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| Titel |
Water quality prognosis of a production well field based on monitoring data and groundwater dating |
| VerfasserIn |
Hans Peter Broers, Ate Visser |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047117
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| Zusammenfassung |
| The water quality of production well fields is determined by the land use in the capture area,
geochemistry of the aquifer and the travel time distributions of the production wells. The aim
of this study was to project the water quality of the production well field Holten (The
Netherlands) based solely on the travel time distributions of the production wells
and the water quality data from the monitoring network in the vicinity of the well
field.
The production well field of Holten is located in the east of the Netherlands, in sandy
ice-pushed ridges and peri-glacial aeolian deposits. Land use in the capture zone is
agriculture and natural forest in approximate equal proportions. The travel time
distributions of 4 shallow production wells (15-45 m below surface) and 3 deep
production wells (45-70 m below surface) have been determined by a combination of
85Kr, 3H/3He and 39Ar dating. Sampled groundwater from 9 monitoring wells (27
screens) has been dated with 3H/3He to relate the water quality data to the time of
recharge.
Water quality data from the monitoring network provided the regional aggregated trend in
water quality parameters, related to the time of recharge. These trends generally
show an increase in agricultural contamination up to the 1980s, but decreasing
concentrations in younger water. The regional aggregated trend of nitrate shows complete
denitrification in older groundwater in deeper parts of the aquifer, confirmed by
high dissolved N2 concentrations causing high total dissolved gas pressures and
occasionally degassing of groundwater. Excess N2, from denitrification, coincides with
elevated sulfate concentrations, indicating denitrification by pyrite oxidation. The
regional aggregated trends from the monitoring wells provided the input for the
water quality prognosis based on the travel time distributions of the production
wells.
In general, shallow production wells with a very large young component are projected to
show water quality improvements in the near future. The response of shallow production
wells with intermediate age distributions is slower. Two of the three deep wells produce a
mixture of groundwater containing a young fraction and these are projected to show
deterioration in water quality in the future, although nitrate concentrations in these wells are
kept low by denitrification and pyrite oxidation. Only a single deep well shows no
vulnerability to water quality deterioration thanks to the travel time distribution containing
exclusively old groundwater.
The combination of 3H/3He dating of the monitoring wells with discrete travel time
distributions of the production wells based on 85Kr, 3H/3He and 39Ar dating provide a robust
water quality prognosis and wells vulnerability assessment. |
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