Groundwater natural background levels and threshold definition in the Kedzierzyn-Glubczyce Subthrough (Southern Poland)
S. Witczak1, J. Karlikowska1, E. Kmiecik1, J. Szczepanska1, T. Szklarczyk1,K. Rozanski2, A. Zuber3
1Faculty of Geology, Geophysics and Environmental Protection, AGH-University of Sciences and Technology, Al. Mickiewicza 30, PL-30059 Krakow, Poland.
2Faculty of Physics and Applied Computer Science, AGH-University of Sciences and Technology, Al. Mickiewicza 30, PL-30059 Krakow, Poland.
3Polish Geological Institute, Carpathian Branch, ul. Skrzatów 1, PL-31560 Krakow, Poland
SUMMARY
A study of a multi-aquifer GWB indicated that proposed within the BRIDGE Project methodology of the TV determinations is rather inferior to the national method of determining the quality of groundwater.
Particularly, the proposed concepts of NBL and TV are not adequately applicable to GWBs characterized by distinctly different zones and to multi-aquifer GWBs.
1. INTRODUCTION
According to the UE Directive (WFD, 2000), the Ground Water Body (GWB) is defined as a distinct volume of groundwater within an aquifer or aquifers. Unfortunately, that definition is not precise, and requires lengthy description of factors which should be considered in the selection of GWBs. As a consequence of imprecise definition, the boundaries of GWBs cannot be chosen unambiguously. Especially great difficulties are encountered for multi-aquifer GWBs, because it remains unclear how to present in a unique way the natural background levels (NBL) and threshold values (TV) defined within the Bridge project, especially if the hydrochemistry of particular aquifers greatly differs and they hydraulic relations are weak or even inexistent.
The GWBs and their boundaries in Poland were introduced by administrative regulations based on the work of experts from the Polish Geological Institute (Herbich et al., 2005). They are not free of the above-mentioned drawbacks, as it will be shown further on in this report. Data available from earlier works are used within this report to describe the most important parts of the GWB-129 (PL_GW_6210_129). That GWB is a multi-aquifer body represented by near- surface Quaternary (Pleistocene) sands and gravels, confined Sarmatian sands together with sands of buried Pleistocene valleys, and Badenian sands. The influence of upward seepage from deeper water bearing formations on the hydrochemistry is observed mainly in the Badenian sands and also in the central part of the Sarmatian sands. As shown further (see Fig. 7), the investigated GWB is a part of the Kedzierzyn-Glubczyce soubtrough (ca. 3675 km2), whereas the whole Sarmatian and buried valleys aquifer is one of the most important aquifers in southern Poland and belongs to the category of the so-called Major Ground Water Basins (MGWB-332), which can be divided by the Odra River line into the Glubczyce and Kedzierzyn parts (Kleczkowski et al., 1990) The recent studies performed under the BASELINE and BRIDGE projects cover the area of ca. 1,500 km2 of the Kedzierzyn part, with the population of 170000 and heavy chemical industry and coke plants concentrated in the Kedzierzyn area. The highest water withdrawal of ca. 44 million m3/a was reached in the eighties of the previous century, which due to positive political and economical changes declined by about 50% in nineties. That decline resulted in the recovery of the water pressure in the Sarmatian aquifer, reaching nearly 10 m in a state monitoring well.
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2. CHARACTERISATION OF THE OF GROUNDWATER BODY 2.1 Physical and hydrogeological description
2.1.1 Geographical boundaries
The study area is situated in south-western Poland with the upper transboundary Odra River flowing through the centre of the basin from the SSE to NNW (Fig. 1). The basin consists of Glubczyce plateau (235-260 m asl) and Raciborz valley (180-200 m asl). The topographic map of the study area is shown in Fig. 2 with indicated boundary of the MGWB-323 and its division into two sub-basins, and boundaries of the related GWBs. As discussed further the hydrodynamic model covers larger area than that of the MGWB, whereas the hydrochemical study covers only the main part of the GWB-129 and a small part of the GWB-130, which together form a part of the MGWB Kedzierzyn.
Fig. 1. Position of the Glubczyce-Kedzierzyn Major Ground Water Basin (MGWB) within the transboundary Odra River watershed.
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Fig. 2. Topography of the Glubczyce-Kedzierzyn area and the boundaries of the GWBs.
The map of land use is shown in Fig. 3. Most of the MGWB Kedzierzyn area (51.8%) is forested, 37.1% is cultivated, 8.4% is urbanized and 2.7% is covered by surface water. The only receptor of groundwater from the Sarmatian and Pleistocene buried-valley aquifer and also from the Badenian aquifer is human health. The terrestrial receptors of groundwater from the shallow Pleistocene aquifer(s) are shown in Fig. 4. The aquatic receptors ecosystems contain waters highly polluted as shown in Fig. 5. All the most important rivers and surface reservoirs are highly polluted but they act as drainage systems for the GWBs. An exception exists for the open pit sand mine “Kotlarnia” which due to dewatering receives polluted water from the Bierawka River through the shallow Pleistocene sands. That pollution of the Pleistocene aquifer is of very local character as it can be deduced from the position of the mine seen in Fig. 5. The polluted water from the mine is pumped out back to the river together with other inflowing waters. The vulnerability of the Pleistocene aquifer(s) in the Glubczyce-Kedzierzyn area is shown in Fig. 6.
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Fig. 3. Land use in the Glubczyce-Kedzierzyn area.(based on CORINE, 2000)
Fig. 4. Forests and wetland with the depth of water table ≤2.5 m in the Glubczyce-Kedzierzyn area. (after Witczak et al, 2006)
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Fig. 5. Map of polluted surface waters which drain aquifers within the Glubczyce-Kedzierzyn subthrough, with an exception for the Kotlarnia open pit sand mine which receives some water from the Bierawka River
Fig. 6. Vulnerability of the Pleistocene aquifer(s) within the Glubczyce-Kedzierzyn subthrough.
Arrows indicate directions and estimated travel times in years of horizontal groundwater flows to rivers. (after Witczak et al, 2006)
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2.1.2 Climate
The climate is moderate with the mean yearly air temperature of about 8.0 °C, precipitation rate of 770 mm/a, and potential evapotranspiration rate of ca. 660 mm/a. The monthly precipitation and evapotranspiration rates as well as monthly temperatures are given in Fig. 7 for the adjacent Opole region situated northwest of the study area. That region can be regarded as representative in the relation to the discussed parameters.
-20 0 20 40 60 80 100
January February March April Mai June July August September October November December
[mm/month]
-4 -2 0 2 4 6 8 10 12 14 16 18 20
[oC]
precipitation, P evapotranspiration, ETP surplus
temperature
Fig. 7. Mean monthly values of precipitation, evapotranspiration and air temperatures observed at the Opole meteorology station in 1951-1970 (Bac and Rojek, 1981).
2.1.3 Water balance
Calculation of the water balance in the study area is difficult due to the lack of data, especially those on volumetric flow rates of transit rivers. The water balance shown in Table 1 was calculated from the hydrodynamic model discussed further for the central area of the Glubczyce-Kedzierzyn subthrough and the era of intensive exploitation (see Fig. 14 further).
Infiltration rates in mm/year are 129 in sands, 57 in loesses, and 25.5 in loams.
Table 1. Annual average values of the water balance components in mm/year estimated for the central area of the Glubczyce-Kedzierzyn subthrough (without transit rivers)
Precipitation Evapotranspiration Infiltration Inflow Outflow Withdrawal
774 660 74 31 86 19
2.1.4 Geology
The geological map of the study area area known as the Glubczyce-Kedzierzyn subthrough is shown in Fig. 8, without the Holocene and Pleistocene cover. The boundaries of the GWB-s and MGWB-332 are also shown in that figure as well as the boundary of the hydrodynamic model 6
and the boundary of the area chosen for water balance calculations. The stratigraphic profile is shown in Fig. 9. The Upper and Lower Carboniferous is represented by folded sandstones and shales. The Carboniferrous is overlain discordantly by dolomitic limestones of the Lower Triassic, limestones and marls of the Middle and Upper Triassic whereas the Cretaceous occurs locally as sands, sandstones and marls, and in the northwest part of the subthrough in a continous form dipping to the north. The oldest Miocene sediments are represented by terrigenic sandy and marly clays of the Carpatian (Klodnica Beds). The Badenian is represented by marine Skawina, Wieliczka and Grabowiec Beds. The Skawina Beds are represented by marly clays, the Wieliczka Beds (also called as the Miocene evaporites) by clays with gypsum and halite inclusions, and Grabowiec Beds by marly clays with interbeds of fine sands. The Sarmatian is represented by terrigenic silty and sandy clays and fine sands, which locally change to coarse sands and gravels (Kleczkowski, 1966) In some areas traces of braun coal are observed. The Pliocene terrigenic sands and gravels occur only locally in the elevated areas. The Pleistocene fluvio-glacial gravels, sands, and loams are mainly related to two older glaciations, though interglacial sands and loams also occur. The Holocene gravels, sands, loams, silts and muds occur in present river valleys.
Fig. 8. Geology of the Glubczyce-Kedzierzyn subthrough without Holocene and Pleistocene cover. Boundaries of the discussed areas and the profile lines are also shown. 1, Sarmatian; 2, Badenian; 3, Upper Cretaceous; 4, Triassic; 5, Carboniferous; 6, outcrops of Sarmatian sands; 7, Pleistocene buried valleys; 8, boundary of the MGBW; 9, 10 and 11 lines of the model cross- sections (Figs. 10, 11 and 14); 12, boundary of the hydrodynamic model; 13, boundary of the area chosen for water balance calculations.
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Fig. 9. The stratigraphic profile of the Glubczyce-Kedzierzyn subthrough.
2.1.5 Hydrogeology
2.1.5.1 Delineation and type of groundwater body
Simplified hydrogeological cross-section of the study area is shown in Fig. 10. The Glubczyce- Kedzierzyn MGWB and within its area also the Kedzierzyn GWB consist of three aquifers listed in the order of their importance: (1) Sarmatian and Pleistocene buried-valley sands and gravels confined in most of the area by semi-permeable Sarmatian clays; (2) unconfined Quaternary (Pleistocene and Holocene) sands and gravels, and (3) Badenian fine sands separated from overlain and underlain permeable formations by other less permeable Badenian sediments. The presence of deeper formations, particularly of Triassic permeable carbonates, can be neglected, though they influence to some degree the hydrochemistry of the Badenian 8
aquifer. Water is mainly exploited from the Sarmatian and buried valleys, much less is exploited from the shallow Pleistocene aquifer(s), and only one well exploits water from the Badenian.
Fig. 10. Simplified hydrogeological profile (the main aquifer is shadowed). 1, sands of Pleistocene buried valley; 2, Sarmatian sands; 3, Shallow Pleistocene and Badenian sands; 4, Triassic and Cretaceous fissured carbonates; 5, Semi-permeable sediments (K = 10-5-10-7 m/s);
6, “impermeable sediments (K<10-7 m/s); 7, faults and stratigraphic boundaries; 8, water table in; the shallow Pleistocene; 9, regional flow directions; 10, interface o brackish water.
(Kleczkowski et al., 1990)
The near surface aquifer(s) consist of Pleistocene unconfined sandy and gravely layers with the depth of 5-30 m. Their boundaries are defined by watersheds of Odra tributaries. However, it is seen in Fig. 2 that in many cases they do not correspond to the chosen boundaries of the GWBs.
The Sarmatian sands were deposited in continental environment and contain traces of lignite.
They have variable grain size composition, from silts and dominating fine-grained sands up to gravel and pebbles. Gravel consists mainly of quartz, with minor addition of glauconite grey sandstone grains. That aquifer is separated from the Pleistocene permeable sediments by semi- permeable Sarmatian clays and silts, and in very small areas by Pliocene silts. In the central part, the Sarmatian aquifer is hydraulically connected with Pleistocene buried valleys filled with sands and gravels, which are separated from the upper peremable sediments by glacial tills. The thickness of the Sarmatian aquifer is 15 to 30 m, and within the central part its depth is 70- 100 m below ground level whereas near the outcrops it is only 30 to 40 m. The maximal depts of Pleistocene buried valleys is 120 m. Deeper formations are little recognised but it is known that underlain Badenian clays separate the Sarmatian sands from permeable fine Badenian sands, which are separated from permeable Triassic carbonates by Badenian evaporite and clayey formations. In the eastern part, impermeable Carboniferous and Permian formations with saline pore waters underlie Triassic carbonates, whereas to the west of the Odra River locally also occur permeable fragments of Cretaceous marls with fresh waters. The hydraulic conductivities of particular aquifers are given in Table 2.
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Table 2. Hydraulic conductivity data of water bearing layers in m/d
Quaternary Tertiary Triassic Carbonifer.
Parameter
Q1 Q2 Q3 Trs2 Trs1 Trb T C
Maximal value 975 192 86.4 81.1 133 12.4 199 7.8 Geometric mean 16.3 13.2 18.3 9.4 11.2 2.1 2.1 1.0 Minimal value 0.11 0.09 1.12 1.44 0.18 0.32 0.06 0.014
Number of data 105 59 34 12 99 5 36 7
The shallow Pleistocene aquifers are recharged directly by precipitation and drained by rivers and streams. The Sarmatian is recharged indirectly: through the shallow Pleistocene aquifers at the outcrops of the Sarmatian, by downward seepage from the Pleistocene aquifers, through the fault and an erosion window(s) at the northern boundary, and by upward seepage from the Badenian sands. The recharge was by upward seepage in the Odra River valley in the pre- exploiation era and by pumping during the last several decades.The Pleistocene buried valleys are mainly recharged by lateral flow from upstream areas where they are unconfined and from the Sarmatian, and they are drained in the central part together with waters from the Sarmatian.
The Badenian aquifer is recharged and drained by seepages.
2.1.5.2 Hydrodynamics
The complex hydrodynamics of the investigated area is represented by numerical flow model constructed with the aid of Visual MODFLOW code (Szklarczyk et al., 2004). The modelled area and the area for which water balance calculations were performed are shown in Fig. 8 whereas the geological structure of the model is shown in Fig. 11.
Fig. 11. An example of cross-section showing the geological structure of the model. 1, porous permeable sediments; 2, porous-fissured rocks; 3, semi-permeable sediments; 4, faults; 5, stratigraphy: Q – Quaternary, Tr-s – Sarmatian, Tr-b – Badenian, K – Upper Cretaceous, T2 – Middle Triassic, T1 – Lower Triassic, C – Carboniferous; 6, layer number in the model.
The flow directions in the shallow Pleistocene aquifer(s) are of local characters as being directed to rivers, streams, and canals. The regional flow in the Sarmatian aquifer and in deeper permeable formations is to the Odra River valley as shown for the Sarmatian in Fig. 12.
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In pre-exploitation era, the Sarmatian aquifer with buried valleys was recharged from and discharged to the shallow Pleistocene aquifer(s) by downward and upward seepages. Similarly, the Badenian aquifer discharged to the Sarmatian in the Odra River valley by upward seepage.
However, the upward seepage from the Sarmatian changed to the downward seepage in the exploitation era due to its intensive withdrawal, as it can be seen from the comparison of Fig. 12 with Fig. 13. The seepage rates to and from the Badenian aquifer practicaly remained unchanged, as it can be deduced from schematic water balance shown in Fig. 14.
An example of a cross-section with chosen flow lines and travel times in the exploitation era is shown in Fig. 15. As mentioned, in the pre-exploitation era, the seepage from the Sarmatian to the Odra River valley was directed upward. The water ages corresponding to the early Holocene in the central part of the Sarmatian were confirmed by 14C data, whereas both 14C data and stable isotope data of oxygen and hydrogen indicated the presence of glacial age waters in deeper formations. Due to the long travel times of seepages, the tracer ages describe the pre- exploitation conditions. Due to the same reason, possible changes in hydrochemistry caused by intensive exploitation will be observed in far future.
Fig. 12. Potentiometric map of the Sarmatian aquifer with main groundwater flow directions in the pre-exploitation era: 1, head contours in m asl; 2, flow directions; 3, boundary of the model;
4, boundary of the area chosen for water balance calculations; 5, artesian pressures in m agl.
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Fig. 13. Potentiometric map of the Sarmatian aquifer with main groundwater flow directions in the exploitation era (1993): 1, head contours in m asl; 2, flow directions; 3, boundary of the model; 4, boundary of the area chosen for water balance calculations; 5, depression levels in m in relation to the pre-exploitation era levels.
Fig. 14. Schematic presentation of water balance calculations with volumetric flow rates in 103 m3/d: a, for 1993; and b, for pre-exploitation era. R, recharge from precipitation; IR, infiltration from rivers; IH horizontal inflow; S, seepages and inflow through hydrologic window; DR, drainage to rivers; W, withdrawal; OH, horizontal outflow; notation of water bearing layers as in Fig. 11.
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Fig. 15. An example of the model cross-section with migration travel times along chosen flow paths in the exploitation era. 1, water level in upper Pleistocene aquifers; 2, semi permeable formations; 3, flow paths with arrows every 0.2 ka and approximate travel times in ka; 4, permeable formations; 5, wells with screens. The cross-section line is shown in Fig. 8.
2.1.5.3 Hydrogeochemistry
No detailed chemical analyses of rock material of the aquifers in the Glubczyce-Kedzierzyn area are available. The hydrochemistry of the Pleistocene aquifers is governed by hydrochemistry of rains and typical water-rock interactions with local influences of pollution from chemical industry and waste disposal sites. The hydrochemistry of the Sarmatian aquifer is governed by typical water-rock interactions in the presence of gypsum. The conceptual model of hydrochemistry based on the numerical flow model is shown in Fig. 16.
Waters in the shallow Pleistocene aquifer(s) are generally of HCO3-Ca type with the exception for the central and north-west part where they are locally polluted in the industrial areas and in areas of industrial and communal disposal sites. Waters in the Sarmatian aquifer are also of HCO3-Ca type except for the north-central area where they become of the HCO3-SO4-Ca type due to the presence of pre-exploitation remnants of upward seepages. At the north-west boundary, they become of the SO4-Cl-Ca types, mainly due to the inflow of polluted waters from the shallow Pleistocene aquifer through a hydrogeological window. In the Pleistocene buried valleys dominate waters of HCO3-Na type. In the Badenian aquifer, waters are of HCO3- SO4-Ca type, which in the central part of the area become of SO4-Cl-Ca types with elevated TDS contents. In the shallow Pleistocene aquifer(s) dominate aerobic conditions, and there are no sufficient data to delineate the redox boundaries. Anaerobic conditions exist in other aquifers, which result in elevated contents of Fe, Mn and NH4.
For the Pleistocene aquifer(s), the following indicator constituents were only measured: pH (low), SEC, DOC, NH4, NO2 NO3, SO4, Al, B, Cd, Hg, Trichloroethylene, and Tetrachloroethylene. Positions of the monitoring wells in the Sarmatian and shallow Pleistocene aquifers are shown in Fig. 17. The cumulative concentration distributions of the major, minor and selected trace components in the Sarmatian and Pleistocene buried-valley aquifer are shown in Fig. 18. In Fig. 19 the aerial distribution of SO42- is shown, which exemplifies the influence of ascending seepage from the Badenian aquifer. Elevated SO42- contents at the northern
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boundary may also result from horizontal inflow from carbonate Triassic formations (see Fig.
10).
Fig. 16. The conceptual model of hydrochemistry based on the numerical flow model.
Equipotential heads in the exploitation era were calculated with the aid of Visual MODFLOW and seepage travel times with the aid of MODPATH.
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Fig. 17. Positions of the monitoring wells investigated within the present work.
Fig. 18. Cumulative concentration distributions of major, minor, and selected trace components in the Sarmatian and Pleistocene buried valley aquifer.
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Fig. 19. Aerial distribution of SO42- in mg/L in the Sarmatian and Pleistocene buried-valley aquifer obtained by kriging. Highly polluted waters in wells 28 and 29 and waters from other aquifers (38 and 40) were not considered.
2.1.5.4 Groundwater receptors
Identify type of dependent aquatic and terrestrial ecosystems (rivers, lakes, wetlands, transitional and coastal waters) and protected areas, and estimate the direction and rates of exchange of water between the groundwater body and associated surface systems.
The only receptor of groundwater from the Sarmatian and Pleistocene buried-valley aquifer and also from the Badenian aquifer is human health as it can be deduced from Figs. 15 and 16. The terrestrial receptors of groundwater from the shallow Pleistocene aquifer(s) are shown in Fig. 4.
The aquatic receptors ecosystems contain waters highly polluted (see Fig. 5).
2.2 Existing natural background levels
2.2.1 National method used for deriving natural background levels
The Polish approach towards the assessment of groundwater quality is focused on human health as a main risk receptor and has been widely used for the past two decades with periodic revisions. No quality standards are so far defined for groundwater-dependent ecosystems. The methodology recommended under WFD (WFD CIS WG_C, 2005) and GWD (GWD, 2006) is under implementation by making use of the national classification of groundwater into five classes. The classes are defined for 55 elements and physicochemical parameters observed in waters withdrawn from monitoring and exploitation wells. The classification serves for detailed insight into the chemical status of groundwater and in consequence allows for more flexible management of groundwater bodies.
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The following classes are defined:
Class I. Chemical composition derived exclusively from natural sources, none of the components exceeds MPL, which means that no treatment is required. There are no indications of anthropogenic influences. Waters of that class are regarded as being of very good quality.
Class II. Chemical composition derived exclusively from natural sources, one or more natural components exceed MPL, which means simple treatment can be required. Anthropogenic influences are negligible. Waters of that class are regarded as being of good quality.
Class III. Chemical composition derived mainly from natural sources, with elevated concentrations of some natural and/or anthropogenic components, the latter being at initial stages without distinct trends. Treatment required because of the elevated concentrations.
Waters of that class are regarded as being of acceptable quality.
Class IV. Chemical composition derived from natural and anthropogenic sources, with elevated and variable concentrations of some components; advanced treatment needed. Waters of that class are regarded as being of poor quality.
Class V. Chemical composition derived from natural and/or anthropogenic sources, with so elevated concentrations of some components that treatment is uneconomical. Waters of that class are regarded as being of very poor quality. Waters with MPL values exceeded solely due to the natural processes also belong to the classes IV and V (e.g. waters with high natural arsenic or fluoride contents, or highly saline waters and brines).
Several water components and their natural background levels (NBL) used for classification of groundwater status in Poland are shown in Table 3. They were determined by experts for typical groundwater systems (GWBs) in Poland. According to the rules specified in WFD and GWD, the first three classes have all concentrations below the threshold values (TV).
Table 3. An example of the Polish classification of groundwater status for selected water components
Polish classification No Parameter Unit Natural Background
Level (NBL)
I II III IV V
9 NO3 mg/L 0–5 10 25 50 100 >100
14 Cl- mg/L 2–60 60 250 300 500 >500
8 As mg/L 0.00005–0.020 0.010 0.010 0.100 0.200 >0.200 22 Cd mg/L 0.0001–0.0005 0.001 0.003 0.005 0.010 >0.010
25 Mn mg/L 0.01–0.4 0.05 0.4 1 1 >1
42 Fe mg/L 0.02–5 0.2 1.0 5 10 >10
2.2.2 Regional natural background levels of selected substances
Each Kedzierzyn GWB layer is characterized by different hydrochemistry, with clearly marked zones of different quality of water resulting from natural and/or anthropogenic processes. For the Sarmatian and Pleistocene buried valley aquifer, 84 physico-chemical parameters were measured in 36 representative wells during three sampling campaigns. Cumulative concentration distributions of the most important constituents obtained after pre-selection of anthropogenic influences (see Fig. 18) yield 2.3 to 97.3 per cent values on the probabilistic plots, which serve for the determination of natural background values. The NBL and TV as proposed in BRIDGE methodology are difficult to determine in unique ways for some constituents due to their wide concentration and space distributions. These difficulties are well
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seen for SO42- due to its distinct aerial differentiation (Fig. 19). Large differences in SO42-
contents are purely of natural origin in the central part of the GWB whereas at north-west boundary they are mainly caused by anthropogenic influences due to the presence of hydrogeological window (wells 28 and 29). The sources of elevated SO42- contents were identified by hydrodynamic modelling and environmental tracer methods.
3. GROUNDWATER STATUS EVALUATION BY THRESHOLD VALUES
Monitored wells supplying water from the shallow Pleistocene aquifer(s) and from the Sarmatian and Pleistocene buried-valley aquifer are shown in Fig. 20, with identification of quality classes according to the national method. Waters from the Badenian aquifer and deeper formations are not considered as they practically have no receptors. Great differences in the quality of water exploited by individual wells are clearly seen. The same wells are shown separately for the shallow Pleistocene aquifer in Fig. 21 and for the Sarmatian and Pleistocene buried-valley aquifer in Fig. 22. The shallow aquifer can be regarded as having poor chemical status but the Sarmatian and Pleistocene buried-valley aquifer have good chemical status. Both aquifers as a whole can be regarded as having good chemical status, but great differences in the chemical quality of groundwater exploited by individual wells in both aquifers can easily be seen.
Fig.20. The area of the MGWB Kedzierzyn (mostly covering the GWB-129) with the positions of all monitored wells and the chemical quality of their waters according to the national classification. The GWB status as a whole is good.
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Fig. 21. The area of the MGWB Kedzierzyn (mostly covering the GWB-129) with the positions of monitored wells in the shallow Pleistocene aquifer(s) and the chemical quality of their waters according to the national classification. The aquifer status as a whole is poor.
Fig. 22. The area of the MGWB Kedzierzyn (mostly covering the GWB-129) with the positions of monitored wells in the Sarmatian and Pleistocene buried-valley aquifer and the chemical quality of their waters according to the national classification. The aquifer status as a whole is good.
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For the sake of clarity of further considerations, the definition of the Threshold Value (TV) is recalled:
(1) "groundwater quality standard" means an environmental quality standard expressed as the concentration of a particular pollutant, group of pollutants or indicator of pollution in groundwater, which should not be exceeded in order to protect human health and the environment;
(2) "threshold value" means a groundwater quality standard set by Member States in accordance with Article 3 of GWD (GWD, 2006).
Within the BRIDGE Project the following formulas are proposed for the calculations of TVs (Case 4 is added within this report as a necessary extension of Case 2):
Case 1: TV = (REF+NBL)/2 for (1/3)REF < NBL < REF Case 2: TV = 2NBL for NBL < (1/3)REF Case 3: TV = NBL for NBL > REF Case 4: TV = (1/2)REF for NBL = 0
According to these formulas, the role of the Member States is to define the quality standards expressed as REFs. The reference standards (REF) can be chosen depending on the receptors of groundwater under consideration.
The natural background levels (NBL) and threshold values (TV) of selected water constituents for the shallow Pleistocene aquifer(s) are shown in Table 4, and for the Sarmatian and Pleistocene buried-valley aquifer in Table 5. The NBLs were determined by using 97.3 and 90 percentiles of the pre-selected cumulative concentration distributions. For the calculations of TVs shown in Tables 4 and 5, the drinking water quality standards recommended by DWD (1998) were used. For the calculations of the TVPL values, the maximum permissible levels (MPL) obligatory in Poland were used.
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Table 4. Natural background levels and TVs of selected water constituents for the shallow Pleistocene aquifer
NBL 2.3%--97.7%
Substance Unit REF N
10%--90%
TV1 TV2 TV3 TVPL
260--780 1 560
EC S/cm 2500 12
300--630 1 260
2500
4--260 260
Cl- mg/L 250 12
7--70 140
300 40--140 195
SO42- mg/L 250 12
50--110 180
250
0.05--3.0 3
NH4+ mg/L 0.50 12
0.11--1.3 1.3
1.5
0.001--20.0 20
Fe mg/L 0.20 12
0.07--4.0 4
5
0.009-1.2 1.2
Mn mg/L 0.05 12
0.02-1.0 1.0
1
0.35--17.0 17
As g/L 10 12
0.72--8.5 9.3
100
0.5--2.0 4
Pb g/L 10 12
0.72--1.5 3
50 0.28--0.9 0.95
Hg g/L 1 12
0.35--0.72 0.86
1
0 5
Trichloroethylen g/L 10 12
0 5
50
0 5
Tetrachloroethylen g/L 10 12
0 5
50
*NBL is shown as a range, for TV assessment upper limit is taken
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Table 5. Natural background levels and TVs of selected water constituents for the Sarmatian and Pleistocene buried-valley aquifer
NBL* 2.3%-97.7%
Substance Unit REF N
10%--90%
TV1 TV2 TV3 TVPL
125—1060 2 310
EC S/cm 2500 36
267—756 1 510
2500
1.12—80.8 162
Cl- mg/L 250 36
1.86—30.0 60
300 3.62—233 242
SO42- mg/L 250 36
5.01—205 228
250
0.05—1.00 1
NH4+ mg/L 0.50 36
0.11—0.84 0.84
1.5
0.002—7.19 7.19
Fe mg/L 0.20 36
0.20—3.75 3.75
5
0.001—0.69 0.69
Mn mg/L 0.05 36
0.058—0.35 0.35
1
0.018—13.7 13.7
As g/L 10 36
0.018—0.65 1.31
100 0.003—0.37 0.74
Pb g/L 10 36
0.016—0.25 0.50
50 0.012—0.13 0.27
Hg g/L 1 36
0.012—0.08 0.15
1
0 5
Trichloroethylen g/L 10 36
0 5
50
0 5
Tetrachloroethylen g/L 10 36
0 5
50
*NBL is shown as a range, for TV assessment upper limit is taken
The TV statistics for the two aquifers considered within the present report are given in Tables 6 and 7. The statistics resulting from the above given formulas are compared with that resulting from the Polish national method (TVPL). The results obtained show that TVs calculated according to the European and Polish standards do not differ significantly, at least in relation to the human receptor.
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Table 6. The TV statistics of selected water constituents for 12 monitoring wells in the shallow Pleistocene aquifer EC
[uS/cm]
Cl- [mg/L]
SO4 2-
[mg/L]
NH4
[mg/L]
Fe [mg/L]
Mn [mg/L]
As [ug/L]
Pb [ug/L]
Hg [ug/L]
Trichloro -ethylene [ug/L]
Tetrachloro- -ethylene [ug/L]
N 12 12 12 12 12 12 12 12 12 12 12
Minimum 320 7.8 19.7 0.03 0.003 0.005 0.37 0.66 0.31 0.025 0.05
Maximum 3075 750 283 151 4.17 1.23 13 2.7 1.61 0.498 1.14
Average 1088 124 113 16.2 0.96 0.37 4.1 1.34 0.86 0.108 0.32
TV97.7 1560 260 195 3 20 1.2 17 4 0.95 5 5
Wells above TV97.7 2 1 2 2 0 1 0 0 5 0 0
% above TV97.7 16.7 8.3 16.7 16.7 0 8.3 0 0 41.7 0 0
TV90 1260 140 180 1.3 4 1 9.3 3 0.86 5 5
Wells above TV90 3 1 2 2 1 2 1 0 5 0 0
% above TV90 25 8.3 16.7 16.7 8.3 16.7 8.3 0 41.7 0 0
TVPL 2500 300 250 1.5 5 1 100 50 1 50 50
Wells above TVPL 1 1 1 2 1 2 0 0 3 0 0
% above TVPL 8.3 8.3 8.3 16.7 8.3 16.7 0 0 25 0 0
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Table 7. The TV statistics of the selected water constituents for 37 monitoring wells in the Sarmatian and Pleistocene buried-valley aquifer EC
[uS/cm]
Cl- [mg/L]
SO4 2-
[mg/L]
NH4
[mg/L]
Fe [mg/L]
Mn [mg/L]
As [ug/L]
Pb [ug/L]
Hg [ug/L]
Trichloro- ethylene [ug/L]
Tetrachloro- ethylene [ug/L]
N 37 37 37 37 37 37 37 37 37 12 12
Minimum 125 1.12 0.38 0.05 0.015 0.001 0.018 0.003 0.012 0.025 0.05
Maximum 2857 295 926 1.68 11.8 1.2 13.7 1.42 1.63 0.128 2.65
Average 642 26.6 110 0.54 2.25 0.242 1.06 0.255 0.157 0.042 0.52
TV97.7 2310 162 242 1 7.19 0.69 13.7 0.74 0.27 5 5
Wells above TV97.7
1 2 5 1 2 2 0 3 4 0 0
% above TV97.7
2.7 5.4 13.5 2.7 5.4 5.4 0 8.1 10.8 0 0
TV90 1510 60 228 0.84 3.75 0.35 1.3 0.50 0.15 5 5
Wells above TV90
2 4 6 4 6 5 6 5 10 0 0
% above TV90 5.4 10.8 16.2 10.8 16.2 13.5 16.2 13.5 27.0 0 0
TVPL 2500 300 250 1.5 5 1 100 50 1 50 50
Wells above TVPL
1 0 4 1 4 1 0 0 1 0 0
% above TVPL 2.7 0 10.8 2.7 10.8 2.7 0 0 2.7 0 0
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4. CONCLUSIONS
The case study presented in this report highlights problems encountered with implementation of the methodology for determination of the Treshold Values (TVs) proposed in the framework of the Bridge project, when applied to complex, multi-aquifer groundwater bodies. Serious problems arise when distinct hydrochemical zones exist within the studied GWB. In the discussed case three zones with the SO42- NBL values of 200, 60 and 20 mg/L were identified. If the highest value is chosen for the determination of the TV for the whole GWB, it should not be understood as acceptation of the appearance of concentrations higher than the initial NBL values in other zones. This generalization may in consequence lead to the situation when possible changes in concentrations in zones with initially low concentrations will be disregarded, though they would indicate appearance or increased influence of anthropogenic or geogenic pollution.
Even small and homogeneous GWBs can be characterized by wide and irregular distributions of NBL values (e.g. as commonly observed for Fe, Mn, SO4 and NH4), which are mainly related to different zones resulting from the conditions of replenishment and timescales associated with travel times of water. Due to that reason, the TV does not necessarily describe adequately the groundwater chemical status. That problem becomes even more acute in presence of anthropogenic influences, and is also of importance for the estimation of uncertainties of the TV values, especially if both the NBL values and the concentrations of anthropogenic pollutants are characterized by wide distributions (see BRIDGE Deliverable D16 - Witczak et al, 2006).
The difficulties outlined above arise to a large extent from the fact that current definition of GWB not precise, particularly in situations when several aquifers exist in the profile of the considered system. In such cases, the NBL values in individual aquifers may differ considerably and their unique representation is not possible. As a consequence, the threshold values (TVs) calculated for the entire GWB may not reflect the true chemical status of groundwater in particular aquifers.
Further problems arise when groundwater-dependent ecosystems are considered. For them, the near surface part(s) of the GWB is (are) the most important. However, the most valuable water resources often exist in confined or semi-confined deeper parts of GWB, which are of little importance for the ecosystems, but are of basic importance as the source of good quality potable water. Therefore, it is virtually not possible to characterize multi-aquifer GWBs by unique NBL and TV values. Perhaps, for such multi-aquifer systems additional definitions should be introduced which would distinguish between the shallow and deeper part of the given GWB.
For instance, one may consider Shallow Ground Water Body (SGWB) and Deep Ground Water Body (DGWB).
Still another problem arises when a large number of small groundwater-dependent ecosystems and numerous local pollution sources exist on the area of a given GWB. The TV values and the status of the entire GWB, determined of the basis of few monitoring sites can be misleading;
some ecosystems can be endangered even in case of a general good chemical status and vice versa, some systems can remain safe in spite of a general poor status.
The above outlined problems can be overcome by introducing a classification of groundwater quality which envisages gradual differentiation of this quality. Such classification was presented 25
in this report. In Poland, the quality of groundwater exploited for drinking purposes is judged according to five quality classes. They can be presented on maps, either for individual monitoring points or in a generalized way for entire GWB. If such classification system is used country-wide, the chemical status of all GWBs and all exploitation wells is comparable on national scale. This system has another important feature, namely it has an “early warning”
principle build-in. This feature allows more flexible management of GWBs and early reaction to any deterioration trends in groundwater quality. Unfortunately, that system does not cover so far the groundwater-dependent ecosystems.
The final note concerns the proposed EU strategy in defining the status of GWBs which states that the threshold values equal to natural background values which are exceeding chosen reference standards, still indicate water of good chemical status. As a consequence, a strange situation is created in which waters of natural poor quality will be regarded by EU regulations as being in good chemical status. This may lead to serious negative consequences, especially for human receptors. This awkward situation can be easily neutralized by introducing adequate definitions of the chemical status of GWB. For instance, one may distinguish between waters of good quality, waters of degraded quality (caused by anthropogenic influences and thus requiring remediation) and waters of poor quality (due to natural reasons). Such modification of definitions would make the situation clear and adequately linked to the reality.
Three selected examples from the Polish territory are given below.
(i) There are two large aquifers in Poland with good quality water except for high fluoride contents up to 8 mg/L. Their exploitation for consumption is forbidden by sanitary inspection.
According to the proposed methodology they would be of good chemical status.
(ii) Waters of natural poor quality (e.g. brines at the Baltic shore in northern Poland, some saline spring in the Carpathians) from deep bodies are sometimes drained locally in near-surface bodies or even as springs on the ground surface. In such cases they influence locally the terrestrial and aquatic ecosystems. Their influence cannot be reduced unless they are exploited, e.g. for balneological purposes.
(iii) In the Busko Spa area, southern Poland, exists an unconfined shallow aquifer containing saline waters with high sulphate and sulphide contents. According to the proposed methodology, that GWB would be of good chemical status, which is unacceptable.
The quality of water from all communal intakes is controlled in Poland by sanitary inspection.
Such controls are limited in comparison with the list contained in Part B of Annex II, but they supply information from a much larger number of sites and should not be ignored in considering the quality status of GWBs.
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