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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2019-499
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2019-499
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 07 Oct 2019

Submitted as: research article | 07 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

On the Conceptual Complexity of Non-Point Source Management: Impact of Spatial Variability

Christopher Vincent Henri1, Thomas Harter1, and Efstathios Diamantopoulos2 Christopher Vincent Henri et al.
  • 1University of California, Davis, Center for Watershed Sciences, Veihmeyer Hall, Davis, CA 95616, USA
  • 2University of Copenhagen, Department of Plant and Environmental Sciences, Thorvaldsensvej 40, Copenhagen, DK-1871, Denmark

Abstract. Non-point source (NPS) pollution has degraded groundwater quality of unconsolidated sedimentary basins over many decades. Properly conceptualizing NPS pollution from the well scale to the regional scale leads to complex and expensive numerical models: Key controlling factors of NPS pollution – recharge rate, leakage of pollutants, and soil and aquifer hydraulic properties – are spatially and, for recharge and pollutant leakage, temporally variable. This leads to high uncertainty in predicting well pollution. On the other hand, concentration levels of some key NPS contaminants (salinity, nitrate) vary within a limited range (< 2 orders of magnitude); and significant mixing occurs across the aquifer profile along the most critical compliance surface: drinking water wells with their extended vertical screen length. Here, we investigate, whether these two unique NPS contamination conditions reduce uncertainty such that simplified spatiotemporal representation of recharge and contaminant leakage rates and of hydraulic conductivity are justified when modeling NPS pollution. We employ a Monte Carlo-based stochastic framework to assess the impact of model homogenization on key management metrics for NPS contamination. Results indicate that travel time distributions are relatively insensitive to the spatial variability of recharge and contaminant loading, while capture zone and contaminant time series exhibit some sensitivity to source variability. In contrast, homogenization of aquifer heterogeneity significantly affects the uncertainty assessment of travel times and capture zone delineation. Surprisingly, regional statistics of well concentration time series are fairly well reproduced by a series of equivalent homogeneous aquifers, highlighting the role of NPS solute mixing along well screens.

Christopher Vincent Henri et al.
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Short summary
Non-point source contaminations of aquifers are complex to model, predict and manage. This study uses numerical and stochastic methods to address the importance of key sources of spatial variability. We show that heterogeneity in recharge and contaminant loading does not significantly impact management metrics, and could be simplified. Also, homogenizing physical properties has more impact on predictions but can provide useful information on concentration statistics in a regional analysis.
Non-point source contaminations of aquifers are complex to model, predict and manage. This study...
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