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Attachment A:Previous Environmental Activities SAIC 2008-2009 MONITORING WELL DESTRUCTION AND SOIL AND GROUNDWATER INVESTIGATION 16 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)17 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 µg/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. SAIC 2009 CENTRAL VALLEY RWQCB SPLIT GROUNDWATER SAMPLING EVENT Prior to issuing approval to destroy wells MW-1 through MW-3, the Central Valley RWQCB requested an additional event where split samples would be collected and submitted to an independent laboratory. On July 15, 2009, SAIC and Central Valley RWQCB staff collected split groundwater samples from MW-3. Concentrations of TPHd were reported at 63 µg/L and no compounds were reported above the respective screening levels in the SAIC sample. The Central Valley RWQCB sample indicated a TPHd concentration of less than 100 gg/L, which was similar to SAIC's result. No COPCs were detected in the Central Valley RWQCB sample. SAIC 2010 MONITORING WELL DESTRUCTION AND SOIL AND GROUNDWATER INVESTIGATION" SAIC completed MW-1 through MW-3 well destruction activities on July 14 through July 16, 2010. In addition, SAIC advanced a total of four soil borings (SB-44 through SB-47)to 45 feet bgs on July 20 through July 22, 2010,to delineate the extent of affected soil and groundwater at the site. 16.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. 17.EPA,2008. Regional Screening Levels for Chemical Contaminants at Superfund Sites. htty://www.eya.eov/region9/waste/sfund/prg/index.html#r)r to able. September. 18.SAIC,2010. Monitoring Well Destruction and Soil and Groundwater Investigation Report, US Can—Welty Road, 35275 Welty Road, Vernalis,San Joaquin County, California. December 28.