Stochastic Approach to Delineating Wellhead Protection Areas

Abstract

Delineating the wellhead protection area (WPA) is a vital component in the development of a comprehensive wellhead protection program. WHPA is a series of computer programs developed for the U.S. Environmental Protection Agency to delineate WPAs. In the state of Tennessee, the WPA is delineated using a two-dimensional particle tracking code (GPTRAC) in a leaky-confined aquifer, or a modified containment front tracking code (RESSQC) in an unconfined aquifer. Both WHPA delineation methods require constant values for all model parameters. To overcome the difficulty of estimating values for each input parameter and to provide some measure of the uncertainty in the size and shape of wellhead protection zones, the Environmental Protection Agency WHPA models are integrated into a parallelized Monte Carlo (MC) simulation. The MC-WHPA model is used to compute a discrete two-dimensional cumulative distribution function for a WPA. MC-WHPA uses a parallel virtual machine computing environment developed over a network of computers. The MC-WHPA model is used to delineate the wellhead protection and management zones for two wellfields in western Tennessee.