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5 GEOMATRIX beneath the project area is prohibited for use as domestic or municipal supply by the City of Tracy for administrative reasons unrelated to the presence of degraded crude oil. Subsurface soil at a nearby property located directly north across West Byron Road(San Joaquin ' County APNs 238-02-10113114)known as the Dividend property has been affected by the same petroleum hydrocarbons as that found at the Nicholaw property. CPL has performed extensive site investigations, and Geomatrix performed a human health risk assessment for the Dividend property, dated 24 May 1995, that was submitted to the DTSC. The purpose of the health risk assessment was to evaluate the potential health risks to future site residents associated with 3.. residual crude oil/Bunker C oil present in subsurface soil along the southern boundary of the Dividend property. The health risk assessment was conducted in accordance with the DTSC's Human Health Screening Evaluation as described in the Preliminary Endangerment Assessment Guidance Manual. The evaluation required the assumption that the affected soil is exposed at the ground surface and that residents are exposed to the maximum concentrations of chemicals detected in the soil. The health risk assessment concluded that potential human exposure to the crude oil/Bunker C oil-affected soil (hereinafter referred to as "oil-affected" soil) would not result in significant health risks to future on-site residents. The DTSC approved the conclusions of the human health risk assessment in a memorandum dated 3 November 1995. Based on the risk assessment results for the Dividend property and the fact that concentrations of petroleum hydrocarbons at the Nicholaw property are lower than those at the Dividend property(2700 mg/kg vs. 7500 mg/kg), the residual petroleum at the Nicholaw parcel should pose no significant risk to future on-site residents. PHS-EHD concurred with this conclusion and issued a conditional closure letter(attached) on 6 November 1996. i. SOIL MANAGEMENT PLAN This management plan is intended to address options available for handling the oil-affected soil L if it is excavated during construction of the subdivision or when placing/repairing below-grade utilities. As previously stated, the area of known impact does not extend more than 50 feet south of the property line and occurs between depths of 5 and 15 feet. 1:1WPD0CS�C34991NICH0SMP.D0C 3