Between September 1997 and October 1998, nine monitor wells were drilled at the AIW Frank/Mid-County Mustang Superfund Site in Chester County, Pa., to determine the horizontal and vertical distribution of contaminated ground water migrating from known contaminant sources. The U.S. Geological Survey conducted borehole geophysical logging and borehole television surveys in these boreholes to identify water-producing zones so that appropriate intervals could be screened in each borehole. Caliper logs and borehole television surveys were used to locate fractures; inflections on fluid-temperature and fluid-resistivity logs were used to locate possible water-bearing fractures, and heatpulseflowmeter measurements verified these locations. The borehole television surveys indicated that locally, the rocks of the Conestoga Limestone and Ledger Dolomite that underlie the site strike generally from northeast-southwest to east-west and dip steeply to the southeast and south approximately 63? to 76?. Slug tests were conducted at six boreholes to estimate transmissivity. Transmissivity from slug tests ranged from 21 feet squared per day in borehole CH-5669 to greater than 12,000 feet squared per day in boreholes CH-5665 and CH-5667. After interpretation of geophysical logs, borehole television surveys, and driller's logs, all boreholes were screened such that water-level fluctuations could be monitored and discrete water samples collected from one or more water-producing zones in each borehole.