Tetrachloroethylene is called PCE and it is widely used for dry-cleaning fabrics. PCE is stored in drums, tanks, and used in dry cleaning machines. Before it was regulated, PCE was used as a de-greaser and equipment cleaner. In the old days, it was commonly thrown out the back door in buckets of wash water so it is common to find PCE in soil, not only beneath dry cleaning stores, but also beneath the back yard, and along sewer and storm drain piping. PCE can also leak through soil to groundwater and it can contaminate drinking water supplies. According to the California State Water Control Board, PCE has contaminated 173 public water supply wells throughout California, with the most wells impacted in Los Angeles (128), San Bernardino (9) and Tulare (5) Counties. The good news is that PCE in groundwater can be remediated before plumes reach public supply wells if the contamination is detected early. Common remediation technologies include pump and treatment of groundwater, in situ chemical oxidation with peroxide or ozone, or de-chlorination by hydrogen-releasing compounds (HRC). Slow natural bio-degradation of PCE may also occur but the breakdown products of PCE is TCE and vinyl chloride which are also considered human carcinogens, so active remediation is preferred and best able to guard against the liability of contaminating public supply wells.