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Appendix A: Previous Environmental Activities 2. COPCs in a well must be stable or declining for at least eight consecutive events where the overall plume is defined. SAIC's review indicated that MW-4 and MW-5 should be destroyed. No COPCs were historically detected above ESLs or WQOs in MW-5. Laboratory analytical results for all COPCs were at non-detect concentrations in MW-4 for the previous four sampling events. SAIC also recommended the destruction of MW-3,based on declining TPHd concentrations. The Central Valley RWQCB agreed that MW-3 and MW-4 should be destroyed,provided that the results of one additional groundwater sampling event satisfied the monitoring-well destruction criteria. The Central Valley RWQCB also recommended a final sampling event for MW-5. However, SAIC was allowed to proceed with the destruction of MW-5 without additional sampling and analysis because continued access to the well for this purpose was denied by Western Farm Service(now CPS), and because the well was unaffected by crude oil from the former OVP or TAOC pipelines.14 SAIC 2008-2009 MONITORING WELL DESTRUCTION AND SOIL AND GROUNDWATER INVESTIGATION 15 SAIC completed MW-4 and MW-5 well destruction activities on August 7 and 8,2008. In addition, SAIC advanced a total of 27 borings in three separate mobilizations(August 2008, November 2008, and March 2009) to delineate the extent of affected soil and groundwater at the site. The borings were advanced to total depths ranging from 10 to 88 feet bgs. Soil analytical results for TPHc exceeded EPA Regional Screening Levels(RSLs)16 and/or ESLs in borings SB-18, SB-20 through SB-26, SB-28, SB-29, and SB-34 with concentrations ranging from 540 mg/kg to 26,000 mg/kg. BTEX concentrations in excess of screening levels were detected in SB-21. PAHs were detected in excess of screening levels in 18 of the 27 borings. Groundwater samples were not collected from SB-20, SB-21, SB-28, SB-34, SB-38 through SB-41, and SB-43 due to the presence of SPO. TPHd concentrations were detected in excess of WQO and/or ESL screening levels in the groundwater samples from SB-18, SB-19, SB-22 through SB-25, SB-29, and SB-42 at levels ranging from 110 gg/L to 130,000 µg/L. PAHs were detected above screening levels in five of 16 groundwater sampling locations. BTEX were not detected above screening levels. Borings SB-38 through SB-41 and SB-43 were transferred to the Ahern Road—Vernalis site(see below). SAIC ANNUAL 2009 GROUNDWATER MONITORING AND SAMPLING17 Groundwater monitoring and sampling was conducted on a periodic basis between 1996 and 2003,on a quarterly basis from 2005 through 2007, and on an annual basis in 2008 and 2009. The monitoring and sampling program consisted of wells MW-1 through MW-5 and CPS well 14.RWQCB,2007. Review of Second Quarter 2007 Groundwater Monitoring and Sampling Report—US-Can Welty Road Property,Vernalis,San Joaquin County. August 16. 15.SAIC,2009. Monitoring Well Destruction and Soil and Groundwater Investigation Report, US Can–Welty Road,35275 Welty Road, Vernalis,San Joaquin County,California. September 24. 16.EPA,2008. Regional Screening Levels for Chemical Contaminants at Superfund Sites. hqp://www.epa.gov/region9/waste/sfund/RrgZindex.html#prgtable. September. 17.SAIC,2009. Annual 2009 Groundwater Monitoring and Sampling Report, US Can–WeltyRoad,35275 WeltyRoad, Vernalis, California. April. A-6 SAIE