Ground water in the area of the Borough of Lansdale has been withdrawn since the early 20th century for use as drinking water and for industrial supply. In 1979, water from public-supply wells in the area was found to be contaminated with trichloroethylene (TCE), tetrachloroethylene (PCE), and other synthetic organic compounds (CH2MHill, 1991). Through additional sampling, an area of ground-water contamination was identified, and the site, known as North Penn Area 6, was placed on the National Priority List (NPL) by the US Environmental Protection Agency (USEPA). The North Penn Area 6 site encompasses about 3 mi2 (2.6 km²) and includes at least six sources of contamination on separately-owned properties largely within the borough of Lansdale (CH2M Hill, 1991). The site is located on the US Geological Survey (USGS) Lansdale and Telford 7.5-minute topographic quadrangle maps (fig. 1, pl. 1).