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�- PUBLIC 1tALTHSERV &ES <br /> Quer„ <br /> �o .ccc <br /> SAN JQAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION x� <br /> Ernest M. Fujimoto, M. D., M.P.H., Acting Health Officer - <br /> 304 E. Weber Ave., Third Floor * P. O. Box 388 • Stockton, CA 95201-0388 <br /> 209/468-3420 <br /> UNOCAL CORPORATION JAN f�� o <br /> BOB BOUST <br /> P 0 BOX 5155 <br /> SAN RAMON CA 94583 <br /> RE. FORMER UNOCAL #2859 SITE CODE: 1213 <br /> 1665 PACIFIC AVE <br /> STOCKTON CA <br /> I <br /> San Joaquin County Public Health Services, Environmental Health Division <br /> (PHSlEHD) has reviewed the November 8, 1996 "Remedial Action Performance <br /> Summary July through September 1996" prepared by Pacific Environmental Group, <br /> Inc. for the above referenced site. The report is an evaluation of the Vapor Extraction <br /> (VES) System pilot test. <br /> The report states that the pilot test of this system was successful at removing nearly <br /> 2,000 pounds of hydrocarbons. The system is now operating at asymptotic levels <br /> meaning that the incremental benefit of continued operation has been lost. The report <br /> states that the internal combustion engine will be moved to another site during the <br /> fourth quarter of 1996. <br /> The efficacy of the VES system has been measured by the influent of hydrocarbons <br /> into the system. Recent groundwater monitoring activities have also provided data on <br /> the effectiveness of the VES system. Since January of 1996 when the VES system <br /> was activated there does not seem to be any significant trends in hydrocarbon <br /> concentrations in the two closest monitoring wells (MW-3 and MW-2 ) to the vapor <br /> extraction wells. There is no clear correlation between removal of vapor phase <br /> hydrocarbons and reduction of dissolved hydrocarbons in groundwater. <br /> The report refers to the vapor extraction system as a pilot test. The purpose of a pilot <br /> test is to gather data on the economic and technical feasibility of a full scale <br /> remediation system. PHSlEHD recommends a report be compiled which will draw <br /> conclusions based on data gathered from 1196-9196 on the feasibility of a full scale <br />` VES system for this site. The fact that the system went asymptotic with such a large <br /> kmass of hydrocarbons remaining in the subsurface indicates either a poorly designed <br /> system or a subsurface environment unfavorable to VES technology. <br /> The current regulatory status of this site is that the assessment of the lateral extent of <br /> groundwater contamination is complete, the assessment of soil contamination is <br /> A Division of San Joaquin County Health Care Services <br />