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Appendix C:Previous Environmental Activities respectively. Several PAHs were also detected in groundwater samples from SB-13 and SB-14. TPHd, TPHg, benzene,naphthalene, and phenanthrene were detected in the grab groundwater sample from SB-17 at concentrations of 150,000,480, 0.6, 0.2, and 0.1 µg/L, respectively. SAIC collected one soil sample from SB-15 at 47 feet bgs to define the vertical extent of affected soil off site. TPHc, TPHg, BTEX, and MTBE were not detected in this soil sample, and thus the vertical extent of affected soil was defined at this depth. SAIC searched DWR files in April 2004 and identified three domestic wells located within 2,000 feet of the former HPP-BTR pipelines adjacent to the Hunter Container facility. One of the domestic wells was located up gradient of the former pipeline alignments, and two were located cross gradient, approximately 1,000 feet and 1,500 feet away. The well completion reports indicated two domestic wells were constructed with minimum sanitary seals extending to 20 feet bgs. The well completion report of the third well did not indicate a seal depth. One industrial well may be located in the vicinity of the site,but the exact location was unspecified. Municipal or agricultural water-supply wells were not identified during the DWR search,but two wells were described on well completion reports as public wells and were located at the site. One well is sealed from the surface to 150 feet, and the other to 200 feet. The DWR search did not yield records of domestic wells down gradient(east) of the site. SAIC concluded that the data collected during this and previous investigations indicated that residual petroleum had affected soil between 5 and 42 feet bgs in the vicinity of SB-17, MW-1, SB-1, SB-2, SB-3, B-1, B-4 through B-7 (MW-2), GMX-3, GMX-8, GMX-1B, and GMX-12. In SB-17, clay and sandy layers below 37 feet bgs appeared to be the most affected. The lateral extent of affected soil appeared to be delineated towards the south, west, north, northeast, and east. However,the lateral extent of affected soil southeast of the former OVP and TAOC alignments and SB-17 was not fully characterized. The area northeast of GMX-6 had likely been affected by a refined-fuel plume as a result of a leaking UST at the former Union Oil Service Station at the eastern corner of Welty Road and Highway 33. The service station operated from 1972 to the mid 1980s. SAIC 2007 MONITORING WELL DESTRUCTION EVALUATION In September 2007, SAIC evaluated historical groundwater monitoring well sampling analytical results—using the following criteria—to determine whether monitoring wells may be destroyed: 1. COPCs in a well must be less than WQOs and San Francisco Bay RWQCB Environmental Screening Levels (ESLs)12 for at least last four sampling events; or 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 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. 12.San Francisco Bay RWQCB,2008 Screeningfor Environmental Concerns at Sites with Contaminated Soil and Groundwater (Interim Final). May. C-5 TM eenhm canes uc SAICA V4,01y Owned Subsxf—V From Science to Solutions