PCBs are chemical compounds that were once used in many industrial, construction, and electrical applications. The largest use of PCBs was in electrical equipment, including transformers and capacitors. PCBs have been also found in a variety of construction materials such as insulation, roofing, and siding materials. Manufacturing of PCBs was banned in 1979. Demolition of older buildings are potential sites of ongoing concern. Stormwater runoff is considered a significant pathway for PCBs to enter the Bay.