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r 1.3 Historic Groundwater Conditions Assessment of petroleum hydrocarbon impact in groundwater has been performed at this site since July 1987 Historic groundwater monitoring Indicates that decreases of petroleum hydrocarbon concentrations have partly occurred due to natural degradation Recent groundwater monitoring indicates that PSC's remedial efforts are having a substantial affect on further reducing petroleum hydrocarbon concentrations Benzene concentrations In groundwater samples collected from well MW-1, located near the source, have ranged from a high of 6,800 I micrograms per liter (µg/L) in July 1987 to a low of 2 9 µg/L in August 2002 (see Table 4) Total petroleum hydrocarbons as gasoline (TPH-G) concentrations in samples from MW-1 have ranged from a high of 196,000 µg/l, in April 1993 to a low of 650 µg/L measured In August 2002 Current petroleum hydrocarbon concentrations are further discussed in Section 3 2 of this report rOxygenate compounds methyl-tert-butyl ether (MTBE), ethyl-tert-butyl ether (ETBE), and tert- amyl-methyl ether (TAME) have never been detected in site groundwater samples (sec Table 5) The oxygenate compound dl-isopropyl ether(DIPE) has historically been measured at concentrations of 140 µg/L, or less in samples collected from wells near the source of the release The N compound tert-butanol (TBA) was detected in one groundwater sample collected from MW-1 on Novoer�ber8lQ ,999, and again in PZ-1 samples collected on October 18, 2001yand Xpn120, 2001, but has never been detected in any other groundwater sample collected at the site Current oxygenate concentrations are further discussed in Section 3 3 of this report As shown in Table 1 and Table 2, recent depths to groundwater average 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 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 at approximately N70E across the site Current groundwater elevation information is summarized in Section 3 1 of this report 1.4 Remedial Action On April 25, 2001, PSC Initiated operation of an air sparging and soil venting remediation system to address subsurface petroleum hydrocarbon impact Air sparging had initially been performed in well SP-1 However, PSC suspected that air sparging at the SP-1 location was not resulting in an adequate decrease of petroleum impact in groundwater Therefore, new sparging well SP-A was drilled and completed on March 14, 2002 New sparging well SP-A was r 6 August 2002 Groundwater Monitoring And Remediation Status Report The Earthgralns Baking Company 2651 South Airport Way Stockton,California Prepared for THF LARTIIGRAINS BAKING COMPANY Prepared by Philip Services Corp H1FNW24001325121382EG\Stockton\Stockton10802mon doc September 2 2002