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L <br /> 1117 Lone Palm Avenue,Suite 201 <br /> `•/� Modesto,California 95351. <br /> ATC` 209-579-2221 <br /> Fax:209-5:79-2225 <br /> Shaping the Future' <br /> mean sea level. The regional surface topographic gradient in the vicinity of the site trends towards the <br /> r west. <br /> �•r The groundwater flow direction beneath the site is generally towards the northeast with a gradient of <br /> approximately 0.01 ft/ft (as recorded in November 2011). Since 2001, depth to groundwater from the <br /> monitoring well network has varied from approximately 36 to 53 feet bgs. Historical groundwater <br /> elevation data are included in Table 1. The subsurface litbology beneath the study area generally consists <br /> of silt with subordinate lenses of sand and clayto depths ranging from the ground surface to <br /> approximately 43 to 48 feet bgs.. <br /> 4.0 INDOOR AIR RISK ASSESSMENT <br /> Soil vapor points were not installed at the site. Soil and water quality data was used to evaluate risk of <br /> soil vapor intrusion. <br /> 4.1 Tier 1 Evaluation <br /> - Cardno ATC compared soil analytical data associated with the site to the values listed in Table C-2 Deep <br /> Soil Screening Levels(>3m bgs)for Residential Land Use where potentially contaminated groundwater-is <br /> a current or potential drinking water resource:of the Tier. 1 Environmental Screening Levels (ESLs) as <br /> published by the San Francisco Bay Regional Water Quality Control Board (SF RWQCB) in November <br /> 2007. Additionally,Cardno ATC compared the soilanalytical data to the EPA Region 9 RSLs. . <br /> Analytes of interest detected in the soil samples were TPHg, toluene, ethylbenzene, xylenes, and MTBE <br /> with the highest concentrations generally reported at an approximate depth of 10 to 15 feet,bgs as <br /> observed from soil borings MW2, OS2, SB 1, SB4 and SB7. As a result, Cardno ATC compared only the <br /> highest reported concentrations for these analytes of interest to the Tier 1 ESLs. <br /> Below is a table depicting the highest reported concentrations in mg/Kg for the analytes of interest <br /> detected in the soil samples collected.from the site, the RWQCB Region 2 Tier 1 ESLs, and the EPA <br /> Region 9 RSLs for soil concentrations as reported in mg/Kg. This table was prepared for the purpose of <br /> comparing the highest reported concentrations from the soil samples collected at the site to the RWQCB <br /> Region 2 Tier 1 ESLs and the EPA Region.9 RSLs(April 2012,industrial soil). <br /> Analyte Highest Reported RWQCB Region 2 EPA Region 9 <br /> Concentration(mg/Kg) ESLs(mg/Kg) RSLs Industrial <br /> Soil(mg/Kg) <br /> TPH-g 10,000 83 <br /> Eth lbenzene 320 3.3 27 <br /> Toluene 390 2.9 45,000 <br /> X lenes 1,700 2.3 2,700 <br /> MTBE 0.042 0.023_ 220 <br /> 1,2-DCA 0.010 0.0045 2.2 <br /> I <br /> S:Enviromental\22493\Reports\Eggiman Closure Report.doc 5 <br /> i <br />