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Groundwater Monitoring <br /> Well Installation and <br /> ARCADIS Sampling Work Plan <br /> PG&E McDonald Island <br /> Compressor Station <br /> compared to Regional Water Quality Control Board, San Francisco Bay Region(San <br /> Francisco Water Board)Environmental Screening Levels(ESLs)for shallow soils with <br /> residential land use(Table A; San Francisco Water Board 2008). BTEX constituents <br /> were not detected above the laboratory reporting limits(which were below the ELSs)in <br /> any sample collected.All detected TPH results were below ESLs,with the exception of <br /> one sample located to the north of the excavation(SB-02)and three samples located <br /> east of the excavation(SB-04 and SB-13)(Figure 3;ARCADIS 2010b). <br /> 2010—Remedial Excavation and Temporary Well Point <br /> Based on the soil 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 2010 <br /> (Figure 3). Following soil removal,the excavation area was backfilled with clean fill <br /> material and the surface was restored to surrounding conditions. Confirmation soil <br /> samples collected from the floors and sidewalls of the excavations indicated that <br /> impacted soil had been removed,with the exception of a small area between the <br /> northern extent of the excavation(in the vicinity of SB-13)and several subsurface <br /> utilities.Additional excavation in this area was not possible without undermining the <br /> utilities and posing a significant hazard to onsite personnel(ARCADIS 2010c). <br /> In August 2010,one temporary well point(TW-01)was installed to the north of the <br /> excavation area(Figure 3). Groundwater was encountered at approximately 12 feet <br /> below ground surface(bgs)and analyzed for TPH-g, TPH-d, TPH-m and naphthalene. <br /> TPH-d was detected at a concentration of 430 micrograms per liter(Ng/L),which <br /> exceeded the Water Quality Objective(WQO)of 100 pg/L for diesel fuel(Central <br /> Valley Water Board 2008). No other constituents were detected above laboratory <br /> reporting limits. <br /> The results of soil sampling, groundwater sampling, and soil removal activities were <br /> presented in the Excavation and Sampling Workplan(ARCADIS 2010b)and the <br /> Excavation and Sampling Report(ARCADIS 2010c). In March 2011,the Central Valley <br /> Water Board requested further evaluation of groundwater conditions in the vicinity of <br /> the C-51 tank site excavations(Central Valley Water Board 2011). <br /> 2011—Monitoring Well Installation and Sampling <br /> One monitoring well(MW-01)was installed at the site in August 2011. Following well <br /> development, groundwater samples were collected in September 2011 (ARCADIS <br /> 2011). Concentrations of TPH-d in the groundwater samples were compared to the <br /> WQO of 100 pg/L.TPH-d was not detected above the laboratory reporting limit in the <br /> Mcdonald Island Addtl MW Installation Work Plan.00cx 3 <br />