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r • i 11 November 2004-~ ` AGE-NC Project No- 02-0962 Page 2 of 14 I 11 a defined but are believed to be metamorphic and igneous in origin - F 1 i} r The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the Y' 2' principal sources of domestic ground water in'the 13,500-square mile San Joaquin Valley Ground' ' Water Basin(Basin 5-22) The estimated depth to ground water at the site is approximately 20 to 25 feet below surface grade(bsg)based on information from quarterly monitoring events performed by ' AGE at the adjacent Nomellini Construction Company, the ground water elevation is estimated at approximately 15 to 20 feet below mean sea level(MSL) Ground water flows generally toward the nbrth'to northeast, however, this may vary due to local recharge and discharge patterns 1 r '- 2 2 FUEL-DISPENSING SYSTEM UPGRADE In February 2003, as part of afuel-dispensing system upgrade, the UST sumps, fuel dispensers and associated piping were excavated by the Filmer Construction Company, excavated soil was ' stockpiled on site for evaluation prior to transport to Forward Landfill for disposal During the excavation, soil samples were collected by an AGE representative from the floor of the piping . excavation, the fuel dispenser excavation and soil stockpiles for analysis The laboratory analysis ' reported total petroleum hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-d), benzene, toluene, ethylbenzene, and xylenes (BTEX), and the fuel additive methyl tert butyl ether (MTBE) from the areas of the former piping and fuel dispensers Analytical results are summarized iii Table 1, Figure 2 depicts the approximate location of the sample collection points 1 2f3 PREVIOUS SITE ASSESSMENTS " On 30 and 31 October 2003, seven soil probe borings (B I though 137)were advanced at the site A ' total of 19 soil samples from the seven soil borings were analyzed for petroleum hydrocarbon products TPH-g and TPH-d were detected in soil samples collected from borings B3 at 10 feet bsg ' (133-10) and 15 feet bsg(B3-15) and boring B7 at 30 feet bsg(B7-30), at maximum concentrations of 47 milligrams per kilogram (mg/kg)TPH-g and 110 mg/kg TPH-d, in sample B3-15 Laboratory chromatograms show the TPH-g concentrations were detected within the diesel-range spectrum, 1 indicating that the TPH-g may actually be degraded diesel fuel MTBE and xylenes were detected in the soil sample collected from boring B3 at,15 feet bsg,at concentrations of 0 045 mg/kg and Q 10 mg/kg, respectively 1r1 ! Grab ground water samples collected from six of seven soil borings were analyzed for petroleum hydrocarbon products TPH-g and TPH-d were detected in,ground water samples collected from ' borings B2 and B4, at maximum concentrations of 190,000 micrograms per liter (µg/l) TPH-g and 2,200,000µg/1 TPH-din boring B4 Laboratory chromatograms show the TPH-g concentrations were ' Advanced GeoEnvironmental,Inc ~ 5 w