Application of the Netherlands Groundwater Model, LGM, for calculating concentration of nitrate and pesticides at abstraction wells in sandy soil areas of the Netherlands
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Open Access
Type
Report
Language
en
Date
1998-02-28
Research Projects
Organizational Units
Journal Issue
Title
Application of the Netherlands Groundwater Model,
LGM, for calculating concentration of nitrate and pesticides at abstraction
wells in sandy soil areas of the Netherlands
Translated Title
Toepassing van het National Grondwater Model LGM
voor de berekening van concentraties van nitraat en pesticiden op
pompstations in de zandgebieden van Nederland
Published in
Abstract
In het kader van een studie naar de gevolgen van
historische en toekomstige stofuitspoeling naar het verzadigde grondwater is
het quasi-driedimensionale RIVM grondwatermodel LGM (versie 2) gebruikt voor
berekening van stroombanen, verblijftijden en concentratie-doorbraakkrommen
op 165 grondwater-pompstations in de zandgebieden van Nederland. Berekend
zijn de toekomstige concentraties van nitraat en pesticiden (atrazin,
bentazon en 1,2-dichloorpropaan). De studie is uitgevoerd in het kader van
de nationale lange-termijn planning voor drink- en
industriewatervoorziening. De berekening is uitgevoerd voor 76 freatische
en 89 semi-spanningslocaties, gebaseerd op de maximale
vergunningshoeveelheid voor 1988. Drie economische scenario's zijn gebruikt
voor de bepaling van stofuitspoeling naar het verzadigde grondwater.
Nitraatuitspoeling is gesimuleerd door een combinatie van methoden,
waaronder het model NLOAD voor het landbouwgebied. De uitspoeling van
pesticiden is gesimuleerd m.b.v. het model GEOPESTRAS. Vervolgens, gebruik
makend van de concentraties van de uitspoelingsflux, is het LGM gebruikt
voor de berekening van concentraties op pompstations. Het LGM is een
numeriek model (gebaseerd op de eindige elementenmethode), dat complexe
geohydrologische systeem-componenten bevat. Het maakt gebruik van
ruimtelijk variabele (heterogene) gegevens voor vier watervoerende pakketten
voor het gehele gebied van Nederland. De doorbraakconcentraties zijn
berekend m.b.v. het module LGMCAM, gebaseerd op de voorwaartse particle
tracking in het verzadigde grondwater. De gebruikte processen zijn advectie
en volledige menging in putfilters. Denitrificatie en degradatie van
pesticiden in het verzadigde grondwater zijn buiten beschouwing gelaten. De
resultaten zijn gepresenteerd als (1) kaarten van concentraties op 165
pompstations voor 2020 en 2050 en (2) als staafdiagrammen van concentraties
in de tijd (1950-2050) voor de getotaliseerde onttrekkingshoeveelheid op
freatische en semi-spanningslocaties. Verder is voor een aantal
pompstations een vergelijking gemaakt van berekende en gemeten
doorbraakkrommen. De hierop gebaseerde conclusie is dat de berekende
concentraties als een 'worst-case' resultaat kunnen worden gezien.
Tenslotte zijn aanbevelingen gedaan voor verdere verbetering van de
berekeningsmethodiek in de toekomst.
In a study aimed at assessing the impact of historical and future solute leaching into saturated groundwater, the quasi-three-dimensional RIVM groundwater model, LGM (version 2), was used for calculating pathlines, travel times and concentration breakthrough curves at 165 groundwater abstraction locations in the sandy soil areas of the Netherlands. The future concentration variations were assessed for nitrate and three pesticides (atrazine, bentazone and 1,2-dichloropropane). This study was carried out in the framework of the Dutch government's long-term planning for industrial and drinking-water supply. The assessment was carried out for 76 phreatic and 89 semi-confined abstraction sites on the basis of the 1988 maximum-permitted abstraction rates. Three economic scenarios were used for generating solute leaching into saturated groundwater for the scenario years 2000 and 2020. The nitrate leaching flux was simulated by a combination of methods, including the NLOAD model for agricultural land. The pesticide leaching flux was simulated by means of the GEOPESTRAS model. Subsequently, LGM was applied to calculate the concentrations at the abstraction wells, using the concentrations in the leaching flux as input. LGM is a numerical model (based on the finite-element method), comprising complex geohydrological system components. LGM uses spatially variable (heterogeneous) data for four aquifers, covering the entire surface area of the Netherlands. The concentration breakthrough curves were calculated with the module LGMCAM, based on forward pathline tracking in saturated groundwater. The processes used in LGMCAM were advection and full mixing in well screens. Neither denitrification nor degradation of pesticides in saturated groundwater were taken into account. The results are presented (1) as concentration maps for the 165 abstraction sites for 2020 and 2050 and (2) by means of time-based concentration bar charts (1950-2050) for the totalized abstraction rate for phreatic and semi-confined abstraction sites. For a number of abstraction sites a comparison has also been made between calculated and observed breakthrough concentrations. The calculated concentrations can be concluded to be a worst-case outcome. Finally, recommendations for future improvements of the method are given.
In a study aimed at assessing the impact of historical and future solute leaching into saturated groundwater, the quasi-three-dimensional RIVM groundwater model, LGM (version 2), was used for calculating pathlines, travel times and concentration breakthrough curves at 165 groundwater abstraction locations in the sandy soil areas of the Netherlands. The future concentration variations were assessed for nitrate and three pesticides (atrazine, bentazone and 1,2-dichloropropane). This study was carried out in the framework of the Dutch government's long-term planning for industrial and drinking-water supply. The assessment was carried out for 76 phreatic and 89 semi-confined abstraction sites on the basis of the 1988 maximum-permitted abstraction rates. Three economic scenarios were used for generating solute leaching into saturated groundwater for the scenario years 2000 and 2020. The nitrate leaching flux was simulated by a combination of methods, including the NLOAD model for agricultural land. The pesticide leaching flux was simulated by means of the GEOPESTRAS model. Subsequently, LGM was applied to calculate the concentrations at the abstraction wells, using the concentrations in the leaching flux as input. LGM is a numerical model (based on the finite-element method), comprising complex geohydrological system components. LGM uses spatially variable (heterogeneous) data for four aquifers, covering the entire surface area of the Netherlands. The concentration breakthrough curves were calculated with the module LGMCAM, based on forward pathline tracking in saturated groundwater. The processes used in LGMCAM were advection and full mixing in well screens. Neither denitrification nor degradation of pesticides in saturated groundwater were taken into account. The results are presented (1) as concentration maps for the 165 abstraction sites for 2020 and 2050 and (2) by means of time-based concentration bar charts (1950-2050) for the totalized abstraction rate for phreatic and semi-confined abstraction sites. For a number of abstraction sites a comparison has also been made between calculated and observed breakthrough concentrations. The calculated concentrations can be concluded to be a worst-case outcome. Finally, recommendations for future improvements of the method are given.
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DGM/DWL