OR/16/033 The Water Framework Directive

Stuart, M E, Ward, R S, Ascott, M, and Hart A J1. 2016. Regulatory practice and transport modelling for nitrate pollution in groundwater. British Geological Survey Internal Report, OR/16/033. 1 Environment Agency

Introduction

The European Water Framework Directive (WFD) (2000/60/EC) which came in to force in 2000 provides a framework for the protection of the water environment including groundwater. It sets out a series of environmental objectives that must be achieved by implementing programmes of measures. The achievement of the objectives for groundwater means that groundwater bodies should have achieved good status by the end of 2015. It is recognised that there are diverse hydrogeological conditions which will require different specific solutions and that this diversity needs to be taken into account when planning and executing the programmes of measures. Additionally time extensions, beyond the 2015 deadline, are possible, up to 2027, provided that a justification can be provided. This includes where natural conditions, such as an unsaturated zone lag time, do not allow the deadline to be met.

The WFD sets out a stepwise process which must be followed and which comprises:

• delineation of groundwater bodies and groups of groundwater bodies (management units);
• characterisation of groundwater bodies including the hydro(geo)logical and baseline conditions, the (abstraction and pollutant) pressures, evidence of impact etc.;
• an evaluation of the risk of failing to meet the relevant environmental objectives for each groundwater body;
• establishment of groundwater monitoring programmes;
• determination of groundwater body status (chemical and quantitative) and pollutant trends;
• identification of programmes of measures to restore groundwater bodies to good status, reverse upward trends in pollutant concentrations and prevent deterioration of bodies currently at good status;
• publication of river basin management plans every six years that set out the strategy/ies for implementing programmes of measures and achieving environmental measures in accordance with the WFD.

The WFD and its daughter directive the Groundwater Directive (GWD) (2006/118/EC) recognises that nitrate is one of the most widespread groundwater pollutants and so requires an assessment of the risks and impact of nitrate pollution to be made and appropriate measures implemented. Whereas the Nitrates Directive focuses on delivering measures to address agricultural sources of nitrate the WFD requires measures for all sources of nitrate. There are other differences between the directives, e.g., dates for achieving objectives, different standards/thresholds and different reporting cycles. However the measures implemented under the Nitrates Directive, e.g. NVZs will contribute significantly to achieving WFD objectives.

To protect groundwater, the WFD, through the GWD, establishes a default groundwater quality standard for nitrate of 50 mg NO₃ l^-1. However the WFD is a risk-based directive and where it is considered that this value would not adequately protect groundwater and/or associated receptors, a lower value (threshold value) must be set. This is the case for protection of drinking water (37.5 mg/l) and groundwater-dependent terrestrial ecosystems (range: 4–26 mg/l depending on ecosystem/wetland type).

Environmental objectives

The WFD contains a number of specific environmental objectives for groundwater. These are to:

• prevent or limit inputs of pollutants to groundwater;
• prevent deterioration in chemical and/or quantitative status;
• restore bodies to good chemical status (from poor status);
• reverse environmentally significant and sustained upward trends in pollutant concentrations;
• achieve Protected Area objectives. These are the specific objectives for; 1) Drinking Water Protected Areas (DrWPA) and; 2) Nitrate Vulnerable Zones (NVZs).

2009 WFD nitrate results

An assessment of groundwater is made at least once every six years for the WFD. Groundwater monitoring data are used to assess groundwater body status and identify pollutant trends. For status assessment the data for the previous six years are used and for trends the previous ten years.

Chemical status assessment comprises the consideration of five tests which each consider one or more of the criteria which all must be met to achieve good status. The criteria are:

1. The chemical composition of the groundwater body is such that concentrations of pollutants: a). do not exhibit the effects of saline or other intrusions; b) do not exceed relevant quality standards; c) are not such as would result in failure to achieve the environmental (and status) objectives for associated surface waters; d) do not cause significant damage to terrestrial ecosystems which depend directly on the groundwater body;
2. Changes in specific electrical conductivity are not indicative of saline or other intrusion into the groundwater body.

Trend assessment comprises, in the first instance, the identification of any significant and sustained upward trend in concentrations of pollutants, groups of pollutants or indicators of pollution in groundwater bodies. Where an ‘environmentally significant’ upward trend is identified, i.e. one that would lead to a future failure of one or more of the criteria for good status, then this must be reversed through the programmes of measures. Subsequent trend assessment (in future river basin planning cycles) should then seek to demonstrate trend reversal.

The first evaluation of status and trends was carried out in 2009 and reported in the River Basin Management Plans. The next evaluation was in 2015. A map showing the groundwater bodies that were at poor status as a result of nitrate pollution and those with upward trends is presented in in Figure 5.1.

Figure 5.1    Groundwater bodies at poor status and/or with upward trends in nitrate concentrations.

In total 63 (21%) of the 304 groundwater bodies across England and Wales were at poor (chemical) status due to nitrate pollution, principally derived from agricultural sources. A total of 54 bodies (18%) failed the trend objective.

A review of the area of land designated as NVZ in 2006 and the groundwater bodies that have failed their good status and trend objectives due to nitrate (ENTEC, 2009) indicated that there was good correlation between the two. Spatial analysis of the differences, where they occurred, showed that these could be accounted for by: a) the NVZ methodology considering all areas, whereas status assessment excluded unproductive strata as these were not designated as groundwater bodies; b) NVZs being based on groundwater data for exceeding the 10 years used for the WFD and; c) difference in delineation method — NVZs were based on field bodies whereas groundwater bodies are based on catchment/hydrogeological boundaries.

A site by site comparison between the WFD and NVZ assessments showed that the WFD dataset identified more exceedances of the relevant threshold value (standard) due to a lower value used in the WFD, 42 mg/l compared to 50 mg NO₃ l^-1 for NVZ delineation.