An integrative method to quantify contaminant fluxes in the groundwater of urban areas |
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Authors: | Thomas Schiedek Meike Beier Götz Ebhardt |
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Institution: | (1) Institute of Applied Geosciences, University of Technology, 64287 Darmstadt, Germany |
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Abstract: | Background, Aims, and Scope Groundwater in urban areas is often contaminated and emission sources can be located close to groundwater wells. The delineation
of contaminant plumes is difficult because of the various potential emission sources. Thus, detection, quantification and
remediation of contaminated sites in a city need more integrative approaches.
Methods A method has been developed which allows quantification of mass fluxes of contaminants in groundwater between control planes.
Budget zones along the flow path are defined to calculate a contaminant balance and to quantitatively reveal input areas.
Concentrations and water budgets are used to calculate mass balances for each contaminant. The city of Darmstadt (Germany)
was chosen to evaluate the method.
Results The groundwater monitoring wells (GMWs) upstream of the city showed anthropogenically superposed background values for all
naturally occurring inorganic species. The contaminant concentrations increased in the city (probably influenced by road traffic,
gas stations, leaking sewers, etc.). Downstream from the city, concentrations usually decreased. Organic compounds typical
for urban environments, such as polycyclic aromatic hydrocarbons (PAH), locally exceeded drinking water regulations. In GMWs
with high concentrations of organic contaminants in the city or downstream from industrial areas, a significant increase in
Fe2+ and Mn2+ could be observed, in some cases coinciding with a decrease in NO3, SO4 and an increase in NH4.
Discussion For typical urban contaminants, a positive budget was calculated in several zones, which shows that emissions from urban sources
are reaching the groundwater. Negative budgets can be mainly explained with diving plumes and degradation. The input calculated
from the individual budget zones is usually higher than the input estimated from urban emissions. Differences between the
calculated and the estimated input can be explained with additional sources or (bio)degradation processes.
Conclusions It was confirmed that high concentrations of contaminants do not necessarily correlate with high fluxes. Integrative approaches
can reveal areas of high contaminant mass input. The results obtained with the new method are plausible compared to the land
use and the estimated urban input. The concentration pattern of Fe2+, Mn2+, SO4 and NO3 is partly due to natural processes, triggered by the degradation of organic matter and organic contaminants.
Recommendations Since this method includes mass balances and flux calculations, avoiding an overestimation of single point contaminant concentration,
it is recommended to use this approach to quantify groundwater contamination in cities. Further research is focusing on the
role of urban soils as natural reservoirs for the input of contaminants. |
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Keywords: | 3-D-groundwater model biological degradation budget zones integrative quantification method mass fluxes natural attenuation organic and inorganic contamination plumes urban areas urban hydrochemistry urban hydrogeology |
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