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NA www.atcassociates.com �- 6.0 LOW RISK CLOSURE CRITERIA Criterion 1: The source of the UST release has been identified and removed. The petroleum hydrocarbon release appears to have been from the petroleum storage tank system (USTs, distribution lines and dispensers). Older non-operational USTs and product lines have been removed as discussed in previous sections of this report, thus eliminating the primary source of the fuel leak. The current UST system adheres to the applicable compliance regulations. Recent analytical data suggest an ongoing fuel release is highly unlikely. Criterion 2: The vertical and horizontal extent of subsurface impact has been adequately characterized. �- The vertical extent of TPHg and MTBE are localized in the vicinity of the current UST system. Historic soil analytical data indicate the area of greatest impact is in the vicinity of soil boring B- 3. Maximum TPHg concentrations were identified in 1990 at 460 mg/Kg(at 15 feet bgs)-with maximum benzene concentrations at 3.9 mg/Kg (at 15 feet bgs r. this area corresponds to the northwestern side of the canopy area where the initial excavation was performed. Additional vertical delineation was conducted in 1999 when boring ATC-5 was advanced to 42 feet bgs. Discrete soil samples collected from 18 feet bgs reported MTBE and TBA concentrations at 0.11 mg/kg and 0.12 mg/kg, respective ly.-�Additional soil samples collected �- from 38 feet bgs did not report constituents above the laboratory reporting limit!Depth discrete groundwater samples collected from 20 feet bgs reported benzene concentrations of 6.7 pg/L, TBA concentrations of 840 pg/L and MTBE concentrations of 2,900 pg/L. An additional groundwater sample collected at 42 feet bgs reported MTBE concentrations of 39 pg/L. Additional depth discrete groundwater samples were collected in January 2010 (SB-4 and SB-5) from a depth of approximately 35 to 40 feet bgs. No constituents were reported above the specific laboratory reporting limits except for MTBE (19 pg/L) and TPHg (78 pg/L) reporting in downgradient boring SB-5. �- Dissolved hydrocarbon and fuel oxygenates in groundwater have been adequately assessed laterally. Data collected from historic on-site and off-site subsurface investigations and groundwater monitoring suggest that the contaminant plumes appear to be localized in the vicinity of monitor wells MW-2 and MW-5. Criterion 3: The dissolved hydrocarbon plume is not migrating Data indicate the TPHg and MTBE plumes are not migrating. Each respective contaminant plume is either decreasing or stable. Criterion 4: No water wells, deep drinking water aquifers, surface water, or other sensitive receptors are likely to be impacted. The California Department of Water Resources records were reviewed in order to determine the location of domestic and production wells within a 2,000 foot radius of the Site. One domestic well was identified % of a mile due north of the Site. The owner explained the well is used for Quik Stop Market No. 132 July 21, 2011 ATC Project Number 75.62503.3206 Page 4 of 5