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ARCADIS Ms. Kathy Amaru <br /> October 19, 2010 <br /> Per RWQCB direction, a four-point composite background surface sample was <br /> collected at the site to determine if the arsenic concentrations detected in the backfill <br /> samples were consistent with site conditions. The four individual samples were <br /> collected outside the immediate vicinity of the C-51 compressor station but within <br /> PG&E property, and composited. The arsenic result of the four-point composite <br /> sample was 6.27 mg/kg, so level of arsenic found in the imported fill appears to be <br /> below the regional background concentrations. <br /> Following RWQCB approval on August 30, 2010, the excavation was backfilled with <br /> the sampled Type 2 Road Base (A/B). Soils were compacted in 4 inch lifts to surface <br /> with a vibratory soil compactor(make/model: CAT CP-433E). This material was <br /> applied at the surface to return the site to surrounding conditions. All sampling <br /> results, along with the laboratory certified analytical reports, are included in Appendix <br /> B. <br /> Following soil removal activities, the excavation was backfilled with certified-clean <br /> Type 2 Road Base(A/B). Soils were compacted in 4 inch lifts to surface with a <br /> vibratory soil compactor(make/model: CAT CP-433E). This material was applied at <br /> the surface to return the site to surrounding conditions. <br /> Soil Sampling Analytical Results <br /> A total of nine soil samples were collected during soil removal activities. Soil sample <br /> results were compared to established screening levels to assess potential residual <br /> risks. Screening levels used for evaluation of confirmation sampling results are <br /> discussed below. <br /> Screening Levels for Contaminates of Concern <br /> As detailed in the Site Sampling and Soil Removal Work Plan and in the responses <br /> to the RWQCB comments(dated April 7, 2010), the soil sample results were <br /> compared to the following screening levels: <br /> • RWQCB ESLs for shallow soils with residential land use for petroleum <br /> hydrocarbons <br /> ESLs are presented in the RWQCB technical document titled Screening for <br /> Environmental Concerns at Sites with Contaminated Soil and Groundwater, dated <br /> May 2008 (RWQCB, 2008). Groundwater results were compared to Table A— <br /> Page: <br /> 0111012775.d. 6/12 <br />