BBRRIIDDGGEE BBaacckkggrroouunndd ccRRiitteerriiaa ffoorr tthhee IIDDeennttiiffiiccaattiioonn ooff GGrroouunnddwwaatteerr tthhrrEEsshhoollddss

(1)

Deliverable 18 1 / 63

Contract n° 006538 (SSPI)

B B R R I I D D G G E E

B B ac a ck kg gr r ou o un nd d c cR Ri it te er ri ia a f fo or r t th he e I ID De en nt ti if fi ic ca at ti io on n o of f G G ro r ou un nd dw w at a te er r t

th hr rE Es sh ho ol ld ds s

Specific targeted Research Project Scientific Support to Policies (SSP)

D18: FINAL PROPOSAL FOR A METHODOLOGY TO SET UP GROUNDWATER TRESHOLD VALUES IN EUROPE

Due date of deliverable: 30 November 2006 Actual submission date: 6 December 2006

The deliverable authors are responsible for the content

Start date of the project : 1 January 2005 Duration : 24 months

AUTHOR: Dietmar MÜLLER AFFILIATION: UBA-A

ADDRESS: Umweltbundesamt GmbH, Spittelauer Lände 5, 1090 Vienna, Austria TEL.: +43-(0)1-31304 5913

EMAIL: dietmar.mueller@umweltbundesamt.at

FURTHER AUTHORS: Ariane BLUM, Alwyn HART, Jan HOOKEY, Ralf KUNKEL, Andreas SCHEIDLEDER, Cath TOMLIN, Frank WENDLAND

Revision 0

Project co-funded by the European Commission within the Sixth Framework Programme (2002-2006) Dissemination Level

PU Public

(2)

1. Introduction

The overall aim of BRIDGE has been to develop and test a method for the derivation of

pollutant threshold values (TV) for groundwater bodies in support of the Status provisions of the Water Framework Directive (WFD) and the Groundwater Daughter Directive (GWDD).

Threshold values are quality standards for pollutants in groundwater which need to be set by individual Member States and represent a concentration of pollutant which must not be exceeded in order to protect human health and the environment.

Such thresholds provide the basis for determination of good status in groundwater bodies established under the WFD and may also represent useful values in assessing pollutant trends in groundwater.

2. Prerequisites of the WFD and the GWDD

2.1 Fundamental aspects on threshold values

The WFD introduces the idea of integrated groundwater management at larger scales.

Groundwater bodies are the management units delineated and characterised by Member States. Accordingly threshold values for pollutants are quality standards to be used for status assessment of groundwater bodies.

The WFD requires Member States to assess the “Status” of their water bodies at the beginning of each river basin management plan (RBMP) cycle, that is every six years. The “Status” is to be assessed against predetermined quality and quantity criteria and for quality these are referred to as “Threshold Values”. The method described is intended to reflect the need for establishing threshold values on the basis of a common approach. We understand that groundwater quality standards for pesticides and nitrates are established at the Community level based on existing Directives although Member States are free to impose stricter thresholds if they need to do this in order to protect particular receptors.

The GWDD and Annex II (Part B) set out when and how Threshold Values should be

established. A Threshold Value should only be determined for a pollutant which is causing the body to be characterised as “at risk”. A minimum list of potential pollutant substances has been agreed though it should also be noted that the chemical status provisions do not apply to high naturally-occurring concentrations of substances or their indicators.

The decision to establish a threshold value should therefore be based on:

• At risk characterisation;

• Conceptual understanding of the groundwater body including:

o the groundwater’s interactions with surface water or dependent terrestrial ecosystems;

o interference with actual or potential legitimate uses or functions of groundwater;

o all pollutants characterising GW bodies as being at risk;

o hydro-geological characteristics including natural background levels (NBL).

Moreover, threshold values should be established taking into account pollutant origin (including any possible natural occurrence), pollutant toxicology and dispersion tendency, plus pollutant persistence and bioaccumulation potential.

(4)

Threshold values should be established for the first time in December 2008, then published in the first river basin management plan (RBMP). Amendment of the TV may take place as part of the periodic reviews of the RBMP.

2.2 Groundwater protection under the WFD and GWDD

The WFD and the GWDD provide a new regulatory setting for the protection of groundwater quality. Together they rely on three main objectives for this protection:

- To achieve good groundwater chemical status by 2015;

- To prevent or limit the inputs of pollutants into groundwater; and

- To 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.

The links between the different objectives are described in more detail by Annex VI. With regard to the methodology recommended by BRIDGE it is crucial to keep in mind the following:

- There are three objectives for groundwater within the WFD which apply to different parts of the groundwater environment, and complement each other in fully protecting groundwater quality.

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

- 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.

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

2.3 Status assessment

For assessing status, the WFD lays down (Annex V, 2.4.5) that the results of individual

monitoring points within a groundwater body shall be aggregated for the body as a whole. The mean value of the results of monitoring at each point in the GW-body or group shall be

calculated and in accordance with Art. 17 t these mean values shall be used to demonstrate compliance with good chemical status.

Based on the specifications laid down in Art 17 of the WFD the GWDD intends to establish specific criteria for the assessment of good chemical status and criteria for the identification of

(5)

significant upward trends and for the reversal of such trends and for the definition of starting points for trend reversal.

According to Art 4 of the GWDD the status provisions for good chemical status will be met if

• The relevant monitoring demonstrates that the conditions set out in 2.3.2 of Annex V to Directive 2000/60/EC are being met; or

• the groundwater quality standard (GQS) or TV is not exceeded at any monitoring point in the groundwater body (or group of bodies); or

• the GQS or TV is exceeded at one or more monitoring points but an appropriate investigation confirms that:

(1) the exceeding concentrations do not represent a significant environmental risk, taking into account the extent of the GW body affected;

(2) the other conditions for good groundwater chemical status of WFD Annex V 2.3.2 are being met,

(3) where appropriate, Article 7(3) WFD requirements are met,

(4) the ability of the groundwater body to support human uses has not been significantly impaired by pollution.

The summary of the assessments shall include an explanation on how such exceedances of GQS and TVs have been taken into account. Furthermore, if necessary measures will have to be taken in order to protect ecosystems and human uses affected by those parts of a

groundwater body which are represented by such monitoring points. Nevertheless although GQS and TVs are exceeded at single monitoring points a groundwater body as a general management unit might be qualified as being in good status.

The WFD and the GWDD do not exactly prescribe the assessment methods to be used. In fact it is the individual duty of the Member States to decide how to perform the required

assessments. How monitoring data is used will have an impact on the precision and the confidence in the status assessment.

2.4 Trend assessment

According to Art 5 and Annex IV of the GWDD statistical trend assessment is to be performed for each individual monitoring point in bodies identified at risk. Trends which represent a significant risk of harm to ecosystems, human health and human uses shall be reversed.

Member States have to derive starting points for trend reversal as a percentage of GQS and TVs.

The starting point for implementing measures for trend reversal is 75% of the GQS or TVs, unless 1) an earlier starting point is required to prevent detrimental changes in GW quality, 2) the detection limit does not allow for establishing trends at 75% GQS or TV or 3) a later starting point still enables a most cost-effective mitigation of detrimental change in GW quality.

Again the WFD and the GWDD do not exactly prescribe the assessment methods to be used.

2.5 Monitoring

The basis of the assessment of whether the Directive’s environmental objectives will be achieved (status and trend) is the monitoring data emerging from the monitoring programmes which have to be established in accordance with the WFD.

(6)

Surveillance monitoring must be undertaken for each GW-body during each planning cycle in order to validate the risk assessment and to provide information for trend assessment. No minimum duration or frequency is specified for the surveillance programme. However, Member States should undertake sufficient surveillance monitoring during each plan period to allow adequate validation of the Article 5 risk assessments and to obtain information for use in trend assessment. Monitoring frequency will generally be based on the conceptual model and in particular, the characteristics of the aquifer and its susceptibility to pollution pressures.

Monitoring frequencies that Member States have found appropriate in a number of

hydrogeological circumstances and in relation to different pollutant behaviours, range from quarterly monitoring to monitoring every 6 years. It should be kept in mind that a sampling frequency of less than once a year seems to be inadequate for trend assessment.

Sufficient operational monitoring must be carried out during periods not covered by surveillance monitoring for GW-bodies identified as at risk, in order to establish the chemical status and to establish the presence of significant and sustained upward trends in pollutant concentrations.

The operational monitoring must be carried out at least once a year. Suggested minimum frequencies for operational monitoring at different aquifer types, range from quarterly to annual monitoring. Sampling for operational monitoring (frequency and locations) should also take into account that according to the GWDD the first trend assessment should be available in 2009 and should be able to distinguish between trends and variations. Operational monitoring must be continued until the groundwater body is determined, with adequate confidence, to be no longer at poor status or at risk and there is adequate data to demonstrate a reversal of trends.

3. Method development process

The method outlined below has been built up around the discussions carried out at 5 main workshops held at Vienna in February 2005 and June 2006, at Tonbridge in November 2005, at Madrid in January 2006 and at Lisbon in September 2006. Additional discussions were held around the WP2 meeting in Orleans in October 2005. Minutes of meetings and the papers which resulted are available on the BRIDGE website (www.wfd-bridge.net).

This final proposal for a methodology has been prepared recognising the results of the case studies performed under Work Package 4 (WP4 “Representative sites studies and compliance testing”) of BRIDGE and comments of the Advisory Board provided at the meetings in Madrid and Lisbon.

The work within BRIDGE was performed in parallel with policy negotiations on the GWDD lasting from the 1^st reading at the European Parliament until the final discussions during the conciliation process. It is worth noting that the draft GWDD evolved considerably during that time. Although BRIDGE as a ‘policy-support-project’ aimed at corresponding with and matching up with discussions on policy level, this paper has not reflect all policy discussions in-depth or anticipated the latest amendments up until the final end of conciliation in October 2006. The final adoption of the GWDD is expected to take place in December 2006. Therefore it will be necessary that further work under the Common Implementation Strategy for the WFD takes both the final version of the GWDD and the proposal on hand as starting points to discuss and develop an integrated understanding on status assessment.

4 Underlying concepts

This section outlines the background and building blocks that underpin the proposed method to establish threshold values. Threshold values for groundwater are defined as being groundwater

(7)

quality standards set by Member States. The concepts and most of the details provided by this report correspond to the GWDD (Annex II, Part A: Guidelines for the establishment of threshold values by Member States) and are seen as relevant for reporting threshold values by December 2008 (see also GWDD, Annex ?, PART C – Information to be provided with regard to the

pollutants and their indicators for which threshold values have been established).

4.1 Conceptual Model of the Groundwater body

The GWDD (Annex II, Part A) requires that threshold values should be established taking into account pollutant origin (including any possible natural occurrence), pollutant toxicology and dispersion tendency, plus pollutant persistence and bioaccumulation potential. This in turn demands a good conceptual understanding of the body, its environmental setting, and relationship with and impacts upon the ultimate receptor. In BRIDGE WP3 we have relied on WP1 and WP2 to provide integrated characterisation information based on the three following pillars:

− Characterisation of potential pollutants and any parameters indicative of pollution, including description of the properties which influence their fate and transport, e.g.

transport through and out of the aquifer, including transport in the unsaturated zone, the behaviour of hydrogeochemical environments, ecotoxicology and toxicology and possible impacts on ecosystems.

− Characterisation of groundwater bodies, including a description of the hydrogeochemical setting of aquifers, the background quality (natural and anthropogenically influenced) and any dependencies of water quality on quantitative aspects (like the variability of water levels due to the hydrological cycles during the year, groundwater to surface water interactions, or the water balance at a long-term).

− Characterisation of receptors, including aquatic ecosystems, dependent terrestrial ecosystems and groundwater.

In the process of determining Status it is essential that a good conceptual model of the groundwater body is drawn up which includes a sound understanding of the pressures, processes, pathways and receptors involved. This will include issues such as the use of land and water, climate and water balances, geology, (bio)geochemistry and hydrogeology, characteristics of the aquifer and the unsaturated zone including soils.

All this should build upon existing information generated by Member States in their

implementation of the WFD thus far. From the delineation of groundwater bodies and the characterisation processes Member States should already understand the nature of the pollutant risk to the receptors (e.g. type of pollution, transport pathways wherever feasible, the natural groundwater quality, etc).

4.2 Significant Impacts

The methodology to derive threshold values must refer to the definitions of good status provided by the WFD and GWDD. These are generally focused on possible impacts on receptors (i.e.

associated surface waters, dependent terrestrial ecosystems or groundwater itself), and the significance of these impacts, for example significant diminution of the ecological or chemical quality of surface water bodies. Consequently any environmental threshold indicating that good chemical status might not be achieved has to be derived by a risk-based approach that is oriented towards receptors (see Figure 1).

(8)

Increasingpollutantconcentration Increasingconcentration

Quality poor due to naturally elevated concentrations, but no human impact (chemical

status: good)

Receptor-oriented standard

Variability in natural quality due to hydrochemistry

Level of detection/

quantification undisturbed groundwater

INDICATION FOR POOR STATUS

GOOD STATUS

ANTHROPOGENICALLY INFLUENCED

Polluted groundwater (significant impacts possible)

alteration of groundwater quality

NATURAL QUALITY

Figure 1: General relationship of groundwater quality and status under the WFD

Some substances, although considered as pollutants, may be present in naturally elevated concentrations. The importance of the natural background level (NBL) of a substance is

recognised by the GWDD defining that groundwater containing naturally high concentrations of some substance should not be defined as poor status for that reason alone. Such water may then be considered to have bad quality but good status.

Finally the differences between synthetic substances and anthropogenically introduced but naturally occurring substances should also be taken into account (see chapter 5.1), together with natural variations in quality both within and between groundwater bodies (see chapter 5.2).

4.3 Tiered Approach

Within a receptor-oriented approach BRIDGE recommends a tiered approach for deriving appropriate environmental threshold values for groundwater bodies. Key starting points for the derivation of a pollutant threshold must come from the reason for the determination that the body is at risk and the natural chemistry of the groundwater itself. Based on the conceptual understanding of a groundwater body and its interactions with receptors, a tiered assessment can then be used to identify an appropriate TV. This conceptual understanding needs to have within it a clear understanding of the extent and limitations of the data¹.

There is a relatively small number of possible receptors to consider the needs of:

- surface water quality and ecology - dependent terrestrial ecosystems

1(Note: Both the conceptual understanding and the understanding of data uncertainties have also to be recognised in a complementary way when a compliance regime for the relevant receptors is defined – see also Chapter 6.8).

(9)

Deliverable 18 9 / 63 - drinking water supply

- other legitimate uses (e.g. irrigation or crop washing) - groundwater (as a resource or itself).

At least for surface waters and drinking water there are quality standards ready to refer into the tiered method i.e. environmental quality standards (EQS) for surface water and drinking water standards (DWS). For example, where the ultimate receptor is a surface water then

ecotoxicology based EQS for surface waters would be the appropriate reference values to be used.

Groundwater as a possible receptor might be understood as being a resource to support human uses or as often discussed as an ecosystem by itself.

The WFD and the GWDD make it clear that the emphasis is on whether groundwater as a resource for human use is impacted by saline intrusion or by widespread pollutantsacross the body. Specific considerations on these issues are described in chapter 6.7.

Using a tiered or stepwise approach allows for variation in the amount of data and work required. Therefore a tiered approach allows the effort to be proportional to the risk involved (greater risks greater effort). With limited data and work, a derivation procedure based on a simple Conceptual Model is applied, and with larger amounts of work and data, the derivation refers to a more advanced Conceptual Model. Thus a tiered approach supports both a practical and cost effective way forward. In moving from a lower to a higher tier there is a growing

demand on data, a reduction in the level of conservatism and assumptions made but the degree of protection remains the same.

Data requirements work, costs

Conservatism

Uncertainty

Protection of

Environmental resources

Figure 2: Effect of increasing Tiers on costs and uncertainty

(10)

5 Pollutants, groundwater bodies and receptors

The risk(s) to a groundwater body that may influence its status determination will depend on several factors including

• the pollutant(s) of concern

• the nature of the groundwater body

• the nature and susceptibility of the receptor

5.1 Characterisation of pollutants

For the purpose of considering groundwater management and as a prerequisite for describing fate and transport of pollutants it is recommended to characterise the properties of substances.

The spread of pollutants is influenced by their physical, chemical and biological properties.

Substance specific data should be assembled for the following:

o physical and chemical properties (e.g. water solubility, vapour pressure),

o environmental fate and partitioning (e.g. partitioning coefficients, abiotic degradation, biodegradation), and

o ecotoxicity data on dose-response-related effects regarding the aquatic environment.

As a basis for a thorough description of the behaviour and occurrence of inorganic and organic groundwater pollutants the BRIDGE WP 1 report (GRIFFIONEN et al, 2006; see www.wfd- bridge.net) can be taken. This report also provides an introduction on research results related to (eco)toxicological effects of potentially harmful substances on groundwater in chapter 8. For priority substances (see WFD, Annex X), which are 33 substances or groups of substances of highest concern in the field of water policy at Community level, substance specific data sheets recording data as described above have been assembled under the Common Implementation Strategy and are publicly available at the homepage of the European Commission

(http://forum.europa.eu.int/Public/irc/env/wfd/library?l=/framework_directive/i-

priority_substances/supporting_background/substance_sheets&vm=detailed&sb=Title).

Furthermore it may be helpful to recognise categories of substances in accordance with how they occur and in particular to note that some substances have both natural and anthropogenic sources whilst others are completely synthetic.

• naturally occurring substances or ions which may also be introduced as pollutants by man.

Variability in the natural background levels of such substances in groundwater (both within and between bodies) may make it impractical to apply environmental thresholds without reference to the conditions in a particular groundwater body, for example ammonium.

• naturally occurring substances that are not normally found in elevated concentrations in groundwater, such that their presence alone would normally indicate either anthropogenic inputs or very unusual hydrogeochemical conditions, for example mercury.

• synthetic (man-made) substances not found in the natural environment, for example trichloroethylene.

• Parameters indicative of pollution, for example Conductivity.

These categories do not relate to chemistry or toxicity but are indicative of potential differences in monitoring, assessment and TV derivation and indeed in potential controls which may be used.

(11)

Deliverable 18 11 / 63 5.2 Characterisation of groundwater bodies

For the purpose of characterising groundwater bodies regarding pollutant behaviour, data are needed on

o the petrographic properties and the physical hydrogeology, o the hydrogeochemical natural background composition, o groundwater hydraulics and

o (bio)-geochemical characteristics.

The general chemical quality of groundwater is determined by a variety of factors, where the petrographic properties of the rocks of the vadose and groundwater saturated zone, and the regional hydrological and hydrodynamic conditions are the major natural factors. To facilitate and as a starting point for describing these elements BRIDGE has come up with a classification of hydrogeological units.

As outlined under 5.1, it is necessary to understand the natural background levels (NBL) of a substance in a groundwater body. NBL is defined as the concentration of a given element, species or chemical substance present in solution which is derived by natural processes from geological, biological or atmospheric sources. Substances need to be understood in the context of their geochemical setting. This may often be difficult where substances exhibit high NBL in relation to any presumed anthropogenic component.

Information on the NBL for a substance may be derived for a specific body from the monitoring carried out either already before the WFD or as part of the implementation of the WFD

provisions. However, where such data are not available or insufficient it would be useful to be able to refer to the composition of similar aquifers from an agreed European typology. Such a typology has been generated within BRIDGE and is described in chapter 6 of the report “Impact of hydrogeological conditions on pollutant behaviour in groundwater and related ecosystems”

(PAUWELS et al, 2006; see www.wfd-bridge.net) and may be of use for defining likely NBL in groundwater bodies.

There are, however, a variety of methods available for defining and determining NBL in practice. Some methods for determining NBL are also described within chapter 6 of the above mentioned report. Annex 1 of this report details a procedure that may be useful within the context of establishing natural background levels. The procedure integrates several

approaches providing flexibility according to data availability within a specific groundwater body.

Groundwater chemistry cannot be understood without an understanding of groundwater hydraulics. Therefore any classification of chemical status and consequently also a

methodology to derive environmental thresholds will often rely on data from any quantitative assessment. Such assessment would in principle have to establish the hydraulic connections between, and degree of impact on, flows and levels in dependent surface waters and terrestrial ecosystems.

In addition, the potential for reversals in flow direction that might result in risk to groundwater (e.g. from saline intrusion) would also have been established. An introduction and further information can be found in chapter 9 of the BRIDGE WP2 report (PAUWELS et al., 2006) Finally aquifers also exhibit variable potential for the attenuation of pollutants within them. This potential will depend on the geochemistry and biochemistry of the body and like the NBL above needs to be determined at the level of the individual body. A more detailed description of concepts for characterisation of aquifers regarding transport and attenuation of substances is provided in the chapters 4 and 5 of the above mentioned BRIDGE WP2 report. However, where data are either not available or insufficient, the typology developed for European aquifers can

(12)

help to provide information for similar circumstances. The summarising tables for sources and controls of naturally occurring contaminants can be considered when assessing status, particularly when undertaking the specific local investigation and assessment when threshold values are exceeded at single monitoring stations.

5.3 Characterisation of Receptors

The GWDD recognises that groundwater is a valuable resource which should be protected from pollution and that this is particularly so for groundwater dependent ecosystems and for drinking water resources.

Obviously, the WFD bodies (both surface and groundwater) have already been delineated and the reasons for “at risk” designations for individual bodies and the characterisation processes are set out in the WDF Article 5 reports. However, for determining Status further

characterisation is needed in order to have a better understanding of the relationship between the groundwater body and final receptor. When the final receptor is the groundwater body itself that may be relatively straightforward but for associated surface ecosystems it becomes more complex.

Hence, it is likely to be the relative mass flow of pollutant(s) exchanged between groundwater and surface water which is important in determining standards for protection of surface waters, rather than the concentration of pollutants in groundwater. This in turn will rely on knowledge of the groundwater contribution within the overall surface water load and may vary considerably between locations, and will also depend on the substance in question. In reality the variability of such relationships across Europe will be substantial, and is a strong argument for the derivation of environmental thresholds on a regional or local basis.

As groundwater dependent terrestrial ecosystems do not have status objectives in themselves, the relationship is somewhat different to surface waters. To date there is very little data on the chemical dependencies of such ecosystems on groundwater inputs. Even the extent of

groundwater support to many sites is unclear so the derivation and use of thresholds at the current stage of knowledge is likely to be unhelpful. Instead of establishing single chemical standards or thresholds a complementary approach using other ecological indicators could facilitate the procedure but probably would go beyond the scope of BRIDGE.

Groundwater is often an extremely important drinking water resource or freshwater resource for other uses (e.g. agriculture, industry) and at a regional scale it often underpins the sustainable development of society by means of social welfare and environmental quality. On the other hand there are geological situations and aquifers which are neither of ecological importance nor are able to support human demands due to their low transmissivity. In characterising

groundwater as the receptor it will be important to understand the reason why groundwater is the receptor and the risks to it. Characterisation may well need to include external factors such as the degree of existing treatment (for drinking water supplies) or the quality needed for other uses such as irrigation, washing or cooling. Therefore a ‘management choice’ can be made for any groundwater body taking into account regional water management considerations. The quality of regionally important groundwater resources needs to be protected to a high level by means of combining status assessment with the prevention and limitation of inputs to

groundwater and trend assessment.

5.4 Groundwater bodies and adoptions considering aquifer properties As BRIDGE has progressed, and through the information assembled within WP2 (see

PAUWELS et al., 2006) as well as by the experiences of the case studies performed under WP

(13)

4, it has become evident that significantly different approaches have been applied in the delineation of groundwater bodies and it seems that some groundwater bodies represent flow systems that may extend across different aquifer types. There is also an issue for aquifers of low velocity and groundwater bodies showing a long residence time (e.g. more than 50 years) in relation to the potential for anthropogenic inputs to affect status determination. Both aspects have implications for natural background conditions and the transport and attenuation processes that may act on pollutants since these will be dependent on flow characteristics, geochemical characteristics and changes of hydrogeochemical conditions along the flow path of groundwater.

As a result (and especially where groundwater is the receptor at risk) it will be difficult if not impossible to aggregate and average natural background levels of substances for some groundwater bodies that extend across different geochemical settings.

This shows the importance of developing a sound conceptual understanding of the body setting and the processes at work. For example, one simplified groundwater flow-system through surface waters and terrestrial ecosystems is shown in figure 3 with local, intermediary and regional type flow systems, which may show a huge variability in travel time between the recharge zone and discharge zones (from a few months to several thousand years).

local recharge local recharge

local recharge regional recharge

discharge

zone of influence of anthropogenic surface originated pollution regional geochemical background contamination

aquiclude

Groundwater body

local geochemical background contamination

Figure 3: Main elements of a subsurface flow system

Alternatively, there may be places where regional and local recharges are overlain; areas of mulit-layered aquifer systems where problems such as up-coning of chemically different groundwater occurs. Plus of course many aquifers show considerable variation in quality with depth.

Many of these issues will be addressed with an appropriate conceptual model, choice of appropriate and relevant monitoring points, and weighting of the monitoring results but it highlights the problem of defining a single threshold value for a pollutant across the entire

(14)

groundwater body. For example, if there is attenuation taking place in a groundwater body with a long travel time from the recharge zone to the surface water receptor, the tolerable

contaminant concentration close to the surface water will be less than in the recharge zone, as a back calculation would allow for attenuation. Expert judgement is needed as to whether it is appropriate (due to long travel times) to set a threshold value for the surface water receptor in this recharge zone. Nevertheless, any recharge zone is an important place to prevent and limit the input of pollutants to groundwater and if these requirements are more stringent, it will take priority over meeting threshold values. Thresholds must not be (mis)understood as an excuse to introduce further pollutants if the actual concentration levels are low (see chapter 2.5 and Annex VI for more detail on the relationship between Prevent/Limit and Status).

In summary, it is important, that Member States, appointed competent authorities and experts involved in developing River Basin Management Plans recognise the importance of controlling and revising the Conceptual Model and the characterisation of groundwater bodies. This is described for example within the Monitoring Guidance under the Common Implementation Strategy (GRATH et al., 2006). Continued improvement in understanding of the natural systems of the management unit needs to be taken account of when developing threshold values for groundwater bodies characterised as being at risk.

6 Procedure for status determination and threshold setting

This section provides the basic methodology proposed for threshold setting within Status determination. The method itself is supported by more detailed Annexes on particular topics.

The method relies initially on knowing the nature of the final receptor at risk and on knowing the natural quality of the groundwater concerned. A tiered approach is adopted which allows the targeted use of resources both in assessment and any remedial measures.

To assess groundwater quality at local scales it is quite common to make use of natural background levels and generic reference values according to possible receptors, which are in general ecosystems and human uses. As status assessment can be understood as being an integrated assessment at the large scale of groundwater bodies, both these criteria have to be included. Moreover status assessment has to take into account that the general chemical quality of groundwater as well as fate and transport of contaminants are determined by a variety of factors, where lithologic properties of rocks in the vadose and groundwater saturated zone, regional hydrological and hydrodynamic conditions and hydrogeochemical processes controlling the behaviour of natural and anthropogenic substances are of major importance. Thus status assessment needs to go beyond quality assessment and consider attenuation criteria like dilution, diffusion, retardation, and degradation. These criteria are specific to the properties of contaminants, hydrogeological units where specific hydrogeochemical processes govern, and the interaction with surface waters.

6.1 Assessing the Natural Background Level (NBL)

In the past there have been many local and regional studies of the ambient quality of

groundwater in terms of both the naturally–occurring and anthropogenic substances that may be present. More recently, cross border and EU-wide projects such as EU BaSeLiNe (Ref EVK-CT-1999-00006) have provided a good basis for understanding the natural background level of some substances in groundwater. The typology presented in the BRIDGE WP2 studies builds on this work and a procedure for determining the NBL in a groundwater body is

presented in Annex 1. The procedure allows NBL determination from monitoring data or by comparison with known similar aquifers in the typology.

(15)

The GWDD recognizes background level as a concentration or value of a substance or indicator in a groundwater body corresponding to no, or only very minor, anthropogenic alterations to undisturbed conditions. Given this definition it is understood that the future regulatory framework asks to determine background level as ‘natural background levels’ as they have been discussed within BRIDGE.

Depending on data availability Natural Background Levels (NBLs) can be defined following a hierarchy of possible options. To unify the starting point for groundwater status assessment BRIDGE has proposed a European aquifer typology, classifying 16 types (see PAUWELS et al, 2006; and Figure 4), and also has referenced NBLs from national studies accordingly. These NBLs might be used if no appropriate groundwater quality data are available but only the hydrogeological units of a specific groundwater body can be described.

Given a groundwater body where a limited set of data on the chemical composition of groundwater is available, a second option by a simplified and practical approach to determine NBLs based on a pre-selection method can be employed. As a prerequisite for applying a simplified pre-selection method common minimum requirements for groundwater quality data (e.g. deviation of the ion balance < 10 %) and appropriate pre-selection criteria to identify groundwater samples showing no significant anthropogenic impact (e.g. Nitrate < 10 mg/l) are to be defined. Finally given a groundwater body where a broad set of quality data is available, the third option to estimate NBLs is to apply scientifically sound methods (e.g. hydrochemical simulations, component separation by concentration separation analysis), which already have been established at national or international level.

Clearly, the procedure described only accounts for substances which occur naturally, whereas for substances that are purely synthetic with no natural sources (for example, TCE) then the NBL will be zero.

Figure 4: European aquifer typology for NBLs – map (Research Centre Jülich, draft November 2006)

(16)

6.2 Selection of the Reference Quality Standard

Generic reference values selected according to receptors which might be harmed by groundwater contaminants are to be used. Giving a focus to ecosystems and human uses means consequently that environmental quality standards (EQS) for surface waters or drinking water standards (DWS) are to be transferred and linked into groundwater status assessment.

The mentioned reference values might be defined at European level or at national level. With respect to the variety of possible substances contaminating groundwater it is also likely that for some substances no reference values are available at all.

As a hierarchy of options exist, it can be envisaged that unified European standards like e.g. the EQS for priority substances set out by the proposal of the European Commission (COM(2006)398 final) are preferable to, and therefore overrule national standards. If no agreed European standards exist, national reference values can be used. The EQS to be introduced in groundwater status assessment need to be expressed as annual average values (EQS-AA see COM(2006)398 final).

Finally for substances without established receptor-oriented reference values at European or national level a survey and evaluation of humantoxicity or ecotoxicity data will be necessary.

Depending on data availability the evaluation of these toxicity data should again be based on and refer to either agreed European procedures or national agreements.

The WFD and the GWDD are understood to outline the following receptors:

- aquatic ecosystems (surface water quality and ecology) - dependent terrestrial ecosystems (plants, vegetation) - drinking water supply

- other legitimate uses (e.g. irrigation or crop washing) - groundwater

These may be compared with the provisions of the GWDD and the appropriate reference quality standard selected (Table 1 and 2).

Table 1. Criteria for Good Chemical Status and suggested reference standards

Receptor Likely Substance Suggested reference standards Surface Water Ecological & Chemical Status

Aquatic ecosystem Any pollutant which causes

risk to a surface water body Surface water EQS (and ecotox data for aquatic organisms)

Dependent Terrestrial Ecosystems terrestrial ecosystems

(plants, vegetation) Any pollutant which causes significant damage to a groundwater dependent ecosystem

To be determined specifically (surface water EQS might be used as screening values)

In selecting the receptor it is important to remember that the Status determination will extend throughout the lifetime of the river basin management plan.

For cases where the human use of groundwater provides the ultimate receptor the choice of quality standard or reference value will depend on the needs of the use and the current

operational treatments being applied. Often, of course, there will not be any effective treatment in place. For example, in many places groundwater can be used directly for drinking water

(17)

without any treatment and so the most appropriate value will be from drinking water standards.

In other places substantial treatment of abstracted water is used to ensure that drinking water standards are met at the point of supply. In this case the value may stem from the existing treatment performance limit.

Table 2. Criteria for Good Chemical Status and suggested reference standards (continued)

Receptor Likely Substance Suggested reference standards Drinking Water Protected Areas

drinking water Any pollutant which causes

risk to a groundwater body Operational performance limit for existing or regionally usual treatment infrastructure Note: For many locations no treat- ments are used and hence Drinking water standards should apply.

Other legitimate uses

e.g. irrigation, crop washing Any pollutant which causes

risk to a groundwater body Dependent on use. Food-related use Drinking Water Standards (DWS), for non-food use suggest process operational needs determined on case-by-case Saline or other Intrusions

groundwater chloride, sulphate and electrical conductivity

NBL

Widespread pollutants

groundwater nitrate, pesticides see WFD and GWDD:

- Nitrate 50 mg/l - Pesticides 0,1 µg/l General Chemical Assessment (pollution significantly impairing the resource)

groundwater Any pollutant which causes risk to a groundwater body

Relevant use related standard (or NBL)

6.3

Attenuation Criteria

Pollutant attenuation may occur along the flow path of groundwater, at the interface in between groundwater and surface waters (the hyporheic zone) and at the surface water itself. General consideration might be given to dilution, dispersion, diffusion, volatilisation, sorption, chemical and biological degradation. The physical, chemical and biological processes which occur in aquifers and which may act to naturally attenuate pollutants are well known and widely reviewed for the purposes to assess point source pollution. The same processes can also act over much larger scales like groundwater bodies. Still it needs to be recognised that a real in- depth conceptual understanding of the groundwater and receptor system is needed and the demand on specific data increases consequently. The current situation for the surface water interface (the hyporheic zone) is that knowledge is not sufficient at the moment and science is on its way.

In contrast, the description of attenuation at the receptor surface water might be described easily, as in general dilution will be the major attenuating process. The estimation of quantity relationships of groundwater flow against surface water flow can be done rather easily by a

(18)

variety of methods to estimate the baseflow (e.g. by hydrograph separation, temperature or water quality surveys, tracer analysis). Therefore a pragmatic approach is to consider dilution at the receptor surface water as a separate generic criteria (see chapter 6.4: Tier 3), whereas the description of all other attenuating processes would need a series of in depth investigations, which might be appropriate to be established at some groundwater bodies at the body scale (see chapter 6.4: Tier 4) or are necessary for a final status assessment taking account of local specificities which can not be considered for the derivation of threshold values.

6.4 Using the Tiered approach

Once the receptor has been identified and the NBL determined then the tiered method below may begin to be employed. In essence, the method relies on a series of steps in which the impact on the receptor from pollution in the groundwater is defined with increasing precision. In the early Tiers the concentration of pollutant in the groundwater is compared with NBL and receptor based standards (for example drinking water standards) whereas in the later Tiers the possible mitigating effects of dilution of the pollutant with water from elsewhere (for example, surface water) and then the attenuation (loss) of pollutant due to (bio)geochemical reactions is considered. Note that, it is not intended that every groundwater body need be assessed at every Tier. The assessment should proceed to the most appropriate Tier based on factors such as data availability, costs and time available etc.

The Tiers are summarised in the Figure below and the individual Tiers are discussed.

The tiers are:

Tier 1: NBL. The derivation is explained more fully in Annex 1. For those pollutants that are synthetic the appropriate NBL is zero.

Tier 2: The receptor based quality standard, which refers to existing relevant standards or reference values (e.g. EQS for priority substances set out by the proposal of the European Commission, COM(2006)397 final, or national EQS; DWS according to the Council Directive 98/83/EC, or national DWS).

Regarding groundwater as a receptor an intermediate step (2a) is introduced to Tier 2, where natural background levels (NBL) are used as the generic environmental criteria and at low concentration ranges a relationship against a reference standard is used to allow and limit minor anthropogenic impacts (see Annex 2).

Tier 3: This Tier allows account to be taken of the proportion of the pollutant mass flow that is due to the groundwater. For many water features there may not be a single source of water but two or more, for example a river may be supported by both surface water drainage and

discharge from groundwater. If the main source of pollutant is from the surface water drainage then the groundwater status should not be penalised unnecessarily. The concept of the Dilution Factor (DF) is intended to provide a mechanism where the proportion of the final impact that may be rightly ascribed to groundwater pollution can be taken into account. The derivation and use of the DF is explained more fully in Annex 4.

Tier 4: This final Tier allows consideration of any attenuating processes that may occur to diminish the impact in the final receptor (water body) from pollutants present in the

groundwater. For example if it is known that the pollutant will react chemically with the rocks of the groundwater body such that it will not reach the receptor, then groundwater Status should not be penalised unnecessarily. The concept of the Attenuation Factor (AF) is intended to provide a mechanism where the proportion of the final impact that may be rightly ascribed to groundwater pollution can be taken into account. The derivation and use of the AF is explained more fully in Annex 5.

(19)

The progress through the Tiers may be viewed as a series of questions seen in Figure 5. The comparison of observed pollutant within each Tier determines whether it is worthwhile

progressing to the next Tier remembering that, in general, progressing to a higher Tier will incur increased data needs and increased cost of assessment.

Tier 2 Is [pollutant] > QS?

Check for trends

Check for trends MONITORED DATA

Is [pollutant] > NBL?

Tier 1

Yes Set threshold= QS (or

NBL if exceeding QS)

Set threshold= QS/DF Status = GOOD

Status = GOOD No

No

Is [pollutant] > (QS/DF)*AF?

Set threshold= (QS/DF)*AF Is [pollutant] > (QS/DF)?

Tier 3

Tier 4

Status = GOOD

Status = POOR

Check for trends Yes

Yes No

Rules

1. Use the appropriate quality standard, QS.

If ecological risk use EQS.

If human health risk use DWS.

2. If dilution factor, DF, not known assume = 1.0 3. If attenuation factor, AF, not known assume =

1.0

4. In check for Trends use ALL triggers-consider need for trend reversal if crossing each trigger Does appropriate

Investigation show that conditions for good chemical

status are not met?

Define Objectives and Measures Yes

No Derive NBL (according to Annex I)

Derive TV (according to

Annex II) Tier 2a

Is [pollutant] > TV?

OR No Set threshold= NBL Check for

trends Status = GOOD

Figure 5: Flow chart for derivation of threshold values

Whereas the different tiers have been numbered according to a scientific logic on how to progress in assessing groundwater quality, administrators might for practical reasons and seeking efficiency at the status assessment process change the order of applying tiers and criteria accordingly. For example for undisturbed groundwater bodies where it is likely that there are hardly any anthropogenic impacts a quick first control of monitoring data by comparison against a reference value could facilitate the status assessment like being a ‘one-stop-shop’.

The definition of receptors (see also chapter 6.2 and Table 1) relevant for a specific groundwater body has to be done by the Member States and the competent authorities

appointed to set up river basin management plan. The following sections try to briefly introduce how to apply the procedure for the different receptors.

6.5 Determining a threshold for a surface water receptor

Starting the tiered approach to determine a groundwater threshold value for protecting a surface water receptor becomes necessary if the groundwater body and the surface water body are

(20)

characterised as being at risk for a specific pollutant, or there is any other evidence for a substantial transfer of pollutants from groundwater to a surface water (e.g. from groundwater monitoring data). Following the GWDD and the procedures described within this report the determination of groundwater threshold values is a rather straight forward procedure using surface water EQS or equivalent reference data. As pointed out under section 4.4 expert judgement might be needed for groundwater bodies with long groundwater residence times, to define whether it is appropriate (due to long travel times) to apply a threshold value for the surface water receptor in the recharge zone, or to limit the compliance regime to areas of limited flow times (e.g. 20 to 50 years) close to the discharge area at the surface water.

6.6 Determining a threshold for a dependent terrestrial ecosystem

Neither within the WFD nor in other Directives have status objectives been defined in a general way. Although it is generally recognized that quality of groundwater is very important for the presence and development of plant species and vegetation in wetlands, there is also hardly any scientific knowledge to describe possible effects of chemical pollution of groundwater

(GRIFFIOEN et al., 2006: chapter 8.7). This lack of legal and scientific background made it impossible to develop a methodological approach on how to determine groundwater thresholds for dependent terrestrial ecosystems.

As terrestrial ecosystems are often situated along surface waters it might be generally assumed that both aquatic and terrestrial ecosystems would need to adapt to similar natural conditions.

Provided this assumption holds true surface water EQS could be introduced for a simplified Tier 1 assessment establishing an approximately similar level of protection for terrestrial ecosystems and plant communities as for surface waters.

As soon as this simplified Tier 1 assessment or monitored damages on dependent terrestrial ecosystems indicate that pollution of groundwater might be the origin of effects on a wetland vegetation, a specific assessment regarding dependent terrestrial ecosystems needs to be started. As a second preparatory step to complete this kind of pre-assessment other possible factors which might impact wetlands will have to be excluded. Major factors governing the environmental conditions for plants are groundwater quantity (groundwater level alterations), pH, buffering effects, oxygen and nutrient concentrations. Given that these factors are not the driving factors for deterioration of wetlands, a specific investigation coordinated together with ecologists will have to be undertaken.

6.7 Determining the threshold for groundwater

Along the work within BRIDGE major discussions took place regarding the understanding of the legal system established by the WFD and the GWDD (and its subsequent interpretation such as that outlined under chapter 2.5 and described in more detail in Annex 6), in particular, the point of view that groundwater should be protected against deterioration in its own right (e.g. see recitals of the GWDD). Whereas this main topic was addressed by the very first conceptual paper by introducing a receptor ‘groundwater as a resource’ (see BRIDGE, Description of Work, Appendix B) it was agreed at the first WP3-workshop (Vienna, March 2005) to acknowledge a scientific point of view of a strong groundwater protection regime by renaming this receptor as

‘groundwater by itself’.

Based on the discussions at further workshops (in particular Madrid, January 2006 and Lisbon, September 2006) and according to comments by the BRIDGE Advisory Board it has to be admitted that although agreeing that groundwater should be protected in general and anthropogenic impacts should be minimized the consortium did not manage to agree on a

(21)

common understanding of the WFD and GWDD and the role of threshold values (e.g. such as described in Annex 6).

Therefore the following tries to explain different possible approaches when groundwater is addressed as being the receptor at risk. Necessarily the issue of understanding the legal system established by the WFD and the GWDD needs to be addressed and clarified at the administrative level under the Common Implementation Strategy of the WFD. Given this

clarification the approaches discussed below could be revised and adopted for implementation.

6.7.1 Groundwater as a resource

The WFD and the GWDD provide some elements of groundwater status assessment which are understood to recognise groundwater as being one of the most important freshwater resources.

In particular these are the following requirements:

o nitrates and pesticides

o pollution which might significantly impair the ability of the groundwater body to support human uses

o saline intrusion

Quality Standards for nitrates and pesticides are given by the WFD and the GWDD.

Further substances will have to be taken into account, if the groundwater body is characterised to be at risk from specific substances and monitoring establishes evidence of widespread impacts to the groundwater body. For these further substances (and only if the body is at risk from these substances) any relevant reference standard related to uses, like drinking water standards, irrigation standards, any other standard in member state legislation has to be taken into account.

To assess status, threshold values need to be used to evaluate monitoring data at each single monitoring station (Tier 2), as well as applied to aggregated and weighted results across the groundwater body. Therefore threshold values determined under these elements of status assessment are not receptor-oriented but try to control the average concentration of substances of all stored groundwater (‘aquifer-storage based’).

To address saline intrusions again specific considerations are necessary. To identify saline intrusions threshold values have to be set according to NBLs for relevant parameters (e.g.

electric conductivity, chloride, sulphate). The exceedance of NBLs is an indication of a possible impact on the groundwater resource . Further investigation will have to clarify whether elevated concentrations are due to anthropogenic activities (like linked to abstraction pressures) and if the extent of any intrusion is likely to impact the freshwater resource significantly.

6.7.2 Groundwater ‘itself’

Many, if not all, of the bodies determined as “at risk” in the characterisation process will relate to identifiable receptors external to the groundwater itself: for example drinking water supply or surface water ecology. According to the point of view that groundwater should be protected against deterioration in its own right (e.g. see recitals of the GWDD) there is an understanding that threshold values have to help and are to be applied to prevent increasing pollutant

concentrations in groundwater (itself). Clearly this could cause some difficulty as few Member States have such groundwater quality standards and there are no community values available except for nitrate and pesticides.

(22)

BRIDGE therefore discussed alternative options for the derivation of, in effect, Tier 2a values where no suitable standard exists, which is based on the NBL of groundwater in a body. By the results of the case studies the finally described option (see Annex II) is felt to be a pragmatic approach referring to NBLs as the only available sound environmental criteria but also recognising that a policy of ‘zero’-pollution is not possible as alterations of environmental conditions due to human activities can not be avoided totally.

6.7.3 Groundwater as an ecosystem

In contrast to status objectives for surface waters the WFD does not give recognition to an

‘ecological status’ of groundwater bodies. Furthermore the knowledge of the ecology of groundwater and aquifers is considered as far too basic to allow the development of scientifically sound values based on sub-surface ecology.

As there are hardly any data for ecotoxicity tests with groundwater organisms available, a transition of test results with aquatic organisms seems to be generally recognised as appropriate approximation (NOTENBOOM et al, 1999; German LAWA 2004). Given long residence times and the relatively slow dynamics of groundwater emphasis could be given to exotoxicity data on chronic effects. Referring to the Commission Proposal on EQS for priority substances [COM(2006)397 final] these would be the annual average EQS or data derived in a comparable way.

Corresponding to Annex I, Part C of the mentioned Commission proposal flexibility is to be left to Member States to take account of natural background concentrations for metals if they are higher than the EQS value or if other water quality parameters (e.g. pH, hardness) affect bioavailability of metals.

6.8 Remarks regarding the definition of compliance regimes

BRIDGE had no mandate or objective to work on and discuss aspects on a compliance regime for different receptors. Nevertheless it has to be pointed out, that a sound concept of status assessment needs to build its compliance regime as a complementary approach to

o the implemented monitoring concept and

o considerations relevant for threshold value determination.

Obviously the compliance regime for different elements of status assessment (see section 6.2 and table 1) will differ. Further specific issues which should be recognised for discussing compliance regimes and are due to properties of aquifers have been discussed under section 4.4.

Furthermore BRIDGE tried to provide further information as possible starting points for the discussion on compliance regimes, which are the reports on Sampling, Measuring and Quality Assurance (WITZAK et al., 2006) and integrated data aggregation methodology

(SCHEIDLEDER et al., 2006).

(23)

7 References

- GRIFFIOEN, J. et al, 2006: State-of-the-art knowledge on behaviour and effects of natural and anthropogenic groundwater pollutants relevant for the determination of groundwater threshold values - Final reference report. (Deliverable D7)

- PAUWELS, H. et al, 2006: Impact of hydrogeological conditions on pollutant behaviour in groundwater and related ecosystems. (Deliverable D10)

- WITZAK et al., 2006: Summary Guidance and Recommendations on Sampling, Measuring and Quality Assurance. (Deliverable D16)

- SCHEIDLEDER et al., 2006: Report on the integrated data aggregation methodology.

(Deliverable D17)

Reports available through: www.wfd-bridge.net

Drinking Water Directive (1998/83/EC): Council Directive of 3 November 1998 on the quality of water intended for human consumption

Notenboom J.A., A. Verschoor, A. van der Linden, E. van de Plassche & C. Reuther (1999):

Pesticides in groundwater: occurrence and ecological impacts. RIVM report 601506002.

Water Framework Directive (2000/60/EC): Directive of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy

Länderarbeitsgemeinschaft Wasser (LAWA, 2004): Derivation of insignificance threshold values (available only in German; www.lawa.de)

COM(2006)397 final: Proposal for a Directive of the European Parliament and of the Council on Environmental Quality Standards in the field of water policy and amending Directive

2000/60/EC

GRATH J.; WARD R. (2006): Monitoring Guidance for Groundwater (final draft November 2006); Drafting Group GW 1 under the Common Implementation Strategy of the Water Framework Directive

STATUS, CONFIDENTIALITY AND ACCESSIBILITY

Status Confidentiality Accessibility

S0 Approved/Released x PU Public x Work-space

S1 Reviewed PP Restricted to other programme participants

(including the Commission Services) Internet x

S2 Pending for review RE Restricted to a group specified by the consortium (including the Commission

Services) Paper

S3 Draft for comments CO Confidential, only for members of the consortium (including the Commission Services)

S4 Under preparation