Department of geology Etude de la contamination de la nappe aquifère de Hesbaye par les nitrates Dr V. Hallet Study of the nitrate groundwater contamination of the Hesbaye aquifer

1950 : first piezometric maps (CILE) 1986 : first groundwater model 1993 – 1996 : Programme Action Hesbaye - Ec Life’s project - Région Wallonne - Université de Liège - Faculté Universitaire des Sciences Agronomiques de Gembloux - Centre de Recherche Agronomique de Gembloux - CILE and SWDE - Agricultural organisations (UPA – UDEF) 1996 – 1997 : investigations for the delimitation of the protection zones along the collecting galleries (CILE) and well fields SWDE) : PhD V. Hallet 2000 : Migration of contaminant through the unsaturated zone MAIN SOURCES OF DATA AND INFORMATION Dpt of geology

HESBAYE CHALKY AQUIFER LOCATION MAP Bovenistier Remicourt Fize-le-marsal Diest-Heur Bassenge Eben-Emael Ver114 The Hesbaye plateau is located at the North-West of Liege; it covers an area of 300 km². The aquifer formation consists of Cretaceous chalk m 3 of drinking water are pumped every year from 12 wells (SWDE) and from 56 km of collecting galleries (CILE). This groundwater supply Liege and the surrounding areas. Jen087 Dpt of geology

HESBAYE AQUIFER SOUTH-NORTH HYDROGEOLOGICAL CROSS SECTION Geological formations observed in the area consist of (from bottom to top) : - Smectite de Herve : clayey formation that is considered as the aquifer basis (thickness of 2 to 10 m); - Senonian chalks : heterogeneous chalk of various permeability (thickness of few to 70 m); - flint conglomerate made of dissolved chalk residues (flint, sand, clay and locally phosphates of maximum thickness of 10 m); - tertiary sand lens deposits (few m); - quaternary loess (variable thickness of 2 to 20 m). Dpt of geology

HESBAYE AQUIFER PIEZOMETRIC MAP (LOW WATER TABLE LEVEL) The groundwater flows from South to North in the direction of the River Geer. The mean hydraulic gradient range from 1 % in the South to 0.3 in the North. Most of the aquifer is unconfined, except in the north, where semi-confined conditions prevail under the Geer alluvial deposits. The piezometric map shows important anomalies that must be related to high permeability axis due to higher fracturation or weathering of the chalk. These axis are more vulnerable to contamination. Dpt of geology

HESBAYE AQUIFER MONTHLY WATER TABLE FLUCTUATIONS AT VIEMME WELL The water table of the Hesbaye aquifer shows pluriannual water table fluctuations. Amplitude varies from place to place but it could range more than 10 m. This is due to the, 2 to 10 m thick, superficial deposits that delay Infiltration (up to 18 months). Hydrogeological water balance indicates that infiltration only occurs between October and May. Dpt of geology

HESBAYE AQUIFER NITRATE CONTENT EVOLUTION IN THE UNCONFINED PART OF THE AQUIFER In the unconfined part of the aquifer, the yearly mean nitrate concentration was, before 1976, around 20 mgNO 3 /l. In 1977, concentrations increase suddenly (up to 10 mgNO 3 /l in some production wells); after, concentrations increase regularly at a range of 0.7 mg NO 3 /l per year. Dpt of geology

HESBAYE AQUIFER NITRATE CONTENT EVOLUTION IN THE SEMI-CONFINED PART OF THE AQUIFER In the semi-confined part of the aquifer (Geer Valley), the yearly mean nitrate concentration was, before 1976, around 15 mgNO 3 /l. In 1977, concentrations increase suddenly (up to 5 mgNO 3 /l in some production wells); after, concentrations increase regularly at a range of 0.35 mg NO 3 /l per year. Dpt of geology

HESBAYE AQUIFER VARIATION OF NITRATE CONCENTRATIONS WITH DEPTH At Bovenistier (5 km east of Waremme), samplers were monthly collected in three piezometers drilled at the same spot but screened at various depth. Measurements show that important variations exist with depth. Mean concentrations range from 40.3 mgNO 3 /l, at the top of the aquifer to 17.2 mgNO 3 /l at the bottom of the aquifer. Dpt of geology

HESBAYE AQUIFER SPATIAL REPARTITION OF NITRATE CONCENTRATIONS In 1993, analyses were carried out in more than 100 wells. Mean nitrate concentration was 57 mgNO 3 /l, ranging from 10 to 200 mgNO 3 /l with high variations observed on short distances. Meanwhile, three zones could be distinguished : - unconfined part of the aquifer where concentrations are higher than 30 NO 3 mg/l; - semi-confined aquifer where concentration range between 15 and 25 mg NO 3 /l; - confined part of the aquifer where concentrations could be less than 10 mgNO 3 /l. Dpt of geology

HESBAYE AQUIFER SEASONNAL EVOLUTION OF NITRATE CONTENTS IN JENEFFE AND VERLAINE WELLS PUITS JEN 087PUITS VER 114 Monthly sampling shows that nitrate contents could varied in relation with water table fluctuations : maximum values (up to 160 mgNO 3 /l at Jeneffe) are observed during high piezometric periods and minimum values (down to 20 mgNO 3 /l at Jeneffe) are observed during low piezometric periods. Dpt of geology

HESBAYE AQUIFER INFLUENCE OF WATER TABLE FLUCTUATIONS ON NITRATE CONCENTRATIONS HAUTES EAUX mai mg/l 97 mg/l 40 mg/l 125 mg/l BASSES EAUX dec. 94 HAUTES EAUX mai 95 Low nitrate contents observed during deep water table levels is due to the fact that the water table drawdown is much faster (0.6 m / month) than nitrate downward fluxes (estimates to 0.10 m/month). During few month, nitrates input could be nil at the top of the aquifer. In consequences, nitrate concentrations decrease and values around 40 mgNO 3 /l are observed. When the water table rise up, it reached the downward nitrates fluxes and concentration increases suddenly. Dpt of geology

HESBAYE AQUIFER ESTIMATION OF THE ORIGIN OF NITRATE INPUTS According to the Geer basin land use, nitrate input could be estimated around 30 kgN/ha/year from which 75% come from agricultural activities. Dpt of geology Sources : Programme Action Hesbaye Unité d’hydraulique Agricole; FUSAGx Pr S. Dautrebande Actual situation

Dpt of geology HESBAYE AQUIFER EVOLUTION OF NITRATE INPUT DUE TO AGRICULTRAL ACTIVITIE BETWEEN 1963 AND 1992 Nitrates fluxes reaching the aquifer vary according to the depth. Between 1963 and 1992, nitrate input in the aquifer has been multiplied by two at a depth of 5 meters. In terms of concentrations, It means that, in 1963, nitrates concentrations were around 20 mgNO 3 /l at 5 meters deep; it actually reaches 40 mgNO 3 /l. Sources : Programme Action Hesbaye Unité d’hydraulique Agricole; FUSAGx Pr. S. Dautrebande

HESBAYE AQUIFER LOCATION OF THE GROUNDWATER MODEL A groundwater models was used to estimated the evolution of nitrate according to various scenario. The selected area is located at Fize-le-Marsal. Nitrate flows were estimated according to the land use (crop land, urban area and grass-land and local contamination) and the depth of the water table. Dpt of geology

HESBAYE AQUIFER GROUNDWATER MODEL RESULTS Dpt of geology The two figures show the nitrates concentration in the aquifer calculated according to the 1962 and 1992 inputs. Highest concentration are observed along the valley axis (A-A’ axis) as the water table is closer to the surface. Along the valley, concentration almost double.

HESBAYE AQUIFER GROUNDWATER MODEL RESULTS Dpt of geology Simulation with real input Simulation with 1992 input Year of simulation Simulation with 1962 input Suppression of local contamination Various simulations show that local contamination (as input due to infiltration basins) induce high contaminations. For local contaminations, concentrations are, due to dilution, effects minimum during high water level. The suppression of a local point of pollution involved a fast decrease of nitrate contents. For diffuse sources of pollution due to agricultural practices, simulations show that concentrations almost double between 1962 and Simulations indicate that it take around 30 year to reach the equilibrium between the nitrates inputs and a stable groundwater concentration. That means that if protection actions are taken, it could take more than 20 years to observed changes. All concerned people have to be aware that changes (degradation or improvement) in groundwater concentration are very slow.