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April 7, 1992 ��MA <br /> ARCO Service Station No 760, Lodi, California <br /> o Residual and waste oil hydrocarbons were detected in soil sampled from <br /> under former tank T9 <br /> ONGOING WORK/PROPOSED WORK <br /> After reviewing the laboratory data from this investigation, it is our opinion that all the <br /> proposed vapor-extraction wells shown on our Proposed Remediation System (July 9, 1991 <br /> submittal) are not warranted Plate P-7 shows our revised locations of vapor-extraction <br /> wells <br /> i On the basis of work conducted during this and previous investigations at the site, ARCO <br /> has approved RESNA to nine soil borings in-the locations shown on Plate 7 to evaluate soil <br /> for gasoline and/or diesel fuel characterization in the following locations 1)-three bonngs <br /> at_and north of the dispenser islands, 2) four <br /> r bonngs near the former_waste oil tank location j <br /> (two of these bonngs will be located beyond the northern property line), 3) one boring <br /> through and below the former-tank cavity and 4)one boring south- of tine-tank cavity in the � <br /> planter_area The bonngs will be terminated at-ground water or when two consecutive soil <br /> samples-with'PlD rezdings` below-50 ppmv are recorded <br /> We- will observe-the conversion- of-a minimum of"four and a maximum of seven bonngs to <br /> `4-inch-diameter vapor-extraction_ wells as follows._1)_the two-boring s-located nnmednately" <br /> to the north of the dispenser islands, 2) the boring located in the immediate vicinity of the <br /> former waste oil- tank and 3) the boring located through the former tank cavity The _ <br /> screened zone for the vapor-extraction wells will be based on existing residual hydrocarbon <br /> concentrations previously detected in the vicinity of the drill site and PID results of soil <br /> samples collected in the field. Based on results of soil sample field screening for the <br /> remaining five bonngs, additional vapor-extraction wells will be constructed if necessary <br /> 38048-5 18 <br />