TY - JOUR
T1 - Anthropogenic contamination of a phreatic drinking water winning: 3-dimensional reactive transport modelling
AU - Griffioen, J.
AU - van der Grift, B.
AU - Maas, D.
AU - van den Brink, C.
AU - Zaadnoordijk, J. W.
PY - 2003/4/1
Y1 - 2003/4/1
N2 - Groundwater is contaminated at the regional scale by agricultural
activities and atmospheric deposition. A 3-D transport model was set-up
for a phreatic drinking water winning, where the groundwater composition
was monitored accurately. The winning is situated at an area with
unconsolidated Pleistocene deposits. The land use is nature and
agriculture. Annual mass-balances were determined using a wide range of
historic data. The modelling approach for the unsaturated zone was
either simple box models (Cl, NO_3 and SO_4) or 1-D transport modelling
using HYDRUS (Cd). The modelling approach for the saturated zone used a
multiple solute version of MT3D, where denitrification associated with
pyrite oxidation and sorption of Cd were included. The solute transport
calculations were performed for the period 1950--2030. The results
obtained for the year 2000 were used as input concentration for the
period 2000--2030. A comparison between the calculated and the measured
concentrations of groundwater abstracted for Cl, NO_3 and SO_4 yields
the following. First, the input at the surface is rather well estimated.
Second, the redox reactivity of the first two aquifers is negligible
around the winning, which is confirmed by respiration experiments using
anaerobically sampled aquifer sediments. The reactivity of the third
aquifer, which is a marine deposit and lies at least 30 meters below
surface, is considerable. The discrepancies between modelled and
measured output are explained by lack of knowledge about the subsurface
reactivity and/or wrong estimates of surface loading and leaching from
the unsaturated zone. The patterns for other hydrogeochemical variables
such as Ca, HCO_3 may further constrain this lack of knowledge. The
results for Cd indicate that Cd becomes strongly retarded, despite the
low reactivity of the sandy sediments. The winning is rather insensitive
to Cd contamination (but the surface water drainage network is not). Two
major uncertainties for input of Cd exist: composition of rain before
1970 and use of sewage sludge as manure in the past.
AB - Groundwater is contaminated at the regional scale by agricultural
activities and atmospheric deposition. A 3-D transport model was set-up
for a phreatic drinking water winning, where the groundwater composition
was monitored accurately. The winning is situated at an area with
unconsolidated Pleistocene deposits. The land use is nature and
agriculture. Annual mass-balances were determined using a wide range of
historic data. The modelling approach for the unsaturated zone was
either simple box models (Cl, NO_3 and SO_4) or 1-D transport modelling
using HYDRUS (Cd). The modelling approach for the saturated zone used a
multiple solute version of MT3D, where denitrification associated with
pyrite oxidation and sorption of Cd were included. The solute transport
calculations were performed for the period 1950--2030. The results
obtained for the year 2000 were used as input concentration for the
period 2000--2030. A comparison between the calculated and the measured
concentrations of groundwater abstracted for Cl, NO_3 and SO_4 yields
the following. First, the input at the surface is rather well estimated.
Second, the redox reactivity of the first two aquifers is negligible
around the winning, which is confirmed by respiration experiments using
anaerobically sampled aquifer sediments. The reactivity of the third
aquifer, which is a marine deposit and lies at least 30 meters below
surface, is considerable. The discrepancies between modelled and
measured output are explained by lack of knowledge about the subsurface
reactivity and/or wrong estimates of surface loading and leaching from
the unsaturated zone. The patterns for other hydrogeochemical variables
such as Ca, HCO_3 may further constrain this lack of knowledge. The
results for Cd indicate that Cd becomes strongly retarded, despite the
low reactivity of the sandy sediments. The winning is rather insensitive
to Cd contamination (but the surface water drainage network is not). Two
major uncertainties for input of Cd exist: composition of rain before
1970 and use of sewage sludge as manure in the past.
M3 - Meeting Abstract
SN - 1029-7006
VL - 5
JO - Geophysical Research Abstracts
JF - Geophysical Research Abstracts
M1 - 08450
T2 - EGS-AGU-EUG Joint Assembly (Nice, France)
Y2 - 6 January 2003
ER -