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PUBLIC HEALTH SERVICES <br /> =mac°y <br /> SAN JOAQUIN COUNTY 'sem <br /> ENVIRONMENTAL HEALTH DMSION <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 COPY <br /> ARCO STATION #4493 <br /> P 0 BOX 6549 DEC 14 11999 <br /> MORAGA CA 94570 <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 groundwater'grab' sample will be collected using <br /> a hydropunch or equivalent method". <br /> The work plan states that the lateral extent of petroleum 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 Med Stockton Waterfront Brownfrelds Project, <br /> Phase II Environmental Investigation Weber Block(Area 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 water 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 were also reported as non-detect upon <br /> analysis for petroleum hydrocarbon constituents. <br /> Four monitoring wells (MW 1 through MW-4) currently exist 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-4evidenced <br /> contamination at the.lune 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 County Health Care Services <br /> -- <br />