SITE INFORMATION AND CORRESPONDENCE

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Spingolo Trucking \WUWOI -4 - v 25 November 2014 . 1011 N. Broadway Ave., Stockton San Joaquin County 13)Site lithology consists of clay, silt, and sand from surface to 65' bgs (Figure 6). Depth to groundwater varied from 45' bgs to 55' bgs. Groundwater flow direction varied from northwest to southwest (Figure 7). The groundwater gradient varied from 0.001 ft/ft to 0.004 ft/ft. 14) The consultant did not calculate initial or residual mass of TPH. Estimated residual mass is calculated by the formula area (A) times thickness (h) times soil bulk density (Pb) times average concentration in kg/kg times 2.2 (lbs. per kg). Staff used the soil data plotted on cross section A-A' (Figure 6), which showed two USTs areas impacted by TPHd and TPHmo at USTs 4 and 5, and by TPHg at UST 1 and MW-3. The USTs 4 and 5 average of nine TPHd soil sample concentrations was 4,837 mg/kg for an impacted soil column measuring 10' by 10' by 35' deep (3,500 ft.3). Estimated TPHd mass of USTs 4 and 5 is 3,500 times 100 (Pb) times 0.0004837 (kg/kg) times 2.2 for 3,724.49 lbs. or 614 gallons. TPHmo was detected in the P-1 samples, so the same soil volume was used for TPHmo as TPHd. The USTs 4 and 5 average of three TPHmo soil sample concentrations was 697 mg/kg. Estimated TPHmo mass of USTs 4 and 5 is 3,500 times 100 times 0.0000697 times 2.2 for 53.67 lbs. or 8.13 gallons. The UST 1 average of four TPHg soil samples concentrations was 13.15 mg/kg for an impacted soil column measuring 5' by 5' by 25' deep (500 ft.3). Estimated mass of TPHg is 500 times 100 times 0.00001315 times 2.2 for 1.45 lbs. or 0.22 gallons. The MW-3 average of two TPHg soil samples was 35 mg/kg for an impacted soil column measuring 10' by 10' by 10' deep. Estimated mass of TPHg is 1,000 times 100 times 0.00000035 times 2.2 for 0.077 lbs. or 0.0012 gallons. Total residual mass estimate for UST-1, USTs 4 and 5, and MW-3 is 622.3512 gallons. Four quarters of groundwater monitoring did not detect TPH, so there is no mass estimate for groundwater. 15) Public participation was conducted from 13 January 2012 to 15 February 2012 with no adverse comments. 16)The Site qualifies for a low risk closure under the State Water Resources Control Board Low Risk Closure Policy, based on the following rationale: 17) Groundwater Specific Criteria Exemption— Soil Only Case (Release has not affected groundwater.) The nearest supply well is 600' east of the Site. Four quarters of groundwater monitoring data from 2006 to 2007 indicated groundwater was not impacted above Water Quality Goals. See above Table 2 and Sensitive Receptor Survey section. 18)Petroleum Vapor Intrusion to Indoor Air 2a - Scenario 3 (example): Dissolved Phase Benzene Concentrations Only in Groundwater. For bioattenuation zone without oxygen measurements or oxygen <4% and benzene concentration are <100 Ng/L, the bioattenuation zone: Is a continuous zone that provides a separation of at least 5 feet vertically between the dissolved phase benzene and the foundation of existing or potential building; and contain total TPH <100 mg/kg throughout the entire depth of the bioattenuation zone. Benzene in groundwater was <0.5 ug/L. The upper five feet of soil is <100 mg/kg. P-1 TPHg samples just outside of UST 1 excavation were <100 mg/kg (8.5 mg/kg to 18 mg/kg)from 15' bgs to 30' bgs. MW-3 soil and P-2 and P-5 soil samples >100 mg/kg were MW-3 TPHg (60' bgs) and UST 4 and 5 TPHd and TPHmo (15' bgs to 50' bgs). 19)Direct Contact and Outdoor Air Exposure Exemption— the upper 10 feet of soil is free of petroleum contamination. The residual soil contamination that exceeds the LTCP for direct contact and outdoor air exposure (TPH >100 mg/kg) is located between 15' bgs and 60' bgs.