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3.3 Physical Characteristics of Saturated Zone Groundwater at this site generally does not occur in clean, well-sorted sands 1 Rather, groundwater is more likely found within the finer grained silty and clayey sediments, which are relatively less permeable than sand As shown in Table 3 and Table 4, recent depths to groundwater average about 45 feet below ground surface The lowest depth to groundwater, observed during PSC's historic site monitoring, was about 60 feet in December 1992 EHD suggests that the groundwater table may have been at a depth of about 80 feet in 1978 Groundwater has consistently been evaluated to flow in a northeasterly direction of approximately N70E across the site As shown in Figure 5, groundwater flowed in this general direction (on June 21, 2004) at a gradient Iof about 3 1 x 10-3 feet per linear foot, typical of historic trends In 1994, PSC submitted the 55-feet depth soil sample from boring MW-11 for ' hydraulic conductivity analysis The hydraulic conductivity for the MW-11 sample was measured at 3 2 x 10-5 centimeters per second (cm/s), which is typical for a silty/clayey strata Pore pressure dissipation tests performed in the May 1999 CPT borings also provided an indication of hydraulic conductivity within the groundwater-beating zone These CPT-evaluated hydraulic conductivities ranged from 1 04 x 10-5 cm/s to 4 15 x 10-6 cm/s 3.4 Chemical Characteristics of Saturated Zone ' Assessment of petroleum hydrocarbon impact in groundwater has been performed at this site since July 1987 Historic groundwater monitoring ' indicates that initial decreases of petroleum hydrocarbon concentrations likely occurred due to natural degradation Recent groundwater monitoring indicates that PSC's remedial efforts haslffad an affect on further reducing petroleum hydrocarbon concentrations Benzene concentrations in groundwater samples collected from well MW-1, located 1 near the source, have ranged from a high of 6,800 micrograms per liter (ug/L) in July 1987 to non detect in November 2002 (see Table 5 and associated graphs) 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 110 pg/L measured in November 2002 Current petroleum hydrocarbon concentrations (from groundwater samples collected in June 2004) are further discussed in Section 3 4 1 of this report Oxygenate compounds MTBE, ETBE and TAME have historically not been detected in site groundwater samples (see Table 6) MTBE was detected in 12 ' June 2004 Site investigation Report The Earthgrams Company Facility 2651 South Airport Way-Stockton,California Prepared for SARA LEE BnKpvc GRO[Sp Prepared by Philip Services Corp H\'V162400132Nl21382EG4StncktonUvne 2004Inveetigatton Report doe August 9,2004