Uncertainties in the transient capture-zone estimates

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XVI International Conference on Computational Methods in Water Resources (CMWR-XVI) Ingeniørhuset

Uncertainties in the transient capture-zone estimates
Author:Velimir Vesselinov <vvv@lanl.gov> (Los Alamos National Lab)
Presenter:Velimir Vesselinov <vvv@lanl.gov> (Los Alamos National Lab)
Date: 2006-06-18     Track: General Sessions     Session: General

Capture zones of water-supply wells are a widely used analysis tool for protection of groundwater resources. Transient analyses of capture zones provide a more complete assessment than the more commonly applied steady-state analyses. Previously, we have demonstrated that advection-only analyses can produce biased transient capture-zone estimates. Therefore, it is important to consider the dispersion of contaminant plumes. Here, we extend our study to incorporate temporal and spatial distribution in the contaminant sources and their respective uncertainties. Our analysis indicates that the capture-zone estimates can be very sensitive to the transients in contaminant releases. Even relatively small uncertainties in the contaminant source, when combined with transient flow effects associated with natural variability of gradients or water supply well pumping, can cause significant uncertainties in capture-zone estimates. This conclusion has important practical implications. The locations and times at which contaminants reach the aquifer are often very uncertain, especially in cases for which upstream source release history and vadose zone transport rates are poorly known. The resulting capture-zone estimates in such systems can be, in effect, completely uncertain. Our current work demonstrates some of the theoretical and computational challenges that we face in the estimation of predictive uncertainties.