SITE INFORMATION AND CORRESPONDENCE

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No Further Action RequiredlOtermination - 2 - 25 September 2008 Mountain House Development Site #1 Source: Historical leak from crude oil pipeline(s) installed in the early 1900's and removed from service during the late 1960's and the early 1970's. Actions: Preliminary investigations commenced in 2001. • In 2001, ten exploratory borings were advanced and soil and groundwater samples were analyzed for TPH constituents of concern. Affected soil was noted in two borings at depths ranging from 12 to 31 feet below ground surface (bgs). Analysis of samples collected at 17 and 26 feet bgs detected TPHc at concentrations of 470 milligrams per kilogram (mg/kg) and 2,100 mg/kg, respectively. TPH quantified as gasoline (TPHg) and as diesel (TPHd) were detected in one boring at concentrations of 60 micrograms per liter (pg/1) and 130,000 pg/I, respectively. Separate phase crude oil was noted in this boring. Subsequent evaluation of chromatograms by laboratory staff determined that the TPHg detections were likely interference due to the crude oil concentrations. • During 2004, an additional investigation included 30 borings and sample collection to further delineate affected soil and groundwater. TPHc concentrations detected in soil samples from 9 to 36 feet bgs ranged from five mg/kg in a 14-foot sample to 29,000 mg/kg in a 14-foot sample. Analytical results of 20,000 and 29,000 mg/kg for two soil samples, exceeded the construction/trench worker ESL of 15,000 mg/kg for TPHc. Benzene was non-detect (ND) for all samples; toluene was detected in samples from three borings, ethylbenzene was detected in samples from eight borings, and xylenes were detected in samples from ten borings. Detection of PAHs was reported in 25 of the 30 borings. No BTEX or PAH constituent concentration exceeded respective ESLs for the construction/trench worker scenario. • From July 2004 to March 2005, a replacement bridge crossing for the highway and railroad was completed. Approximately 27 dewatering wells were installed to allow installation of the bridge footings. Groundwater was treated by granular activated carbon vessels to remove TPH constituents. Treatment, sampling and analysis, monitoring, and disposal were conducted in accordance with General Order No. R5- 2003-0044, Land Disposal of Groundwater or Surface Water from Cleanup of Petroleum Pollution. Approximately 59,000,000 gallons of water was extracted, treated, and discharged to land. Approximately 75 cubic yards of soil was removed and disposed at Altamont Landfill. Withdrawal of the Notice of Applicability for the General Order was issued 11 April 2005. • In 2006, SAIC completed the ERE to evaluate exposure by comparing the analytical results to the 2005 ESLs for a construction/trench worker scenario. As noted above, BTEX and PAH constituent concentrations did not exceed the ESLs. Detected concentrations of TPHc in 2 of 45 soil samples (20,000 mg/kg and 29,000 mglkg) exceeded the TPHc concentration ESL (15,000 mg/kg) for a construction/trench worker. To evaluate the TPHc relative to the ESL, a 95-percent upper confidence limit (UCL) was calculated for the TPHc data, using ProUCL software developed by the U.S. Environmental Protection Agency. The calculated 95-percent UCL was 9,971 mg/kg, which is below the ESL of 15,000 mg/kg for TPHc. The average TPHc concentration detected for soil samples analyzed is 2,019 mg/kg. Thus, SAIC concluded that the TPHc concentrations detected does not pose a threat to human health for the construction/trench worker scenario. • In early January 2008, SAIC provided a No Further Action Required Request Report (NFAR) for consideration of site closure. The NFAR included documentation of site