The U.S. Environmental Protection Agency (EPA) has reached an agreement with the Orange County Water District to conduct a remedial investigation and feasibility study to address a large area of groundwater contamination in Northern Orange County known as the “North Basin.” The work required by the agreement is expected to take up to two years to complete and is estimated to cost up to $4 million.

“The Orange County groundwater basin is a vital source of drinking water for the 2.4 million people it serves,” says Alexis Strauss, EPA’s acting regional administrator for the Pacific Southwest. “Protecting this resource is critical for our long-term water sustainability.”

The investigation and study will include the installation and sampling of 14 groundwater monitoring wells and data collection to determine the extent of contamination in the North Basin and provide EPA with information needed to develop an initial cleanup plan. Contamination in the North Basin is believed to be the result of industrial solvent spills and leaks from manufacturing, metals processing businesses and dry cleaning facilities over the last several decades.

The North Basin is located in the northern portion of Orange County and includes parts of Fullerton, Anaheim and Placentia, Calif. The Orange County groundwater basin is a source for drinking water for the region, providing the majority of the water used in 22 cities. The area of groundwater contamination is several miles long and over a mile wide. All drinking water publicly served meets federal and state drinking water standards.

Historical industrial activity is thought to have contaminated the soil and groundwater with chemicals, including tetrachloroethene (PCE), trichloroethene (TCE), 1,1-dichloroethene (1,1-DCE), and 1,4-dioxane. Federal standards for drinking water for both TCE and PCE are 5 parts per billion. Initial investigation of the groundwater in the North Basin has detected PCE concentrations up to 3,300 parts per billion and TCE concentrations up to 23,000 parts per billion, and four contaminated drinking water wells have been shut down. 

Exposure to PCE can have health impacts including liver damage and increased risk of cancer. TCE has been linked to various health conditions, including impacts to the central nervous system, immune and endocrine systems, fetal heart development, kidney and liver cancer, and non-hodgkins lymphoma. The extent and nature of potential health effects depends on many factors, including the contaminant levels and the length of exposure to the pollution.

Under the agreement, the district will reimburse EPA for the cost of overseeing the work. The district is volunteering to complete this study under EPA oversight so that cleanup can begin as soon as possible. EPA is working to identify potentially responsible parties to carry out the cleanup plan after it is finalized.  In addition, EPA is working with the Santa Ana Regional Water Quality Control Board and the California Department of Toxic Substances Control to clean up soil and groundwater at a number of facilities believed to have contributed to the regional contamination.