Example

The (E)QS for pollutant X in a stream (the receptor for this example) is 10.

The Flow into the receptor from groundwater comprises 80% of the flow i.e. the dilution factor (DF) is 4/(4+1).

Hence the Dilution Tier (Tier 3) value for the groundwater = 10/0.8 = 12.5

Scenario 1. The monitored concentration in the groundwater Cmon is >12.5 and the observed concentration in the stream Cobs is the same. No evidence of attenuation so retain the Tier 3 value

Scenario 2. The monitored concentration in the groundwater Cmon is >12.5 but the observed concentration in the stream Cobs is lower. There is evidence that attenuation is occurring so either:

1) utilise existing data to calculate the extent of attenuation observed and hence the observed attenuation factor (note this will have the effect of allowing existing Cmon concentration as the Tier 4 value but no greater), or

further develop the attenuation calculation based on a fate and transport model such as those in Section 4.2 and hence generate an AF value independent of the current

observed concentration.

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Annex VI: The links between the objectives for

prevent or limit, and status

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Annex VI

The links between the objectives for prevent or limit, and status Cath Tomlin

This section outlines the role of threshold values for assessing status, the link between status assessment and limiting inputs of pollutants, and how “limit values” to comply with the

prevent or limit objective differ to threshold values.

1 Background

The WFD and the GWDD provide a new regulatory setting for the protection of our groundwater quality environment. Together they set three main objectives by which to achieve this protection:

- Achieve good groundwater chemical status by 2015;

- Prevent or limit the inputs of pollutants into groundwater; and

- Implement measures to reverse any significant and sustained upward trend in pollutant concentrations.

The three objectives for groundwater noted above differ in relation to the parts of the groundwater environment they apply to. The Status objective applies to all bodies of groundwater and concerns large-scale issues. The objectives to prevent or limit the inputs of pollutants, and to reverse any significant and sustained upward trends apply to all groundwater, and can therefore be applied on a much smaller “local” scale. These objectives complement each other to fully protect groundwater quality.

The timescales over which action is taken and assessed also differ. The assessment of trends can take many years and can be viewed as a long-term check on the effectiveness of protection measures. Status is assessed every six years for an entire groundwater body.

Prevent or limit measures are the day to day controls on inputs and their effectiveness needs to be assessed both in the short term (to prevent local pollution) and also over longer periods to determine their contribution to the status and trend objectives.

2 Groundwater chemical status

Achieving ‘good chemical status’ for groundwater involves meeting a series of conditions which are defined in Annex V of the WFD, and further elaborated within the GWDD. They are applied to the whole of the groundwater body. These conditions drive the setting of criteria (standards and thresholds) against which status will be assessed.

For chemical status, the GWDD indicates that Member States are obliged to use prescribed groundwater quality standards for nitrates and pesticides, and locally, nationally or internationally derived threshold values for other pollutants that have been identified as contributing to the characterisation of the groundwater bodies as being at risk. Compliance is first assessed by comparing the standards with groundwater quality data at operational monitoring points, and second with an appropriate investigation at the GWB level.

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Neither the prescribed quality standards nor the threshold values represent the boundary between good and poor status. If they are exceeded at any monitoring point, Member State competent authorities are required to undertake further investigation to determine whether the conditions for good status have been met.

Threshold values:

- will be set for groundwater bodies and pollutants characterised as “at risk”;

- will be set at the start of each River Basin Plan cycle;

- will be used to determine Status at the start of each River Basin Plan cycle;

- are not intended for use at a local scale to assess pollution – they are not limit values for use in preventing or limiting the input of pollutants.

The standards and conditions that are applied to environmental permits should reflect the need to meet all WFD objectives, including good chemical status, but these will not necessarily be the same as threshold values (either numerically or in terms of their associated compliance regime).

3 Prevent and Limit

The existing Groundwater Directive 80/68/EC requires that Member States take the necessary measures to prevent “List I” substances from entering groundwater, and to limit the entry of “List II” substances so as to prevent pollution of groundwater.

The WFD extends controls of the inputs to all pollutants (substances liable to cause pollution). Article 4(1)(b)(i) requires Member States to implement measures necessary to prevent or limit the input of pollutants into groundwater. This was introduced into the WFD to ensure that the groundwater protection regime established by Directive 80/68/EEC would not be lost upon its repeal in 2013.

This prevent/limit objective applies to all groundwater, whereas the objective to achieve good status applies only to groundwater bodies.

For example, water within discontinuous river terrace gravel deposits or perched water in a peat deposit above a boulder clay are both groundwater, and inputs of pollutants have to prevented or limited to ensure that pollution of any receptors does not occur. However, neither of these examples are management units and are therefore not groundwater bodies.

They therefore do not have to be classified into good or poor status, and will not have threshold values set for them.

The GWDD elaborates on the WFD Article 4 requirements, and states that member states shall establish all measures necessary to

- prevent hazardous substances from entering groundwater; and

- limit inputs of non-hazardous substances into groundwater so as to ensure that such inputs do not cause deterioration of good groundwater chemical status, do not cause any significant and sustained upward trends in the concentration of pollutants in groundwater, and do not otherwise cause pollution.

It is thus a requirement of the “limit” objective to ensure that inputs are insufficient to cause any of the criteria for good chemical status to not be met. However, as Status is assessed

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across the groundwater body, it will only be large-scale inputs (from either large point sources or from diffuse sources occurring across the body) that will cause failure of Status.

Much smaller inputs may have the capability of causing an upward trend in pollutant concentrations and/or causing pollution.

The most stringent requirement therefore, will always be to ensure that pollution does not occur as this is measured at a local scale by assessing the impact on receptors. For example, a single discharge of waste water may be capable of polluting groundwater (and therefore need to be controlled), but it is very unlikely that it will cause the conditions for good status to not be met across the whole body.

In essence, this requirement to “prevent or limit” provides the driver to avoid “filling up” some permissible pollution loading below the level that would cause a deterioration in status.

In order to ensure that inputs comply with these requirements, “limit values” have to be developed which ensure that pollution does not occur, i.e. compliance is measured locally to the source of the input. For hazardous substances, the limit value is effectively zero, as these substances should be prevented from entering groundwater.

Limit values may need to be set for any pollutant in discharges/inputs subject to regulatory control. In most cases limit values will be more stringent (lower) than Threshold Values set for assessing status, and in some cases may be derived from them. For example, for pesticides, the quality standard that applies to the assessment of status is 0.1 µg/l. Those pesticides which are hazardous may have a limit value of zero (the level of detection), subject to the exemptions within the GWDD.

These limit values will form part of the conditions set on environmental permits within the regulatory regimes operated by the competent authorities. Limit Values meet the prevent or limit requirements by being set:

- at a local scale to protect all the uses of groundwater set out in the definition of pollution (see below);

- at a level that prevents pollution;

- with a compliance point at or near to the point of input.

Limit values are not intended to be used in the determination of status.

Concerns regarding the protection of the groundwater resource where there are no existing nearby receptors may be addressed by setting a compliance point at an agreed distance from the input that would limit any deterioration in quality to only a local effect in the vicinity of the input or discharge. The location of the compliance point would vary according to the prevailing hydrogeological characteristics and the perceived long-term value of the

groundwater resource. This approach strikes a balance between risk-based regulation and long-term protection of groundwater resources from deterioration in groundwater quality.

4 Summary

1. The three objectives for groundwater within the WFD apply to different parts of the groundwater environment, and complement each other in fully protecting groundwater quality.

2. Status assessment deals with large scale issues across the groundwater body.

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3. The Prevent or Limit objective primarily prevents pollution and is applied at the local scale. Implementing measures to comply with this objective is the main mechanism for protecting groundwater quality.

4. Threshold Values used in status assessment are not the same as Limit Values used to prevent and limit the entry of pollutants into groundwater.