San Gabriel Valley (all Areas)

Description and History

The San Gabriel Valley Superfund sites include multiple areas of contaminated groundwater in the 170-square-mile San Gabriel Valley. The contaminated areas underlie significant portions of the cities of Alhambra, Arcadia, Azusa, Baldwin Park, Industry, Irwindale, El Monte, La Puente, Monrovia, Rosemead, South El Monte, and West Covina. The groundwater contamination was first detected in 1979. Following this discovery, the California Department of Health Services (CDHS) initiated a well sampling program to assess the extent of contamination. By 1984, when EPA added four areas of contamination to the National Priorities List (NPL), 59 wells were known to be contaminated with high levels of volatile organic compounds (VOCs).

The San Gabriel Basin aquifer is a critical source of drinking water for Southern California. Despite the contamination, the Valley’s groundwater continues to provide approximately 90 percent of the drinking water used by San Gabriel Valley businesses and residents. EPA’s Superfund projects are assisting in restoring water supplies that have been affected by the contamination. Additional projects have been funded by Federal grants, local assessments on water sales, and water rates.

Four areas of groundwater contamination have been listed in the National Priorities List (NPL). They are known as: San Gabriel Valley Area 1. San Gabriel Valley Area 2, San Gabriel Valley Area 3, and San Gabriel Valley Area 4.

Cleanup projects ("Operable Units") are underway in each of the four areas. In San Gabriel Vally Area 1 there are the El Monte, Richwood, South El Monte, Suburban Water Systems, and Whittier Narrows Operable Units. In San Gabriel Valley Area 2, there is the Baldwin Park Operable Unit. In San Gabriel Valley Area 3, there is the Alhambra Operable Unit. In San Gabriel Valley Area 4 there is the Puente Valley Operable Unit.

Contaminants and Risks

Groundwater contaminants include volatile organic compounds such as perchloroethylene (PCE) and trichloroethene (TCE), perchlorate, 1,4-dioxane, and N-nitrosodimethylamine (NDMA).

Who is Involved

Cleanup Results to Date

Potentially Responsible Parties

Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.

More than one hundred facilities are believed to have contributed to the contamination through improper handling and disposal of chemicals.

Community Involvement

Public Meetings:

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