' ''Water for people and the environment: Water Resource Strategy for Wales''. (Bristol: Environment Agency.)

'''Farr, G and Bottrell, S.H. 2013.''' The hydrogeology and hydrochemistry of the thermal waters at Taffs Well, South Wales, UK. ''Cave and Karst Science Transactions of the British Cave Research Association.'', 40 (1). 5-12.

'''Ford, T D. 1989.''' The caves of Nant y Glais, Vaynor. 153-154 in ''Limestones and Caves of Wales.'' T D Ford (editor). (Cambridge: Cambridge University Press.)

'''Gascoine, W. 1989.''' The hydrology of the limestone outcrop north of the coalfield. 40-55 in ''Limestones and Caves of Wales'' T D Ford (editor). (Cambridge: Cambridge University Press.)

'''Gibbons, W.''' 1983. The Moinian ‘Penmynydd Zone of metamorphism’ in Llyn, North Wales. ''Geological Journal'', Vol. 18, 21-41.

'''Greenly, E. 1919.''' The Geology of Anglesey. ''Memoirs of the geological Survey of England and Wales''.

'''Gunn, J. 1992.''' Hydrogeological contrasts between British Carboniferous Limestone aquifers. 25-42 in ''Hydrogeology of selected Karst regions'', International Association of Hydrogeologists International Contributions to Hydrogeology, No. 13.

'''Haria, A H, and Shand, P. 2004.''' Evidence for deep subsurface flow routing in forested upland Wales: implications for contaminant transport and stream flow generation. ''Hydrology and Earth Systems Sciences'', Vol. 8, 3, 344-344.

'''Heathcote, J A, Lewis, R T, and Sutton, J S. 2003.''' Groundwater modelling for the Cardiff Bay Barrage, UK – prediction, implementation of engineering works and validation of model. ''Quarterly Journal of Engineering Geology and Hydrogeology'', Vol. 36, 2, 159-172.

'''Hiscock, K, and Paci, A. 2000'''. Groundwater resources in the Quaternary deposits and Lower Palaeozoic bedrock of the Rheidol catchment, west Wales. 141-155 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Hobbs, S L. 1993'''. The hydrogeology of the Schwyll Spring catchment Area, South Wales. ''Proceedings of the Bristol Speleological Society'', Vol. 19, 3, 313-335.

'''Hobbs, S L. 2000.''' Influent rivers: a pollution threat to Schwyll Spring, South Wales? 113-121 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Ineson, J. 1967.''' Groundwater conditions in the Coal measures of the South Wales Coalfield. ''Water Supply Papers of the Geological Survey of Great Britain,''Hydrogeological Report No. 3.

'''Jones, F. 1992'''. ''The Holy Wells of Wales''. (Cardiff: University of Wales Press.)

'''Jones, H K, Morris,B L, Cheney, C S, Brewerton, L J, Merrin, P D, Lewis, M A, MacDonald, A M, Coleby, L M, Talbot, J C, MacKenzie, A A, Bird, M J, Cunnigham, J, and Robinson, V K. 2000''' The physical properties of minor aquifers in England and Wales. ''British Geological Survey Technical Report,'' WD/00/4. ''Environment Agency R & D Publication,'' No. 68.

'''Jones, N, Walters, M, and Frost, P , 2004'''. Mountains and orefields: metal mining landscapes of mid and north-east Wales. ''Council for British Archaeology Research Report,'' No. 142.

'''Kirchner, J W, Feng, X H, and Neal, C. 2001'''. Catchment-scale advection and dispersion as a mechanism for fractal scaling in stream tracer concentrations. ''Journal of Hydrology'', Vol. 254, 82-101.

'''Lambert, A O. 1981.''' The River Clwyd Augmentation/Abstraction Scheme. ''Journal of the Institution of Water Engineers and Scientists'', Vol. 35, 125-134.

'''Lambert, A O, English, K B, Skinner, A, Fleet, M, and Wilkinson, W B. 1973.''' ''Groundwater resources of the Vale of Clwyd''. ''Water Resources Board, Reading'', Publication No. 20.

'''Lovelock, P E R. 1977.''' Aquifer properties of the Permo-Triassic sandstones of the United Kingdom. ''Bulletin of the Geological Survey of Great Britain'', No. 56, 50.

'''Maurice, L, and Guilford, T. 2011.''' The hydrogeology of Ogof Draenen: new insights into a complex multi-catchment karst system from tracer testing. ''Cave and Karst Science'', Vol. 38, 1, 23-30.

'''NRA, 1993'''. ''Low Flows and Water resources, facts on the top 40 low-flow rivers in England and Wales''. (Bristol: National Rivers Authority.)

'''Neal, C, Robson, A J, Shand, P, Edmunds, W M, Dixon, A J, Buckley, D K, Hill, S, Harrow, M, Neal, M, Wilkinson, J, and Reynolds, B. 1997'''. The occurrence of groundwater in the Lower Palaeozoic rocks of Central Wales. ''Hydrology and Earth Systems Sciences'', Vol. 1, 3-18.

'''Nichol, D , Bassett, M G, and Deisler, V K (editors). 2004.''' Urban Geology in Wales. ''National Museum of Wales, Cardiff. Geological Series'', No. 23

'''Ranwell, D S. 1959.''' Newborough Warren Anglesey. I. The dune system and dune slack habitat. ''Journal of Ecology'', Vol. 47, 571-601.

'''Rees, S B, Bowell, R J, and Wiseman, I. 2002.''' Influence of mine hydrogeology on mine water discharge chemistry. 379-390 in Younger, P L, and Robins, N S (editors). ''Mine water hydrogeology and geochemistry''. Geological Society of London Special Publications, No. 198.

'''Robins, N S. 1999.''' Groundwater occurrence in the Lower Palaeozoic and Precambrian rocks of the UK: implications for source protection. ''Journal of the Chartered Institution of Water and Environmental Management'', Vol. 13, 6, 447-453.

'''Robins, N S. 2005.''' Fracture flow and preferential groundwater flow paths in hard rocks - illustrations from Precambrian and Lower Palaeozoic strata in Wales.'' 25th Anniversary Groundwater Seminar, International Association of Hydrogeologists'', Tullamore, April 2005.

'''Robins, N S. 2009'''. Regional hydrogeological assessment of Wales. 141-150 in ''Urban Geology in Wales: 3''. Bassett,M G, Boulton, H, and Nichol, D (editors). National Museum of Wales, Cardiff, Geological Series, No. 29.

'''Robins, N S, and McKenzie, A A. 2005.''' Groundwater occurrence and the distribution of wells and springs in Precambrian and Palaeozoic rocks, north-west Anglesey. ''Quarterly Journal of Engineering Geology and Hydrogeology'', Vol. 38, 1, 83-88.

'''Robins, N S, Shand, P, and Merrin, P D. 2000.''' Shallow groundwater in drift and Lower Palaeozoic bedrock: the Afon Teifi valley in west Wales. 123-131 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Robins, N S, Davies, J, Cheney, C, and Tribe, E L. 2005.''' Groundwater in a water-rich environment: Wales, a land of plenty. ''Journal of the Chartered Institution of Water & Environmental Management'', Vol. 19, 1, 62-67.

'''Robins, N S, Davies, J, and Dumpleton, S. 2008.''' Groundwater flow in the South Wales Coalfield – historical data informing 3D modelling. ''Quarterly Journal of Engineering Geology and Hydrogeology''. Vol. 41, 4, 477-486.

'''Shand, P, Edmunds, W M, Wagstaff, S, Flavin, R, and Jones, H K. 1999'''. Hydrogeochemical processes determining water quality in upland Britain. '' British Geological Survey, Hydrogeological Report,''.

'''Shand, P, Darbyshire, D P F, Gooddy, D C, Darling, W G, Neal C, Haria, A H, and Dixon, A J. 2001.''' The application of Sr isotopes to catchment studes: the Plynlimon upland catchment of Central Wales. ''Water-Rock Interaction'', Vol. 10, 1577-1580.

'''Shapiro, A M. 1993.''' The influence of heterogeneity in estimates of regional hydraulic properties in fractured crystalline rock. ''Memoirs of the 24th Congress of the International association of Hydrogeologists'', Oslo, 125-129.

'''Squirrell, H C, and Downing, R A. 1969.''' Geology of the South Wales Coalfield, Part 1. The country around Newport (Mon). ''Memoirs of the Geological Survey of Great Britain''.

'''Stratford, C, Ratcliffe, J, Hughes, A G, Roberts, J, and Robins, N S. 2007.''' Complex interaction between shallow groundwater and changing woodland, surface water, grazing and other influences in partly wooded duneland in Anglesey, Wales 2007.''' '''Proceedings CD XXXV Congress International Association of Hydrogeologists ''Groundwater and Ecosystems'', Lisbon, 17-21 September 2007.

'''Stratford, C, Robins, N S, and Hollingham,M. 2009.''' An assessment of the interactions between hydrology, land use and climate change at two coastal dune systems in Wales, UK. Proceedings of the Second Multidisciplinary Conference on Hydrology and Ecology, Vienna, April 2009 (CD).

'''Stratford, T. 1995.''' ''Caves of South Wales: A Caver’s Guide Book.'' (Leicester: Cordee.)

**'''Thomas, L P.''' 1974. The Westphalian (Coal Measures) in South Wales. IN: T R Owen (Editor)

'''Warren, P T, Price, D, Nutt, M J C, and Smith, E G. 1984'''. Geology of the country around Rhyl and Denbigh. ''Memoir of the British Geological Survey'', Sheets 95 and 107 and parts of sheets 94 and 106 (England and Wales).

'''Waters, C N, Price, S J, Davies, J, Tye, A M, Brown, S E, and Schofield, D I. 2005.''' Urban geology of Swansea-Neath-Port Talbot. 7-22 in ''Urban Geology in Wales 2''. Bassett, M G, Deisler, V K, and Nichol, D (editors). ''National Museum of Wales, Cardiff, Geological Series'', No 24.

'''Watson, J W, and Sissons, J B (editors). 1965.''' ''The British Isles a systematic geography''. (London: Thomas Nelson & Sons.)

'''Webb, M M. 2000.''' The water resources of Bardsey, North Wales. 239-246 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors). ''Geological Society of London Special Publications'', Vol. 182.

'''WRB, 1973.''' Groundwater resources of the Vale of Clwyd. ''Water Resources Board, Reading''. Publication No. 20,

'''Younger, P L, Jenkins, D A, Rees, S B, Robinson, J, Jarvis, A P, Ralph, J, Johnston, D N, and Coulton, R H. 2004.''' Mine waters in Wales: pollution, risk management and remediation. 138-154 in ''Urban Geology in Wales''. Nichol,D, Bassett, M G, and Deisler, V K (editors). National Museum of Wales, Cardiff, Geological Series, No. 23.

''UNPUBLISHED''

'''Aldous, P J. 1988a'''. Groundwater transport and pollutant pathways in Carboniferous Limestone Aquifers. The Cardiff-Cowbridge Block: Final report. WRc Technical Report CO 1820/M/1/EV 8663.

'''Aldous, P J. 1988b.''' Investigation of the geology, hydrogeology and environmental impact of a proposed landfill at Stormy Down – tracer studies. WRc Technical Report CO 1990/M/EV 8716.

'''Aspinwall & Co. 1993.''' Vale of Glamorgan Carboniferous Limestone study. Report for National Rivers Authority, Aspinwall & Co., Shrewsbury.

'''Banks, D, Farr, G, Inman, P, and Low, R. 2007.''' Groundwater quality and supply survey for the Precambrian Gwna Group Anglesey. Environment Agency, Bristol, Technical Report.

'''Banks, D, Boland, M, Farr, G, Inman, P, and Low, R. 2008.''' Groundwater quality and supply survey for the Carboniferous Limestone, Anglesey. Environment Agency, Bristol, Technical Report.

'''Burgess, W G, Edmunds, W M, Andrews J N, Kay R L F, and Lee, D J. 1980.''' The hydrogeology and hydrochemistry of the thermal waters in the bath-Bristol basin. Institute of Geological Sciences Technical Report (Investigation of the Geothermal Potential of the UK series).

'''Celtic Water Management, 2005.''' Pumping 2004 & 2005: Yield & Sand Ingress Test Pumping. Technical Report Celtic Water Management, Cardigan, for Dwr Cymru.

'''Cheney, C S, Davies, J R, Hughes, A G, Darling, W G, and Macdonald, D M J. 2000.''' An assessment of the possible effects of dewatering proposed extensions to quarries in the South Cornelly area, South Wales, ''British Geological Survey Technical Report'', WD/00/21.

'''CWPU, 1978.''' Groundwater resources in the coalfields of England and Wales – the South Wales Coalfield. Central Water Planning Unit Technical Note.

'''Entec, 1996.''' Cardiff Bay Barrage groundwater characterisation. Technical report Entec Ltd, Shrewsbury.

'''Entec 2009.''' Source protection zone for Lovesgrove boreholes. Technical report Entec Ltd, Shrewsbury, for Environment Agency Wales.

'''ESI, Ltd. 2003.''' Vale of Clwyd aquifer study Phase 1. Technical report ESI Ltd, Shrewsbury, for Environment Agency Wales.

'''ESI, Ltd. 2006.''' The hydrogeology of three catchments of the River Wye. Technical report ESI Ltd, Shrewsbury, for Environment Agency Wales.

'''Fahrner, S, Gomme, J, Farr, G, and Mann, A. Undated.''' Groundwater quality review: Clwyd Permo-Triassic sandstone. Environment Agency, Bristol, Technical Report.

'''Fahrner, S, Gomme, J, Davies, B, and Farr, G. 2008.''' Groundwater quality review: The Carboniferous Limestone of the Pembrokeshire Carboniferous Limestone groundwater monitoring unit. Environment Agency, Bristol, Technical Report.

'''Glendining, S J. 1981.''' Hydrogeological reconnaissance study: Dyfi Valley, Wales. Institute of Geological Sciences Technical Report, ENPU 81-2.

'''Griffiths, K J, Shand, P,and Ingram, J. 2002.''' Baseline report series 2: The Permo-Triassic sandstones of west Cheshire and the Wirral. ''British Geological Survey Technical Report'', CR/02/109.

'''Howard Humphreys, 1984'''. The Olwen borehole, Lampeter. Howard Humphreys & Partners, London.

'''Jones, D A. 2007.''' Hydrogeological investigation of a Carboniferous Limestone aquifer near Rest Bay. Unpublished MSc Thesis, University of Cardiff.

'''Jones, P S. 1993.''' Ecological and hydrological studies of dune slack vegetation at Kenfig National Nature Reserve, Mid-Glamorgan. Unpublished PhD Thesis, University of Cardiff.

'''Lewis, B J, Leighfield, K G, and Cox, S J. 2000.''' The South Wales Coalfield (including the Pembrokeshire Coalfield): A review of mine water recovery. Report Wardell Armstrong for the Coal Authority, job No. NL02906.

'''Monkhouse, R A. 1977.''' Yields of public wells in the more important aquifers of England and Wales. Central Water Planning Unit Technical Report 1977/11.

'''Monkhouse, R A. 1982.''' A note on groundwater in Wales. ''Institute of Geological Sciences Technical Report,'' WD/82/3.

'''Moreau, M, Shand, P, Wilton, N, Brown, S, and Allen, D. 2004.''' Baseline Report Series 12. The Devonian sandstone aquifer of South Wales and Herefordshire. ''British Geological Survey Commissioned Report,'' CR/04/185.

'''Rae, G W. 1978a.''' Mine drainage from coalfields in England and Wales, a summary of its distribution and relationship to water resources. Central Water Planning Unit Technical Note.

'''Rae, G W. 1978b.''' Groundwater resources in the coalfields of England and Wales – the South Wales Coalfield. Draft Central Water Planning Unit Technical Note.

'''Richards, H J. 1959.''' Draft report on the hydrogeology of the Carboniferous Limestone of Wales. ''Geological Survey Technical Report'', WD/59/3

'''Robertson, A S. 1974.''' Flow measurements made by IGS in boreholes EP4, EP5, EP7 and EP9 at the Dinorwic Site Llanberis 5-9 March 1974. ''Institute of Geological Sciences Technical Report'', WD/ST/74/9.

'''Shand, P, Edmunds, W M, Wagstaff, S, and Flavin, R. 1995.''' The application of hydrogeochemical data and maps for environmental interpretation in upland Britain. ''British Geological Survey Technical Report'', WD/94/57.

'''Shand, P, Abesser, C, Farr, G, Wilton, N, Lapworth, D J, Gooddy, D C, Haria, A, and Hargreaves, R. 2005'''. Baseline Report Series 17, The Ordovician and Silurian metasedimentary aquifers of central and south west Wales. ''British Geological Survey Commissioned Report'', CR/05/34.

'''Shand, P, Edmunds, W M, Lawrence, A R, Smedley, P R, and Burke, S. 2007'''. The natural (baseline) quality of groundwater in England and Wales. ''British Geological Survey Research Report,'' RR/07/06.

'''Thomas, L P, Evans, R B, and Downing, R A. 1983'''. The geothermal potential of the Devonian and Carboniferous rocks of South Wales. ''Institute of Geological Sciences Technical Report'' (Investigation of the Geothermal Potential of the UK series).

'''Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009.''' A lithostratigraphical framework for the Carboniferous successions of southern Great Britain (onshore). ''British Geological Survey Research Report'', RR/09/01.

'''Welsh Office Agriculture Department. 1986.''' Letter dated 19 March 1986 from Regional Soil Scientist. BGS Wellmaster record SH45/3.

'''Wilson, D; Davies, J R; Fletcher, C J N; and Smith, M. 1990.''' Geology of the South Wales Coalfield, Part VI, the country around Bridgend. ''Memoir of the British Geological Survey'', Sheets 261 and 262.

'''Wilson, D; Waters, C; and Rollin, K E. 2002'''. A geological and geophysical desk study of the Vale of Clwyd. ''British Geological Survey Commissioned Report'', CR/02/177.

==Hydrogeology of Wales - contents==
{{HOWpages}}

[[category:Hydrogeology of Wales | 045]]

Hydrogeology of Wales: References

2015-07-28T19:27:30Z

Gareth Farr: add Farr&Bottrell, 2013 ref

{{HofW}}
''PUBLISHED''

'''Allen, D J, Brewerton, L J, Coleby, L M, Gibbs, B R, Lewis, M A, MacDonald, A M, and Wagstaff, S J. 1997.''' ''The physical properties of major aquifers in England and Wales''. Environment Agency R&D Publication, No.8.

'''Appleton, P. 1974.''' Subterranean courses of the River Alyn, including Ogof Hesp Alyn, North Wales. ''Transactions of the British Cave Research Association'', Vol. 1, 29−42.

'''Ball, T K, and Jones, J C. 1990.''' Speleogenesis in the limestone outcrop north of the South Wales Coalfield: the role of micro-organisms in the oxidation of sulphides and hydrocarbons. ''Cave Science'', Vol. 17, 1, 3−8.

'''Banks, D, and Robins, N S. 2002.''' ''An introduction to groundwater in crystalline bedrock''. Norges geologiske undersøkelse, Trondheim.

'''Bassett, D A. 1969.''' The study of groundwater, with particular reference to Wales and the Welsh Border. ''Transactions of the Cardiff Naturalists’ Society'', Vol. 94, 62−87.

'''Bassett, M G , Deisler, V K , and Nichol, D , (editors) 2005.''' Urban Geology in Wales: 2. ''National Museum of Wales Geological Series, No. 24,'' Cardiff. 262pp.

'''BGS, 1986.''' ''Hydrogeological map of South Wales, Scale 1: 125 000''. (Keyworth, Nottingham: British Geological Survey.)

'''BGS, 1989.''' ''Hydrogeological map of Clwyd and the Cheshire Basin, Scale 1: 100 000''. (Keyworth, Nottingham: British Geological Survey.)

'''BGS, 2000'''. ''Regional geochemistry of Wales and part of west central England: stream sediment and soil''. (Keyworth, Nottingham: British Geological Survey.)

'''Brabham, P J. 2004.''' The Rhondda Valleys: using GIS to visualise the rise and fall of coal mining and its industrial heritage. 193-206 in ''Urban Geology in Wales'', (Cardiff: National Museum of Wales.)

'''Campbell, S, Gunn, J, and Hardwick, P. 1992.''' Pant-y-Llyn – the first Welsh turlough? ''Earth Science Conservation'', Vol. 31, 3-7.

'''CEH/BGS, 2003.''' ''Hydrometric register and statistics 1996-2000.'' (Wallingford, Oxford: Centre for Ecology and Hydrology/British Geological Survey.)

'''Coase, A, and Judson, D. 1977.''' Dan yr Ogof and its associated caves. ''Transactions of the British Cave Research Association'', Vol. 4, 1/2, 247-344.

'''Crowther, J. 1989'''. Karst geomorphology of South Wales. 20-39 in ''Limestones and Caves of Wales,'' T D Ford (editor), (Cambridge: Cambridge University Press.)

'''Davies, J R.''' 1991. Karstification and pedogenisis on a late Dinantion carbonate platform, Anglesey, North Wales. ''Proceedings of the Yorkshire Geological Society'', Vol, 48, 297-321.

'''Davis, P'''. 2003. ''Sacred Springs: In search of the Holy Wells and Spas of Wales''. (Abergavenny: Blorenge Books.)

'''Davy, A J, Hiscock, K M, Jones, M L M, Low, R, Robins, N S, and Stratford, C. 2010.''' ''Ecohydrological guidelines for wet dune habitats''. Environment Agency Report Wet Dune Habitats, No. 2.

'''Drew, D P, Newson, M D, and Smith, D I. 1970.''' Water tracing of the Severn Tunnel Great Spring. ''Proceedings of the University of Bristol Speleological Society'', Vol. 12, 203-212.

'''EC, 1991.''' European Community Nitrates Directive, (91/676/EEC).

'''EC, 2000.''' European Community Water Framework Directive, (2000/60/EC).

'''Edmunds, W M. 1986.''' Geochemistry of geothermal waters in the UK. In ''Geothermal energy – the potential in the United Kingdom''. Downing, R A, and Gray, D A (editors). (London: HMSO)

'''Edmunds, W M, Robins, N S, and Shand, P. 1998.''' The saline waters of Llandrindod and Builth, Central Wales. ''Journal of the Geological Society of London'', Vol, 155, 627-637.

'''Environment Agency, 2008.''' ''Underground, Under threat: The state of groundwater in England and Wales''. (Bristol: Environment Agency.)

'''Environment Agency, 2009.''' ''Water for people and the environment: Water Resource Strategy for Wales''. (Bristol: Environment Agency.)

'''Farr, G & Bottrell, S.H. 2013.''' The hydrogeology and hydrochemistry of the thermal waters at Taffs Well, South Wales, UK. ''Cave and Karst Science Transactions of the British Cave Research Association.'', 40 (1). 5-12.

'''Ford, T D. 1989.''' The caves of Nant y Glais, Vaynor. 153-154 in ''Limestones and Caves of Wales.'' T D Ford (editor). (Cambridge: Cambridge University Press.)

'''Gascoine, W. 1989.''' The hydrology of the limestone outcrop north of the coalfield. 40-55 in ''Limestones and Caves of Wales'' T D Ford (editor). (Cambridge: Cambridge University Press.)

'''Gibbons, W.''' 1983. The Moinian ‘Penmynydd Zone of metamorphism’ in Llyn, North Wales. ''Geological Journal'', Vol. 18, 21-41.

'''Greenly, E. 1919.''' The Geology of Anglesey. ''Memoirs of the geological Survey of England and Wales''.

'''Gunn, J. 1992.''' Hydrogeological contrasts between British Carboniferous Limestone aquifers. 25-42 in ''Hydrogeology of selected Karst regions'', International Association of Hydrogeologists International Contributions to Hydrogeology, No. 13.

'''Haria, A H, and Shand, P. 2004.''' Evidence for deep subsurface flow routing in forested upland Wales: implications for contaminant transport and stream flow generation. ''Hydrology and Earth Systems Sciences'', Vol. 8, 3, 344-344.

'''Heathcote, J A, Lewis, R T, and Sutton, J S. 2003.''' Groundwater modelling for the Cardiff Bay Barrage, UK – prediction, implementation of engineering works and validation of model. ''Quarterly Journal of Engineering Geology and Hydrogeology'', Vol. 36, 2, 159-172.

'''Hiscock, K, and Paci, A. 2000'''. Groundwater resources in the Quaternary deposits and Lower Palaeozoic bedrock of the Rheidol catchment, west Wales. 141-155 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Hobbs, S L. 1993'''. The hydrogeology of the Schwyll Spring catchment Area, South Wales. ''Proceedings of the Bristol Speleological Society'', Vol. 19, 3, 313-335.

'''Hobbs, S L. 2000.''' Influent rivers: a pollution threat to Schwyll Spring, South Wales? 113-121 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Ineson, J. 1967.''' Groundwater conditions in the Coal measures of the South Wales Coalfield. ''Water Supply Papers of the Geological Survey of Great Britain,''Hydrogeological Report No. 3.

'''Jones, F. 1992'''. ''The Holy Wells of Wales''. (Cardiff: University of Wales Press.)

'''Jones, H K, Morris,B L, Cheney, C S, Brewerton, L J, Merrin, P D, Lewis, M A, MacDonald, A M, Coleby, L M, Talbot, J C, MacKenzie, A A, Bird, M J, Cunnigham, J, and Robinson, V K. 2000''' The physical properties of minor aquifers in England and Wales. ''British Geological Survey Technical Report,'' WD/00/4. ''Environment Agency R & D Publication,'' No. 68.

'''Jones, N, Walters, M, and Frost, P , 2004'''. Mountains and orefields: metal mining landscapes of mid and north-east Wales. ''Council for British Archaeology Research Report,'' No. 142.

'''Kirchner, J W, Feng, X H, and Neal, C. 2001'''. Catchment-scale advection and dispersion as a mechanism for fractal scaling in stream tracer concentrations. ''Journal of Hydrology'', Vol. 254, 82-101.

'''Lambert, A O. 1981.''' The River Clwyd Augmentation/Abstraction Scheme. ''Journal of the Institution of Water Engineers and Scientists'', Vol. 35, 125-134.

'''Lambert, A O, English, K B, Skinner, A, Fleet, M, and Wilkinson, W B. 1973.''' ''Groundwater resources of the Vale of Clwyd''. ''Water Resources Board, Reading'', Publication No. 20.

'''Lovelock, P E R. 1977.''' Aquifer properties of the Permo-Triassic sandstones of the United Kingdom. ''Bulletin of the Geological Survey of Great Britain'', No. 56, 50.

'''Maurice, L, and Guilford, T. 2011.''' The hydrogeology of Ogof Draenen: new insights into a complex multi-catchment karst system from tracer testing. ''Cave and Karst Science'', Vol. 38, 1, 23-30.

'''NRA, 1993'''. ''Low Flows and Water resources, facts on the top 40 low-flow rivers in England and Wales''. (Bristol: National Rivers Authority.)

'''Neal, C, Robson, A J, Shand, P, Edmunds, W M, Dixon, A J, Buckley, D K, Hill, S, Harrow, M, Neal, M, Wilkinson, J, and Reynolds, B. 1997'''. The occurrence of groundwater in the Lower Palaeozoic rocks of Central Wales. ''Hydrology and Earth Systems Sciences'', Vol. 1, 3-18.

'''Nichol, D , Bassett, M G, and Deisler, V K (editors). 2004.''' Urban Geology in Wales. ''National Museum of Wales, Cardiff. Geological Series'', No. 23

'''Ranwell, D S. 1959.''' Newborough Warren Anglesey. I. The dune system and dune slack habitat. ''Journal of Ecology'', Vol. 47, 571-601.

'''Rees, S B, Bowell, R J, and Wiseman, I. 2002.''' Influence of mine hydrogeology on mine water discharge chemistry. 379-390 in Younger, P L, and Robins, N S (editors). ''Mine water hydrogeology and geochemistry''. Geological Society of London Special Publications, No. 198.

'''Robins, N S. 1999.''' Groundwater occurrence in the Lower Palaeozoic and Precambrian rocks of the UK: implications for source protection. ''Journal of the Chartered Institution of Water and Environmental Management'', Vol. 13, 6, 447-453.

'''Robins, N S. 2005.''' Fracture flow and preferential groundwater flow paths in hard rocks - illustrations from Precambrian and Lower Palaeozoic strata in Wales.'' 25th Anniversary Groundwater Seminar, International Association of Hydrogeologists'', Tullamore, April 2005.

'''Robins, N S. 2009'''. Regional hydrogeological assessment of Wales. 141-150 in ''Urban Geology in Wales: 3''. Bassett,M G, Boulton, H, and Nichol, D (editors). National Museum of Wales, Cardiff, Geological Series, No. 29.

'''Robins, N S, and McKenzie, A A. 2005.''' Groundwater occurrence and the distribution of wells and springs in Precambrian and Palaeozoic rocks, north-west Anglesey. ''Quarterly Journal of Engineering Geology and Hydrogeology'', Vol. 38, 1, 83-88.

'''Robins, N S, Shand, P, and Merrin, P D. 2000.''' Shallow groundwater in drift and Lower Palaeozoic bedrock: the Afon Teifi valley in west Wales. 123-131 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors) . ''Geological Society of London Special Publications'', Vol. 182.

'''Robins, N S, Davies, J, Cheney, C, and Tribe, E L. 2005.''' Groundwater in a water-rich environment: Wales, a land of plenty. ''Journal of the Chartered Institution of Water & Environmental Management'', Vol. 19, 1, 62-67.

'''Robins, N S, Davies, J, and Dumpleton, S. 2008.''' Groundwater flow in the South Wales Coalfield – historical data informing 3D modelling. ''Quarterly Journal of Engineering Geology and Hydrogeology''. Vol. 41, 4, 477-486.

'''Shand, P, Edmunds, W M, Wagstaff, S, Flavin, R, and Jones, H K. 1999'''. Hydrogeochemical processes determining water quality in upland Britain. '' British Geological Survey, Hydrogeological Report,''.

'''Shand, P, Darbyshire, D P F, Gooddy, D C, Darling, W G, Neal C, Haria, A H, and Dixon, A J. 2001.''' The application of Sr isotopes to catchment studes: the Plynlimon upland catchment of Central Wales. ''Water-Rock Interaction'', Vol. 10, 1577-1580.

'''Shapiro, A M. 1993.''' The influence of heterogeneity in estimates of regional hydraulic properties in fractured crystalline rock. ''Memoirs of the 24th Congress of the International association of Hydrogeologists'', Oslo, 125-129.

'''Squirrell, H C, and Downing, R A. 1969.''' Geology of the South Wales Coalfield, Part 1. The country around Newport (Mon). ''Memoirs of the Geological Survey of Great Britain''.

'''Stratford, C, Ratcliffe, J, Hughes, A G, Roberts, J, and Robins, N S. 2007.''' Complex interaction between shallow groundwater and changing woodland, surface water, grazing and other influences in partly wooded duneland in Anglesey, Wales 2007.''' '''Proceedings CD XXXV Congress International Association of Hydrogeologists ''Groundwater and Ecosystems'', Lisbon, 17-21 September 2007.

'''Stratford, C, Robins, N S, and Hollingham,M. 2009.''' An assessment of the interactions between hydrology, land use and climate change at two coastal dune systems in Wales, UK. Proceedings of the Second Multidisciplinary Conference on Hydrology and Ecology, Vienna, April 2009 (CD).

'''Stratford, T. 1995.''' ''Caves of South Wales: A Caver’s Guide Book.'' (Leicester: Cordee.)

**'''Thomas, L P.''' 1974. The Westphalian (Coal Measures) in South Wales. IN: T R Owen (Editor)

'''Warren, P T, Price, D, Nutt, M J C, and Smith, E G. 1984'''. Geology of the country around Rhyl and Denbigh. ''Memoir of the British Geological Survey'', Sheets 95 and 107 and parts of sheets 94 and 106 (England and Wales).

'''Waters, C N, Price, S J, Davies, J, Tye, A M, Brown, S E, and Schofield, D I. 2005.''' Urban geology of Swansea-Neath-Port Talbot. 7-22 in ''Urban Geology in Wales 2''. Bassett, M G, Deisler, V K, and Nichol, D (editors). ''National Museum of Wales, Cardiff, Geological Series'', No 24.

'''Watson, J W, and Sissons, J B (editors). 1965.''' ''The British Isles a systematic geography''. (London: Thomas Nelson & Sons.)

'''Webb, M M. 2000.''' The water resources of Bardsey, North Wales. 239-246 ''in'' Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology. Robins, N S, and Misstear, B D R (editors). ''Geological Society of London Special Publications'', Vol. 182.

'''WRB, 1973.''' Groundwater resources of the Vale of Clwyd. ''Water Resources Board, Reading''. Publication No. 20,

'''Younger, P L, Jenkins, D A, Rees, S B, Robinson, J, Jarvis, A P, Ralph, J, Johnston, D N, and Coulton, R H. 2004.''' Mine waters in Wales: pollution, risk management and remediation. 138-154 in ''Urban Geology in Wales''. Nichol,D, Bassett, M G, and Deisler, V K (editors). National Museum of Wales, Cardiff, Geological Series, No. 23.

''UNPUBLISHED''

'''Aldous, P J. 1988a'''. Groundwater transport and pollutant pathways in Carboniferous Limestone Aquifers. The Cardiff-Cowbridge Block: Final report. WRc Technical Report CO 1820/M/1/EV 8663.

'''Aldous, P J. 1988b.''' Investigation of the geology, hydrogeology and environmental impact of a proposed landfill at Stormy Down – tracer studies. WRc Technical Report CO 1990/M/EV 8716.

'''Aspinwall & Co. 1993.''' Vale of Glamorgan Carboniferous Limestone study. Report for National Rivers Authority, Aspinwall & Co., Shrewsbury.

'''Banks, D, Farr, G, Inman, P, and Low, R. 2007.''' Groundwater quality and supply survey for the Precambrian Gwna Group Anglesey. Environment Agency, Bristol, Technical Report.

'''Banks, D, Boland, M, Farr, G, Inman, P, and Low, R. 2008.''' Groundwater quality and supply survey for the Carboniferous Limestone, Anglesey. Environment Agency, Bristol, Technical Report.

'''Burgess, W G, Edmunds, W M, Andrews J N, Kay R L F, and Lee, D J. 1980.''' The hydrogeology and hydrochemistry of the thermal waters in the bath-Bristol basin. Institute of Geological Sciences Technical Report (Investigation of the Geothermal Potential of the UK series).

'''Celtic Water Management, 2005.''' Pumping 2004 & 2005: Yield & Sand Ingress Test Pumping. Technical Report Celtic Water Management, Cardigan, for Dwr Cymru.

'''Cheney, C S, Davies, J R, Hughes, A G, Darling, W G, and Macdonald, D M J. 2000.''' An assessment of the possible effects of dewatering proposed extensions to quarries in the South Cornelly area, South Wales, ''British Geological Survey Technical Report'', WD/00/21.

'''CWPU, 1978.''' Groundwater resources in the coalfields of England and Wales – the South Wales Coalfield. Central Water Planning Unit Technical Note.

'''Entec, 1996.''' Cardiff Bay Barrage groundwater characterisation. Technical report Entec Ltd, Shrewsbury.

'''Entec 2009.''' Source protection zone for Lovesgrove boreholes. Technical report Entec Ltd, Shrewsbury, for Environment Agency Wales.

'''ESI, Ltd. 2003.''' Vale of Clwyd aquifer study Phase 1. Technical report ESI Ltd, Shrewsbury, for Environment Agency Wales.

'''ESI, Ltd. 2006.''' The hydrogeology of three catchments of the River Wye. Technical report ESI Ltd, Shrewsbury, for Environment Agency Wales.

'''Fahrner, S, Gomme, J, Farr, G, and Mann, A. Undated.''' Groundwater quality review: Clwyd Permo-Triassic sandstone. Environment Agency, Bristol, Technical Report.

'''Fahrner, S, Gomme, J, Davies, B, and Farr, G. 2008.''' Groundwater quality review: The Carboniferous Limestone of the Pembrokeshire Carboniferous Limestone groundwater monitoring unit. Environment Agency, Bristol, Technical Report.

'''Glendining, S J. 1981.''' Hydrogeological reconnaissance study: Dyfi Valley, Wales. Institute of Geological Sciences Technical Report, ENPU 81-2.

'''Griffiths, K J, Shand, P,and Ingram, J. 2002.''' Baseline report series 2: The Permo-Triassic sandstones of west Cheshire and the Wirral. ''British Geological Survey Technical Report'', CR/02/109.

'''Howard Humphreys, 1984'''. The Olwen borehole, Lampeter. Howard Humphreys & Partners, London.

'''Jones, D A. 2007.''' Hydrogeological investigation of a Carboniferous Limestone aquifer near Rest Bay. Unpublished MSc Thesis, University of Cardiff.

'''Jones, P S. 1993.''' Ecological and hydrological studies of dune slack vegetation at Kenfig National Nature Reserve, Mid-Glamorgan. Unpublished PhD Thesis, University of Cardiff.

'''Lewis, B J, Leighfield, K G, and Cox, S J. 2000.''' The South Wales Coalfield (including the Pembrokeshire Coalfield): A review of mine water recovery. Report Wardell Armstrong for the Coal Authority, job No. NL02906.

'''Monkhouse, R A. 1977.''' Yields of public wells in the more important aquifers of England and Wales. Central Water Planning Unit Technical Report 1977/11.

'''Monkhouse, R A. 1982.''' A note on groundwater in Wales. ''Institute of Geological Sciences Technical Report,'' WD/82/3.

'''Moreau, M, Shand, P, Wilton, N, Brown, S, and Allen, D. 2004.''' Baseline Report Series 12. The Devonian sandstone aquifer of South Wales and Herefordshire. ''British Geological Survey Commissioned Report,'' CR/04/185.

'''Rae, G W. 1978a.''' Mine drainage from coalfields in England and Wales, a summary of its distribution and relationship to water resources. Central Water Planning Unit Technical Note.

'''Rae, G W. 1978b.''' Groundwater resources in the coalfields of England and Wales – the South Wales Coalfield. Draft Central Water Planning Unit Technical Note.

'''Richards, H J. 1959.''' Draft report on the hydrogeology of the Carboniferous Limestone of Wales. ''Geological Survey Technical Report'', WD/59/3

'''Robertson, A S. 1974.''' Flow measurements made by IGS in boreholes EP4, EP5, EP7 and EP9 at the Dinorwic Site Llanberis 5-9 March 1974. ''Institute of Geological Sciences Technical Report'', WD/ST/74/9.

'''Shand, P, Edmunds, W M, Wagstaff, S, and Flavin, R. 1995.''' The application of hydrogeochemical data and maps for environmental interpretation in upland Britain. ''British Geological Survey Technical Report'', WD/94/57.

'''Shand, P, Abesser, C, Farr, G, Wilton, N, Lapworth, D J, Gooddy, D C, Haria, A, and Hargreaves, R. 2005'''. Baseline Report Series 17, The Ordovician and Silurian metasedimentary aquifers of central and south west Wales. ''British Geological Survey Commissioned Report'', CR/05/34.

'''Shand, P, Edmunds, W M, Lawrence, A R, Smedley, P R, and Burke, S. 2007'''. The natural (baseline) quality of groundwater in England and Wales. ''British Geological Survey Research Report,'' RR/07/06.

'''Thomas, L P, Evans, R B, and Downing, R A. 1983'''. The geothermal potential of the Devonian and Carboniferous rocks of South Wales. ''Institute of Geological Sciences Technical Report'' (Investigation of the Geothermal Potential of the UK series).

'''Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009.''' A lithostratigraphical framework for the Carboniferous successions of southern Great Britain (onshore). ''British Geological Survey Research Report'', RR/09/01.

'''Welsh Office Agriculture Department. 1986.''' Letter dated 19 March 1986 from Regional Soil Scientist. BGS Wellmaster record SH45/3.

'''Wilson, D; Davies, J R; Fletcher, C J N; and Smith, M. 1990.''' Geology of the South Wales Coalfield, Part VI, the country around Bridgend. ''Memoir of the British Geological Survey'', Sheets 261 and 262.

'''Wilson, D; Waters, C; and Rollin, K E. 2002'''. A geological and geophysical desk study of the Vale of Clwyd. ''British Geological Survey Commissioned Report'', CR/02/177.

==Hydrogeology of Wales - contents==
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[[category:Hydrogeology of Wales | 045]]

Hydrogeology of Wales: Acknowledgements

2015-07-28T19:21:48Z

Gareth Farr: updated EAW to NRW in text and added some people who reviewed original text when in review at EAW

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Groundwater investigation in Wales has tended to be piecemeal with project reports and technical papers issued from time to time. The only holistic review of groundwater in Wales was written by [[Hydrogeology of Wales: References|'''Bassett (1969)''']] although various regional compilations, such as the two available hydrogeological maps ([[Hydrogeology of Wales: References|'''BGS, 1986; 1989''']]), have updated Bassett’s work. More recently the regulator, Environment Agency Wales, has published catchment-scale reports and has commissioned a range of in depth studies, while others have worked at project-level providing insight into aspects of a variety of groundwater occurrence problems peculiar to Wales.

This report attempts to provide an updated review of the occurrence of groundwater throughout Wales. It is part of a series of regional- and aquifer-scale reports issued by the British Geological Survey, the Groundwater Programme Research Report series. An introductory chapter is followed by chapters on each lithostratigraphical system. These describe the outline geology and hydrogeology and highlight the availability of groundwater, its quality and any issues pertaining to the hydrogeology of the units within each system. In addition a concluding chapter describes the past and present regulatory framework in Wales and the modern-day management tools used by Environment Agency Wales with illustrations of some of the problems that need to be addressed.

The report draws on data available in the public domain, both published and unpublished. The reference list provides a valuable record of all these sources. In addition datasets held by both the British Geological Survey and Natural Resources Wales have been consulted along with data held by Dŵr Cymru Welsh Water and Cardiff University.

Although the report was compiled by Nick Robins and Jeff Davies, an important contribution was also prepared by David Jones Natural Resources Wales and Gareth Farr (previously of Environment Agency Wales) who drafted the bulk of Chapter 8 on management and regulation. The principal authors are also grateful to Kay Roberts and Beth Davies and others at Natural Resources Wales for valuable peer review comments on the manuscript. Peter Neve is thanked for comments on hydrogeology in north east Wales. David Schofield and Colin Waters provided geological advice including validation of stratigraphical terminology.

Others who have provided data or helped in the preparation of this report include: the late David Headworth at Environment Agency Wales; Ian Brown at Dŵr Cymru Welsh Water; Glyn Hyett of Celtic Water Management Ltd. Cardigan; Emma Paris, Tim Jones and Charlie Harris at Cardiff University; Ron Fuge, University of Wales, Aberystwyth; Paul Younger, University of Strathclyde, formerly University of Newcastle-upon-Tyne; Ab Grootjans at University of Groningen, Netherlands; John Ratcliffe and colleagues at the Countryside Council for Wales; Charlie Stratford and Laurence Jones at the Centre for Ecology and Hydrology.

==Hydrogeology of Wales - contents==
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[[Category:Hydrogeology of Wales| 0001]]

Hydrogeology of Wales: Introduction - groundwater regulation

2015-07-28T19:14:20Z

Gareth Farr: updated text to include new regulator body for wales ' Natural Resources Wales' that replaces Environment Agency Wales

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The Water Act 1989 converted ten previously existing regional Water Authorities in England and Wales into privatised water and sewerage undertakings and created the National Rivers Authority as the new environmental regulator. The National Rivers Authority was subsumed into the newly formed Environment Agency in 1996. Several separate statutes, including the Water Act 1989 and the Water Resources Act 1963, were consolidated into the Water Resources Act 1991 to become the main statutory framework for the duties and powers of the Environment Agency. On the 1st April 2013 Environment Agency Wales was replaced with a new regulatory body, Natural Resources Wales. Natural Resources Wales combines the roles of Environment Agency Wales, Countryside Council for Wales and the Forestry Commission Wales.

Natural Resources Wales has a duty to secure the proper use of water resources. It is responsible for monitoring groundwater level and quality at 180 and 250 monitoring points respectively, and carries out additional monitoring work in the vicinity of groundwater-dependent terrestrial ecosystems. It issues licences for abstractions that exceed 20 m3 d-1 in order to regulate taking water from the environment, and to determine the volume that can be taken over a given period of time. Some rural areas of Wales remain license exempt because of the prevailing poorly yielding aquifers. Natural Resources Wales is also responsible for maintaining or improving the quality of fresh, marine, surface and groundwater and aims to prevent or reduce the risk of water pollution wherever possible, and to ensure that it is cleaned-up should pollution occur which could affect ecosystems or people.

Water quality standards for both public and private supply have been tightened in recent years and consolidated within the Water Supply (Water Quality) Regulations (2000). Some of the European directives have been implemented as Statutory Instruments whilst others became law as part of the Pollution Act, Part II. The Natural Mineral Waters Regulation (Statutory Instrument No. 1540 of 1999) provides for the recognition and exploitation of Natural Mineral Waters (as bottled groundwaters), their chemistry and potability.

The protection of surface and groundwater from pollution is provided for by the Environmental Permitting Regulations (2010), which define the requirements of sanitary landfill and other potentially hazardous activities.

The ongoing implementation of the Water Framework Directive ([[Hydrogeology of Wales: References|'''European Community, 2000''']]) includes a need to assess the pressures and impacts affecting groundwater bodies with a view to determining the degree to which they are at risk from failing to meet Article 4 objectives. The Article 4 objectives in turn require that groundwater bodies achieve good chemical and quantitative status by the year 2015. Part of the assessment of whether a groundwater body is ‘at risk’ involves an evaluation of the likelihood that polluting activities will cause deterioration of the water quality in the groundwater body, to the extent that it will fail to have good chemical status by 2015.

The main water company operational in Wales is Dŵr Cymru Welsh Water. Since May 2001, Dŵr Cymru has been owned by Glas Cymru, a non-profit-making company, whose operational surplus is returned to customers as an annual dividend — £18 in the 2005/2006 fiscal year and up to £19 the following year. Dŵy Cymru is a management company with a small staff complement. Many of its service departments are contracted out, most to other UK water companies, including Thames, Severn Trent and United Utilities.

==Hydrogeology of Wales - contents==
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[[Category:Hydrogeology of Wales| 004]]

Hydrogeology of Wales: Introduction - geology and groundwater

2015-07-28T19:00:25Z

Gareth Farr: small typo

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[[Image:P841814.jpg|thumb|300px|Solid geology in Wales. P841814.]]
The geology of Wales is extraordinarily diverse; the geological descriptions in this report are based on those presented in the regional geochemistry atlas for Wales ([[Hydrogeology of Wales: References|'''BGS, 2000''']]) although some terminology has since changed. The stratigraphical sequence in Wales extends from the Precambrian through to recent. The oldest rocks occur in north Wales and are mainly metamorphic and igneous Precambrian and Cambrian rocks ('''Figure P841814'''). Central Wales is dominated by Lower Palaeozoic age sediments (Ordovician and Silurian) trending south-west to north-east. The Precambrian and early Lower Palaeozoic rocks are overlain by Devonian sandstones, mudstones and conglomerates in east Wales and the Welsh Borderland. Carboniferous strata are present in south Wales and parts of the north, Triassic strata occur in the Vale of Clwyd and Jurassic deposits occur in the Vale of Glamorgan. Till and associated glacial material are widespread on the lower-lying ground but tend to be absent in many upland areas. Alluvium and glacial outwash material occur in many valleys and there are several large groundwater dependent peat bogs. Soil cover is typically thin on the higher ground, particularly in parts of Snowdonia where outcrop is extensive.

Hydrogeological maps for northern and southern Wales ([[Hydrogeology of Wales: References|'''BGS, 1986; 1989''']]) provide a valuable graphical summary of the occurrence and nature of groundwater in the Principality. Marginalia to these maps include cross-sections, hydrochemical information, selected hydrographs, rainfall distribution and a summary description of groundwater availability. However, such maps are not available for central Wales as the groundwater systems contained within the basement rocks in this area have not previously been considered in resource terms.

The Late Neoproterozoic, Cambrian, Ordovician and Silurian rocks have a low interstitial porosity and permeability, although many have a limited fracture permeability and porosity. Depth of weathering tends to be shallow especially on valley sides where glacial erosion has removed weathering products. Groundwater occurs within an otherwise shallow weakly permeable aquifer that is capable of maintaining rural domestic and limited agricultural and industrial demand.

The Upper Old Red Sandstone in south to mid Wales consists mainly of unconsolidated, well-cemented, flaggy sandstones with thin sandy marls. Most groundwater flow is limited to fractures, but marl bands limit vertical flow and promote hillside springs. The Devonian aquifer is regionally important in sustaining a large number of public and private water supplies, although groundwater yields and springs may decline during prolonged periods of dry weather and some may dry up completely. The Lower Old Red Sandstone is essentially mudstone and siltstone.

Carboniferous sediments, mainly limestones overlain by Coal Measures Facies, occur both in the south and north-east of Wales and in Anglesey. The limestones represent an important groundwater source and have a high fracture permeability resulting from a well-developed joint and fracture system, but with low matrix permeability. Karstic flow conditions occur throughout the limestones other than those in Anglesey. Significant yields are obtained from major spring resurgences that generally occur near the base of the sequence or along faults. Groundwater flow velocities can be rapid with movement taking place along a small number of large fractures. Recharge processes are supplemented by shallow holes or dolines that form point sources for recharge. Significant quantities of groundwater were formerly pumped from mainly fractured sandstones of the Middle Coal Measures and Pennant Sandstone Formation within the South Wales Coalfield both for mine dewatering and public water supply.

Triassic-age sandstones are found in north-east Wales in the Clwyd–Merseyside Basin and form a small aquifer that is exploited for public supply in the Vale of Clwyd. The strata comprise cross-bedded, well-cemented, fine- to medium-grained sandstones with thin lenses of mudstone. The sediments generally exhibit high fissure and intergranular permeability. Clay-grade superficial deposits cover the Triassic outcrop restricting recharge in some places and confining the underlying aquifer to generate artesian heads of up to 6 m above ground level.

Local Quaternary deposits (mainly glaciofluvial, alluvial and colluvial) throughout Wales are thin and variable in nature but have a high permeability and are useful in providing local domestic supplies especially in low-lying areas. They may be poorly protected and vulnerable to surface pollution.

Most of the aquifers in Wales are unconfined and have shallow flow systems. The groundwater is generally well oxygenated and weakly mineralised with calcium and bicarbonate forming the main ionic components. More strongly mineralised groundwater, depleted in oxygen, occurs in deeper aquifer systems. Groundwater from the Silurian and Ordovician strata is generally of good quality, varying from Ca-HCO3 to Ca-Na-Cl types in relation to local geology, residence time and drift type. Deeper water from the confined Coal Measures facies is typically of poor quality due to the solution of iron and sulphate resulting from many years of mining below the water table. The Triassic strata are typically moderately mineralised and of the Ca-HCO3 type.

[[Image:P859258.jpg|thumb|300px|Distribution of water boreholes recorded by BGS/EA. P859258.]]

Whereas the groundwater potential of much of Wales has traditionally been ignored ([[Hydrogeology of Wales: References|'''Bassett, 1969''']]), the requirements of European Community Directives such as the Water Framework Directive have provided a new focus. Data are available on the Triassic and Devonian aquifers but remain scarce for much of the Carboniferous, other than the Carboniferous Limestone, and the fractured hard-rock aquifers which prevail in central and west Wales ([[Hydrogeology of Wales: References|'''Robins et al., 2005)''']]. The distribution of water boreholes based on British Geological Survey/Environment Agency records ('''Figure P859258''') indicates a paucity of data outside north Wales and the Cheshire Basin and parts of south Wales.

Although Wales has never been dependent on its groundwater resources, there have been some significant innovative groundwater schemes. These include the Clwyd Augmentation/Abstraction Scheme ([[Hydrogeology of Wales: References|'''Lambert, 1981''']]; [[Hydrogeology of Wales: References|'''ESI, 2003''']]), the Dee Regulation Scheme and hydrogeological investigations carried out during the development of the Cardiff Bay Barrage ([[Hydrogeology of Wales: References|'''Heathcote et al., 2003''']]).

==Hydrogeology of Wales - contents==
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[[Category:Hydrogeology of Wales| 002]]

Hydrogeology of Wales: Introduction

2015-07-28T18:57:55Z

Gareth Farr: some small typos, removal of principal A as there are no Principal A aquifers, just Principal.

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Wales receives wet westerly winds and is consequently well-endowed with water resources. In addition to its surface waters, Wales also has a wide range of aquifers that reflect its diverse geology, and although groundwater cannot compete with the surface water resources in terms of volume, it does offer a valuable alternative or supplementary source, particularly in rural areas. Groundwater has stable physical and chemical properties, which are beneficial to a number of industries including brewing, distilling, fish farming and dairy processing and it provides a source of alkalinity when blended with the often-acidic surface waters derived from upland gathering grounds. Groundwater is not only an important resource but it also maintains low river flows during drier periods with continued discharge of groundwater base flow into surface waters. Groundwater is also a potential hazard — mine dewatering has taxed Welsh mining engineers ever since the Industrial Revolution. Coal production in south Wales peaked at the start of World War One only to decline during hostilities; recovery to full production was achieved by 1926, the year of the General Strike, but has declined steadily since ([[Hydrogeology of Wales: References|'''Brabham, 2004''']]).

Groundwater is available throughout Wales, the more productive aquifers being the Carboniferous Limestone of north and south Wales and the Triassic sandstones in the Vale of Clwyd, the only aquifers designated as Principal type by Environment Agency Wales, and the Devonian age sandstones bordering Herefordshire and to the north of the South Wales Coalfield. There are, however, abundant surface water resources. Approximately 91 Mm3 a-1 or about 8 per cent of the total water in public supply in Wales derives from groundwater and a further 34 Mm3 a-1 is abstracted for private consumption from about 21 000 boreholes, wells and springs ([[Hydrogeology of Wales: References|'''EA Wales, 2009''']]). The main water undertaking is Dŵr Cymru — Welsh Water. The estimated annual abstraction against likely overall annual renewable resource potential, based on an analysis by the then Welsh Water Authority undertaken in the mid 1970s when abstraction for industrial use was at its peak is shown in the '''resource potential and annual abstraction table '''([[Hydrogeology of Wales: References|'''Monkhouse, 1982''']]). This analysis shows that only about 10 per cent of the estimated groundwater resource potential was then used. However, the total estimated abstraction in the 1970s (111 Mm3 a-1) was only slightly less than that estimated for today (125 Mm3 a-1) and the groundwater resource potential remains to this day underutilised.
<center>
{|class="wikitable"
|+ Estimated annual renewable groundwater resource potential and annual abstraction in 1977 (after '''Monkhouse, 1982''').
|-
| Aquifer
| Annual renewable resource potential (Mm3 a-1)
| Annual abstraction (Mm3 a-1)
|-
| Quaternary deposits
| 206
| 11
|-
| Permo-Triassic age sandstones
| 27
| 12
|-
| Coal Measures facies
| 412
| 37
|-
| Basal Grits
| 22
| 1
|-
| Carboniferous Limestone facies
| 376
| 46
|-
| Devonian
| 379
| 5
|-
| Total
| 1421
| 111*
|-
| colspan="3" | *In 2009 the overall likely estimate by the Environment Agency Wales was 125 Mm3 a-1.
|}
</center>

Private abstraction is largely of a limited and local-scale because of the indurated and fractured nature and modest permeability of many of the aquifers. It is nevertheless of significant social and economic importance and is used for drinking water, farming, and light industry. There are several reasons why groundwater is important even in areas where surface water is abundant. Groundwater offers consistent and generally favourable quality and is readily accessible at least in small quantities. It is also inexpensive to develop and is largely abstraction license exempt. Overall development of groundwater is patchy, partly due to a perception that groundwater is unlikely to be present in usable quantities in areas such as the hard rock terrains typical, for example, of much of central and west Wales.

High rainfall and recharge coupled with low transmissivities, promote shallow water tables in many areas with a consequent complex relationship between surface water and groundwater [[Hydrogeology of Wales: References|'''(Robins, 2009)''']]. Karst conditions in the Carboniferous Limestone have created pathways between sinks and risings in which surface water may be diverted underground to emerge in an adjacent catchment. Contamination of groundwater by acid mine drainage in parts of south Wales, west Wales and north-east Wales, coupled with risks from contaminated land, the latter a legacy of the heavy industry that used to be prevalent in the valleys of the south and north-eastern Wales, may have an adverse impact on groundwater (and surface water) quality. Diffuse pollution from agriculture and forestry is also a problem in some areas. Nevertheless, the potential exists for abstraction of good-quality groundwater in much of Wales, particularly in remote areas where pollution risks are low.

Groundwater has also fostered a number of high-profile industries. At one time brewing relied on groundwater for make-up water, as the mineralisation of the water not only offset the need to add brewing salts but also provided a unique product flavour. Today there are still a few brewers using groundwater including the Felinfoel Brewery Company near Llanelli and the Penderyn Distillery near Aberdare, both drawing groundwater from Carboniferous strata. Welsh groundwater is also bottled at various locations and sold as Natural Mineral Water, and at a price significantly in excess of that of an equivalent volume of petrol or diesel.

==Hydrogeology of Wales - contents==
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[[Category:Hydrogeology of Wales| 001]]