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PUBLIC HEALTH SERVICES OpgU�N <br /> �.` .. <br /> SAN JOAQUIN COUNTY a:: <br /> JOGI KHANNA M.D.,M.P.H. 1 <br /> Health Officer <br /> P.O. Box 2009 . (1601 East Hazelton Avenue) Stockton,California 95201 <br /> c4�iFo'R�''`P <br /> (209) 468-3400 <br /> rJAN 31 MI <br /> Glenn Dembroff U <br /> Ultramar, Inc. �. � `� L1 <br /> P.O. Box 466 <br /> Hanford, CA 93232-0466 <br /> RE: Beacon Station No. 502 IN REPLY REFER TO SITE CODE: 1320 <br /> 35 N. Cherokee Lane <br /> Lodi, CA <br /> Please be advised that this office has reviewed the Third Quarter <br /> 1990 Letter Report and Ultramar's request for site "closure. " <br /> Recent sampling events and laboratory analysis have found no <br /> detectable concentrations of hydrocarbon contamination. However, <br /> the groundwater surface has dropped significantly and MW #1 could <br /> not be sampled. Detection of hydrocarbon contamination was as high <br /> as 48 parts per billion (ppb) benzene in MW #4 and 27 ppb benzene <br /> in MW #1 on September 28, 1989. Monitoring well #1 again exhibited <br /> benzene contamination (0. 6 ppb) on June 29, 1990. <br /> With these levels of benzene detected so recently, San Joaquin <br /> County, Public Health Services, Environmental Health Division <br /> (PHS/EHD) cannot agree that "closure" is an appropriate course of <br /> action. The drop in groundwater elevation does not indicate that <br /> remediation has taken place. <br /> In similar situations of deepened water table elevations, vapor <br /> extraction has proven to be a viable remedial action for source <br /> reduction. This may be a viable course of action for Ultramar to <br /> pursue during interim site remediation. <br /> In addition, the groundwater plume of contamination has not been <br /> adequately defined. Additional wells are necessary in downgradient <br /> locations of the former tank excavation and piping systems to <br /> insure that contamination has not migrated away from the site. <br /> Off-site wells (downgradient of MW #1) may be appropriate. <br /> Replacement of MW #1 is also advised. <br /> A work plan for groundwater contamination plume definition and an <br /> interim remediation (vapor extraction) should be submitted to <br /> PHS/EHD and the Central Valley Regional Water Quality Control Board <br /> (CVRWQCB) by March 5, 1990. <br /> A Division of San Joaquin County Health Care Services <br />