and 5 of the final proposal present methods to estimate the actual dilution and attenuation factors in
a given system. Unfortunately, time and data did not generally allow these evaluations to be
performed in the BRIDGE project. However, investigations and research projects on this subject
will be of great importance in the coming years in order to be able to establish proper threshold
values based on the environmental quality standards for dependent aquatic and terrestrial
ecosystems.
28 Table 8. Comparison of groundwater threshold values derived based on groundwater itself as a receptor (tier 2a) and the p90 NBL and based on reference values for dependent aquatic ecosystems for groundwater bodies in the Austrian, Belgian, Danish, Hungarian and Dutch case study areas.
Austria Belgium Denmark Hungary Netherlands
TV90_gw TV_eco TV90_gw TV_eco TV90_gw TV_eco TV90_gw TV_eco TV90_gw TV_eco
DF=1a DF=0.3b DF=1 AF=0.5
As 2 24 80 30 30 11 0.8 8 15 11
Cdc 3 1 3.3 1 0.75 0.6 0.25/1.5 ? 0.4 0.2 0.4
Cuc 2 9.3 31 16 16 1.2 10 1.5
Crc 2 9 30 8 8 1.1 2.5 8.7
Hg 1 3.3 0.5 0.4 0.006 0.01 0.3 0.06
Pb 2 11 37 10 10 2 7.2 10 4 8
NH4 0.02 0.89 3 1 1.6* 0.52 0.5 - 0.03
NO2 0.04 0.18 1 0.06 0.02
N (19) 4.1** 4** (0.5) 4 8
PO4_P 0.026 0.52 0.48*** 0.15*** 0.08*** 0.15***
TCE 5 10 33 - - 10
PCE 5 10 33 - - 10
a Haschendorf site b Fischamend site c Hardness dependent (see com(2006)397/appendix 5) and Coetsiers and Walraevens 2006)
* NH4_N ** NO3 + NO2 ***total P
6. Summary of findings and suggestions
The general conclusion from the conducted case studies is that the general concept of the developed methodology seems logical and that it is easy and practical to apply although it may be simplified in some parts (e.g. case definitions) and should be developed in further detail in other (e.g. preselection criteria for NBL derivation).
The case studies revealed the following issues, which still need clarification and development:
6.1 Comments and suggestions to the derivation of natural background levels The following issues regarding NBL derivation were raised by different partners:
1) Related to preselection of data used for derivation of NBLs a) Aerobic versus anaerobic groundwater bodies b) Fresh versus saline groundwater bodies
c) Delineation of groundwater bodies and hydrochemistry d) Deep groundwater bodies without dependent ecosystems
2) It is important to recognise the variability of the natural background concentration – the natural background is a range not a fixed value,
3) NBL selection at what percentile (90 or 97.7) ? 4) Selection of relevant reference values
5) What is a reasonable level of the TVs between the NBL and REF?
6) How to deal with increasing or decreasing trends – what part may/should be used for NBL derivation?
7) Derivation of threshold values for organic pollutants and harmful substances 8) how to treat detection limit and level of quantification in the NBL calculations
Re 1)
a) The BRIDGE pre-selection method simply suggest to select data sets with NO3 concentrations less than 10 mg/l as a natural groundwater level – all analyses from monitoring points with median NO3 concentrations above 10 mg/l are excluded. This raises the following issues:
This preselection method will include natural quality groundwaters in some areas and groundwater with human impact in others.
30 bodies it is suggested to derive threshold values separately for aerobic (O2 > 1 mg/l) and anaerobic (O2< 1 mg/l) parts, separately, and/or e.g. use the oxidation capacity approach suggested in the Dutch report (Hinsby et al. 2006, Passier et al. 2006) or the use of other additional indicator substances, e.g. NH4 (Berthold et al., 2006). Additionally it should be emphasized that the simplified Bridge preselection method is only to be used where data do not allow for a more detailed evaluation of the natural background levels e.g. by including evaluation of environmental tracers, fertilizer and pesticide co-pollutants etc. (see Appendix 3, Griffioen et al. 2006, Edmunds and Shand 2007, Hinsby et al. 2001).
b) It has been argued that the additional pre-selection criteria of removal of monitoring points with Na+Cl >
1000 mg/l is not scientifically sound and reasonable in coastal/marine sediment areas. NBLs should therefore be derived for both fresh and brackish waters instead in order to be able to manage the fresh/brackish water interfaces properly (see Dutch document in app.5 and summary sheets in Appendix 1).
c) The threshold value derivation method as described above strongly depends on the established natural background value, and the selection of one or more relevant reference values. Hence the method is very sensitive to the selection of reasonable natural background and reference values. Concern was therefore expressed about the issue of delineation of similar groundwater types, since the same groundwater bodies may have very different hydrochemical “populations” this concern is somewhat along the lines of bullet a and b above (For further information see Polish summary sheets in Appendix 1)
d) Uncertainty was expressed regarding whether or not it was requested to establish TVs for deep systems with purely “natural impacts” by upconing of e.g. saline waters and in this case what NBL to use in case of a continuous trend (see Lithuania summary sheets in appendix 1)
Re 2)
The natural background levels are reported as a single value e.g. as the 90th percentile of the preselected data set. However, it is important to recognize that the natural background concentration is not a single value but a range of values, which may vary considerably between different groundwater bodies. It is therefore recommended always to report the percentiles 2.3, 10, 50, (90) and 97.7 in addition to the NBL selected at the 90th percentile (p90) in order to illustrate the natural variability of a given element or substance in a given groundwater body (see Polish summary sheet in appendix 1).
Re 3)
Some (most) case studies recommend to use the 90th percentile, while other recommend to use the 97.7th percentile. Generally, it seems that the 90th percentile is the most reasonable to use in data sets which may include some human impact and/or are relatively small (< 60 monitoring points ?), while the 97.7th percentile is the most reasonable to use in relative large data sets, which do not include any groundwater with human impact.
WP4 Case study summary report
Re 4)
Generally the information on EQS values for dependent ecosystems is scarce and often no national or EU values exist. Hence the drinking water standards have been used as an example of reference values considering groundwater itself as a receptor in all cases. This may not always be sufficient for groundwater itself, and is not sufficient in some cases for dependent ecosystems. The derivation of TVs based on dependent ecosystems increase the need for fully understanding the system and information on both deep and shallow groundwater systems and their interaction with surface water in order to be able to quantify substance fluxes. In case EQS values for surface waters exist but sufficient data is not available to quantify fluxes it is necessary to use dilution and attenuation factors of 1.
Re 5)
There is some concern about using the case 2 method for derivation of TVs – this will in some cases, like e.g. in the Finnish study, derive very small TVs, which may be difficult to accept politically. This was also a major concern of the advisory board, which stated that this approach was not scientifically sound. Case 2 has been removed in the final proposal (Müller et al. 2006).
Minor revisions and clarification are needed in the data preselection method for derivation of natural background levels. The proposed preselection method is rough, and should be used to approximate the true natural background levels only where the data do not allow a more detailed evaluation. It is recommended to use more detailed evaluations including e.g. environmental tracers and organic contaminants whenever possible.
Note of caution: The natural background level is a range rather than a fixed value as mentioned earlier and in some cases it varies over an order of magnitude or more. By selecting the 90th and 97.7th percentiles as the NBL value, the NBL may actually be considerably higher than the common (e.g. “median”) natural concentration, and in some cases these relatively high levels may include contaminated waters or rare high natural concentrations, which potentially can harm the dependent ecosystems.
6.2 Reference values for derivation of TVs for groundwater itself at tier 2a
The knowledge on relevant reference values for groundwater itself is limited. Hence, there has been
some uncertainty about what values to use. Most have used the drinking water standards as these
are the most widely established and well known. The deliverable D7 from the BRIDGE WP1
32
European groundwater bodies, the conducted investigations demonstrate the following:
•
the knowledge about groundwater and surface water interaction is generally limited.
•
Data from shallow groundwater monitoring networks are not existing or insufficient
•
Data on reference values for dependent ecosystems are scarce.
•
Data on reference values for groundwater itself are scarce (or non-existing)
•