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f - Ms Margaret Lagono S E C ® R August 1, 2005 L Page 4 • wells (MW1 through MW3), four on-site, dual-casing groundwater monitoring wells (MW4S/D through MW7S/D), one on-site UST cavity well, and nine off-site groundwater monitoring wells (MW8S/I/D through MW10S/I/D) consisting of three wells nested at each location SENSITIVE RECEPTORS A 1996 Department of Water Resources (DWR) survey identified 10 wells located within the survey area These wells are located northeast to southeast of the site and are apparently utilized as cathodic protection or irrigation wells MONITORING AND SAMPLING Groundwater monitoring and sampling has been performed at the site since the second quarter 1996 From 1996 to 2000, the site was monitored and sampled quarterly In 2001, the site was monitored and sampled monthly In 2002, the site was monitored and sampled bi-monthly From 2003 to the present, the site has been monitored and sampled quarterly Currently, 11 wells (MW-1 through MW-4S and D, MW-6S and D, MW-8D, and MW-10S, I, and D) are monitored and sampled quarterly and 9 wells (MW- 5S and D, MW-7S and D, MW-8S and I, and MW-9S,1, and D) are monitored and sampled semi-annually in the first and third quarters Samples are analyzed for Total Petroleum Hydrocarbons as gasoline (TPHg), benzene, toluene, ethyl-benzene and total xylenes (BTEX) and the fuel oxygenates tertiary-butyl alcohol (TBA), methyl tertiary-butyl ether (MTBE), di-isopropyl ether (DIPE), ethyl tertiary-butyl ether (ETBE), tertiary-amyl . methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), ethylene di-bromide (EDB) and ethanol by Environmental Protection Agency (EPA) Method 8260B During the second quarter 2005 monitoring and sampling event, the following maximum concentrations were reported in TRC's Quarterly Monitoring Report (QMR) TPHg 150 pg/L (micrograms per liter) (MW-1) (TRC 2Q'05 QMR) Benzene 0 53 pg/L (MW-6S) (TRC 2Q'05 QMR) MTBE 240 pg/L (MW-1) (TRC 2Q'05 QMR) TPHg and MTBE concentrations in groundwater continue to decline, particularly in source area wells MW-1 and MW-2 Based upon data collected during ongoing quarterly groundwater monitoring and sampling, dissolved hydrocarbons are effectively delineated both laterally and vertically in the vicinity of the site CHARACTERIZATION STATUS Contamination in soil and groundwater has been adequately delineated REMEDIAL PERFORMANCE SUMMARY An ozone sparge system has operated at the site since August 15, 2002 The operation . of the ozone injection system and monthly groundwater sampling activities are summarized below 5886 2Q2005 QSSR SECOR International Incorporated