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Ms Margaret Lagorio S E C O R April 28, 2005 Page 3 • monitoring wells (MW8S/I/D through MW 10S/IID) consisting of three wells nested at each location SENSTIVE 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,1, 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 first quarter 2005 monitoring and sampling event, the following maximum concentrations were reported in TRC's Quarterly Monitoring Report (QMR) TPHg 220 pg/L (micrograms per liter) (MW-1) (TRC 1Q'05 QMR) Benzene <1 0 pg/L (TRC 1Q'05 QMR) MTBE 400 fag/L (MW-1) (TRC 1Q'05 QMR) TPHg and MTBE concentrations in groundwater continue to decline, particularly in source area wells MWA 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 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 Ozone Sparge System Operation The ozone sparge system consists of panel mounted KVA C-Sparge TM panel that produces 4 grams of ozone per hour (0 009 pounds per hour) The system injects to 10 sparge points AS1 through AS10 Between December 30, 2004 and March 22, 2005, the system ran for 168 hours, resulting in 1 5 pounds of ozone injected and 9 percent runtime System data is presented in Table 1 The system often shuts down due to a I