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ARCADIS Ms. Kathy Amaru <br /> May 26, 2011 <br /> (TPH-g)and diesel (TPH-d), benzene, ethylbenzene, and xylenes. These impacts <br /> are thought to be related to the lube oil storage tank or gas condensate storage tank <br /> that were formerly located in that area of the site. The excavation was stopped <br /> pending additional soil characterization to delineate the area of impacts. Excavation <br /> boundaries are shown on Figure 3. <br /> Additional soil sampling activities were conducted by ARCADIS in April 2010 in <br /> accordance with the Site Sampling and Soil Removal Work Plan, dated February 19, <br /> 2010. A total of 18 soil borings were advanced in the vicinity of the excavation and <br /> soil samples were collected from depths of 2, 4, 6, and 8 feet below ground surface <br /> (bgs). These samples were analyzed for TPH-g, TPH-d, TPH as motor oil (TPH-m), <br /> and benzene, toluene, ethylbenzene and xylenes (BTEX). Soil BTEX results were <br /> compared to United States Environmental Protection Agency(USEPA) Regional <br /> Screening Levels (RSLs)for residential soil (USEPA, 2009). Because there are no <br /> RSLs for TPH constituents, concentrations of TPH-g, TPH-d, and TPH-m were <br /> compared to San Francisco Bay Regional Water Quality Control Board <br /> (SFBRWQCB) Environmental Screening Levels (ESLs)for residential soil where <br /> groundwater is a current or potential drinking water source (Table A; SFBRWQCB, <br /> 2008). No BTEX constituents were detected above the laboratory reporting limit in <br /> any sample collected. All detected TPH results were below ESLs, with the exception <br /> of one sample located to the north of the excavation (from SB-02)and three samples <br /> located east of the excavation (from SB-04 and SB-13). <br /> Based on these sampling results, an additional 48 cubic yards of impacted soils were <br /> removed from the areas to the north and east of the original excavation in August <br /> 2010 (Figure 3). Following soil removal, the excavation area was backfilled with <br /> clean fill material and the surface was restored to surrounding conditions. <br /> Confirmation soil samples collected from the floors and sidewalls of the excavations <br /> indicated that all impacted soil had been removed, with the exception of a small area <br /> between the northern extent of the excavation (in the vicinity of SBA 3)and several <br /> subsurface utilities. Additional excavation in this area was not possible without <br /> undermining the utilities and posing a significant hazard to onsite personnel. <br /> Groundwater was not encountered during soil removal or soil sampling activities. <br /> However, in August 2010 one temporary well point(TW-01)was installed to the north <br /> of the excavation area (Figure 3). Groundwater was encountered at approximately 12 <br /> feet bgs and analyzed for TPH-g, TPH-d, TPH-m, and naphthalene. TPH-d was <br /> detected at a concentration of 430 micrograms per liter(Ng/L), which exceeded the <br /> Water Quality Objective(WQO) (100 pg/L)for diesel fuel, which is the USEPA <br /> Page: <br /> McD Island Well Install Woftlan_Final.WC 2/8 <br />