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ENVIRONMENTAL HEALTH DEPARTMENT <br /> Pp U.IN SAN JOAQUIN COUNTY Unit Supervisors <br /> =Lf COG <br /> r' `^ Donna K.Director <br /> R.E.H.S. Carl Bergman,R.R.E.H.S. <br /> D;recror 304 East Weber Avenue, Third Floor Mike Huggins,R.E.H.S.,R.D.I. <br /> At Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> hp, Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 Mark Barcellos,R.E.H.S. <br /> SEP 18 2003 <br /> HAROLD & DENA KNOWLES <br /> C/O LAW OFFICE OF PATRICK D RIDDLE <br /> 1811 GRAND CANAL BLVD STE 2 <br /> STOCKTON CA 95207-8107 <br /> RE: 102 S. Wilson Way Site Code: 9031 <br /> Stockton, CA <br /> San Joaquin County Environmental Health Department (EHD) has reviewed <br /> Second Quarter 2002 Groundwater Sampling and Vapor Extraction Report, <br /> dated 27 June 2002, Monitoring Well Installation and 1St Quarter 2003 Sampling <br /> Report, dated 24 June 2003, and data from other reports prepared on your behalf <br /> by Ground Zero Analysis, Inc. (GZA) for the above referenced site to evaluate <br /> GZA's recommendations to remove the soil vapor extraction (SVE) system <br /> currently installed on the site referenced above and to reduce the quarterly <br /> ground water monitoring requirements. <br /> GZA conducted intermittent rebound testing of the system during the first two <br /> quarters of 2002, each test of the system lasting approximately one week with <br /> approximately one week of non-operation between tests. The system was <br /> reported to have operated a total of 1,186 hours, removing an estimated 520 <br /> pounds of hydrocarbons, approximately 4% of the total 13,200 pounds of <br /> hydrocarbon removed. GZA estimated the cost of hydrocarbon removal to have <br /> been $ 240 per gallon. GZA did not provide the cost basis to demonstrate the <br /> estimated cost per gallon for removal. GZA estimated the hydrocarbon removal <br /> rate to be 5.5 pounds per day at the conclusion of the tests. <br /> During February 2001, GZA installed five confirmation borings designated C61 <br /> through CB5. Vadose zone and saturated zone soil samples were collected from <br /> CB1 through C134, saturated zone soil samples were collected from all five <br /> borings, and a grab ground water sample was collected from CB5. The vadose <br /> zone soil samples generally yielded nondetectable hydrocarbon and oxygenate <br /> concentrations, while several saturated zone soil samples yielded significant <br /> TPH-g concentrations. Most of the confirmation borings were not advanced <br /> directly adjacent to borings with previously acquired analytical data, but were <br /> located between one boring with impacted soil and a second boring with no soil <br /> data or nondetectable concentrations, leading to some ambiguity as to whether <br /> the confirmation borings are outside, along, or well within the margins of the <br /> plume of impacted soil. The most directly comparable sample pair was from CB4- <br /> 40 and VW1/VW4, approximately 5 feet apart, which suggests a TPH-g <br />