SITE INFORMATION AND CORRESPONDENCE

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Former Chevron Station 9-5775 - 3 - 12 May 2009 301 W Kettleman Lane, Lodi Risk Assessment In June 2001, a risk assessment was submitted to assess the potential for soil and groundwater contamination to volatilize as vapor and migrate into adjacent building and homes. Potential exposure pathways at the site were evaluated using a conservative tiered approach similar to the Risk Based Corrective Action (RBCA) method from American Society for Testing and Materials (ASTM) W 1739-95 and ASTM PS 104-98 guides for RBCA screening levels for soil and groundwater. Regional Board staff approved the use of the San Francisco Bay Regional Water Quality Control Board, Environmental Screening Levels (ESLs). A Tier 2 Johnson and Ettinger model was also used for the risk assessments of chemicals not addressed in the ESLs (methanol, ethanol, tertiary butyl alcohol, and ethylene dibromide). All Tier 1 and Tier 2 soil and groundwater constituent concentrations were below the risk assessment levels for vapor intrusion. On 10 October 2007, Regional Board staff requested assessment of the residual soil contamination to evaluate the effectiveness of the soil vapor extraction system and to compare soil concentrations with the November 2007 ESLs as a condition for Site closure. In March 2008, one direct push boring was advanced in the proximal location of the former USTs (Figure 4). Soil samples were collected from 10 ft. bgs to 56.5 feet bgs, the total depth of the boring. Only TPHg and MtBE were detected in soils at the following depths and concentrations in mg/kg. The ESLs were not exceeded by the soil sample results. Table 1 March 2008 Post -remediation _Confirmation Soil Sampling Results ESLs 21_5' 25.5' 33' 43.5' 45' 46.5' 48' TPH_ 1_0_0 <1 75. 5.9 <1 <1 <1 <1 MtBE 0.023 0.0007 <0.005 <0.0005 0.0005 0.004 0.0006 0.001 Sensitive Receptor Survey: A Sensitive Receptor Survey of water supply wells, including domestic and municipal wells, was conducted in 1999. Only one Lodi municipal well (Well 12) was identified within 2500 feet of the site. Well 12. located approximately 350 feet southwest of the site, was monitored monthly from 1999 to 2003 by the City of Lodi for another petroleum hydrocarbons release adjacent to the Well 12 (Shell, 420 W. Kettleman Lane). and reported no impacts to the drinking water supply from petroleum hydrocarbons, including MtBE. Currently, Well 12 is only used for emergency supply by the City of Lodi. No additional domestic wells were reported within 2,500 feet of the site. The nearest surface water is South Main Canal, located approximately 0.75 mile west of the site. Site Geology and Hydrogeology: The site topography is relatively level, and the ground surface is located at 43 feet above mean sea level. Subsurface soils consist of poorly sorted beds of clay, silt, sand and gravel to 220 ft. bgs. the total depth investigated. Depth to water from 1999 to 2006 varied from 52 to 65 ft. bgs. Based on the assessment activities performed on the Site, four water -bearing zones have been identified beneath the Site: Zone A, shallow groundwater, extends from 55 to 65 ft. bgs, and Zone B, from 70 to 90 ft. bgs. The downgradient direction of groundwater in