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Work Plan to Delineate Soil Contamination in the Ag Chem Area ARCADIS Former Occidental Chemical Corporation Lathrop, California evaluation and determining which areas may require excavation and/or treatment to meet closure requirements is presented in Section 4. 2. Historical Investigation and Remediation Activities In February through May 1996, Simplot and OCC's consultant Geomatrix conducted several activities to facilitate closure of the former Ag Chem Area, including the following: • Former UST Area: Excavating and scrapping one UST and contaminated asphalt.soil and concrete associated with these facilities(Geomatrix, 1996). Wipe samples and soil samples(B-18, B-22 through B-25, B-39 through B-41) were collected(Figure 3). • Former Tank Farm Area: Scrapping two ASTs and aboveground piping associated with the tanks, and decontaminating or scrapping of pumps associated with the tanks(Geomatrix, 1997).Approximately 47 cubic yards of contaminated asphalt, soil and concrete associated with these facilities was also removed (Geomatrix, 1996).Wipe samples and soil samples(B-1 through B-17, B-19 through B-21, B-26 through B-38)were collected(Figure 4). All soil samples were analyzed for pesticides. Based on a comparison with published regional screening levels(RSLs), potential contaminants of concern(COCs)identified included toxaphene, DDT and breakdown products,dieldrin, aldrin,alpha-benzene hexachloride(u-BHC), delta-BHC also known as lindane, chlordane,heptachlor, pentachloronitrobenzene(PCNB),and DBCP(Table 1). Concurrent with submittal of the Closure Report(Geomatrix, 1996), OCC agreed to take the lead role in completing closure of the Ag Chem Area. This agreement was documented in a July 25, 1996 letter from OCC to DTSC. In September 1996, OCC, Simplot and Geomatrix proposed an interim remediation plan to winterize the Ag Chem Area and allow Simplot to continue warehouse operations in the area.With DTSC's agreement,the interim remediation plan was implemented in October and November 1996. Activities included the following: • Former UST Area: Backfilling the former UST excavation,covering the area with laterally extensive asphalt pavement designed for truck traffic loading,and sealing the pavement surfaces with asphalt slurry. • Former Tank Farm Area: Removing concrete from AST foundations and surficial asphalt for off-site disposal or recycling,consolidating the tank farm berm soil and grading the surface to drain,covering the area with laterally extensive asphalt pavement designed for truck traffic loading,and sealing the I A-pe,-penwpperre—.west eg—05017012 d— 2