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Pore pressure dissipation tests performed in the May 1999 CPT borings also provide an indication of the groundwater bearing zone's hydraulic conductivity References included in Appendix C document the relationship between hydraulic conductivity and CPT data Pore pressure dissipation tests were performed in borings CPT-1, CPT-2 and CPT-3 for zones located below the groundwater table Hydraulic conductivities calculated from this CPT data (also shown in Appendix C) ranged from 1 04 x 10-5 cm/s to 4 15 x 10-6 em/s 22 Chemical Characteristics of Subsurface Soil During the April 1987 UST removals, impacted soil was overexcavated to a depth of 28 feet Approximately 450 cubic yards of soil, including some 120 cubic yards that was noted to be impacted with gasoline, was removed Subsequent drilling, sampling and analysis performed at this site indicates that the mass of remaining petroleum impact in soil is relatively limited It appears d4 a� that the overexcavatiori performed in 1987 removed most of the impacted soil J%, in the vicinity of the USTs -N, i 04—r—, 4%,I1 As shown in Table 3, there are relatively few soil samples that contained detectable concentrations of TPH-G or BTEX compounds Several of these soil samples were collected at depths below the groundwater table, which were likely cross-contaminated by impacted groundwater at that depth and location The deepest soil sample with measurable petroleum impact was -- BPZ�'l u/aS collected at 55 feet from the MW-1 boring location This indicates that thecvk- vertical extent of petroleum hydrocarbon impact is less than 60 feet Geologic ✓r�tt��c ,x ��, � �� cross sections, shown in Figure 4 and Figure 5, also illustrate petroleum _-rte,i,,,w4d hydrocarbon concentrations in soil samples 1 p,,,o��KO,, VM 23 Chemical Characteristics of Groundwater 6) 02 Assessment of petroleum hydrocarbon impact in groundwater has been performed at this site since July 1987 Historielgroundwater monitoring indicates that initial decreases of petroleum hydrocarbon concentrations likely 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 I from well MW-1, located near the source, have ranged from a high of 6,800 micrograms per liter (µg/L) in July 1987 to non detect in November 2002 (see Table 4 and associated graphs) Total petroleum hydrocarbons as gasoline (TPH-G) concentrations in samples from MW-1 have ranged from a high of � EO Remedial Action Completion Report The Earthgralns Company i acihty 2651 South Airport Way Stockton California Prepared for 1 Ht FARTHCRArNS COMPANY Prepared by Philip Services Corp H IENV16246p1,25121382CG15tackton\StocktonlRemed+alComplettonRepondoc April 14 2003