SITE INFORMATION AND CORRESPONDENCE

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Donna Gardner 2 29 September 2006 26056 Thornton Rd., Thorn. , 143 to 150 Sand it II 150 to 155 Clay LI 155 to 164 , Sand 160 to 185 LI - 164 to 231 - clay and Shale 225 to 235 tt 231 to 245 Sand 2 245 to 350 Clay 350 to 360 Sand 360 to 371 Clay and Shale 371 to 376 Sand 376 to 380 Shale 380 to 395 Sand 395 to 4203 Shale 1 — depths in feet bgs 2 — Total Depth of Well Casing, 245 feet bgs 3 — Total Depth of 28-inch Diameter Boring, 420 feet bgs While Well #2 is screened below 135 feet bgs and has a 70-foot cement sanitary seal, the drilling log shows sand pack from 0 (surface) to 245 feet bgs. If the drilling log is correct, then the construction of Well #2 could present a preferential pathway for groundwater pollution deeper than 70 feet into the deeper water zones. However, monitoring of Well #2 has shown no impact from petroleum hydrocarbons to date. In November 1990, WaterWork (A.K.A. RESNA), a consultant for Wilson, Hoslett and Whitridge installed monitoring wells MW-1 through MW-3 to 28 feet bgs (Figure 2). The depth to shallow groundwater was 12 feet bgs. Soil samples were not analyzed since sample holding times were exceeded. Maximum 1990 groundwater groundwater concentrations were: TPHg, 45,000 pg/L; benzene, 270 pg/L; toluene, 15 pg/L; ethylbenzene, 63 pg/L; and xylenes, 110 pg/L. Three additional monitoring wells (MW-4 through MW-6, Figure 2) were installed in October 1991 and screened from 5 to 15 feet bgs. The downgradient groundwater direction was towards the west. Two areas of soil contamination (near MW-3 and MW-4) were noted in the January 1992 Interim Problem Assessment Report, Soil and Groundwater Contamination. MW-3 is located immediately northwest of the former USTs, while MW-4 is approximately 20 feet south of Well #2. The maximum groundwater results (MW-4) in October 1991 were: TPHg, 19,000 pg/L; benzene, 110 pg/L; toluene, 79 pg/L; ethylbenzene, 640 pg/L; and xylenes, 1,700 pg/L. The service station buildings were removed in November 1994, and eight soil borings were advanced from 20 to 45 feet bgs to assess the vertical and lateral extent of the soil contamination. The maximum vertical extent of soil contamination was reported as 30 feet bgs. Approximately 1,400 cubic yards of soil and 10,000 gallons of excavation water were removed in February 1995. The excavated soil was stockpiled onsite and aerated In November 1996. No petroleum hydrocarbons were detected in the analyses of the stored excavation water, and the water was discharged to land at the Site in May 1995 without a Regional Board permit. The October 1997 Problem Assessment Report recommended a pilot study for soil vapor extraction and air sparging, which was approved by SJCEHD but was not implemented. In March 2001, a groundwater pumping test was proposed by consultant ATC