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Treadwell&Rollo <br /> • <br /> calculated background concentration of 8.76 mg/kg at one location(I OB-6-3.0). Residential <br /> non-cancer hazard-based risk is driven by arsenic and naphthalene in soil. No cancer or <br /> non-cancer hazard risks were determined to be associated with groundwater. <br /> At Area 11, cancer risk for landscape maintenance workers and residents is based on arsenic in <br /> soil (exceeded background concentrations in one sample) and PNAs. Arsenic and PNAs were <br /> found in the upper 6.5 feet of soil. Groundwater does not present a cancer or non-cancer hazard <br /> risk at Area 11. <br /> Arsenic at Area 20 exceeded background concentrations at three areas (20TP-1-1.0, 20TP-4-1.0, <br /> and 20TP-5-6.0), resulting in excess cancer risk to landscape maintenance workers and residents, <br /> construction workers, and commercial workers. Non-cancer hazard risk values were exceeded <br /> for residents, construction and landscape workers. Arsenic was generally found at the highest <br /> levels in the upper one foot of soil. Groundwater does not present a cancer or non-cancer hazard <br /> • risk at Area 11. <br /> The City of Stockton intends to redevelop these sites for recreational and commercial uses. <br /> Given the geotechnical conditions at the sites, it is highly unlikely that basement structures or <br /> significant below-grade construction will be used. Typical likely building foundation <br /> alternatives include slab-on-grade, pile, and mat foundations. Reworking of near-surface soil <br /> may be necessary to achieve the required soil compaction for foundation construction. Utility <br /> trenching may go to six feet below grade. Parking associated with new buildings will likely be <br /> asphalt over imported subgrade crushed rock. <br /> The DTSC has agreed to wave the preliminary alternatives screening step, and to focus the <br /> alternatives analysis on remedial alternatives likely to be used. In keeping with the type and <br /> extent of soil contamination and anticipated end-uses of OU 1, the following remedial <br /> alternatives have been evaluated: <br /> • 1. No further action <br /> 18 <br /> 25970318.PGS 15 November 2000 <br />