OR/18/012 Appendix 3 – Defining groundwater
|Loveless, S, Lewis, M A, Bloomfield, J P, Terrington, R, Stuart, M E, and Ward, R S. 2018. 3D groundwater vulnerability. British Geological Survey Internal Report, OR/18/012.|
DEFINING GROUNDWATER STATUS
Groundwater status, defined in Article 2.19, is:
- “the general expression of the status of a body of groundwater, determined by the poorer of its quantitative status and its chemical status”,
and good groundwater status, Article 2.20 means:
- “the status achieved by a groundwater body when both its quantitative status and its chemical status are at least good”.
Good groundwater chemical status, Article 2.25 is defined as:
- “the chemical status of a body of groundwater, which meets all the conditions set out in table 2.3.2 of Annex V”,
and available groundwater resource, Article 2.27 is defined as:
- “the long-term annual average rate of overall recharge of the body of groundwater less the long-term annual rate of flow required to achieve the ecological quality objectives for associated surface waters specified under Article 4, to avoid any significant diminution in the ecological status of such waters and to avoid any significant damage to associated terrestrial ecosystems”.
Further characterisation of groundwater bodies, or groups of bodies, Annex 2, section 2.2. of the WFD consists of the following activities:
- “geological characteristics of the groundwater body including the extent and type of geological units”;
- “hydrogeological characteristics of the groundwater body including hydraulic conductivity, porosity and confinement”;
- “characteristics of the superficial deposits and soils in the catchment from which the groundwater body receives its recharge, including the thickness, porosity, hydraulic conductivity, and absorptive properties of the deposits and soils”;
- “stratification characteristics of the groundwater within the groundwater body”;
- “an inventory of associated surface systems, including terrestrial ecosystems and bodies of surface water with which the groundwater body is dynamically linked”;
- “estimates of the directions and rates of exchange of water between the groundwater body and associated surface systems”;
- “sufficient data to calculate the long term annual average rate of overall recharge”, and
- “characterisation of the chemical composition of the groundwater, including specification of the contributions from human activity. Member States may use typologies for groundwater characterisation when establishing natural background levels for these bodies of groundwater”.
COMMON IMPLEMENTATION OF THE WFD
After the WFD was adopted, a Common Implementation Strategy (CIS) (EC, 2001) was developed and agreed in May 2001. This established a mechanism for developing a common understanding of approaches to, and implementation of, the WFD, as well as examples of good practice. Working groups were convened to exchange information and experience related to the implementation of the WFD. In 2003 the working group on water bodies produced a guidance document (EC, 2003) on the identification of water bodies. The following is a summary of the salient points from the guidance that was also re-iterated in the technical report on groundwater body characterisation and risk assessment issued by Working Group C (the groundwater-specific working group of the EC) in December 2005 (EC, 2005).
The CIS guidance notes that:
- “a body of groundwater must be within an aquifer or aquifers. However, not all groundwater is necessarily within an aquifer”.
It goes on to note that:
- “the environmental objectives of preventing deterioration of, and protecting, enhancing and restoring good groundwater status apply only to bodies of groundwater. However, all groundwater is subject to the objectives of preventing or limiting inputs of pollutants and reversing any significant and sustained upward trend in the concentration of any pollutant”.
The document, for the first time, sets out more detailed guidance on the implementation of the WFD, indicating how to delineate groundwater bodies, including their upper and lower boundaries. The guidance notes that the first step to identifying groundwater bodies is to interpret the WFD definition of aquifers, i.e.
- “in respect of what constitutes a significant flow of groundwater” and “what volume of abstraction would qualify as a significant quantity [of groundwater]”.
The guidance defines a significant flow of groundwater as one that:
- “were it [prevented] from reaching an associated surface water body or a directly dependent terrestrial ecosystem, would result in a significant diminution in the ecological or chemical quality of that surface water body or significant damage to the directly dependent terrestrial ecosystems” and a significant quantity of groundwater as “abstraction of more than 10 m3 of drinking water a day as an average” or “or sufficient to serve 50 or more people”.
If either of these criteria is satisfied then the geological strata should be regarded as an aquifer. With regard to delineation of groundwater bodies, the guidance states that:
- “this does not mean that a body of groundwater must be delineated so that it is homogeneous in terms of its natural characteristics, or the concentrations of pollutants or level alterations within it. However, bodies should be delineated in a way that enables an appropriate description of the quantitative and chemical status of groundwater”
and that delineation must be undertaken in such a way that:
- “any groundwater flow from one groundwater body to another (a) is so minor that it can be ignored in water balance calculations; or (b) can be estimated with adequate precision [such that it] will facilitate the assessment of quantitative status.”
Finally, with respect to the identification of upper and lower boundaries to groundwater bodies, the guidance recommends that:
- “groundwater bodies should be delineated in three dimensions”; and that “the depth of groundwater within an aquifer or aquifers that needs to be protected and, where necessary, enhanced through its inclusion in a body of groundwater should depend on the risks to the Directive’s objectives”.
The guidance notes that the latter:
- “is a matter for Member States to decide based on their assessments of groundwater characteristics and the risks to the Directive’s objectives. It should be noted that all groundwater is subject to the ‘prevent or limit’ objective [Article 4.1(b)(i)] whether or not it is identified as being part of a body of groundwater”.
More generally, the guidance notes that:
- “although most pressures will affect the relatively shallow component of a groundwater flow, groundwater flow [and chemical status] at depth can still be important to surface ecosystems — even though this may be over an extended timescale. Human alterations to groundwater flow [and chemical status] at depth can affect shallow groundwater and thus potentially the chemical and ecological quality of connected surface ecosystems. Deep groundwater may also be an important resource for drinking water or other uses. However, Member States would not be expected to identify deep groundwater as water bodies where that groundwater (a) could not adversely affect surface ecosystems; (b) are not used for groundwater abstraction; (c) was unsuitable for drinking water supply because of its natural qualities or because its abstraction would be technically unfeasible or disproportionately expensive; and (d) could not place the achievement [of] any other relevant objectives at risk”.
In addition, it notes that:
- “the Directive’s definitions of aquifer and body of groundwater …permit groundwater bodies to be identified either (a) separately within different strata overlying each other in the vertical plane, or (b) as a single body of groundwater spanning the different strata. This flexibility enables Member States to adopt the most effective means of achieving the Directive’s objectives given the characteristics of their aquifers and the pressures to which they are subjected. For example, where there are major differences in status of the groundwater in strata at different depths, it may be appropriate to identify different bodies of groundwater (i.e. one on top of another) to ensure the status of groundwater can be accurately described, and the Directive’s objectives appropriately targeted. Similar criteria should be applied in defining the upper and lower boundaries of the groundwater body as to the geographical boundaries ... . In other words, to facilitate the estimation of quantitative status, the upper and lower boundaries should be based first on geological boundaries and then on other hydraulic boundaries such as flow lines.”
In conclusion, the Guidance (EC, 2003) recommended that an iterative, hierarchical approach be adopted to identifying aquifers and the boundaries to groundwater bodies. It recommended that some combination of geological boundaries:
- “the starting point for identifying the geographical boundaries of a groundwater body should be geological boundaries to flow, unless the description of status and the effective achievement of the Directive’s environmental objectives for groundwater require sub- division into smaller groundwater bodies”
and groundwater highs or divides:
- “sub-divisions of an aquifer or aquifers that cannot be based on geological boundaries should be based initially on groundwater highs or, where necessary, on groundwater flow lines”
and flowlines should be used. However, the details of how this was done was to left to individual Member States to decide according to best local practice. Specifically it was stated that:
- “The degree of subdivision of groundwater into bodies of groundwater is a matter for Members States to decide on the basis of the particular characteristics of their River Basin Districts. In making such decisions, it will be necessary for Member States to balance the requirement to adequately describe groundwater status with the need to avoid the fragmentation of aquifers into unmanageable numbers of water bodies”
In 2009 the European Commission published Guidance Document 22 (EC, 2009) which sets out the common implementation strategy for the Geographical Information System (GIS) elements of reporting related to EU water policy, including the WFD and Groundwater Directive. Appendix 13.3 to report No. 22 (EC, 2009) specifically dealt with issues associated with reporting of geographical data including the reporting of 3D groundwater bodies. Appendix 13.3 notes that under the WFD the following data are requested as a minimum to be provided for each groundwater body: a unique identification code, name of groundwater body, x (longitude) co-ordinate of the centroid of the body, y (latitude) co-ordinate of the centroid, and size (surface area, m2). However, reporting information about groundwater horizons and whether or not overlying groundwater bodies exist is optional.
Annex 15 of Appendix 13.3 notes that:
- “GWBs [groundwater bodies] are three-dimensional entities; however the representation of the feature will be as 2-D polygons… it is necessary in case of more groundwater bodies above them with not identical boundaries to distinguish them in different horizons (layers). Groundwater bodies like this overlay each other and should be differentiated through horizon code or separated files. Some countries delineated groundwater bodies in this way (alluvial deposit horizon (layer), main horizon (layer), deep horizon (layer), thermal or mineral water horizon (layer) etc.)”
LATERAL BOUNDARIES TO GROUNDWATER BODIES
UKTAG (2011) extends the CIS guidance (EC, 2003) on the identification of groundwater lateral boundaries by proposing that lateral boundaries to groundwater bodies can be identified using the following features:
- “Groundwater flow divides, using surface water catchments and geological boundaries as proxies where information is limited”;
- “Pressure variations, where these are significant at a river basin level and where they require variations in management”;
- “Natural chemistry variations, where they impose a limit on the value of the resource for potable abstraction, or where they influence the susceptibility to, and management of, pressures. For example, groundwater is considered to have limited resource value where its natural salinity exceeds the limit for human consumption, and is considered to have no resource value where it exceeds that of seawater”; and,
- “Coastline, unless there is specific evidence to suggest that groundwater beyond the coastline has a resource value”.
It is also noted that:
- “hydraulic boundaries should be used wherever feasible to avoid the requirement under WFD to calculate flows between groundwater bodies”.
EXAMPLES OF INTERNATIONAL BEST PRACTICE
Despite the development of a common implementation strategy (CIS), the manner in which the WFD and Groundwater Directive has been applied in relation to the identification of aquifers, and in particular the identification of the boundaries of deep groundwater bodies varies between Member States. However, details of how Member States have gone about the process of identifying deep groundwater cannot be assessed systematically as they are not obliged by the Commission to publish the detailed methods that have been used. There is some limited information, obtained primarily through grey literature or through a few peer-reviewed papers in academic journals, related to the processes by which individual Member States have identified the boundaries of aquifers and defined groundwater bodies. The table below provides links to some of the limited information related to how individual Member States undertake such tasks.
Generally, since groundwater systems and groundwater bodies are invariably defined in the first instance on the distribution of rock types within a region or country, differences in the way Member States have defined boundaries to aquifers and groundwater bodies reflects the wide range of hydrogeological contexts and settings across Europe. The following are some selected, non-systematic, examples and illustrations of how Member States have, or have not, defined deep groundwater systems.
For some Member States and regions within Europe, deep groundwater systems have not been considered at all due to the hydrogeological setting. For example, on relatively small island states such as Cyprus and Malta, groundwater systems are typically relatively shallow. Aquifer and groundwater boundaries are controlled not just by the extent of geological formations but by the location of coastlines and the extent and nature of the resulting interfaces between fresh water and seawater. For example, in Cyprus half of the groundwater bodies “have a connection with the sea”, and most of these are subject to significant seawater intrusion (Republic of Cyprus, 2016). Another example is the Maltese islands which are composed of two porous fractured limestone aquifers, the Upper Coralline Limestone and the Globigerina-Lower Coralline Limestone separated by a sequence of clays and marls (Maltese Resources Authority, 2016).
A second group of Member States where deep groundwater systems, deep aquifers and groundwater bodies are not important features of their groundwater resources are in Scandinavia, such as Sweden and Finland. Groundwater bodies in this hydrogeological setting are typically restricted to shallow weathered basement systems or fluvioglacial deposits in connection with numerous small, often isolated surface water bodies. For example, Sweden has about 3000 groundwater bodies primarily in small Quaternary deposits of sand and gravel throughout the country (McCarthy and Gustafsson, 2011; Lang et al., 2011) although some sedimentary bedrock groundwater bodies have been identified. In this setting, the base of the groundwater bodies is the base of the Quaternary deposits where it rests on the underlying metamorphic or igneous basement and is typically very shallow.
However, across much of Europe aquifers are present over a wide range of depths. Member States have used a variety of information sources, criteria and procedures to define the extent of aquifers and groundwater bodies. Information used may include data on geological units, and the hydrogeological characteristics of those units — including hydraulic conductivity, water chemistry, and degree and nature of confinement, as well as evidence for hydraulic boundaries or groundwater divides and flow lines (as recommended in EC, 2003). What is typically lacking is any description of the criteria or procedures that have been used to define groundwater bodies and particularly deep groundwater systems. Even when there is some information about how aquifer and groundwater bodies have been defined it is typically restricted to the identification of lateral boundaries and rarely is the identification of the base of aquifers explicitly addressed.
For example, Czarniecka-Januszczyk et al. (2011) and Sanchez et al. (2009) presented graphical representations of how groundwater bodies are defined in Poland and in Malaga, Spain based on a combination of considerations related to geology and hydrogeological characteristics. In both cases the conceptualisations focus on identification of lateral boundaries of groundwater bodies based on changes in geology or hydrogeological divides at or near the land surface. However, in both cases the base of the lowest aquifer/groundwater body is undefined in the schematic cross-sections and no criteria have been set to define the base of the system within the wider studies. The lack of an explicit definition of the base of an aquifer or groundwater body is a common deficiency in the description and characterisation of European groundwater systems.
In France, the principles for defining the groundwater bodies closely follow the Groundwater Directive and CIS Guidance. For example, Barraque et al (2010) describe the process used as follows:
- “geologic and hydrogeologic criteria, a groundwater body is one (or part of a) hydrogeologic unit, decomposed into 6 types of aquifers (alluvial/bedrock/volcanic/mostly non alluvial sedimentary/mountain composite hydrogeological systems intensely folded/impervious systems but locally containing small disjoint aquifer units);
- the limits of groundwater bodies are stable and not variable in time (impervious geologic limits, stable piezometric tops; flow lines);
- all boreholes giving more than 10 m3/d of drinking water or used for producing drinking water for more than 50 people must belong to a groundwater body, therefore in practice all aquifers are considered;
- deep groundwater, unconnected to rivers or surface ecosystems, in which there is no withdrawal and which cannot be used for drinking water supply because of its poor quality or for technical-economical reasons may be excluded from the list of groundwater bodies;
- groundwater bodies may exchange water as long as this can be understood/quantified;
- for large groundwater bodies, they may have spatially variable heterogeneity of their hydrogeological characteristics and quantitative or qualitative status;
- subdividing groundwater bodies for taking into account human pressure must be limited; it is acceptable only for particular problems (e.g. point pollution plumes from;
- industrial sites, active or not, piezometric depressions linked to overexploitation; this subdividing can only be made if the zone of interest needs that specific objectives be defined, different from the rest of the groundwater body, with a different management”
Note that deep groundwater systems are specifically excluded from the groundwater body designation on the grounds of lack of connection with rivers and surface ecosystems and an absence of abstraction for drinking water because of poor quality or for technical or economic reasons. However, no specific criteria related to these considerations, for example thresholds for quality or abstraction are noted by Barraque et al. (2010).
Another example of how groundwater bodies have been defined for a Member State can be found in the report by the Umwelt Bundesamt (2007) on the implementation of the WFD in Bulgaria, and specifically for the Osan and Vit sub-basins of the Danube River Basin.
The following summary of how the boundaries of groundwater bodies have been defined is given:
- “the boundaries of the groundwater bodies are placed in 4 layers. Without applying a strict stratigraphic sequence, the first layer contains mainly Quaternary aquifers, the second Neogene and Paleogene aquifers, the third mostly Karst aquifer massifs and basins and the fourth is the location of the most deeply located water bodies. The denomination of the bodies follows the largely used denomination of aquifers in the specialized literature ... when the GWB consists of two or more layers, a focus is given to the overlaying and/or the most productive one. The basic materials used are a geological map [and] hydrological maps.”
It is primarily based on pre-existing hydrostratigraphic mapping, with aquifers and groundwater bodies ranging from alluvial sediments with an average thickness of about 10 m and a transmissivity of 60 to 1100 m2/d, to suites of sandy marls down to depths of 2500 m with spring discharges of about 1 l/s. However, there is no indication of how the base of any of these units is defined based on hydrostratigraphic criteria.
The lack of any explicit criteria to define the base of groundwater bodies, or even the conceptualisation of deep groundwater systems, appears to be a common failing throughout Member States. Although some Member States do have explicit criteria for the designation of the lower boundary of groundwater bodies, such as Croatia (Brkic, 2008) where the base of Groundwater Bodies is defined by groundwater temperatures of greater than 20°C and mineralisation >1000 mg/l. Although it is also noted that:
- “Aquifers of thermal [sic] and mineral water is not included in groundwater bodies because there is not enough data”.
Other states who have also given some consideration to the regulation of deep groundwater systems, even if it is not clear if there are specific criteria related to the delineation of deep groundwater bodies, are those with relatively deep karst systems that are used for both water supply and for the production of geothermal energy. For example, Sanchez et al. (2009) describe how the effective exploitation depth of a deep limestone aquifer, the Sierra de Mijas aquifer from Malaga, Spain is used to define the base of the Groundwater Body as follows:
- “Sierra de Mijas groundwater body is made up of Triassic marbles partially covered by Neogene and Quaternary detrital deposits belonging to the Bajo Guadalhorce groundwater body. In this area the abstraction boreholes are rarely deeper than 500 m… when the depth to the Sierra de Mijas aquifer is greater than 500 m, pumping wells are not deep enough to abstract water from it and then only one groundwater body (the upper one) is considered.”
Another example of regulation of deep karst systems is Hungary where licences for abstraction of thermal waters down to 2500 m below ground level are granted, but not below 2500 m (Szocs, 2013).
As part of the national water quality management strategy for Australia, guidelines for groundwater quality protection (Australian Government, 2013) state that a risk-based approach should be used, the concepts of intergenerational equity, polluter pays and precautionary principles should all be applied, and that:
- “The process for managing the protection of groundwater quality is one of risk assessment that identifies where action is required, followed by implementation of management measures to protect groundwater quality”
and that as part of this process it is noted that:
- “understanding the groundwater system to be protected is an important initial step in applying the risk-based framework”.
This initial understanding should be based on a conceptual model of the groundwater system and include consideration of the system boundaries, stratigraphy, geological structure, groundwater flow paths, hydraulic properties of the aquifers and other factors including:
- “historical, current and expected future groundwater uses and demands”
And although no details are provided as to how this initial conceptualisation should be undertaken reference is made to the Australian Groundwater Dependent Ecosystems Toolbox (NWC, 2011). There is no specific reference in the guidance (Australian Government, 2013) to the identification of deep groundwater systems, but the following observations are pertinent to deep systems:
- “In data poor environments many components of the conceptual model may not be known. These knowledge gaps can be dealt with in two ways: either further research/investigation should be undertaken to address the knowledge gaps, or they should be identified as areas of uncertainty to which the precautionary principle is applied in the groundwater quality protection plan. A lack of knowledge concerning the potential impacts of a hazard should not be used to justify a delay in establishing groundwater protection measures. Rather, the knowledge gaps should be identified and addressed through adaptive management where necessary within a risk-based approach. The level of risk will assist in determining the most appropriate course of action where data is limited, as high risk areas may warrant further investment to fulfil knowledge gaps, while in lower risk areas acknowledgment of the uncertainties and application of precautionary measures may be sufficient.”
The Environmental Value concept of a groundwater system is the key tool used to set water quality objectives (Australian Government, 2013) as follows:
- “An Environmental Value is a particular value or use of the groundwater that is important for the maintenance of a healthy ecosystem or for public benefit, welfare, safety or health, and which requires protection from the effects of contamination, waste discharges and deposits. Different Environmental Values are values or uses of the groundwater that support aquatic ecosystems, primary industries, recreation and aesthetics, drinking water, industrial water, and cultural and spiritual values.”
When introducing a framework for assigning environmental value categories to groundwater systems, the guidance cites the Victorian State Environment Protection Policy (EPA Victoria, 1997) which gives examples of how total dissolved solids (TDS) can be used to determine appropriate environmental value categories for groundwater, and notes that:
- “This approach recognises that salinity often determines the possible uses of groundwater. The policy also includes provision for precluding certain beneficial uses if another background quality indicator will be detrimental to the beneficial use (determined based on salinity); if aquifer yields cannot sustain a particular beneficial use; or if an existing polluted groundwater zone has been identified”.
Note that the indicated maximum TDS for acceptable potable water supply of 1000 mg/l is the same as used by Croatia to define their groundwater bodies (Brkic, 2008) and considered unpalatable by the WHO (2011).
Commentary on the application of the Environmental Value categories does, however, include a consideration of potentially deep groundwater sources, as follows:
- “Physical constraints on groundwater extraction may cause some Environmental Value categories to be disregarded through community consultation, for example where aquifer yields or soil characteristics mean groundwater cannot be extracted for industrial or agricultural use. …Similarly, aquifer depth is not a sufficient reason to disregard certain Environmental Value categories since the economics of water supply could make deep groundwater sources viable in the future. Potential use of the groundwater in the future should also be a determinant of Environmental Value”
- “There may be circumstances where a groundwater system has no obvious current or future Environmental Value category, due to its depth, remote location or poor quality water. An example of this is where a deep confined aquifer in a stable geological formation contains extremely poor natural quality water (for example due to high salt or radionuclide levels) and there are no current users of the aquifer. This confined aquifer may be sought to be developed as a long term depository for wastes. As a consequence, an Environmental Value of industrial water use would apply and this would set the baseline for future groundwater quality protection measures. Another example is the extraction of poor quality groundwater associated with coal seam gas extraction. In such situations, these guidelines should be applied, particularly the precautionary principle, to ensure that changes in pressure and quality do not result in deterioration of the assigned Environmental Values of overlying or adjacent aquifers. The long timeframes involved in contaminant transport in deep confined groundwater systems mean that impacts may not be observed for a long time, are difficult to predict, and remediation may not be possible. Waste disposal and further degradation of aquifers must be assessed with a strong emphasis on the precautionary, intergenerational equity and polluter pays principles. These principles imply that an aquifer should not be further degraded if there is a chance of significant future problems or if the potential to assign certain Environmental Value categories in the future could be precluded.”
The Clean Water Act (CWA, 2002) established the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters only. Groundwater in the United States of America is subject to regulation and protection through the Safe Drinking Water Act (SDWA) of 1974 which protects drinking water sources including rivers, lakes, reservoirs, springs and groundwater wells (with the exception that it does not regulate private wells that serve fewer than 25 individuals). A summary of the regulations and a history of amendments to the Act can be found on the United States Environmental Protection Agency (US EPA or just EPA) website at: https://www.epa.gov/sites/production/files/2015-04/documents/epa816f04030.pdf.
Essential components of the SDWA include protection and prevention, whereby States and water suppliers must conduct assessments of water sources to see where they may be vulnerable to contamination. Water suppliers may also voluntarily adopt programs to protect their watershed or wellhead, and states can use legal authorities from other laws to prevent pollution.
The SDWA is designed to prevent threats to what is termed ‘Underground Sources of Drinking Water (Section 1421(b)), where EPA regulations (40 CFR 144.3) define a USDW as follows: an aquifer or its portion: which supplies any public water system; or which contains a sufficient quantity of ground water to supply a public water system; and that currently supplies drinking water for human consumption or contains fewer than 10 000 mg/l TDS; and which is not an exempted aquifer. Note that there is no guidance on how to define the lateral or vertical extent of aquifers.
Individual states and federal agencies define freshwater as typically in the TDS range <1,000 mg/l to <3,000 mg/l (Kang and Jackson, 2016).
Exemptions to the Act remove the protection to groundwater and are regulated by the EPA. To grant an exemption, the EPA must determine that the proposed exemption area is not a current or future source of drinking water following the criteria at 40 CFR 146.4 (more details regarding exemptions and the framework for the EPA Underground Injection Control (UIC) program to control the injection of wastes into groundwater can be found at https://www.epa.gov/uic/aquifer-exemptions-underground-injection-control-program). The EPA and States implement the UIC program, which sets standards for safe waste injection practices and bans certain types of injection altogether.
Additional regulation of groundwater includes the ‘Ground Water Rule’ or GWR which came into force in 2006 and which provides protection against microbial pathogens in public water systems using groundwater sources (see https://www.epa.gov/dwreginfo/ground-water-rule for more information).
In this context, the EPA provides oversight, guidance and regulation related to shale gas and environmental protection summarised here https://www.epa.gov/hydraulicfracturing#providing. Specifically with respect to groundwater protection, the EPA provide technical recommendations for protecting USDWs for a range of well-based activities including (Calls II) oil and gas related injection wells, with specific technical guidance when diesel fuels are used in fracturing fluids or propping agents (https://www.epa.gov/uic/diesel-fuels-hydraulic-fracturing-dfhf). Their current position is summarised in their recent report — ‘Assessment of the Potential Impacts of Hydraulic fracturing for Oil and Gas on Drinking Water Resources (US EPA, 2015).
Groundwater quality in England
TDS-depth as a function of lithology
Based on data from the Geothermal catalogues.
Maps of deep groundwater chemistry data from geothermal catalogues
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