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Oxygenate compounds methyl tert butyl ether(MTBE), ethyl tert butyl ether (ETBE), tert butyl alcohol (TBA), and tert amyl methyl ether (TAME) have never been detected in site groundwater samples The oxygenate compound dl-isopropyl ether (DIPE) has been measured at concentrations less than 16 µg/L in samples collected from wells near the source of the release Monitoring data indicates that the lateral extent of DIPE Impact is limited to Earthgrain's property boundaries Current depth to groundwater averages about 40 feet below ground surface (bgs) The lowest depth to groundwater, observed during our historic site monitoring, was about 60 feet bgs in December 1992 The PHS/EHD suggests that groundwater was at a depth of about 80 feet in 1978 Groundwater has consistently been evaluated to flow in an east-northeast direction across the site (see Figure 3) Groundwater flow has ranged from a direction of 53 degrees east of north(N53E) to N83E The historical mean direction of groundwater across the site is approximately N70E Current groundwater elevation data and historical elevation data are presented in Table 1 and Table 2, respectively Groundwater analytical data for this quarter is in Table 3 A summary of historic BTEX and TPH-G concentrations in groundwater is contained in Table 4 A summary of historic oxygenate concentrations in groundwater is contained in Table 5 1.4 Natural Biodegradation of Petroleum in Groundwater Groundwater samples were collected in December 1996 and analyzed for various parameters to indicate the occurrence of natural intrinsic biodegradation of the petroleum hydrocarbon impact Groundwater sampling and analytical procedures followed those described in Protocol for Monitoring Intrinsic Bioremediation in Groundwater (Chevron Research and Technology, March 1995) A copy of the Chevron document and results of our assessment are contained in Philip's February 21, 1997 Quarterly Groundwater Monitoring And Natural Biodegradation Assessment Report The tested parameters included alkalinity, dissolved oxygen, oxidation- reduction (redox) potential, pH, specific conductivity, temperature, nitrate, sulfate, and ferrous iron Philip observed definite correlations between petroleum hydrocarbon concentrations and the location of samples within the plume, to dissolved oxygen, nitrate, sulfate, and redox potential values These results, and the observed decreases in petroleum concentrations over time, 1 strongly indicate that naturally occurring biodegradation is occurring in groundwater at this site May 1999 Subsurface Investigation and Groundwater Monitoring Report The Earthgrams Company Facility 2651 South Airport Way Stockton,CaliforniaPrepared for THE EARTHGRAINS COMPANY Prepared by Philip Services Corp C V21382\121382CGI1259971o599REP DOC June 22,1999 3