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1 t + <br /> 1 <br /> S 5 <br /> ' 31 ,October 2005 <br /> • " AGE-NC Project No 03-1080 <br /> Page 7 of 10 <br /> B1 and dispenser D1 is uncertain, and the vertical extent is undefined in the area immediately <br /> ' surrounding boring B 1 and dispenser D 1 �` <br /> Drinking water at the site is supplied by a domestic well(DM-1,Figure 2),installed in October 1997 <br /> ' and screened from 340 feet to 360 feet bsg Another domestic well is located south of the site at i <br /> 14852 South Highway 99,according to the CVRWQCB letter File reviewfor Closure Concurrence, <br /> 1 <br /> Moore Petroleum, Frank's Exxon 44, 14800 W Frontage Road(HWY 99), Manteca, San Joaquin <br /> ' County, dated 04 September 1998, this well was to be replaced with a deeper well Based on the <br /> lateral extent of contaminated ground water at the site and general ground water flow direction, it <br /> is unlikely for'the drir&ing water wells to be contaminated by impacted ground water from the site, <br /> ' <br /> 'in addition,a fate and transport analysis(Section 7 0 below)of the extent of contaminant migration <br /> from the dispenser area indicated that there should not be any additional contamination to ground <br /> water from the degraded petroleum hydrocarbons remaining in soil <br /> 11 <br /> The nearest surface water feature to the site is the San Joaquin River,located approximately 5 miles <br /> west of the site It is unlikely that water in Smith Canal is contaminated by impacted ground water 4 <br /> ' from the site based on its distance and direction (up-gradient) from the site <br /> j <br /> 1 <br /> lie7.0. FATE AND TRANSPORT ANALYSIS <br /> AGE utilized RISC Workbench, a commercial risk assessment and fate and transport software <br /> ' developed by British Petroleum Company in 1994,to analyze any impacts to ground water wells in <br /> the proximity of the contaminant source (dispenser D1) The assessment was conducted for <br /> ' petroleum hydrocarbon compounds detected in soil at the time of dispenser and piping upgrade in <br /> 2003 and the subsequent subsurface soil and ground water investigation in 2004 <br /> ' Based on AGE's contaminant mass model, AGE had calculated that an estimated 52 lbs, or <br /> 7 8 gallons, of total petroleum hydrocarbappear to appeto remain in app_roximately 940 ft3 of <br /> predominantly silty sand/sil soil the-average concentrations of TPH-g and TPH-d in the soil plume <br /> woul,b_4,,21!5 <br /> g M-243_ rig/k ( pA pendix F) However, for fate and transport analysis, AGE <br /> —,,-elected to utilize more conservative values for the contaminant concentrations Based on the average <br /> concentration ofjust the two impacted soil samples(D 1 and B 1-15)at the dispenser D 1 location,the <br /> ' TPH-g and TPH-d concentrations used for fate and transport analysis were 3,175 mg/kg and <br /> 4,345 mg/kg,respectively,the average ethylbenzene and xylenes concentrations were 5 5 mg/kg and <br /> 68 8 mg/kg, respectively, and the average MTBE concentration was 0 019 mg/kg (Table 4) AGE <br /> ' also simplified the soil model to a 15-foot by 15-foot by 15-foot mass, increasing the volume of the <br /> mass to approximately 3,375 ft3 (Table 5, Appendix G) <br /> ' The analysis assumes that the TPH-g and TPH-d consisted of aged petroleum hydrocarbons, with <br /> little or low concentrations of volatile organic carbons(aromatic fractions)remaining,therefore,the <br /> Advanced GeoEnvironmental,Inc el <br />