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M. Scott Mansholt -2 - 27 March 2009 4 Banta Road-UPRR Analytical results were compared to the lowest conservative applicable Regional Screening Levels' (RSLs) and Environmental Screening Levels Z (ESLs) for evaluation and delineation purposes. Visually affected soil was not observed by SAIC field staff in the boring cuttings, and results of analyses did not exceed the RSLs or ESLs for soil and/or was ND for the petroleum hydrocarbons constituents listed above. The analytical results for TPHd for the groundwater samples were ND for two samples and 55 micrograms per liter (pg/L) for the third, less than the ESL of 100 pg/L considered protective of human health. Additionally, the TPHd concentrations reported are less than 100 pg/L, which is the Water Quality Objective (WQO) for toxicity and the taste and odor threshold for diesel that is considered protective of groundwater. The RSLs, ESLs, and/or WQO constituent concentrations are used as screening levels to assist delineating the extent of affected soil and groundwater and not to assess health or ecological risk or to establish cleanup levels. The analytical results for the groundwater sample submitted for water quality parameter determination reported TDS at 650 milligrams per liter (mg/L), does not exceed the drinking water Secondary Maximum Contaminant Level (MCL). However, chloride, manganese, and sodium exceed the WQO levels for adverse taste and odor that cause nuisance or adversely affect beneficial uses. SAIC's report concluded the following: • According to the findings, no chemicals of potential concern (TPHc, BTEX, or PAHs) were detected in soil exceeding applicable RSLs or ESLs. The extent of affected soil is below applicable screening levels and no further soil delineation is needed. • The lateral extent of affected groundwater has been adequately defined and additional characterization is not needed. • Water quality parameters exceeding WQOs indicate the uppermost water bearing zone is not suitable for drinking water use. • An environmental screening evaluation using applicable screening levels should be completed, provided Central Valley Water Board staff concurs with the findings of this report. US Environmental Protection Agency Region 9, Regional Screening Levels (RSLs) for Chemical Contaminants at Superfund Sites, September 2008. 2 San Francisco Regional Water Quality Control Board - Environmental Screening Levels (ESLs) provided in Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater, Interim Final May 2008. 3 Central Valley Regional Water Quality Control Board -- Water Quality Control Plan (Basin Plan) for the Sacramento River Basin and the San Joaquin River Basin, 4th edition, revised August 2006.