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. FILE COPY . <br /> • ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> Donna K.Heran,R.E.H.S. Carl Bergman,R.E.H.S. <br /> Q. 304 East Weber Avenue, Third Floor <br /> Director Mike Huggins,R.E.H.S.,R.D.I. <br /> ' Al Olsen,R.E.H.S. Stockton, California 95202-2708 <br /> • Douglas W.Wilson,R.E.H.S. <br /> c4 FORa P Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. Fax: (2O9) 464-0138 Robert McClellon,R.E.H.S. <br /> Program Manager Mark Bareellos,R.E.H.S. <br /> JUL 17 2002 <br /> PAUL SUPPLE <br /> ARCO PRODUCTS COMPANY <br /> P O BOX 6549 <br /> MORAGA CA 94570 <br /> RE: ARCO #6100 SITE CODE: 1708 <br /> 25775 Patterson Pass Road <br /> Tracy, CA <br /> San Joaquin County Environmental Health Department (EHD) has reviewed <br /> Quarterly Status Report, Fourth Quarter 2001, dated 28 February 2002, <br /> (4QR01); Quarterly Status Report, First Quarter 2002, dated 30 April 2002, <br /> (1QR02); Subsurface Assessment and Well Installation Report, dated 28 <br /> February 2002 (the SAWI Report); and Soil Sampling Report (SSR), dated 30 <br /> April 2002, for the above-referenced site - all prepared by Delta Environmental <br /> Consultants, Inc. (Delta). A brief summary of recent site activities and findings is <br /> as follows: <br /> During the fourth quarter 2001, six exploratory borings (B-33 through B-38) were <br /> advanced to depths ranging from 135 to 140 feet below surface grade (bsg) to <br /> collect soil and ground water samples to assess the vertical and lateral extent of <br /> the fuel-impacted soil and ground water. In addition, four clusters of two 4-inch <br /> diameter PVC monitoring wells (MW-2 through MW-9, eight wells total) were <br /> installed to further assess impacted ground water. Only the new MW-2 well <br /> encountered enough water to measure and sample. Two cross sections were <br /> prepared showing the subsurface geological framework and the relationship of <br /> selected wells and borings to that framework with the analytical results posted. <br /> The greater portion of the contaminant mass was reported as being encountered <br /> between 35 and 65 feet below surface grade (bsg); previous investigations have <br /> encountered significant mass at depths as great as 80 feet bsg, with reduced <br /> concentrations extending to depths as great as 106 feet bsg. Free product occurs <br /> just offsite at a depth of approximately 106 feet bsg (MW-1), where various <br /> hydrocarbons have been detected to depths as great as 201 feet bsg (total <br /> depth). <br /> Quarterly ground water monitoring events were conducted during the fourth <br /> quarter 2001 and first quarter 2002. Measurable ground water was encountered <br />