Department of geology Etude de la contamination de la nappe aquifère de Hesbaye par les nitrates Dr...
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Transcript of Department of geology Etude de la contamination de la nappe aquifère de Hesbaye par les nitrates Dr...
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.