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ENSR AECOM r Hydrocarbons as gasoline(TPHg) and benzene were detected in soils within 15 feet of former 1,000-gallon USTs. Quarterly groundwater sampling initiated;TPHg and benzene detected in all 3 wells. 1995 Limited Phase I ESA performed to identify other potential sites in area(GSI, 1995a). The nearby site identified as most significant was Jackson Buick, a leaking UST site, located approximately 100 feet south (generally cross-gradient) of the site. 1995 Five monitoring wells(U-4 through U-8) installed to 55 feet bgs; 3 soil borings (U-N through U-P/UV-1) drilled to 45 feet bgs; and vapor extraction well UV-1 installed to 45 feet bgs(GSI, 1995b). Soil concentrations at or near non-detect at soil borings U-N and U-O. TPHg and benzene detected in all wells except U-5 and U-6. 1997 Review of California Department of Water Resources files identifies 12 water supply wells within 1/z-mile of the site: 4 municipal supply wells, 6 domestic supply wells and 2 industrial supply wells. The nearest downgradient well is a municipal supply well, 1,580 feet east- northeast from the site (GSI, 1997). 1997 Monitoring well U-9 installed to 55 feet bgs downgradient of California Street(GSI, 1997). No soil impacts observed. TPHg and benzene detected above California Maximum Contaminant Limits(MCLs). Previously proposed soil vapor extraction (SVE) pilot test not performed due to 15-foot rise in water table between 1994 and 1997, which saturated zone of greatest soil impacts (i.e., 40-45 feet bgs). 1998 Two nested piezometers (NP-1-22/65/111 and NP-2-22/60/116) installed on either side of California Street. TPHg and benzene detected in soil in near-site boring NP-1. Benzene was detected above MCLs(PEG, 1998). 2000 Downgradient monitoring well U-10, downgradient monitoring well triplet U-11/U-12JU-13 (G-R,2000a), upgradient monitoring well couplet U-14/U-15, and off-site monitoring well couplets U-16/U-17, U-18/U-19, U-20/U-21, U-22/U-23 and U-24/U-25 installed (G-R, 2000b). Well couplets were screened from 65 to 75 and 110 to 120 feet bgs (groundwater Zone A and Zone B, respectively). U-10 was installed adjacent to, and with similar screen interval as NP-2-116, to test the reliability of the nested piezometers. Benzene was detected above CA ' MCLs in wells U-12, U-13, U-19 and U-21. Benzene was detected below MCLs in wells U-20 and U-23. Methyl tertiary-butyl ether(MTBE) was detected below MCLs in wells U-10, U-12, U-13 and U-22. 2000 Vapor extraction wells UV-2 and UV-3 were installed to a depth of 25 feet bgs. A 5-day SVE pilot test was performed, during which vapors were extracted from wells UV-1, UV-2 and UV-3 at rates of between 9 and 23 standard feet per minute(scfm)at applied vacuums of between 9 and 17 inches of water column. The pilot test report(G-R,2000b) did not recommend further SVE operations, due to a limited area of vacuum influence and a low rate of hydrocarbon recovery(G-R, 2000b). Approximately 25 pounds of total hydrocarbons were recovered. 2000 Ozone sparge well couplets SP-1 AIB, SP-2A/B and SP-3/B were installed below the water table at depths of 120(A wells)and 75 feet bgs.(B wells), and ozone sparge wells SP-4A and SP-4B were installed to depths of 119 feet bgs and 72 feet bgs, respectively(G-R, 2000b). A - C-SpargeTM ozone microsparging system began operations on December 12,2000. 2002 Ozone sparge wells SP-1 C and SP-3C were installed to a depth of 45 feet bgs. Sparge well triplets SP-5A/B/C and SP-6A/B/C were installed to depths of 40 (C wells), 65 (B wells)and 111 feet bgs (A wells)and added to microsparge system. 2002 Monitoring well U-26 installed. No constituents detected in soil. MTBE detected below MCLs in groundwater. J:1Rem_EnglPro]ect Files1P60(6000- 2_2 January 2006 6999)16940-UNOCAL Portfolio Closure%940- UNOCAL Portfolio Closure\Site 0167-Stockton East Minor\CSM ReportlCSM Report_Final.doc