ARCHIVED REPORTS_SOIL MANAGEMENT PLAN

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GEOMgTRIX • The subsurface soil in the project area is predominant) silt and Y clay, with isolated sandy lenses, to a depth of at least 25 feet. The water table is approximately 11 feet bgs. It should be noted that shallow groundwater beneath the project area is prohibited for use as domestic or municipal supply by the City of Tracy Municipal Code (Section 1 1.1.16) for reasons unrelated to the presence of degraded crude oil. The potential health risk posed by the residual petroleum constituents detected in soil and groundwater at the sites were evaluated based on the methodology presented in the Human Health Screening Evaluation of the PEA; a detailed description of these evaluations were presented in previously cited reports prepared by Geomatrix. The PEA evaluation consists of a compilation of methods, models, and assumptions commonly used by California and United States Environmental Protection Agencies (Cal-EPA and U.S. EPA) to quantify human health risk and hazard at a site. The PEA evaluation is intended to provide conservative estimates of the theoretical excess lifetime cancer risk and noncancer hazard index based on reasonable maximum exposure in a residential setting. The theoretical excess lifetime cancer risk for an adult and child resident is 1x10"6 for both sites; this value is at the lower end of the acceptable risk range of 1x10"6 to 1x10 used by Cal-EPA and U.S. EPA for sites where remediation is considered (CCR Division 4.5, Title 22 §67500.15 and U.S. EPA, 1990). The noncancer hazard index for an adult and child resident is 0.37 and 0.65 for the Pombo and Burns sites, respectively; these values are less than 1, indicating that the predicted exposure to petroleum constituents detected on the sites should not result in an adverse noncarcinogenic health effect (U.S. EPA, 1989). Therefore, the presence of residual petroleum constituents in soil and groundwater at the sites does not pose an unacceptable human health risk to hypothetical future residents, under the conditions evaluated. In addition, based on the conservative nature of the PEA evaluation, the presence of residual petroleum constituents in soil and groundwater should also not pose an unacceptable human health risk to future commercial and construction workers. 3.0 SOIL MANAGEMENT PLAN This management plan is intended to describe options for handling the soil affected by degraded crude oiUBunker C oil if it is excavated during construction or when placing/repairing belowgrade utilities. The areas where oil-affected soil was encountered during previous investigations are shown on Figure 2. \�sf3\dcptdata\DOc_Safe\6000s\6115.014\SMP.doc 3