ARCHIVED REPORTS_ENVIRONMENTAL SITE ASSESSMENT ADDENDUM

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D. SOIL MATRIX SAMPLING Three soil borings (SB-1001, -1002, and -1003) were placed adjacent to the septic tanks (Figure 2). Boring SB-2 was placed within the leach field of the septic system. Two borings (SB-1003 and -1007) were placed adjacent to the former location of a UST located at the southeast corner of the building. One boring (SB-5) was placed in the backfill of the former location of a UST east of the main building. One boring (SB-4) was placed west of the septic system after it was determined that groundwater moves in a westerly direction. The final boring (SB-7) was placed near a concrete patch inside the building. Refer to Figure 3 for well locations around the septic system. Discrete soil samples were collected for laboratory analysis at selected depths in all borings. Disposable gloves (changed between each sample) were utilized to limit cross-contamination between samples. Soil samples were collected in one-foot-long by 1.5-inch-diameter clear acetate sleeves cut from 4-foot-long sampling sleeves (direct-push samples). The soil samples were sealed with TeflonTM sheets, capped, and placed in a cooler maintained at 4°C with ice. Soil samples were transferred to a California-certified fixed-base laboratory(Enviro-Chem) for analysis under chains-of-custody. All soil samples were analyzed for VOCs by USEPA Method 8260B and for Total Petroleum Hydrocarbons (TPH - carbon-chain lengths identified) by USEPA Method 8015B. Chains-of- custody are provided, together with the laboratory reports, in Appendix B. E. GROUNDWATER SAMPLING Groundwater was encountered at approximately 27 feet bgs in all seven temporary groundwater monitoring wells installed (SB-1 through SB-7). Groundwater samples were collected with disposable bailers from each temporary monitoring well. (See Appendix C for well construction details.) Groundwater samples were analyzed for VOCs by USEPA Method 8260B and for TPH-cc by USEPA Method 8015B. Laboratory reports and chains-of-custody are provided in Appendix B. The tops of the temporary well casings were surveyed relative to the surface elevation of the property(approximately 13 feet above mean sea level(msl)). By using these elevation data and by measuring the depth to groundwater in the well casing, the elevation of groundwater in each temporary well was calculated, plotted, and contoured (Figure 3). The resulting groundwater surface has an overall dip to the northwest/west. The groundwater high at SB-1002 may be due to the leach field beneath this location. The groundwater low beneath SB-1005 may be due to the excavation pit at that location. The distribution of benzene and 1,2-DCP in groundwater (concentrations apparently decrease from southeast to northwest) is explained by the direction of groundwater movement (from southeast to northwest), as suggested by Figure 4. Addendum to Limited Phase II Environmental Site Assessment Report Pinnacle Environmental,Inc. 248 Industrial Avenue,Stockton,CA 95206 Page 7