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 theHesbaye aquifer

1950 : first piezometric maps (CILE)1986 : first groundwater model1993 – 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)

1998-1999 : PhD V. Hallet2000 : Migration of contaminant through the unsaturated zone

MAIN SOURCES OF DATA AND INFORMATION

Dpt of geology

HESBAYE CHALKY AQUIFERLOCATION 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 aquiferformation consists of Cretaceous chalk. 32.106 m3 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 AQUIFERSOUTH-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 gradientrange from 1 % in the South to 0.3 in the North. Most of the aquifer is unconfined, except in the north, wheresemi-confined conditions prevail under the Geer alluvial deposits. The piezometric map shows important anomalies that must be related to high permeability axis due to higherfracturation or weathering of the chalk. These axis are more vulnerable to contamination.

Dpt of geology

HESBAYE AQUIFERMONTHLY WATER TABLE FLUCTUATIONS AT VIEMME WELL

0

20

40

60

80

100

120

140

01/5

1

03/5

2

05/5

3

07/5

4

09/5

5

11/5

6

01/5

8

03/5

9

05/6

0

07/6

1

09/6

2

11/6

3

01/6

5

03/6

6

05/6

7

07/6

8

09/6

9

11/7

0

01/7

2

03/7

3

05/7

4

07/7

5

09/7

6

11/7

7

01/7

9

03/8

0

05/8

1

07/8

2

09/8

3

11/8

4

01/8

6

03/8

7

05/8

8

07/8

9

09/9

0

11/9

1

01/9

3

03/9

4

05/9

5

07/9

6

Date

Infi

ltra

tio

n (

mm

)

110

115

120

125

130

135

140

Ha

ute

ur

pie

zo

mé

triq

ue

(m

)

Infiltration (mm) Viemme

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, superficialdeposits that delay Infiltration (up to 18 months). Hydrogeological water balance indicates thatinfiltration only occurs between October and May.

Dpt of geology

HESBAYE AQUIFERNITRATE 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 mgNO3/l. In 1977, concentrations increase suddenly (up to 10 mgNO3/l in some

production wells); after, concentrations increase regularly at a range of 0.7 mg NO3/l per year.

Nitr

ates

(mg/

l)

: Captage de Remicourt

0

10

20

30

40

50

: Captages de Waremme

1960 1965 1970 1975 1980 1985 1990 1995

: Captage de Fize-le-Marsal

Dpt of geology

HESBAYE AQUIFERNITRATE 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 mgNO3/l. In 1977, concentrations increase suddenly (up to 5 mgNO3/l in some

production wells); after, concentrations increase regularly at a range of 0.35 mg NO3/l per year.

0

10

20

30

40

50N

itrat

es (p

pm

)

: Captage de Bassenge : Captage d'Eben Emael

1960 1965 1970 1975 1980 1985 1990 1995

: Captage de Diets-Heur

Dpt of geology

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan113

114

115

116

117

118

1/1/1994 au 1/1/1996

Ten

eur e

n ni

trat

es (m

g/l)

: hauteur piézométrique

Niv

eau

piéz

om

ètriq

ue (m

)

0

10

20

30

40

50

60

969594

: SGB 2 (profondeur : 9 à 16 m) : SGB 3 (profondeur : 16 à 26 m) : SGB 1 (profondeur : 30 à 40 m)

HESBAYE AQUIFERVARIATION OF NITRATE CONCENTRATIONS WITH DEPTH

At Bovenistier (5 km east of Waremme), samplers were monthly collected in three piezometersdrilled at the same spot but screened at various depth. Measurements show that important

variations exist with depth. Mean concentrations range from 40.3 mgNO3/l, at the top of the aquifer to 17.2 mgNO3/l at the bottom of the aquifer.

Dpt of geology

HESBAYE AQUIFERSPATIAL REPARTITION OF NITRATE CONCENTRATIONS

In 1993 , analyses were carried out in more than 100 wells. Mean nitrate concentration was57 mgNO3/l, ranging from 10 to 200 mgNO3/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 NO3mg/l; - semi-confined aquifer where concentration range between 15 and 25 mg NO3 /l; - confined part of the aquifer where concentrations could be less than 10 mgNO3/l.

Dpt of geology

HESBAYE AQUIFER SEASONNAL EVOLUTION OF NITRATE CONTENTS IN

JENEFFE AND VERLAINE WELLS

Infil

trat

ion

men

suel

le (m

m)

: Infiltration mensuelle (mm)

125

126

127

128

129

130

: Niveau de la nappe (m)

1/01

/94

1/02

/94

1/03

/94

1/04

/94

1/05

/94

1/06

/94

1/07

/94

1/08

/94

1/09

/94

1/10

/94

1/11

/94

1/12

/94

1/01

/95

1/02

/95

1/03

/95

1/04

/95

1/05

/95

1/06

/95

1/07

/95

1/08

/95

1/09

/95

1/10

/95

1/11

/95

1/12

/95

1/01

/960

20

40

60

80

100

120

140

160

180

Ten

eur e

n ni

trat

es (m

g/l)

Niv

eau

piéz

om

étriq

ue (m

)

Date

: Teneurs en nitrates (mg/l)

: Infiltration mensuelle (mm)

1/1

0/9

3

1/1

1/9

3

1/1

2/9

3

1/0

1/9

4

1/0

2/9

4

1/0

3/9

4

1/0

4/9

4

1/0

5/9

4

1/0

6/9

4

1/0

7/9

4

1/0

8/9

4

1/0

9/9

4

1/1

0/9

4

1/1

1/9

4

1/1

2/9

4

1/0

1/9

5

1/0

2/9

5

1/0

3/9

5

1/0

4/9

5

1/0

5/9

5

1/0

6/9

5

1/0

7/9

5

1/0

8/9

5

1/0

9/9

5

1/1

0/9

5

1/1

1/9

5

1/1

2/9

5

1/0

1/9

6

0

20

40

60

80

100

120

140

160

180

Infil

trat

ion

men

suel

le (m

m)

Niv

eau

piéz

om

étriq

ue (m

)

: Teneurs en nitrates (mg/l)

Ten

eurs

en

nitr

ates

(mg/

l)

Date

168

169

170

171

172

173

: Niveau de la nappe (m)

PUITS JEN 087 PUITS VER 114

Monthly sampling shows that nitrate contents could varied in relation with water table fluctuations : maximum values (up to 160 mgNO3/l at Jeneffe) are observed during high piezometric periods

and minimum values (down to 20 mgNO3/l at Jeneffe) are observed during low piezometric periods .

Dpt of geology

HESBAYE AQUIFER INFLUENCE OF WATER TABLE FLUCTUATIONS ON NITRATE CONCENTRATIONS

HAUTES EAUXmai 94

40 mg/l

97 mg/l

40 mg/l

40 mg/l

40 mg/l

125 mg/l

BASSES EAUXdec. 94

HAUTES EAUXmai 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 mgNO3/l are observed. When the water table rise up, it reached the downward nitrates fluxes and concentration increases suddenly.

Dpt of geology

0

5

10

15

20

25

30

35

40

Com

mun

e ag

ricol

eég

outt

ée(u

rban

isat

ion

6%)

Com

mun

e ur

bain

eég

outt

ée(u

rban

isat

ion

91 %

)

Com

mun

e m

ixte

non

égou

tée

(urb

anis

atio

n 36

%)

Com

mun

e m

ixte

égou

ttée

(urb

anis

atio

n 36

%)

Bas

sin

du G

eer

(urb

anis

atio

n 14

%)

Azo

te le

ssiv

é en

moy

enne

par

an

(kgN

/ha/

an)

: Exutoires localisés : Rejets domestiques diffus : Rejets sous prairie : Rejets sous culture

HESBAYE AQUIFERESTIMATION OF THE ORIGIN OF NITRATE INPUTS

According to the Geer basin land use, nitrate input could be estimated around30 kgN/ha/year from which 75% come from agricultural activities.

Dpt of geology

Sources : Programme Action HesbayeUnité d’hydraulique Agricole; FUSAGx

Pr S. Dautrebande

Actual situation

0,0 E+00

1,0 E-07

2,0 E-07

3,0 E-07

4,0 E-07

5,0 E-07

6,0 E-07

7,0 E-07

8,0 E-07

63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

Date

Inp

ut

en

nit

rate

s (m

g/m

².s)

0

100

200

300

400

500

600

Infi

ltra

tio

n a

nn

ell

e (

mm

)

: Infiltration

: 20 m sous cultures

: 15 m sous cultures

: 10 m sous cultures

: 5 m sous cultures

Dpt of geology

HESBAYE AQUIFEREVOLUTION 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 mgNO3/l at 5 meters deep;it actually reaches 40 mgNO3/l.

Sources : Programme Action HesbayeUnité d’hydraulique Agricole; FUSAGx

Pr. S. Dautrebande

HESBAYE AQUIFERLOCATION 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

1962 1963

HESBAYE AQUIFERGROUNDWATER MODEL RESULTS

Dpt of geology

The two figures show the nitrates concentration in the aquifer calculated according to the 1962 and1992 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 AQUIFERGROUNDWATER MODEL RESULTS

Dpt of geology

0 20 40 60 80 100 1200

5

10

15

20

25

30

35

40

45

50

CO

NC

EN

TR

AT

ION

EN

NIT

RA

TE

S (

mg

/L)

Suppression de la pollution ponctuelle

SIMULATION AVECINTRANTS DE 1963SIMULATIONS AVEC INTRANTS DE 1992

Basses eaux

Hautes eaux

SIMULATIONS AVECINTRANTS REELS

19921963

ANNEES DE SIMULATION

: 100 m à l'aval de la pollution ponctuelle (sommet de la nappe : 10 m sous culture)

: 100 m à l'aval de la pollution ponctuelle (base de la nappe : 10 m sous culture)

: pollution diffuse (15 m sous culture) : pollution diffuse (20 m sous cuture)

Simulation withreal input

1962 1992

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 highcontaminations. For local contaminations, concentrations are, due to dilution, effects minimum duringhigh 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 almostdouble between 1962 and 1992. Simulations indicate that it take around 30 year to reach the equilibriumbetween the nitrates inputs and a stable groundwater concentration. That means that if protection actionsare taken, it could take more than 20 years to observed changes. All concerned people have to be awarethat changes (degradation or improvement) in groundwater concentration are very slow.