Twelvemile Creek flows southwest to Lake Hartwell through Pickens County, South Carolina. A narrow riverine channel, the creek has steep, heavily vegetated shorelines. Approximately seven miles upstream from Lake Hartwell, the lower portion of Twelvemile Creek contains three impoundments, each associated with a dam (Easley-Central, Woodside I, and Woodside II dams from upstream to downstream).

The presence of PCBs in Twelvemile Creek/Lake Hartwell was discovered when surface water, sediment, and fish from the area were sampled in the mid-1970s. The source of this contamination was determined to be the Sangamo-Weston, Inc. capacitor manufacturing plant in Pickens, South Carolina.

Sangamo-Weston, Inc. operated the plant from 1955 to 1987. The liabilities associated with that operation were subsequently assumed by Schlumberger Technology Corporation (STC). Dielectric fluids, used in the manufacture of capacitors until 1977, contained PCBs, and materials containing these fluids were disposed via land burial. In addition, PCBs were present in discharges from the plant to Town Creek (a tributary of Twelvemile Creek). Surface water and sediment contaminated by the discharged PCBs eventually migrated downstream to Twelvemile Creek and Lake Hartwell.