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PUBLIC HEALTH SERVICES �a>R <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DMSION <br /> Kasen Furst, M D , M P H , Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 <br />' 2091468-3420 Py <br /> PETER NEMIEC [ j <br />' ASSISTANT COUNSEL <br /> UNOCAL CORPORATION <br /> DIVERSIFIED BUSINESS GROUP UN 2 91M <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 wasris 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 contammation has been demonstrated <br /> A Division of San Joaqum County Heilch Cue Services <br />