Capture zone analysis using standard EPA methods and Bayesian uncertainty analysis in Spanish Springs Valley, Nevada.

摘要

A 1999 study in Spanish Springs Valley, Nevada, concluded that increasing nitrate levels could be linked to local septic systems (Seiler, 1999). This study identifies the capture zone for a production well located adjacent to the septic systems. A previously constructed, transient groundwater flow model developed by the United States Geological Survey (USGS) is used as the basis for the capture zone analysis. Two basic EPA methods for capture zone analysis are compared to a more advanced stochastic method. The stochastic methodology is used to evaluate the uncertainty in the groundwater flow model and associated well capture zones. Specifically, a Bayesian approach utilizing the Generalized Likelihood Uncertainty Estimator (GLUE) methodology is used to calculate a likelihood (probability) for every realization based on the model's ability to match the temporal evolution of water levels within the basin. The likelihoods are used to quantify the uncertainty in the capture zones and to quantify the uncertainty in the input parameter distributions. The efficacy of various likelihood measures is also investigated. (Abstract shortened by UMI.)