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' y 4 <br /> �� c? cffy cion of n <br /> ENVIRONMENTAL SOLUTIONS ir unCo <br /> 31 17 <br /> July 29, 1998 <br /> Projcct 20805-147.004 <br /> Ms. Carol Oz <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 East Weber, Third Floor <br /> Stockton, California 95202 <br /> Re: ARCO Service Station 2186 located at 3212 N. California Street, Stockton, <br /> California <br /> Dear Ms. Oz: <br /> On behalf of ARCO Products Company, Pinnacle Environmental Solutions, a division of <br /> EMCON (Pinnacle), is responding to the request for vertical definition of soil impacts <br /> presented in your letter dated May 13, 1998, This letter response is being sent in lieu'of <br /> the requested workplan. Additionally, the well survey you requested has been initiated and <br /> a report will be submitted upon completion. The request for vertical characterization to a <br /> minimum depth of 75 feet below ground surface (bgs) using continuous sampling methods <br /> was based upon detected concentrations of total petroleum hydrocarbons as gasoline <br /> (TPHG), benzene, toluene, ethylbenzene, and total xylenes (BTEX) in soil samples <br /> collected from 56.5 bgs. The 75 feet bgs depth was cited to correspond to the historical <br /> groundwater level low. <br /> Review of the soil analytical results shows that the detected TPHG concentration was <br /> 1.1 milligrams per kilogram (mg/kg); the method reporting limit is 1 mg/kg. The detected <br /> benzene concentrations were 0.015 mg/kg and 0.019 mg/kg for borings B-1 and B-3, <br /> respectively. Toluene, ethylbenzene, and total xylenes were also detected at low <br /> concentrations, below 1 mg/kg. These low concentrations do not suggcst that a large mass <br /> of undefined residual petroleum hydrocarbon contamination is now present below the <br /> current groundwater table and providing a source for ongoing groundwater impacts. <br /> Further vertical definition appears unwarranted based upon the low detected petroleum <br /> hydrocarbon concentrations in soil. <br /> We also request the source of the information for the 75 feet bgs historical groundwater <br /> level cited in order to evaluate the range of groundwater levels during the period of site <br /> operation. The ARCO station has been in operation since 1973. <br /> SA0 AA2186LETR.DOC-961mttJ <br /> 3939 Cambridge Road,Suite 220 Cameron Park,California 95682 (530)676-6884 ($30)676-6885 Fax <br />