OR/15/009 Introduction

Lapworth D J, Carter R C, Pedley S and MacDonald A M. 2015. Threats to groundwater supplies from contamination in Sierra Leone, with special reference to Ebola care facilities. British Geological Survey Internal Report, OR/15/009.

The outbreak of Ebola virus disease in West Africa has resulted in new care facilities being built, with associated water supplies, latrines, waste sites and burial sites. Although Ebola is not a water-borne disease, other diseases, such as cholera have been shown to spread through shallow groundwater from latrines and waste sites to water supplies. Often a pragmatic safe spacing of between 20–50 m is assumed, however, safe spacing is highly dependent on the hydrogeology of the shallow soil, the climate and the quality of the construction of both water points and latrines.

Objectives and key questions

The objective of this rapid desk study is to assess existing literature and evidence for sub surface transport of pathogens in relation to both the hydrogeological and socio-economic environment of Sierra Leone to provide: advice on the robustness of a single minimum figure for spacing between latrines (and other point sources of contamination) and water supply; recommendations for protecting water supplies for care facilities.

Key questions and work plan for the rapid desk study are:

1. What is known about the prevailing hydrogeological conditions within Sierra Leone?
2. What is known about available water quality data for Sierra Leone, or analogous urban areas in Africa?
3. What is known about pathogen survival and transport in the sub surface and shallow permeability in tropical soils?
4. Interpret the data from 1–3 within a source-pathway- receptor framework to provide recommendations on the robustness of a single minimum separation and appropriate designs to increase the protection of treatment centre water supplies.
5. Write up the results of 1–4 into an open report

This report starts by giving a brief overview of the public health and natural physical conditions of Sierra Leone. It then provides a review of the hydrogeology, water quality and pathogen survival conditions in Sierra Leone and analogous hydrogeological settings in Africa. The risks to groundwater supplies are then presented using a source-pathway-receptor framework. Finally recommendations for the protection of water supplies for care facilities and communities made and evidence gaps highlighted.

Background and public health issues in Sierra Leone

Having only emerged from a ten-year civil war in 2002, during which most of the nation’s public services and physical infrastructure were destroyed, Sierra Leone’s public services are weak, and investment in new services has barely begun. As a consequence, water and sanitation coverage are extremely low. Table 1 sets out the most recent JMP data for Sierra Leone. The high rates of open defecation (especially in rural areas) and high dependence on surface water in rural areas present a particular public health hazard. In urban areas one-third of the population either practice open defecation and or use unimproved sanitation, and much of the access to ‘improved’ water supply is by illegal and unsafe connections to public supply mains.

Table 1 Sanitation and water supply coverage, Sierra Leone, Source JMP 2014 update
(a) Sanitation coverage 2012 (%)

Urban				Rural				Total
Improved	Shared	Other unimproved	Open defecation	Improved	Shared	Other unimproved	Open defecation	Improved	Shared	Other unimproved	Open defecation
22	42	26	10	7	19	35	39	13	28	31	28

(b) Water supply coverage 2012 (%)

Urban					Rural					Total
Total improved	Piped on premises	Other improved	Other unimproved	Surface water	Total improved	Piped on premises	Other improved	Other unimproved	Surface water	Total improved	Piped on premises	Other improved	Other unimproved	Surface water
87	11	76	5	8	42	1	41	17	41	60	5	55	12	28

The 2014 Ebola outbreak

The first cases of the current Ebola outbreak were reported in neighbouring Guinea and then later in Liberia: by 20 April 2014, 242 suspected cases had resulted in 147 deaths in Guinea and Liberia (Gatherer 2014). A recent study using genome sequencing by Gire et al (2014) suggest that this West African variant likely diverged from the central African lineages around 2004.

The Ebola crisis in Sierra Leone began with the first cases in the eastern districts of Kailahun and Kenema in early May 2014, close to the border with Guinea and Liberia. During the period June to November 2014 the infection spread westwards through Bo, Tonkolili, Bombali and Port Loko districts, reaching Western Area Rural and Western Area Urban (i.e. Freetown) from October onwards (Figures 1 and 2). By the end of January 2015 more than 10 340 cases (confirmed, probable and suspected) and 3145 deaths had been reported by WHO.

From December 2014 significant numbers of Ebola Care Facilities (and beds) were established. Prior to this, most victims recovered or died in their communities. Therefore, through most of 2014 it is probable that the contaminated body fluids, wastes and corpses were handled and managed in the community rather than at dedicated care facilities. The risk of contamination of the general environment (however short-lived because of the limited survival time of the virus) was consequently higher in 2014 than subsequently. From December 2014, an increasing number of victims were treated at Ebola Care Facilities, giving greater opportunity for safe handling and containment of contaminated wastes.

Nevertheless, in the latter part of 2014 and into 2015 disturbing (mainly anecdotal) evidence has emerged of poor practices, including:

• Health workers taking used personal protective equipment off-site into their homes;
• Ambulances being washed out in local watercourses;
• Solid wastes being dumped outside of care facilities; and
• Ebola care facilities being sited only metres away from pre-existing wells (see Figures 3 and 4).

Figure 1 Ebola cases in Sierra Leone, weekly May 2014 to February 2015. Data source, Ministry of Health Sierra Leone. Weekly patient database statistics downloaded from WHO.

Water-borne epidemics are a recurring problem in Sierra Leone. There have been several cholera and Shigella outbreaks reported in different parts of Sierra Leone since the mid 1990’s (e.g. Guerin et al. 2004; O Dyer 1995). A recent study by Nguyen et al. (2014) found that the consumption of unsafe water, and street vended water was a significant risk factor for V. cholera transmission during a 2012 cholera epidemic in Sierra Leone, despite recorded high levels of access to ‘improved’ water sources in urban areas as shown in table 1b above.

This was the largest reported outbreak in the country since 1995 with a total of 22 800 reported cases and 296 deaths. This study underlines the risks of such outbreaks occurring even where reported improved water source coverage is high, particularly in densely populated urban areas. Testing for residual chlorine in stored water and public supplies suggested that treatment was inadequate given the risks of transmission. The authors argue that the JMP classification of 'improved' water sources is inadequate since it does not include water quality criteria. This is supported by a systematic review prepared for the JMP that indicated 1.8 billion people with access to improved water sources drink water that is faecally contaminated (Bain et al., 2014).

Figure 2 Spread of Ebola in Sierra Leone, June to November 2014, Source MapAction http://www.mapaction.org/?option=com_mapcat&view=diary&id=51

Figure 3 A well close by the care facility at Magburaka Hospital. Used with permission from Ishmail Kamara (source: Ministry of Water Resources/ASI).

Figure 4 An Oxfam well close to the community care facility at Kumala Primary School. Used with permission from Enam Hoque (source: Oxfam).

Climate, hydrology, geology and physical relief

Climate

Sierra Leone experiences a humid tropical climate in which mean annual rainfall is approximately twice the mean annual potential evapotranspiration. Rainfall is unimodal and highly seasonal, with a peak in August and dry season from December to March. Temperatures are relatively uniform throughout the year.

Rainfall over most of Sierra Leone commences in or around April, peaks in August, and reduces to near-zero in December (Figure 5). Inter-annual variation is generally limited as shown by the small interquartile ranges, however some extremes are possible as indicated by the large monthly ranges. Ambient air temperatures vary only within a narrow range 24–28 degrees C) over the year. The lowest temperatures occur in July, August and September, in the middle of the rainy season, and the highest in February and March in the latter part of the dry season.

Figure 5 Monthly rainfall and temperature for Sierra Leone, source CRU data (Jones and Harris 2013) 1950–2012 median, interquartile range and max and min for each month.

Mean monthly potential evapotranspiration (ET) has been estimated by FAO Climwat at six locations According to these estimates, mean annual potential ET ranges from 1332 to 1639 mm across Sierra Leone.

The spatial distribution of mean annual rainfall is shown in Figure 6. Panels (a) and (b) show the patterns for two overlapping periods, from different sources. Panels (c) and (d) show as insets the rainfall pattern over the hilly Freetown peninsula. Mean annual rainfall ranges from around 1750mm in the north-east to over 4000 mm in the Freetown peninsula.

There is some evidence of warming over recent decades (McSweeney et al, 2010) that mean annual temperature has increased by 0.8 ̊ C since 1960, an average rate of 0.18 ̊ C per decade and the frequency of hot nights has also increased. There is less convincing evidence for a long term trend in rainfall, and insufficient rainfall monitoring to determine changes in rainfall intensity.

Figure 6 Rainfall over Sierra Leone. Sources of original data shown in Figure. This version is reproduced with permission from the Ministry of Water Resources/ASI.

Hydrology

Five main rivers (Little Scarcies, Rokel, Jong, Sewa and Moa) flow from north-east to south- west, draining most of Sierra Leone’s land surface. In addition six smaller basins and drainage areas (Great Scarcies, Lokko, Rokel Estuary, Western, Robbi/Thauka and Sherbro Water Resources Areas) complete the picture (Figure 7).

FAO (Aquastat) estimate Sierra Leone’s total renewable water resources as 160km3/year (out of 182.6km3/year which is estimated as rain. This estimate of the nation’s water resources – at 88% of mean annual rainfall - is certainly a gross over-estimate, as it fails to account adequately for evapotranspiration (Carter et al, 2015). A more realistic estimate is that given by Schuol et al (2008), of 59.3-98.4 km³ per year, between 32% and 54% of mean annual rainfall.

Figure 7 Sierra Leone’s river basins and drainage areas. Source, reproduced with permission from the Ministry of Water Resources/ASI (2015).

Runoff is highly seasonal, reflecting the seasonal distribution of rainfall. Figure 8 shows the mean monthly flows for the Rokel river at Bumbuna (latitude 9.05N, longitude 11.73W), derived from what is probably the best river flow record in Sierra Leone. Discharge increases from May, peaking in September and decreasing to near-zero by March.

Figure 8 Mean monthly flows, Rokel river at Bumbuna, 1970-1978, m3/s. Source, Nippon Koei UK (2005).

A number of studies (including Akiwumi, 1994; Nippon Koei, 2005; Carter et al 2015) have demonstrated that approximately 40% of the Rokel river flow (and by extension that of the other major rivers) consists of shallow seasonal baseflow – water which enters the shallow aquifers during the rainy season, and which discharges to the river within months in response to hydraulic gradients towards those rivers.

Geology

Figure 9 is a simplified geological map of Sierra Leone. Most of the country (with the exception of the Freetown Complex and the Bullom Group) is underlain by sedimentary, meta- sedimentary, igneous and metamorphic rocks of the Archaean Basement Complex and Lower Palaeozoic/Upper Proterozoic Consolidated Sedimentary formations. Table 2 sets out brief descriptions of the main geological units. These units are further described in section 2 in hydrogeological terms.

Figure 9 Simplified geological map of Sierra Leone. Source, Ministry of Water Resources/ASI (2015), relief from USGS SRTM data (accessed Feb 2015).

Table 2 Descriptions of the main geological units in Sierra Leone. Source, Ministry of Water Resources (2015)

Geological Unit	Age	Descriptions
Bullom Group: unconsolidated sedimentary rocks	Cenozoic (Tertiary and Quaternary to recent)	Poorly consolidated marine and estuarine sediments — sands, gravels and kaolinitic clays with some lignite
Ultrabasic Igneous Intrusives	Mesozoic (Jurassic and Triassic)	Freetown Peninsula Complex and other intrusive
Saionya Scarp and Rokel River Group: consolidated sedimentary rocks	Lower Palaeozoic (Cambrian) and Proterozoic	Variegated shales, siltstone, mudstone interbedded with volcanic and quartzite bands
Precambrian Basement Complex: ancient crystalline granitic gneiss with supracrustal volcanic and sedimentary belts	Neoarchean and Archean	Marampa Group: metasediments and volcanics Kasila Group: granulites basement granites, gneisses and migmatites. Volcanic greenstone, amphibolite and gneiss

Physical relief and soils

A coastal strip approximately 50 km in width, covering about 15% of the country, gives way to inland plains and plateaus in the interior. The lower plains, covering 43% of the country rise from 40 m in the west to 200 m in the east. Swampy depressions in the west are known as bolilands. Figure 10 shows an elevation map of Sierra Leone (10a) and two insets which show detailed elevation models for two areas of Sierra Leone, the Freetown Peninsula (Figure 10b) and Lunsar (Figure 10c). Figures 10b and 10c illustrate the extensively weathered tropical soil terrain, including the distinctive duricrust development (see Bowden 1997) and the well-developed fracture network associated with the intrusive granites.

Figure 10 Physical relief of Sierra Leone a) Sierra Leone and surrounding region, b) Freetown peninsula, c) Lunsar. Data source, USGS SRTM data (accessed Feb 2015).

In the north-east and south-east, the plateaus range from 300m to 700 m altitude, and cover 22% of the country. Hills and mountains in the east reach a maximum elevation of nearly 2000 m at Mount Bintumani in the Loma Mountains, while the hills formed by the Freetown Complex reach 800m around Sierra Leone’s capital.

Figure 11 shows the distribution of soils in Sierra Leone. The lowland area in the western half of Sierra Leone is dominated by strongly weathered Ferrasols with low nutrient levels. The upland area to the east has a partial cover of Pisoplinthic Plinthosols, soils with accumulations of iron that hardens irreversibly when exposed to air and sunlight.

Figure 11 Soil map of Sierra Leone (soil data from Jones et al 2013, topography data (SRTM) from USGS, accessed in February 2015).

For simplicity these two iron rich soils are referred to as 'tropical soils' in the following sections of this report. Toward the coast these become yellow in colour. Elsewhere there are Lithic Leptosols, shallow soils over hard rock with bedrock close to the surface.

In many cases tropical soils contain openings and macropores which permit rapid movement of water. These also have non-linear increases in horizontal permeability as moisture content increases during the onset of the rainy season, and under high water table conditions.

Summary physical geography of Sierra Leone: The physical context forming the background to this report is one in which poor sanitary conditions conspire with high and intense rainfall, rapidly responding hydrology, unfavourable geology and physical relief to pose significant threats to groundwater from human pathogens.