SITE INFORMATION AND CORRESPONDENCE

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No Further Action Required Request Report 1 Mountain House Development Site#6 September 15,2011 which have been replaced by Regional Screening Levels [RSLs; EPA, 2008]) and San Francisco Bay RWQCB Environmental Screening Levels (ESLs; San Francisco Bay RWQCB, 2008). Similarly, groundwater analytical results were compared to WQOs and ESLs. Note that the RSLs and ESLs have changed over time, but they have always been conservative for delineation 1 purposes as used at HPP-BTR sites. 2.1 SOIL INVESTIGATION, 2001 Condor conducted an environmental investigation along and adjacent to West Byron Road in ' Mountain House. The investigation included sampling 185 soil borings to assess petroleum hydrocarbon-affected soil and groundwater associated with the former OVP. Condor advanced soil borings GP 150 through GP 163 within the site boundaries (Figure 2). Affected soil was 1 observed at the Site in borings GP 152, GP 156 through GP 158, GP 160, and GP 161 at depths ranging from 4.5 to 20 feet below ground surface (bgs). Condor collected soil samples from the borings and submitted the samples to a laboratory for analytical testing. Laboratory analytical results indicated detectable TPH quantified as crude oil (TPHc) in soil samples at concentrations ranging from 880 milligrams per kilogram (mg/kg) in GP 152 at 15.5 feet bgs to 29,000 mg/kg in GP 156 at 12 feet bgs. ' Condor collected grab groundwater samples from borings GP 152, GP 156, and GP 161, and submitted them to a laboratory for analytical testing. TPH quantified as diesel (TPHd) was detected at concentrations ranging from 2,200 micrograms per liter(pg/L) in GP-152 to 260,000 ug/L in GP 161. TPH quantified as gasoline (TPHg) was also detected at concentrations ranging from 8,500 µg/L in GP 156 to 9,900 µglL in GP 161. Groundwater was encountered beneath the Site at depths ranging from 7 to 17 feet bgs. 2.2 SOIL AND GROUNDWATER INVESTIGATION, 2008 Pursuant to RWQCB acceptance of an SAIL 2005 work plan and a 2006 work plan addendum (RWQCB, 2006; SAIC, 2005b and 2006) SAIC advanced 29 borings (SB-1 through SB-29) between March 17 and April 1, 2008,using a Geoprobeo 6600 direct-push rig. Borings were advanced to total depths ranging between 12 and 40 feet bgs. Hydrocarbon-affected soil was encountered in SB-1, SB-2, SB-5, SB-8 through SB-16, SB-18, and SB-21 through SB-23. TPHc was detected above ESLs in I I soil borings. The highest concentration was detected in boring SB-21 at 6 feet bgs (29,000 mg/kg). Benzene, toluene, ethylbenzene, and total xylenes (BTEX) were detected above ESLs or RSLs in two soil borings with a maximum concentration (ethylbenzene at 0.14 mg/kg) detected in SB-10 at 18 feet bgs. Polynuclear aromatic hydrocarbons (PAHs) were detected in soil samples from 15 borings with a maximum concentration (chrysene at 1.6 mg/kg) detected in SB-21 at 5 feet bgs. Three samples (SB-5 at 14 feet bgs, SB-10 at 17 feet bgs, and SB-14 at 23 feet bgs) were submitted to Chevron Energy Technology Company(ETC) for fuel-fingerprint analyses. ETC concluded that the three samples contained moderately weathered San Joaquin Valley crude oil (SJV crude). Groundwater samples were collected from 20 borings. TPHd was detected above ESLs in groundwater samples from three borings. The highest TPHd concentration was detected in groundwater from boring SB-15 at 30 feet bgs (1,000 pg/L). BTEX constituents were not detected above ESLs or WQOs in any samples. PAHs were detected in groundwater samples ' from three borings with a maximum concentration detected in a sample from SB-2 (dibenz[a,h]anthracene at 0.0064 pg/L). Total dissolved solids (TDS) concentrations ranged 1 2 SAIC 1