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fTi Subsurface Investigation Report-Tosco(Former BP)Service Station No. 11 195 Lathrop,California April 11,2002 ground surface to depths ranging from 6 feet bgs to approximately 10.5 feet bgs. Generally, underlying the poorly graded sand in all borings, are layers of silt with sand or silty sand, which are in turn underlain by well graded sand to the total explored depth of 12 feet bgs, except in B-3, in which the well graded sand was not encountered. In B-5, a layer of silt was encountered, extending from approximately 7.5 feet bgs to approximately 8.5 feet bgs,and was interbedded with poorly graded sand. Underlying the poorly graded sand in B-5,is a layer of well graded sand extending from approximately 10 feet bgs to the total explored depth of 12 feet bgs. Detailed descriptions of the soil encountered during this investigation can be found in the boring logs in Appendix B. 4.2 Soil Analytical Results Analytical results of the soil samples collected during this investigation showed no detectable concentrations of hydrocarbon constituents in any of the samples. The stockpile sample, Comp-1(A,B) contained concentrations of lead that are acceptable for disposal at Allied Waste Forward Landfill. The analytical results from the soil samples are summarized in Tables 2 and 3. 4.3 Groundwater Analytical Results Grab groundwater sample B-6 did not contain detectable concentrations of any hydrocarbon constituents analyzed. Samples B-1,B-2, B-4 and B-5 contained MtBE at 95, 10,000,25 and 3.0 ppb, respectively(EPA Method 8260). TPHg and BTEX constituents were not detected in any of the groundwater samples collected during this investigation, except groundwater sample B-5, which contained Total Xylenes at 2.8 ppb. The analytical results of the grab groundwater samples are summarized in Table 1. 5.0 . INTERIM REMEDIAL ACTION 5.1 Groundwater Removal and Disposal Groundwater has been purged on a weekly basis from conductor casing CC-WS and monitoring wells MW-3, MW5 and MW-10. The groundwater is purged from the wells directly into vacuum trucks by Onyx and transported to the Tosco Refinery in Rodeo,California for disposal. During UST replacement activities in 1999, approximately 39,000 gallons were purged from the former LIST pit. Between May 5, 2000 and February 5,2002 approximately 136,367 gallons of groundwater were removed from CC-WS, approximately 29,917 gallons of groundwater were removed from MW-3, approximately 209,267 gallons-of groundwater were removed from MW-5 and approximately 33,950 gallons of groundwater were removed from MW-10. From the start date of January 19, 1999 to February 5,2002 approximately 609,261 gallons of groundwater were removed from the site. Groundwater removal totals and dates are summarized in Table 4. 5.2 Groundwater Sampling Groundwater samples have been collected periodically from the conductor casing CC-WS,MW-3,MW-5 and MW-10 and analyzed for TPHg by EPA Method 8015, and BTEX by EPA Method 8020, MtBE by EPA Methods 8020 or 8260. The results have been used to document hydrocarbon concentration trends and comply with Tosco Refinery requirements. Sample dates and analytical results are summarized in Table 4. % 140193.11-2 6 I i