Approximately 42 percent of all West Virginians rely on groundwater for their domestic water supply. However, prior to 2008, the quality of the West Virginia's groundwa-ter resource was largely unknown. The need for a statewide assessment of groundwater quality prompted the U.S. Geo-logical Survey (USGS), in cooperation with West Virginia Department of Environmental Protection (WVDEP), Divi-sion of Water and Waste Management, to develop an ambient groundwater-quality monitoring program.