European Water Framework Directive
Results of the initial characterisation of the groundwater bodies in the state Hesse, FRG
J.-G. Fritsche, Bernd Leßmann [1]
1.Groundwater Bodies in Hesse and SurroundingAreas
Delimitation: River catchment areas of 1.500-5000 km2 (groups of groundwater bodies) have been intersected with hydrogeological subzones to establish 127 groundwater bodies with an average area of 173 km2. The delimitation of groundwater bodies at the Hessian borderline has been coordinated with the neighbouring states.
2.Hydrogeological Subregions in Hesse
Entire Germany has been divided into large hydrogeological regions, hydrogeological regions and hydrogeological subregionsby the geological surveys and the BGR in close cooperation. The common and most important hydraulic and geochemical characteristics of the geological strata determine each of these subregions, giving a spatial survey. 25 hydrogeological subregions are covering Hesse. In addition to the map, texts and lists have been worked out, describing the characteristics of the hydrogeological units in each subregion (e.g. rock type, consolidation, hydraulic conductivity, geochemical type of rocks, type of porosity and intensity of groundwater abstraction). The map is one part of a project to establish a hydrogeological map of Germany in scale 1 : 200.000 to meet the needs of the EU-WFD.
3.Characterisation of the Overlying Strata of the Aquifers
The map is based on a previously published vulnerability map of Hessia, scale 1 : 300.000 (A. Hoppe & G. Mittelbach (1999): Geowissenschaftlicher Atlas von Hessen. –Geologie in Hessen, Bd. 4. HLfB, Wiesbaden). The 5 classes of vulnerability of the aquifers shown there, had been derived from the geological strata represented in the Geological Map of Hessia, scale 1 : 300.000. The protection property resulted from a divisioninto 3 classes according to the LAWA (Länderarbeitsgemeinschaft Wasser) working aid recommendations. In this map, only the properties of wide-spreading lithological units have been estimated empirically, the soil properties and the depths to water table havenot been taken into consideration. Therefore, this map is to be understood only as a general survey.
4.Inventory of GroundwaterAssociated Surface Systems (e.g. Terrestrial Ecosystems)
For this theme, a great amount of different layers has been considered, e.g. nature protection areas, FFH-areas (Fauna, Flora, Habitat), groundwaterdependent biotopes, groundwater influenced soils and others. The examination has shown that there is no groundwater body without groundwaterdependent biotopes. This means that there will be a further characterisation carried out on every groundwater body in Hesse. In the further characterisation, only the groundwaterdependent biotopes lying in nature- and FFH-protection areas and in the area of influence of artificial abstraction of groundwater, combined with depths to water table less than 10 m, will be examined.
5.Groundwater Quality Status: Point Sources of Pollution
For the point sources, the Hessian register of contaminated sites and former waste disposal sites (ALTIS) has been evaluated. The risk assessment concentrated on the sites where a need for remediation had been found out. As a result, 457 contaminated sites and 222 former waste disposal sites were selected. To refer to an area of impact of these contaminations on the groundwater, a circle of 1 km2 around each site was set into relation to the area of the groundwater body affected. The “at risk” criterion of 33% of the area of a groundwater body covered by the impact areas is not reached in any of the groundwater bodies.
6.Groundwater Quality Status: Diffuse sources of Pollution
For the estimation of the possible risk caused by diffuse sources, three factors have been taken into consideration in the initial characterisation:
1. Nitrogen balance surplus on agricultural areas (Bach et. al., 1999), input of 20 kg/ha N in forest areas and 5 kg/ha N in remaining areas. If more than 33% of these areas in a groundwater body have got an average N-content of more than 50 kg/ha, the groundwater body is estimated to be “at risk”.
2. Share of settlement areas related to the areas of the groundwater bodies (more than 33%: “at risk”).
3. NO3-Concentration in the groundwater (wells, springs, piezometers), selected from the Hessian Groundwater Data Bank (GRUWAH). These values have been extrapolated to small catchment areas (<10 km2). Criterion of being “at risk”: An area of more than 33% of a groundwater body is covered by small catchment areas with more than 25 mg/l NO3 in the groundwater.
Further characterisation:
- The Nitrogene balance surplus is converted into Nitrate concentrations of the seepage water(mg NO³/l = (N-balance [kg N/ha]*4,43*100) / GWrecharge).
- For the GWB stated “possibly at risk” in the initial characterisation because of NO3 contents in groundwater, consideration of additional informations:
NO3 contents in groundwater [mg NO³/l] / NO3 contents in seepage water [mg NO³/l] / Additional informations, e.g. Trend / Risk
> 50 / - / - / at risk
25 – 50 / > 40 / - / at risk
25 – 50 / < 40 / positive / at risk
25 – 50 / < 40 / negative / not at risk
- For the GWB stated “possibly at risk” in the initial characterisation because of nitrogene balance surplus, consideration of additional informations:
NO3 contents in seepage water [mg NO³/l] / NO3 contents in groundwater [mg NO³/l] / Additional informations, e.g. Trend / Risk
> 50 / >15 / positive / at risk
> 50 / 15 / negative / not at risk
> 50 / 15 / - / not at risk
7.Groundwater Quantity Status: Abstraction and artificial recharge
The groundwater recharge of hydrogeological units in Hessia has been determined by measurements of dry weather flow of surface waters and published in the texts of the geological maps 1 : 25.000 and in water balance estimations for several regions for a long time by the HLUG (former HLfB). These data and data of climatic water balances have been collected for depiction in a map and summarized for each groundwater body. The sum of groundwater recharge has then been related to the water abstraction rights for wells in the groundwater bodies. If the abstraction by wells is more than 50% of the groundwater recharge, the groundwater body is determined as “possibly at risk” and needs further characterisation, which focuses on real abstraction data, refined recharge data, infiltration an others.
8.Analysis of other impacts on the status of groundwater
For the analysis of other impacts on the groundwater bodies, the water administrations (Regierungspräsidien, environmental agencies) and the HLUG selected possible wide spread impacts of other human activities on the groundwater. As a result, only the deep well disposal of waste brine of the potash factories in the catchment areas of rivers Werra an Fuldaremained. In these regions, since 1928 waste brine is disposed off into the Plattendolomit (Zechstein 1), which is a naturally salty aquifer, confined by thick clayey and silty layers in the base and roof strata. Nevertheless, therecan be local impacts on the overlying strata in the Bunter, Quarternary and on a few surface waters.These are controlled by means of a monitoring net with more than 350 piezometers, wells and springs. The area covered by this monitoring net has been set into relation to the area of the affected groundwater bodies. If more than 33% of a groundwater body is covered by the observation area, the groundwater body is declared to be “at risk”.
9.Determination of groundwater bodies “at risk”
The final determination of groundwater bodies at risk is a result of the previously described steps. The reason of being considered“at risk” is shown for each groundwater body in a map and in a list.
[1]J.-G. Fritsche, Bernd Leßmann: Hessian Agency for the Environment and Geology, Postfach 3209, 65022 Wiesbaden