Abstract

The ground-water professional given the task of delineating drinking-water source-protection areas for wells completed in fractured-rock aquifers often uses available hydrologic information derived from pumping tests of wells and assumes an equivalent porous media in order to justify the use of simplistic computer models to calculate time-dependent protection areas. These methods often ignore obvious fracture trends and flow anisotropy that control ground-water flow patterns in fractured rock. This paper is designed to not only recognize the wealth of hydrologic data available from wells and springs tapping fractured-rock aquifers, but also offer some alternative approaches to delineating ground-water protection areas in aquifers with ground-water flow anisotropy. Ground-water protection areas for wells completed in anisotropic aquifers can be delineated through the use of conventional methods with subsequent adjustments to account for uncertainty in flow directions. These methods are illustrated for a wellfield in the Navajo Sandstone serving Moab, Utah and a well in the Twin Creek Limestone near Park City, Utah.