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PUBLIC HEALTH SERVICES <br /> SAN JOAQUIN COUNTY <br /> to. <br /> ENVIRONMENTAL HEALTH DWISION <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 <br /> 2091468-3420 <br /> PAUL SUPPLE <br /> ARCO STATION #4493 <br /> P O BOX 6549 <br /> MORAGA CA 94570 DEC 141999 <br /> RE: ARCO Station #4493 SITE CODE- 1042 <br /> 205 N Center Street <br /> Stockton CA 95202 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHSIEHD) has <br /> reviewed the"Work Plan for Additional Assessment" dated November 29, 1999 that was prepared <br /> by Secor International Inc, on behalf of the above referenced site and has the following <br /> comments. <br /> The lateral and vertical extent of the documented petroleum hydrocarbon contamination at the <br /> above referenced site has not been defined. The work plan proposes to continue the <br /> investigation of this contamination by,drilling one continuous core soil boring in the area of on-site <br /> monitoring well MW-4. The work plan states that the boring will extend to approximately 60-feet <br /> below surface grade (bsg), or until three consecutively clean ' soil samples are collected, and "If <br /> a second water-bearing zone is encountered, a ground ater'grab' sample will be collected using <br /> a hydropunch or equivalent method". <br /> The work plan states that the lateral extent of petroleu hydrocarbon contamination in soil and <br /> groundwater downgradient of the subject site has been defined by two soil borings, GW-1 and <br /> GW-2, that were part of an April 1998 Phase II site assessment that took place at the site referred <br /> to as the Weber Block site, which is located directly east of and downgradient from the subject <br /> site. These borings are described in a report titled Stockton Waterfront Brownfields Project, <br /> Phase 11 Environmental Investigation Weber Block(Ara 9) dated November 1998, that was <br /> prepared by Black&Veatch. Boring GWA was advanced to a total depth of 16-feet bsg and <br /> boring GW-2 was advanced to 20-feet bsg. Grab wate samples were collected from first <br /> encountered groundwater, reported as 14.1-feet bsg in GW-1 and 17.7-feet bsg in GW-2. <br /> Analytical results were reported as non-detect for petroleum hydrocarbon constituents. Soil <br /> samples collected at maximum depth of 13.5-feet bsg ere also reported as non-detect upon <br /> analysis for petroleum hydrocarbon constituents. <br /> Four monitoring wells (MW-1 through MW-4) currentlyexist at the subject site. Each well extends <br /> to maximum depth of 25-feet bsg, with screen intervals from 5 to 25-feet bsg. MW-4 evidenced <br /> contamination at the June 17, 1999 monitoring event oF 10,800 parts per billion (ppb) total <br /> petroleum hydrocarbons as gasoline,(TPHg) and 766-ppb methyl tertiary butyl ether(MtBE). <br /> MW-3 had 144-ppb MtBE at the same event. <br /> A Division of San Joaquin Coun Health Care Services <br />