2. CHARACTERISATION OF THE CKS_0200_GWL_1 GROUNDWATER BODY Geographical boundaries. 2.1 Physical and hydrogeological description

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1 Groundwater natural background levels and threshold definition in the CKS_0200_GWL_1 groundwater body of the Central Campine System (Flanders, Belgium). M. Coetsiers & K. Walraevens Laboratory for Applied Geology and Hydrogeology, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium SUMMARY In the frame of the BRIDGE-project the CKS-0200_GWL_1 groundwater body is chosen as a case study in WP4. The aim of this report is to derive and evaluate the threshold values by means of the methodology described in WP3. After a pre-selection on a database with 540 groundwater samples the natural background level is determined as the 90- and 97.7 ; both options are still open in the present development state of the methodology. The threshold values are calculated by comparing the natural background level with a reference value, which is dependent on the receptor. This methodology is applied to the CKS_0200_GWL_1 for four receptors: - groundwater itself - groundwater dependent terrestrial ecosystems - aquatic ecosystems - drinking water 1. INTRODUCTION The Central Campine System is located in the northeast of Flanders, in the provinces of Antwerp and Limburg, at the border with the Netherlands. The Central Campine System is built up partly by the Neogene Aquifer and by the Pleistocene Campine Complex Aquifer. Four groundwater bodies are distinguished of which the CKS_0200_GWL_1 is the largest one. CKS_0200_GWL_1 is made up of the unconfined part of the Neogene Aquifer. The Neogene Aquifer contains large volumes of drinking water resources and is extensively pumped for public water-supply. Furthermore groundwater abstraction for agricultural, industrial and private purposes results in large pumped volumes of groundwater. Drinking water companies in Antwerp, Limburg and Brabant extract about 90 million m 3 per year. Industries, farms and households account for more than 200 million m 3 per year. A large number of groundwater dependent terrestrial ecosystems is present in the discharge areas of the CKS_0200_GWL_1 groundwater body. In the north of the region coalmines and metallurgic industries were operating in the past and have caused pollution with heavy metals.

2 2. CHARACTERISATION OF THE CKS_0200_GWL_1 GROUNDWATER BODY 2.1 Physical and hydrogeological description Geographical boundaries The Central Campine System occurs in the northeast of Flanders where it covers an area of 4210 km 2 and is subdivided into four groundwater bodies (Fig. 1). The Central Campine System is bounded by the occurrence of the Boom Clay in the south and southwest. In the east the boundary is formed by the groundwater divide between the Scheldt and Meuse river basins. Towards the north the Campine basin continues over the border with the Netherlands. The largest groundwater body in the Central Campine System is built up by the unconfined Neogene deposits: CKS_200_GWL_1. In the south an erosion gully is present in the Boom Clay and a different GWB is delineated: CKS_250_GWL_1. Here, the Neogene Aquifer is in direct contact with the underlying Oligocene Aquifer. To the north the semi-confined part of the Neogene Aquifer, where it is overlain by the Campine Clay, is delineated as a separated GWB: CKS_0200_GWL_2. The last GWB is formed by the Pleistocene deposits on top of the Campine Clay: CKS_0220_GWL_1. Both latter groundwater bodies occur in the same region. The groundwater bodies CKS_0200_GWL_1, CKS_0220_GWL_1 and CKS_0200_GWL_2 are cross bordering with the Netherlands. Fig. 1 Location of the groundwater bodies in the Central Campine System, groundwater dependent terrestrial ecosystems and protection zones of drinking water wells The topography is mainly dominated by the occurrence of two cuestas and the Campine Plateau (Fig. 2). In the south the occurrence of the Boom Clay has formed a cuesta in the landscape because clay is less affected by erosion. The rivers Scheldt, Nete and Demer have a breakthrough in this cuesta. In the north the occurrence of the Campine Clay is also expressed in the landscape as a cuesta, which forms the northern watershed between the Scheldt and Meuse basins (Fig. 2). In the southeast and east the Campine Plateau behaves as this watershed. In between these higher elements a saddle-shaped basin is formed. The ground elevation ranges from +100 m a.s.l. on the highest points of the Campine Plateau to less than +5 m a.s.l. in the basin. The river basins are indicated on Fig. 2. The Nete, Demer and Dijle Basin belong to the larger Scheldt Basin. 2

3 Fig. 2: Topography and river basins in the Central Campine System The soils are mainly formed from aeolian Quaternary wind-borne sand deposits, which were deposited at the end of the last glacial period. Most of these wind-borne sand deposits are made up of sand and only a small amount of loam (10 %) is present and an even smaller amount of clay (2 %). By sorting according to grain size a number of soils with finer texture came into existence. In the Campine area the main soil type is podzol, a strongly leached out, acid soil with a poor nutrient content. The main land use in the Campine area is agriculture with 51.2 % of the area, followed by urban use (27.8 %), woodland (12.3 %) and other uses (8.7 %). Groundwater dependent ecosystems are mainly present on the flanks of the saddle-shaped basin (Fig. 1), where groundwater discharge occurs by means of rivulets and small rivers Climate Flanders has a moderate maritime climate, characterized by relatively fresh summers and soft winters, with an average precipitation of 800 mm yr -1 and an average temperature ranging from 2 to 17 C. The rainfall is more or less equally distributed over the entire year (Fig. 3). The temperature on the other hand is lowest during winter and highest during summer (Fig. 3) Water balance The average monthly meteoric data for precipitation and evapotranspiration for the Mol meteoric station are indicated on Fig. 3. The data used for Fig. 3 are based on meteorological data from the Royal Meteorological Institute (KMI) for the period 1970 to It can be seen from Fig. 3 that precipitation exceeds evapotranspiration during the months January, February, March, September, October, November and December. During the other months of the year the evapotranspiration is higher than the precipitation. The average surplus equals 291 mm/yr for the Mol site. CIW (2004) report a surplus of 267 mm/m 2 in CKS_0200_GWL_1 and 238 mm/m 2 for CKS_0250_GWL_1. 3

4 Precipitation Evapotranspiration Surplus Temperature mm/month Temperature ( C) January February March April May June July Augustus September October November December Fig. 3: Monthly average in mm of water balance components (P, ETP, surplus) and temperature at the Mol meteoric station Geology The Campine Basin was filled from Late-Oligocene to Pliocene times with marine to continental sediments. The geology of the area is schematically illustrated in Fig. 4. The deposits dip gently towards the north-northeast and are in the east disturbed by different faults. The base of the aquifer is formed by the occurrence of the Boom Clay, a stiff, silty clay, which reaches a thickness of 60 to 130 m (Laga, 1973). Late-Oligocene Formations of Voort and Eigenbilzen occur at the bottom of the aquifer system. These sediments consist of glauconitic, clayey sands. The Formations of Bolderberg and Berchem represent the Lower-Miocene. The Bolderberg Formation contains glauconitic, micaceous sands with phosphate boulders (mainly vivianite) at the bottom. The upper part of the Bolderberg Formation has a continental origin and consists of white sands with limonitic lenses and lignite layers. In the west the marine Formation of Berchem replaces the Formation of Bolderberg and is composed of glauconitic, slightly clayey sands with layers enriched in shells and phosphate. The Formation of Diest contains strongly glauconitic sands with limonite-sandstones and phosphate concretions. The Pliocene Kasterlee Formation is built up by glauconitic fine sands without fossils. More towards the west the Kattendijk Formation replaces the Kasterlee Formation and contains glauconitic fine, slightly clayey sands with shells and a layer with phosphate nodules at the bottom. The upper Pliocene deposits change from fluviatile in the east (Mol Sands) over coastal sands (Poederlee Sands) to shallow marine sands (Lillo Sands) in the west. The Lillo Sands are clayey in the lower part and contain some shell layers. The Pleistocene Formation of Brasschaat consists of white sands with phosphate minerals and is in the west replaced by the Formation of Merksplas, which is composed of sand with shells and clay lenses. The Formation of Weelde consists of fine sands with clay lenses, which sometimes form a clay layer, and is often referred to as the Campine Complex. 4

5 Fig. 4: Geological cross-section of the groundwater body (location see Fig. 1) Hydrogeology Delineation and type of groundwater body The Central Campine system is divided into four groundwater bodies. Two of these four groundwater bodies (CKS_0200_GWL_1 and CKS_0250_GWL_1) are situated in the Scheldt river basin, while the other two (CKS_0200_GWL_2 and CKS_0220_GWL_1) are situated in the Meuse river basin (Fig 1 and Fig. 2). The type of all these groundwater bodies is Sands and gravels as defined in D9 chapter 4. The groundwater body CKS_0200_GWL_1 consists of a succession of Miocene to Quaternary sands, alternating with more or less important clay layers. The groundwater body has a phreatic nature. Groundwater flow is partly to the Scheldt river (in the western part) and to the Nete river in the south (in the central part). The groundwater body CKS_0200_GWL_1 is at the bottom delineated by the Boom Aquitard, at the top by the topography, and in the northern part by the appearance of the Campine Complex. The eastern and northern boundaries are formed by a combination of the border with the Netherlands and the water divide between Scheldt and Meuse river basins. The western boundary is formed by the Dutch border, the outcropping of the Boom Clay (where the Neogene Aquifer is absent) and by the occurrence of salinized groundwater. The outcrop area of the Boom Clay defines the southern boundary. The salinized part in the west is defined as a different groundwater body and is subdivided with the Coast and Polder System. The unconfined groundwater body CKS_0250_GWL_1 is built up by a excavated gully that was excavated through the Boom Clay during the Miocene, and that was later filled up with Sands of Diest. This groundwater body is built up by sand and sandstone banks. Groundwater flow is determined by the topography but is strongly influenced by the Demer river basin. The lower limit of this groundwater body is the bottom of the Sands of Diest and the upper limit is the topography. In the east, west and north the GWB is delimited by the occurrence of the Boom Aquitard. The southern and a part of the western boundary are formed by the absence of the Sands of Diest. 5

6 Groundwater body CKS_0220_GWL_1 consists of the Quaternary Aquifer system, with alluvial covering layers and in the northeast deposits of the High Terrace, and the Campine Aquifer System, with the Campine Clay-Sand Complex. The bottom of the GWB is formed by the occurrence of the base of the Campine Complex, which mainly consists of the Clay of Rijkevorsel. The western boundary is partly formed by the salinized area and the Dutch border. The groundwater body CKS_0200_GWL_2 is at the top delimited by the base of the Campine Complex and at the bottom by the top of the Boom Aquitard. The northern, western and eastern boundaries are formed by the Dutch border. The southern boundary is coinciding with the water shed between the Meuse Basin and the Scheldt Basin. Groundwater flow is orientated northwards, towards the Meuse river Hydrodynamics Groundwater recharge takes mainly place in the topographically elevated areas like the Campine Plateau and the cuesta of the Campine Complex. A calculated piezometric map (Coetsiers et al., 2005) in natural conditions for the groundwater bodies CKS_0200_GWL_1, CKS_0250_GWL_1 and CKS_0200_GWL_2 is given in Fig. 5. Table 1 gives the main hydraulic properties of the different groundwater bodies in the Central Campine System. Groundwater infiltrating on the west side of the Campine Plateau will flow towards the Scheldt basin in the west, while water infiltrating on the east side of the plateau flows towards the Meuse basin. In the north of the study area groundwater infiltrates mainly on the cuesta of the Campine Complex. Water infiltrating on the south flank will flow to the Scheldt basin and water infiltrating on the north side will flow to the Meuse basin. In the south of the study area, smaller local infiltration areas exist where remnant hills form topographical elevations. In between the small rivers local recharge areas are present resulting in small flow cycles that are superposed on the regional groundwater flow cycle. Groundwater discharge occurs mainly by outflow to rivers and rivulets in the lower lying areas Table 1: Main hydraulic properties of the groundwater bodies (CIW, 2004 after Bronders & De Smedt, 1991) GWB Thickness (m) Kh (m/d) T (m 2 /d) Average precipitation (mm/year) Recharge (mm/year) CKS_0200_gwl_ *10 2 to 8.78*10 2 CKS_0250_gwl_ *10 2 to 8.78*10 2 CKS_0200_gwl_ *10-6 to 4.88*10-4 to CKS_0220_gwl_ *10-5 to * *10-4 to

7 Piezometry m Rivers and Fig. 5: Calculated potentiometric map of the study area with indication of rivers and main groundwater flow directions in the groundwater bodies CKS_0200_GWL_1, CKS_0250_GWL_1 and CKS_0200_GWL_2 (Coetsiers et al., 2005) Hydrogeochemistry Coetsiers & Walraevens (2006) studied the evolution of groundwater quality along a groundwater flow line in the Neogene Aquifer and found following reactions to be important: silicate dissolution, redox reactions, calcite dissolution and cation exchange. Shallow groundwater in CKS_0200_GWL_1 has a low mineralisation and is acid because the groundwater body is largely decalcified. The Sands of Berchem to the west and in the deeper parts of the GWB and the Sands of Lillo to the north still contain calcite, resulting in calcite dissolution reactions (crosshatched parts in Fig. 6). In the largest part of the aquifer, silicate dissolution will influence groundwater quality by increasing the cation and silicate content. Redox reactions play an important role in the chemistry of groundwater quality in CKS_0200_GWL_1. A succession of oxic, suboxic, nitric, Mn, Fe, sulphidic and methanic zones is observed in this GWB (Coetsiers & Walraevens, 2006). On Fig. 6 the redox zones are indicated in the profile. Oxygen and nitrate are consumed in the uppermost meters, followed by the reduction of Mn and Fe oxides and hydroxides. Deeper in the groundwater body sulphate reduction occurs. In the deepest parts of the groundwater body the marine depositional environment is still slightly present and cation exchange occurs, leading to the exchange of Ca 2+ from the groundwater for Na +, K + and Mg 2+ adsorbed to the clay minerals. Pyrite oxidation in the unsaturated zone causes an increase in sulphate content. Elevated arsenic concentrations are encountered and are related to redox conditions. The Fe 2+ originating from pyrite oxidation is immediately oxidized to Fe 3+ and precipitates as oxides or hydroxides. The arsenic and other heavy metals released from the oxidation of pyrite are incorporated in these iron oxides and hydroxides. In more strongly reducing conditions the arsenic enters into solution by reduction of the iron (hydr)oxides. Phosphate concentrations in groundwater can locally be high due to the dissolution of the phosphate mineral vivianite (Fe 3 (PO 4 ) 2.8H 2 O). The precipitation of hydroxyapatite can remove phosphate from the groundwater. Agricultural pollution gives rise to the local appearance of CaNO 3 water types in shallow wells. 7

8 Diffuse pollution from former metallurgic industries and mining activities is responsible for elevated Zn, Ni, Cd, Pb and Cu concentrations (Walraevens et al., 2003). Fig. 6: Characterization of groundwater hydrochemical evolution along flowpath showing redox boundaries, recharge - throughflow-discharge zones (crosshatching indicates presence of calcite) Groundwater receptors Groundwater receptors for the CKS_0200_GWL_1 are in the first place groundwater itself. Secondly a large number of groundwater dependent terrestrial ecosystems are present and thus groundwater dependent terrestrial ecosystems is the second receptor. The third receptor is formed by aquatic ecosystems. Finally drinking water is considered, although it is not a receptor considered in the BRIDGE project, since public drinking water companies pump large amounts of groundwater. On Fig.1 the groundwater protection zones for public drinking water companies are indicated in red, while the groundwater dependent terrestrial ecosystems are indicated in green. The dependent aquatic and terrestrial ecosystems and protected areas are mainly rivers and wetlands, which are fed by groundwater. These zones coincide with areas where groundwater outflow occurs. Fig. 7 shows the results of a regional groundwater flow model and the groundwater discharge zones are indicated in green. The areas with a nature function that coincide with humid and wet areas are delineated as the groundwater dependent terrestrial ecosystems. All surface waters in Flanders have to comply with the basic water quality standards. Selected surface waters in Flanders have been designated a specific destination (drinking water, swimming water, fish water and shellfish water) according to the Decision of the Flemish Executive of 21/10/1987 B.S. 6/1/1988) (Fig. 8). Specific, more stringent standards have been set for specific destinations. Most surface waters in Flanders have to comply to the basic quality. In canals the water has the destination fish and drinking water and only a small amount of rivers has fish or drinking water destinations (Fig. 8). 8

9 Fig. 7: Hydrodynamical model of the Neogene aquifer in North-Belgium, piezometric levels and discharge zones (Coetsiers et al., 2005) Fig. 8: Destination of surface waters according to the Flemish Executive of 21/10/1987 (B.S. 6/1/1988) 2.2 Identification of pressures Groundwater abstraction The Neogene aquifer is a very important resource for drinking water abstraction. In the Neogene Aquifer more than 300 M m 3 /year is abstracted for drinking water, industrial uses, agricultural uses and private households. Fig. 9 indicates the largest groundwater abstraction points in the 9

10 aquifer. Most of these wells are situated in the CKS_0200_GWL_1 groundwater body. A preliminary quantitative evaluation of the groundwater body was done in CIW (2004) by looking at time series of piezometric measurements of more than 10 years. The CKS_0200_GWL_1 has a stable trend with seasonal variations and has been given a good quantitative status although the number of measuring points in the groundwater body is low. Fig. 9: Location of pressures: large groundwater extraction wells and point sources of pollution Pollution Diffuse sources A preliminary qualitative evaluation of the groundwater bodies in Flanders is based on the nitrate concentration in the phreatic monitoring network. This phreatic monitoring network contains ca monitoring points in Flanders. The Flemish Environmental Administration (AMINAL) defines a good qualitative status if at least 95 % of monitoring points in the GWB is not exceeding the standard for nitrate (50 mg/l). By doing so, all phreatic groundwater bodies, like CKS_0200_GWL_1 have a poor status and are at risk. Diffuse pollution from former metallurgic industries and mining activities is responsible for elevated Zn, Ni, Cd, Pb and Cu concentrations in the CKS_0200_GWL_1 (Walraevens et al., 2003) Point sources The identification of point sources of groundwater pollution is based on following criteria (CIW, 2004): Groundwater pollution must be an issue, in the sense that the Flemish soil sanitation standards for groundwater have been exceeded The point source must contaminate a relevant part of the groundwater. The Flemish Public Waste Agency (OVAM) has put forward a contaminated volume of soil of at least 1 million m 3. 10

11 There are/were no measures undertaken to remove the pollution or to have control on the pollution. Different pollutions from point sources are being or have already been cleaned up, for others the research stage is finished and these will be sanitated in the near future. Those cases were not considered. In CKS_0200_GWL_1 there are three point sources of pollution: the nonferrous pollution in Balen and Olen and the chloride pollution at the river Grote Laak. These point sources are linked to heavy polluting industry in the past. OVAM chooses not to mention other smaller point sources, as it is believed that these small contamination plumes don t affect a relevant part of the groundwater body and steps are taken to remove or control the impact on the groundwater. The groundwater pollution with heavy metals in Balen is caused by different point and line sources. The largest part of the pollution is due to indirect draining and leaching out. A large amount of heavy metals has fallen in the neighbourhood of the industrial sites by means of atmospheric deposition. The residues (cinders) of these nonferrous activities were used for asphalting of roads and heightening of land. 2.3 Conceptual model The CKS_0200_GWL_1 groundwater body is a large unconfined groundwater body. Pressures on the groundwater body include large groundwater abstraction (Fig. 8), diffuse pollution by agricultural activities and point sources of pollution by nonferrous industries. The main geochemical processes that determine groundwater quality in the CKS_0200_GWL_1 are redox reactions, calcite dissolution, silicate dissolution and cation exchange. The groundwater flow is simulated by means of a regional groundwater flow model indicating the recharge and discharge areas. Groundwater flow is mainly influenced by the topography of the area. There are four main receptors for groundwater in the CKS_0200_GWL_1: groundwater itself, groundwater dependent terrestrial ecosystems, aquatic ecosystems and drinking water. 2.4 Review of impacts Monitoring networks (groundwater and surface water) The primary monitoring network in Flanders consists of monitoring wells with one or more screens in the major aquifers and contains a total of 376 screens. Piezometric measurements are executed monthly but groundwater chemistry is up to now not measured on a regular base. For 62 wells groundwater quality was analysed in 2004 for the parameters ph, EC, T, O 2, Eh, TOC, Na +, K +, Mg 2+, NH 4 +, Ca 2+, Fe tot, Mn 2+, Al 3+, Cl -, SO 4 2-, HCO 3 -, CO 3 2-, NO 3 -, NO 2 - and PO During about 130 deep monitoring wells with screens in the major aquifers are being installed in Flanders to enlarge the primary monitoring network. 42 screens of the primary network at 24 locations are installed in the CKS_0200_GWL_1 groundwater body (Fig. 10). The phreatic monitoring network contains 2113 wells with ca monitoring points and is operational since the beginning of 2004 (Eppinger, 2005). Nearly each well is equipped with three screens at different depths. Twice to four times a year the groundwater quality is analysed and piezometry is measured. The measured parameters are dissolved oxygen (O 2 ), electrical conductivity (EC), ph, redox potential (Eh), TOC, Na +, K +, Mg 2+, Ca 2+, NH 4 +, Fe tot, Mn 2+, Al 3+, Cl -, SO 4 2-, HCO 3 -, CO 3 2-, NO 3 -, NO 2 - and PO screens of the phreatic monitoring network at 254 locations are installed in the CKS_0200_GWL_1 groundwater body (Fig. 10). Other monitoring networks include networks for temporary projects (like sanitation projects), the shallow network in nature reserves, monitoring wells of drinking water companies, monitoring wells of private companies and extraction wells. The surface water monitoring network in Flanders contains 3250 measuring points in brooks, rivers, canals, lakes and the sea. These points are not all sampled in one year. There is a subdivision into different monitoring networks: the physico-chemical, Nutrient Management Plan, biological, bacteriological and water soils monitoring networks. 11

12 Fig. 10: Location of the monitoring wells of the primary network and of the phreatic network in CKS_0200_GWL_ Effects of abstraction on groundwater quantity Extensive pumping takes place in the Neogene Aquifer with extraction of more than 300 M m 3 of groundwater per year. Fig. 11 shows the results of the regional groundwater flow model of the Neogene Aquifer taking large pumping activities into account (Coetsiers, in prep). Groundwater depression cones are present close to large pumping wells. Close to large pumping activities the groundwater flow pattern will be disturbed although the overall groundwater flow still reflects the natural flow pattern. 12

13 Piezometry m Rivers and Fig. 11: Calculated groundwater piezometry influenced by groundwater extraction in CKS- 0200_GWL_1, CKS_0200_GWL_2 and CKS_0250_GWL_1 (Coetsiers, in prep) Effects of abstraction on groundwater quality Salinisation Not relevant / not known Changes in redox conditions Lowering of the water table in the neighbourhood of pumping wells can cause changes in the redox environment in the aquifer. A larger part of the aquifer becomes oxidized leading to the oxidation of pyrite, which was formerly present in the reduced zone. Pyrite oxidation can lead to an increase of the arsenic content in the groundwater. This phenomenon is observed in a pumping well at Ravels where a clear increase in arsenic is observed from 1990 to 2000 (Fig. 12). Fig. 12: Time series of arsenic in the pumping well of Ravels 13

14 Other geochemical processes Not relevant / not known Effects of abstraction on dependent ecosystems Evaluate impacts on discharge to dependent aquatic and terrestrial ecosystems. Estimate the induced decrease in surface water flow and water level in terrestrial ecosystems. No data available Effects of artificial recharge Consider both groundwater quantity and quality issues and effects on dependent ecosystems At Grobbendonk an artificial recharge pilot project is running since Water from the Albert Canal is infiltrating in an open basin in order to compensate the lowering of the groundwater table caused by drinking water extraction. The canal water has undergone purification before it is infiltrated. The total infiltration capacity is 150 m 3 per hour in the sand layers of the Formation of Diest and Berchem. There is however no chemical data available Effects of pollutant pressures on groundwater quality As anthropogenic pollution mainly affects the phreatic zone of groundwater systems, the qualitative evaluation in the Flemish region is limited to phreatic or shallow groundwater bodies. The preliminary evaluation of groundwater quality was performed for each groundwater body by means of the results of the phreatic monitoring network, focusing on the nitrate concentration. The phreatic groundwater bodies CKS_0200_GWL_1, CKS_0250_GWL_1 and CKS_0220_GWL_1 have a poor qualitative status while the semi-confined groundwater body CKS_0200_GWL_2 has a good status. Fig. 13 shows the zone of the aquifer influenced by nitrate contamination. In the uppermost meters of the groundwater body high nitrate concentrations are encountered and deeper in the groundwater reservoir nitrate reduction occurs. Fig.13 Cross-section with zone of influence indicated (NO 3 concentration) (Coetsiers, in prep) 14

15 2.4.7 Effect of groundwater induced pollutant pressures on dependent ecosystems Estimate groundwater induced loads (if possible relative to total surface water load in a baseflow situation) Shallow groundwater in nature reserves can contain high levels of nitrate (NARA, 2003). Measurement data of 96 nature reserves in Flanders and 1448 monitoring points is available. These measurements were obtained from different studies with various objectives and don t give a representative picture but rather an indication. For 18 % of the investigated nature reserves at least one well exceeds the nitrate standard of 50 mg/l Pollutants selected for threshold methodology evaluation The threshold methodology is applied to parameters of the Environmental Quality Standards (EQS) for each receptor for which analytical data was available. The EQS used for each receptor are: - groundwater itself: Environmental Quality Standards for groundwater as defined in the VLAREM II legislation (Annex 2.41 of VLAREM II) - groundwater dependent terrestrial ecosystems: the Environmental Quality Standards (EQS) for List 1 and List 2 dangerous substances and for Hardness Related List 2 dangerous substances - EC Dangerous Substances Directive (76/464/EEC) - aquatic ecosystems: EQS for surface water as defined in the VLAREM II legislation as a function of the destination (Annex for basic EQS for surface water, Annex for EQS for surface water reserved for drinking water, Annex for EQS for surface water with swimming water destination, Annex for EQS for surface water with fish water destination and Annex for EQS for surface water with shellfish destination) - drinking water: drinking water standards The parameters that are handled are: ph, EC, Na, K, Ca, Mg, Fe, Mn, NH 4, SO 4, NO 3, NO 2, PO 4, Al, Zn, As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, F and B. 15

16 3. GROUNDWATER STATUS EVALUATION BY THRESHOLD VALUES 3.1 Application and evaluation of proposed threshold methodology 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 Assessing the Natural Background Level (NBL) The CKS_0200_GWL_1 groundwater body belongs to unconsolidated aquifer group (WP1) and more detailed to the Sands and gravels (WP2). There is no national approach to derive natural background levels in groundwater in Flanders but a large amount of monitoring data is available. For this reason the natural background levels are derived based on the simplified pre-selection approach as described in Annex 1 of D15. A database with chemical analyses of 540 groundwater samples is available. Groundwater samples with NO 3 > 10 mg/l were excluded from the database. Furthermore the database should fulfill some minimum requirements: samples with an error > 10% on the ionic balance should be removed samples of unknown depth should be removed monitoring data not attachable to WP1 aquifer typologies should be removed data from hydrothermal aquifers should be removed data from salty aquifers should be removed time series should be eliminated by median averaging After pre-selection and data processing analysis of 453 groundwater samples remained. For statistical purpose half of the detection limit was used for samples with analytical results below detection limit. The natural background level (NBL) is determined as the concentration at the 90- or the 97.7-; both are presented in Table 2. In case of ph the 10- and 2.3- are used to define the lower boundary for the NBL. Table 2: Determination of the Natural Background Level (NBL) based on the 90 and 97.7 s and number of samples used and maximum value per parameter. parameter Unit Number after Maximum pre-selection ph ph O 2 mg/l EC µs/cm Na ppm K ppm Ca ppm Mg ppm Fe ppm Mn ppm NH4 ppm Cl ppm SO 4 ppm HCO 3 ppm NO 3 ppm NO 2 ppm PO 4 ppm Al ppb Zn ppm As ppb Cd ppb Cr ppb Cu ppb Hg ppb Ni ppb

17 parameter Unit Number after Maximum pre-selection Pb ppb Sb ppb Sr ppb B ppb F ppb Selection of the Reference Quality Standard Threshold values (TV) are established with reference to natural background levels (NBL) and a chosen reference standard (REF). There are 3 possible cases for calculating the TV: - 1: if NBL REF (but > 1/3 REF): TV = (REF + NBL)/2-2: if NBL 1/3 REF: TV = 2 NBL - 3: if NBL REF: TV = NBL The receptors for groundwater of the CKS_0200_GWL_1 groundwater body are groundwater itself, groundwater dependent terrestrial ecosystems, aquatic ecosystems and drinking water. In Flanders authorities are legally bound by VLAREM II (Decision of the Flemish Government implying general and sectoral provisions towards environmental protection (VLAREM II) (June 1, 1995; BS July 31,1995)) to handle the defined environmental quality standards for the planning and the execution of the policy. The standards are guiding the evaluation of requests for environmental licenses. The REF values used for the different receptors are: - groundwater itself : the Environmental Quality Standards for groundwater as defined in the Vlarem II legislation. These standards however are largely based on drinking water standards. - groundwater dependent terrestrial ecosystems : the Environmental Quality Standards (EQS) for List 1 and List 2 dangerous substances and for Hardness Related List 2 dangerous substances EC Dangerous Substances Directive (76/464/EEC). - aquatic ecosystems : EQS for surface water as a function of the destination defined in VLAREM II are used. - drinking water : Drinking water standards 3.2 Results and compliance testing The threshold values are calculated for the receptors groundwater itself, groundwater dependent terrestrial ecosystems, aquatic ecosystems and drinking water supply. The results of the calculation of TVs for groundwater itself as a receptor are given in Table 3. Table 4, 5 and 6 show the threshold values calculated for groundwater dependent terrestrial ecosystems as receptor. Tables 5 and 6 show the results of the TV derivation for the hardness related dangerous substances with the 90- and respectively. Of these lists, only analytical data for ph, As, Cd, Hg, Fe, B, Cr, Cu, Pb, Ni and Zn are available and are evaluated for the proposed methodology. Table 7 shows the threshold values for the receptor aquatic ecosystems with the basic water quality standards. Tables 8 and 9 show the results for the aquatic ecosystems with drinking water and fish water as a destination. Finally Table 10 shows the threshold values for the receptor drinking water supply. In case of ph the 10- and 2.3- are used to define the lower boundary for the NBL. 17

18 Table 3: Determination of threshold values (TV) for 90- and NBL and for Maximum Admissible Concentration (MAC) of the Environmental Quality Standards for groundwater (VLAREM II) used as the reference standard (REF) (receptor: groundwater itself) Parameter Unit REF 90- TV TV Na ppm K ppm Mg ppm Fe ppm Mn ppm NH4 ppm SO4 ppm NO3 ppm NO2 ppm PO4 ppm Al ppb As ppb Cd ppb Cr ppb Hg ppb Ni ppb Pb ppb Sb ppb F ppb Table 4: Determination of threshold values (TV) for 90- and NBL and for Environmental Quality Standards for Dangerous Substances used as REF (receptor: groundwater dependent terrestrial ecosystems) Parameter Unit REF 90- TV TV ph (high) ph (low) As ppb Cd ppb Hg ppb Fe ppm B ppm

19 Paramete Table 5: Threshold value derivation for Environmental Quality Standards for hardness related List 2 dangerous substances (EC dangerous Substances Directive (76/464/EEC) as REF (receptor: groundwater dependent terrestrial ecosystems) and for the 90- as NBL 0-50 mg/l CaCO 3 > mg/l CaCO 3 > mg/l CaCO 3 > mg/l CaCO 3 > mg/l CaCO 3 >250 mg/l CaCO 3 r REF 90 % TV REF 90 % TV REF 90% TV Cr Cu Pb Ni Zn REF 90% TV REF 90% TV REF 90 % TV

20 Table 6: Threshold value derivation for Environmental Quality Standards for hardness related List 2 dangerous substances (EC dangerous Substances Directive (76/464/EEC) as REF (receptor: groundwater dependent terrestrial ecosystems) and for the as NBL 0-50 mg/l CaCO 3 > mg/l CaCO 3 > mg/l CaCO 3 > mg/l CaCO 3 > mg/l CaCO 3 >250 mg/l CaCO 3 Paramete r REF 97.7 % TV REF 97.7 % TV REF 97.7 % TV Cr Cu Pb Ni Zn Zn REF 97.7 % TV REF 97.7 % TV REF 97.7 % TV 20

21 Table 7: Determination of threshold values (TV) for 90- and NBL and for EQS for surface water, basic water quality standards, used as REF (receptor: aquatic ecosystems) parameter Unit REF 90- TV TV O 2 ppm ph (high) ph (low) EC µs/cm NH 4 -N ppm NO 3 +NO 2 ppm P ppm Cl ppm SO4 ppm Cu ppb Pb ppb Zn ppb Cr ppb Ni ppb As ppb Fe ppb Mn ppb Cd ppb Hg ppb Table 8: Determination of threshold values (TV) for 90- and NBL and for EQS for surface water with drinking water destination used as REF (receptor: aquatic ecosystems) parameter Unit REF 90- TV TV ph (high) ph (low) EC µs/cm NH 4 ppm NO 3 ppm Cl ppm Cu ppb Pb ppb Zn ppb Cr ppb Ni ppb As ppb Fe ppb Mn ppb Cd ppb Hg ppb

22 F ppm B ppm Table 9: Determination of threshold values (TV) for 90- and NBL and for EQS for surface water with fish water destination used as REF (receptor: aquatic ecosystems) parameter Unit REF 90- TV TV ph (high) ph (low) NH 4 ppm P ppm Cu ppb Zn ppb NO 2 ppm Table 10: Determination of threshold values (TV) for 90- and NBL and for Drinking Water Standards used as REF (receptor: drinking water supply) parameter Unit REF 90- TV TV ph (high) ph (low) EC µs/cm Ca ppm Mg ppm Na ppm K ppm PO 4 ppm Fe ppm Mn ppm NO 3 ppm NO 2 ppm NH 4 ppm Cl ppm SO 4 ppm Al ppb As ppb Zn ppm Cd ppb Cr ppb Cu ppb Hg ppb Ni ppb Pb ppb Sb ppb

23 parameter Unit REF 90- TV TV F ppm B ppb The calculated threshold values are larger than the REF values (case 3) in the case of groundwater itself as a receptor for: 90-: Fe (44.2 > 0.2 mg/l), Mn (1.1 > 0.05 mg/l), NH 4 (1 > 0.5 mg/l) and Al (1554 > 200 µg/l) 97.7-: K (22.1 > 12 mg/l), Fe (87 > 0.2 mg/l), Mn (2.6 > 0.05 mg/l), NH 4 (4.1 > 0.5 mg/l), SO 4 (311 > 250 mg/l), PO 4 (2.5 > 2.2 mg/l), Al (2934 > 200 µg/l) and As (69 > 50 µg/l) In the case of TV determination for the receptor groundwater dependent terrestrial ecosystems the TV is larger than the REF for: 90-: ph (5.0 < 6.0) and Fe (44.2 > 1 mg/l) 97.7-: ph (4.0 < 6.0), Fe (87 > 1 mg/l) and As (69 > 50 µg/l) For the hardness related dangerous substances the TV is higher than REF for Cr, Cu, Pb and Zn for different hardness bands in the case of the 90- and for Cr, Cu, Pb, Ni and Zn in the case of the The highest number of TVs above REF occurs for the lowest hardness band (Tables 5 and 6). The calculated TV for the receptor aquatic ecosystems in the case of basic surface water quality is above REF for: 90-: ph (5.0 < 6.5), Fe (44200 > 200 ppb), Mn (1100 > 100 ppb) 97.7-: O 2 (5.9 > 5 mg/l), ph (4.0 < 6.5), SO4 (311 > 250 ppm), Zn (420 > 200 ppb), As (69> 30 ppb), Fe (87000> 200 ppb), Mn (2600 > 100 ppb) In the case of drinking water destination of surface water the TV is larger than REF for: 90-: ph (5.0 < 5.5), Fe (44200 > 200 ppb) and Mn (1100 > 1000 ppb) 97.7-: ph (4.0 > 5.5), Fe (87000 > 200 ppb) and Mn (2600 > 1000 ppb) In the case of fish water destination of surface water the TV is above REF for: 90-: ph (5.0 < 6), 97.7-: ph (4.0 < 6), NH 4 (3.2 >1 ppm) and NO 2 (0.07 > 0.07 ppm) The TVs for the receptor drinking water are larger than the REF for the same parameters as for the receptor groundwater itself and: 90-: ph (5 < 5.5) 97.7-: ph (4 < 5.5) and PO 4 (2.5 > 2.2 mg/l) Generally it is seen that for the calculations, TV is above REF for more parameters. Since these higher TVs for K, Fe, Mn, NH 4 SO 4, PO 4, Al and As have a natural origin, it is recommended to use the in preference to the 90-. The obtained NBL and TV for the receptor groundwater itself are compared to the standards for groundwater sanitation defined in the Flemish Soil Sanitation Legislation (VLAREBO), shown in Table 11. The TV for arsenic is higher than the sanitation standard for the calculation with the 90- and 97.7-, which indicates that the sanitation standard is too stringent. Furthermore the TV obtained with the calculation exceeds the sanitation standard for nickel and zinc. The other parameters have TV below the sanitation standards. Walraevens et al. (2003) remark that there are strong indications that the BS is too low compared to the natural values observed in Flanders for Zn and As. For the other parameters they found no convincing ground to reconsider the BS. 23

24 Table 11: Comparison of TV at 90- and and standards for groundwater sanitation in the Flemish Soil Sanitation Legislation (VLAREBO) Heavy Sanitation Background TV 90- TV metals and standard standard metalloids (µg/l) (µg/l) Arsenic Cadmium Chromium Copper Mercury Lead Nickel Zinc CONCLUSIONS Groundwater quality threshold values for the CKS_0200_GWL_1 groundwater body are calculated for 4 different receptors: - groundwater itself - groundwater dependent terrestrial ecosystems - aquatic ecosystems - drinking water In a first step the natural background level (NBL) is calculated in case of the 90- and s. The TVs are calculated based on the NBL and a REF value derived from environmental quality standards. The REF values vary between the different receptors. The calculated TV exceeds the existing REF values for: - groundwater itself : 90-: Fe, Mn, NH 4 and Al 97.7-: K, Fe, Mn, NH4, SO 4, PO 4, Al and As - groundwater dependent terrestrial ecosystems : 90-: ph and Fe, Cr, Cu, Pb and Zn 97.7-: ph, Fe, As, Cr, Cu, Pb, Ni and Zn - aquatic ecosystems - basic : 90-: ph, Fe and Mn 97.7-: O 2, ph, SO 4, Zn, As, Fe and Mn - aquatic ecosystems - drinking water : 90-: ph, Fe and Mn 97.7-: ph, Fe and Mn - aquatic ecosystems fish water : 90-: ph 97.7-: ph, NH 4 and NO 2 The CKS-0200_GWL_1 is characterized by low ph and high levels of iron, manganese, arsenic, NH4, PO 4, aluminum, sulphate and zinc. The exceedings of the REF at the are thus of a natural origin and it is recommended to use the for the NBL rather than the 90- since geochemistry of the groundwater body is well known. There was no data available to take into account attenuation and dilution. 24

25 5. REFERENCES Bronders, J. & De Smedt, F. (1991). Geostatistical anaysis of the hydraulic conductivity from water bearing layers in Middle- Belgium (in Dutch). Water, 59, p Coetsiers, M. (in prep.). Hydrogeological and hydrogeochemical investigation of the Neogene Aquifer in the northeast of Flanders (in Dutch). PhD thesis, Ghent University Coetsiers, M., Van Camp, M. & Walraevens, K. (2005). Influence of the former marine conditions on groundwater quality in the Neogene phreatic Aquifer, Flanders. In: Araguas, L., Custodio, E. and Manzano, M. (Eds.) Groundwater and saline intrusion selected papers from the 18 th Salt Water Intrusion Meeting, Cartagena, Spain, pp Coetsiers, M. & Walraevens, K. (2006). Chemical characterization of the Neogene Aquifer, Belgium. Hydrogeology Journal, published online DOI /s Coördination Commission Integral Water Policy (CIW) (2004). Characterisation of the Flemish part of the international stream district of the Scheldt (in Dutch). Eppinger, R. (2005). The phreatic groundwater monitoring network a new view on the quality evolution of shallow groundwater in Flanders with respect to the occurrence of nitrate (in Dutch). Water NARA (2003). Dumortier, M., De Bruyn, L., Peymen, J., Schneiders, A., Van Daele, T., Weyemberg, G. Van Straaten, D., Kuijken, E.. Natuurrapport (Red.) State of the nature in Flanders: figures for the policy (in Dutch). Communications of the Institute for Nature Preservation, Brussels, 21, pp 352. Walraevens, K., Mahauden, M. & Coetsiers, M. (2003). Natural background concentrations of trace elements in aquifers of the Flemish Region, as a reference for the governmental sanitation policy. 8 th International FZK/TNO Conference on Contaminated Soil (ConSoil), Ghent 2003, Proceedings, pp