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remedial alternatives involvingexcavation ould entail excavation of 6,222 cubic yards <br /> of soil (assuming aerial extent of 4,8 square feet) or 3,111 cubic yards (assuming <br /> aerial extent of 2,400 square feet). Furthermore, access to the subsurface is restricted <br /> by surface structures and operations. Thus, the estimated volume and depth of <br /> contaminated soils the presence of overl ung structures, and nt uses of the facility <br /> indicate that excavation and disposal is not a viabl tion for soil remediation. <br /> Greyhound proposes to pe orm a final off-site drilling program and then evaluate in- <br /> situ methods, such as bioventing, for soil remediation. <br /> SUMMARY AND CONCLUSIONS <br /> Field Work Implementation <br /> In August 1994, eight exploratory boreholes were advanced at the Greyhound <br /> Terminal in Stockton, California. These boreholes were successfu_1 in defining <br /> ? the vertical and horizontal extent of subsurface soil contamination on-site. <br /> • Soil samples were collected at 5-feet intervals during advancement of the <br /> ' boreholes All of the samples in each borehole were submitted for chemical <br /> analyses. Soil samples were analyzed for TPHD and BTEX. <br /> • A Photographic Log of the field activities and has been included as Appendix C. <br /> Site Stratigraphy and Hydrogeology <br /> • Subsurface materials consist of clayey silts and silty clays with moderate to <br /> well-sorted, fine sand lenses. <br /> Shallow groundwater underlying the site occurs under unconfined conditions. <br /> Groundwater was encountered at depths. between 40 to 42 feet. <br /> ' Groundwater flows toward the south under a low hydraulic gradient of 0.003 <br /> feet per foot. <br /> Soil Chemistry <br /> TPHD was detected in 21 of the 71 samples submitted for analysis. <br /> Concentrations ranged from non-detect to 16,000 mg/kg. <br /> • BTEX was detected in 27 of the 71 samples submitted for analysis. Total <br /> BTEX concentrations ranged from non-detect to 3,910 µg/kg. <br /> ' The highest TPHD and BTEX concentrations occurred in the area of borings <br /> SB-2, SB-7, and SB-8 at a depth of 15 to 30 feet below grade. <br /> Analytical results suggest that soil contamination is not limited to Greyhound <br /> property. A limited off-site drilling program is recommended to completely <br /> define the extent of the soil contaminant plume to the west of the facility. <br /> 1 <br /> PARESSYROIIVOLI WP1725396 08969125386R02 DOC <br /> � 5 <br />