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E <br /> grade in the immediate vicinity of four 5000-gallon <br /> of these w611s. Analysis of <br /> underground storage tanks. In 1987, WCC performed ground <br /> Nater monitoring and sampling petroleum <br /> the ground water samples detect) ranging <br /> from 154,000 parts <br /> hydrocarbons as gasoline (TPH-Gg- <br /> per billion (ppb) in MW-2 to 231,000 Pb in MW-3, <br /> 1? <br /> Concentrations at these levels are indicative of Alemulsified <br /> free product. The well locations wefound by orted b <br /> Geosci on <br /> iierto be eferenceset0 wellled f locationshreflectthose <br /> those foundby <br /> WCC. <br /> Alton Geoscience. of the <br /> WCC. subcontracted NET to perform a soil gas survey <br /> underground ste"zge tanY. area. In Jura 1988andEbenzene, <br /> ed for TPH-G, <br /> 26 soil gas samples and analYConcentrations of TPH--G.and/or <br /> toluene, and xylenes (BTX) • of the samples collected at <br /> BTX were detected in the majority hest <br /> depths below grade ranging from 7was detected inhthe�area of <br /> concentration of TPH-G (300 pp ) depth of 7 feet below <br /> the underground storage tanks at a <br /> grade.' ' <br /> ound storage tanks, and the <br /> in February 1989, the four undergr <br /> val <br /> was oil tank were removed by Placer Tractor Services. <br /> r Eight soil samples were taken from the orgak remo <br /> nic lead, and <br /> t excavation and analyzed for as detected <br /> ethylene dibrles <br /> omide• TPH-G was detected in the rang ng from <br /> taken from the ations <br /> tank cavity <br /> attl4cfsetn6rinches below ngra a to <br /> 0.023 spm in the west <br /> 3.7 ppr; in the southeast <br /> corner at 14 lesttaken cfrom the <br /> grade. TPH-D was detected in t- .� ncen <br /> north end H the tank cavity t bslowngradeoand 1.7. ppmpinln i <br /> the northwest corner at <br /> the northeast corner at lelie4dibromidefeet a nwere not detected at or <br /> organic lead and y <br /> above reported detection limits in all soil samples. € <br /> ilnder the direction of the California RRegiBnala�site <br /> Quality <br /> i <br /> Control Board, Central valley Region ( 4 actives of the <br /> investigation was completed by WC <br /> C• The obi <br /> site investigation werel o remedialefine halternatives.extent of Monitoring <br /> contamination and <br /> identify in March and April 1990• <br /> Wells MW-1 th�rvu9h MW-4 were dry borings were drilled and <br /> March and April 1990,and EXvwere idetected i.n.only two of the <br /> sampled. TPH <br /> soli samples. The five soil borings were converted <br /> ground water Monitoring Wells MW-5 through MW-9. to <br /> May 1390, the average <br /> depth to ground Water was determined al <br /> be app �.5 feet below ground surface. The general <br /> approximately $. <br /> ter gradient across the site at this <br /> direction of ground wa <br /> 'i <br /> 2 <br />