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1 v <br /> 1 <br /> %TC <br /> A S S O C I A T E S I N C <br /> Groundwater <br />' Constituent of Groundwater Indoor Outdoor Representative Required <br /> P 9u <br /> Concern Ingestion Inhalation Inhalation Concentration CRF <br />' (Resid on site) (Comm on site) (Comm on site) <br /> SSTL m SSTL m SSTL m m <br /> Benzene 000085 021 170 000065 <1 <br /> 1 Ethylbenzene 3 7 >Sol >Sol 00012 <1 <br /> Toluene 73 >Sol >Sol 000032 <1 <br /> Xylenes 73 >Sol >Sol 000063 <1 <br /> 1 MTHE 0 18 7,300 >Sol 00025 <1 <br /> Notes >Sol indicates the nsk-based target concentration is greater than the constituent solubility value (see Tier 2 <br /> Worksheet 9 3,Appendix D) <br /> 1 When the COC's representative concentration is greater than the calculated SSTL, this indicates <br /> that the selected target level has been exceeded As shown in the above tables, the representative <br />' concentrations of each constituent are below their respective SSTL <br /> Tier 2 RBCA assumptions, parameters utilized, and related supporting documentation are <br /> included in Appendix D <br /> 1 6.0 DISCUSSION <br /> The following paragraphs summarize the results of the subsurface investigation performed at the <br />' project site <br /> The soil analytical data indicates that petroleum hydrocarbon analytes have historically impacted the <br /> 1 subsurface soils and/or the groundwater in the vicinity of the former USTs <br /> I <br /> 1 The vadose zone is estimated to be from approximately 0 to 75 feet bgs and generally <br />' consist of poorly drained soil This soil consists of clay, silt and some sand deposited during <br /> flood stages of major streams in the delta area including mud, muck, loam and sand <br /> Permeability is slow in the"Jacktone" soil Available water capacity is moderate The rate of <br />' water intake in irrigated areas is 0 1 inch per hour Apparent fill material consisting of sand <br /> was observed in the upper 6 5 to I 1 feet of soil borings SB 1 and S132 <br />' 2 Groundwater is estimated to be present at approximately 75 to 80 feet bgs Regional <br /> groundwater flow direction has been reported to be northeasterly (Spring 1997 Report) <br /> 1 3 Petroleum hydrocarbon-affected soils are present primarily the vadose zone at <br /> approximately 15 to 45 feet bgs The highest concentrations of TPHg and/or BTEX are <br /> present in the immediate vicinity of the former USTs The residual petroleum <br /> hydrocarbons appear to attenuate rapidly with depth as indicated greatest by soil samples <br /> w 1148851reportslNFA-RequesLdoc 1 <br />