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17 March 2003 AGE-NC Project No. 01-0886 Page 2 of 5 The Modesto, Riverbank and Turlock Lake Formations and overlying recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22). This basin is drained primarily by the San Joaquin River. The closest surface water feature to the site is the Mormon Slough and Stockton Diverting Channel, located approximately 1,500 feet south and 2,000 feet east of the site,respectively.Water from Canals drains into the San Joaquin River Deep Water Channel and is primarily used for commercial and recreational boating. Based upon ground water monitoring well information obtained from Main Street and Oro Avenue (50 feet north of the site),ground water flow direction is southeast to easternly and currently occurs at a depth of approximately 55 feet bsg within ground water wells.The sedimentary units are thought to be relatively horizontal and continuous over the area. 2.3. UNDERGROUND STORAGE TANK REMOVAL On 06 March 2002,three USTs,dispenser island and associated piping were removed from the site under AGE supervision. Six samples were collected beneath the USTs and three laboratory- composited/discrete soil samples were collected from the excavated soil. Total petroleum hydrocarbons quantified as gasoline and as diesel(TPH-g and TPH-d)were detected at concentrations up to 86 milligr.:m per kilogram(mg/kg)and 0.015 mg/kg.Toluene,ethyl benzene and xylenes (TEX) were detected at concentrations of up to 13 mg/kg (xylene); benzene was not detected in the excavation soil samples.The highest concentrations of contaminants was present in the southern samples from tanks#2 and#3; this location was the fill area to both USTs. Approximately 200 tons of soil were excavated during removal of the USTs. Two laboratory- composited and one-discrete samples were collected from the stockpiled soil prior to placement back into the excavation after completion of UST removal;the soil was placed back into the excavation because of the proximity to a major road way(adjacent). Subsequent analytical results of the discrete soil sample from one stockpile of approximately 25 yards of soil detected TPH-g at 13 mg/kg and benzene at 0.023 mg/kg. S p (�. 0 3 f2 i 1 )04,41 0.1 I I Y'� E 4-�4 Fuel additives were not detected in the samples. Analytical results of soil sample are summarized in Tables 1 and 2. 3.0. SCOPE OF WORK Based on analytical data from the UST system removal,hydrocarbon-impact to soil was encountered in the south end of the common UST excavation at the site; the EHD has requested an assessment