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PUBLIC HEALTH SERVICES PAuI~•. <br /> �o <br /> SAN JOAQUIN COUNTY ` <br /> ENVIRONMENTAL HEALTH DMSION ` <br /> Karen Furst, M.D., M.P.H., Health Officer .,a. ". <br /> 304 East Weber Avenue, Third Floor• Stockton, CA 95202 <br /> 209/468-3420 <br /> PETER NEMIEC FILE COPY <br /> ASSISTANT COUNSEL <br /> UNOCAL CORPORATION <br /> DIVERSIFIED BUSINESS GROUP UUN 2 9 1998 <br /> 376 VALENCIA AVENUE <br /> BREA CA 92823 <br /> RE: UNOCAL SITE CODE: 1181 <br /> 437 E. Miner Avenue <br /> Stockton, CA <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) <br /> has reviewed the "Vertical Fuel Hydrocarbon Plume Delineation Hydropunch <br /> Investigation/Piezometer Installation' work plan dated May 26, 1998, prepared by <br /> ARCADIS Geraghty & Miller, Inc. for the above referenced site. <br /> PHS/EHD does not agree that the investigation proposed will complete the site <br /> investigation necessary to provide data for the preparation of a corrective action plan <br /> (CAP). <br /> Information collected to date indicates that the petroleum hydrocarbon contamination at <br /> this site is the result of an unauthorized release from the underground storage tanks that <br /> were operated from 1922 until 1967. PHS/EHD has not been provided records of depth <br /> to groundwater during these years, but historically there have been significant variations <br /> in depth to groundwater in this area. For instance, in 1978 depth to groundwater in the <br /> area of this site was about 70 feet below surface grade (bsg). In 1986 and currently, <br /> depth to groundwater at the site was/is about 27 feet bsg. It is not known when the <br /> unauthorized release of petroleum hydrocarbons occurred. Therefore, the depth to <br /> groundwater at the time of the release(s) is not known. <br /> Soil contamination was documented at a depth of 45.5 feet bsg by a soil sample <br /> collected at that depth during boring of UL. The vertical extent of soil contamination has <br /> not been defined and the proposed work will not provide that definition. Petroleum <br /> hydrocarbons that have absorbed to the soil and have not dissolved into the <br /> groundwater yet are a continuing source of groundwater contamination. The <br /> investigation should not be limited to current dissolved-phase hydrocarbons. The <br /> potential for future releases to the groundwater from contaminated soil should also be <br /> investigated by sampling of the soil above and below current groundwater until the <br /> vertical extent of soil contamination has been demonstrated. <br /> A Division of San Joaquin County Health Care Services <br />