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App/led GeoSystems 43255 Mission Blvd. Suite B Fremont, CA 94539 (415)651-1906 <br /> May 29, 1987 <br /> AGS 87050-1 <br /> Mr. Robert Niblack <br /> Central Valley Regional Water <br /> Quality Control Board <br /> 3443 Routier Road <br /> Sacramento, California 95827-3098 <br /> Subject: Work plan for hydrocarbon contaminant delineation and <br /> hydrogeologic characterization at USA Station #65, <br /> 2500 West .Lodi Avenue, Lodi, California. <br /> Dear Mr. Niblack: <br /> The following represents a summary of work that Applied <br /> GeoSystems proposes to conduct at the above-referenced station. <br /> We propose this work to delineate potential on-site hydrocarbon <br /> contamination in soil and ground water and to characterize the <br /> site hydrogeology. We include a work plan that describes in more <br /> detail the procedures that will be followed during this <br /> investigation. <br /> We understand that Pacific Environmental Group, Inc. (PEG) <br /> installed monitoring wells S-1 and S-2 and drilled two other soil <br /> boreholes on site in March, 1987. Evidence of relatively high <br /> levels of hydrocarbon constituent contamination was encountered <br /> in the ground water of both S-1 and S-2 . The wells were <br /> installed adjacent and to the north and south of the tank cavity. <br /> Moderate to strong product odor between the 30- and 40-foot <br /> depths was encountered in soil samples collected from the two <br /> holes. No 'product odor was found when drilling the two shallower <br /> boreholes. PEG inferred a ground water gradient toward the <br /> northwest, on the basis of general surface topography and <br /> drainage patterns. Because there are only two observation wells <br /> present at the site, the ground water flow direction could not be <br /> measured. <br /> It is our understanding, from information supplied by USA <br /> Petroleum, that the tanks passed a recent precision pressure <br /> test. The reported presence of slight hydrocarbon odor <br /> contamination from approximately 15 to 30 feet and moderate to <br /> strong hydrocarbon odor from 30 to 40 feet in both S-1 and S-2 <br /> suggest that the USA' tank cavity may be the source of the <br />