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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> a' y <br /> Donna K. Heran, R.E.H.S. UnitSupervisors <br /> Fl <br /> East WCarl Bor man, R.E.H.S. <br /> 9 304 Easeber Avenue, Third g <br /> Director Mike Huggins, R.E.H:S., R.D.I. <br /> Ai Olsen, R.E.H.S. Stockton, California 95202-2708 <br /> � Douglas W. Wilson, R.E.H.S. <br /> Program Manager Telephone: 209 468-3420 <br /> � iFba Laurie A. Cotuna, R.E.H.S. p ( ) Margaret Lagorio, R.E.H.S. <br /> Fax: (209) 464-0138 Robert McClellon, R.E.H.S. <br /> Program Manager Mark Barcellos, R.E.H.S. <br /> JUS! 0 3 2005 <br /> RODGER LISTON <br /> DARPETRO INC USA SERVICE STATION <br /> 3450 EL CAMINOCERES CA 95307 <br /> RE: DARPETRO, INC Site Code: 1060 <br /> 749 E CHARTER WAY <br /> STOCKTON, CA 95202 <br /> San Joaquin County Environmental Health Department (EHD) has received and <br /> reviewed Amended Work Plan to Work Plan Dated October 16, 2004 (AWP), <br /> dated 27 May 2005 , to install one assessment boring . <br /> CGG proposes in AWP to advance one cone penetration test (CPT) boring to a <br /> target depth of 160 feet below surface grade in the former UST pit near boring B- <br /> 1 to collect soil samples at unspecified depth intervals and ground water samples <br /> at 10-foot intervals from 60 feet below surface grade (bsg ) to total depth . CGG <br /> proposed to collect no soil samples from the vadose zone in the CPT boring as <br /> analytical data has previously been collected from boring B-1 . <br /> EHD approves the method and target depth for the proposed CPT boring , but <br /> recommends several changes to the proposed scope of work: <br /> Locate the CPT boring near BMA and collect vadose zone soil samples <br /> for laboratory analysis from depths previously tested in boring BM-1 . The <br /> soil analytical data indicates that BM- 1 is located in an area of more <br /> intense contamination where contaminants have a greater potential for <br /> deeper migration . Also , vadose zone soil data from the CPT boring can be <br /> utilized to evaluate the effect of the soil vapor extraction (SVE ) <br /> remediation and assess the current potential for further impact to <br /> groundwater. <br /> • Rather than mechanically collection groundwater samples at 10-foot <br /> intervals , utilize the lithological interpretation and the pore pressure data <br /> shown on the CPT log to identify intervals of potentially higher <br /> permeability and target these intervals for obtaining the groundwater <br /> samples . These higher permeability zones , usually comprised of coarse- <br /> grained soil , may act as lateral contaminant migration pathways and are of <br /> significant interest. <br /> I <br />