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Stantec <br /> No Further Action Request Report <br /> Chevron and ARCO Commingled Plume No. CP0034 <br /> April 10, 2012 <br /> Current Water Quality t/ <br /> Concentration Objective Projected Date to Achieve <br /> Contaminant Well (pg/L) (pg/L) Water Quality Objectives <br /> GRO MW-2R 01110 100" August 2015 <br /> GRO MW-5R p140 100a January 2012 <br /> GRO E-10 21300; 1005 February 2021 <br /> Benzene E-10 0450 1.01 September 2024 <br /> MTBE E-10 �L67, 13b June 2013 <br /> pg/L=micrograms per liter <br /> a = Environmental Screening Level (ESL), from Screening for Environmental Concerns at Sites with Contaminated Soil and <br /> Groundwater,California Regional Water Quality Control Board San Francisco Bay Region,Interim Final—November 2007(Revised <br /> May 2008). Table A—Groundwater Screening Levels—Shallow Soils(groundwater is current or potential source of drinking water). <br /> b=California Primary Maximum Contaminant Level(MCL),Title 22 of California Code of Regulations—November 2008. <br /> TBA concentrations have decreased to below laboratory MRLs in all wells with the exception of <br /> Chevron wells MW-5R (22 pg/L) and ARCO well E-10 (4,800 pg/L). TBA concentrations are <br /> known to fluctuate as hydrocarbon and MTBE degradation occurs. <br /> Based upon the mass calculations included as Table 6, approximately 1.48 lbs of GRO, 0:169 <br /> lbs of benzene, 0.0264 lbs of MTBE, and 0.050 lbs of TBA remain in groundwater. GRO, <br /> benzene, MTBE, and TBA plumes are currently defined by low to non-detect concentrations <br /> from the current monitoring well network. An evaluation of the historical groundwater data'and <br /> the most recent groundwater isoconcentration contour maps indicate that the plume is stable <br /> and decreasing. Groundwater isoconcentration contour maps for GRO, benzene, MTBE, -!and <br /> TBA are included as Figures 22 through 25. <br /> ii <br /> 94275 NFAR 2012.doc 11 <br />