SITE INFORMATION AND CORRESPONDENCE

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SITE BACKGROUND On October 30, 1991, Warren E. Gomes Excavating, Inc., of Rio Vista, California, excavated and removed three USTs (TK1, TK2 and TK3) from the site. The USTs contained gasoline and diesel fuel. A Condor representative was on site during the UST removal to collect soil samples. The field activities were observed by Carol Oz of the PHS/EHD. A small hole was found on the lower fill end of TK3 (diesel tank). Petroleum staining and odors were noted in the soil beneath the former locations of the USTs. Groundwater was not encountered during the UST removal. Six soil samples were collected by Condor from the UST excavation at depths of 9 to 12 feet below the ground surface The samples were analyzed for TPH-G(gasoline), BTEX, TEPH (diesel), EDB (ethylene dibromide), and total lead. Laboratory analyses indicated elevated concentrations of TPH-G, TEPH, and BTEX constituents in the soil samples. For additional information, refer to Tank Pull Testing Results, prepared by Condor, dated November 18, 1991. At the direction of the PHS/EHD, Condor prepared a work plan to investigate the gasoline and diesel contamination associated with the former USTs (Soil and Groundwater Investigation Work Plan, dated May 30, 1995). The work plan was approved by the PHS/EHD and the Reclamation District#2029. On August 22, 1995, three hydropunch boreholes (HP-1, HP-2, and HP-3) were drilled at the site (see the figure attached to the back of Appendix B for borehole locations). Ronald Rowe of the PHS/EHD was on site periodically to observe the fieldwork. Gilbert Cosio of Murray, Burns, and Kienlen Engineering was on site to observe the drilling activities as a Reclamation District representative. Two of the hydropunch boreholes (HP-1 and HP-2) were located on the levee and were drilled to depths of approximately 16 and I 1 feet below the top of the levee (btl), respectively. The third hydropunch borehole (HP-3) was located below the levee and was drilled to a depth of approximately 6 feet below ground surface (bgs). Soil samples were collected at five foot intervals. Groundwater samples were collected using a Hydropunch II groundwater sampler. Gasoline odors were noted in each borehole. Laboratory analyses indicated concentrations of TPH-G and BTEX in the soil and groundwater samples analyzed from each borehole (see Tables B.1 and B.2, below). T EB Laboratory Result it-August 1995) B T E X TPH-G TEPH Detection 5.0 5.0 5.0 5.0 1.0 1.0-10 Sample I.D. Limits: mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg 1432-HPI-II (#) 1,200 3,100 5,500 22,000 300 190(diesel) 1432-HP2-11 (#) ND ND 130 2,800 22 ND 1432-HP3-5.5 61 68 5.2 91 7.5 16(diesel) Note:The last number in each sample to indicates the depth at which the sample was collected. Unit Conversions: Analytical mg/kg:parts per million(ppm) BTEX=benzene,toluene,ethyl benzene,and total xylenes. TPH-G=total petroleum hydrocarbons,quantified as gasoline. TEPH=total extractable petroleum hydrocarbons,quantified as diesel,motor oil, and kerosene. ND=none detected at or above laboratory detection limits. 9=detection limits raised due to gasoline interference.