SITE INFORMATION AND CORRESPONDENCE

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PUBLIC HEALTH SEWICES o� SAN JOAQUIN COUNTY �' T JOGI KHANNA M.D.MT H , Health Officer P.O. Box 2009 0 (1601 East Hazelton Avenue) 0 Stockton, California 95201 C� ON , (209) 468-3400 RICHARD CALLISTRO (C O� [PY SAN JOAQUIN COUNTY ADMINISTRATOR CAPITAL PROJECTS 222 EAST WEBER AVE ROOM 678 STOCKTON CA 95202 JUN 1 2 1992 RE: San Joaquin County Human Services SITE CODE: 1257 145 South Sutter Street Stockton, CA 95202 APN 149-120-11 San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has completed review of the "Phase II, Groundwater Investigation" dated June 1, 1992 and prepared by Weston. PHS/EHD has the following comments for your consideration. The report stated that monitoring well, MW1, was destroyed during construction of the Human Services Building. PHS/EHD does not have record of a destruction permit having been issued. Please provide PHS/EHD with details of the destruction of MW1. In 1989 significant levels of hydrocarbon contamination were detected in the groundwater, 28,000 ppb benzene in MW2 and 2.8 ppb benzene in MW3. The extent of groundwater contamination, at the 1989 water table level, was not determined. Once hydrocarbon contaminants reach the water table, contaminants generally float on top of the water and migrate with the water as it moves in its flow path or gradient direction. The contaminants may also move vertically up and down, with corresponding fluctuations in the water table. Monitoring wells, MW2 and MW3, installed in 1988 were reported to be dry in 1991. The depth to water data collected for this site shows a vertical drop in the water table of approximately 26 feet between 1989 and 1991, indicating a vertical zone of contamination within the unsaturated soils. This "smearing' of contamination within the unsaturated zone can contribute to the general soil contaminate plume. A Dmvnn of San Jmqum("unw Hca1N(:ue Xmcce