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NPL Site Narrative for Modesto Ground Water Contamination

Modesto, California

Federal Register Notice:  March 31, 1989

Conditions at proposal (June 24, 1988): The City of Modesto, Stanislaus County, California, began monitoring ground water in September 1984 to test 25 percent of its municipal water supply, as required by California Assembly Bill 1803. Of the 24 wells tested, 12 were contaminated. Municipal Well #11 was found to be contaminated with 16.7 parts per billion (ppb) of tetrachloroethane; the State action level is 4 ppb. The well has been taken out of service. The area obtains all its drinking water from wells. An estimated 142,000 people obtain drinking water from Modesto municipal wells within 3 miles of the site.

The California Department of Health Services (CDHS) and the Stanislaus County Environmental Health Department have identified Halford's Cleaners, which is less than 0.5 mile upgradient of Municipal Well #11, as a likely source of the contamination. These agencies found up to 176,000 ppb of tetrachloroethane in soil at Halford's where a buried storage tank was being excavated and determined that Halford's discharge to the sewer was contaminated. CDHS also found 84.6 ppb of tetrachloroethane in a private well adjacent to Halford's. CDHS is conducting an area-wide search to determine if there are additional sources of contamination.

Status (March 31, 1989): CDHS has identified five additional potentially responsible parties based on a soil vapor investigation.

For more information about the hazardous substances identified in this narrative summary, including general information regarding the effects of exposure to these substances on human health, please see the Agency for Toxic Substances and Disease Registry (ATSDR) ToxFAQs. ATSDR ToxFAQs can be found on the Internet at ATSDR - ToxFAQs (http://www.atsdr.cdc.gov/toxfaqs/index.asp) or by telephone at 1-888-42-ATSDR or 1-888-422-8737.

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