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FORMER MOBIL BULK TERMINAL 04-343, TRACY, CALIFORNIA <br /> CALCULATION OF INCREMENTAL CANCER RISKS AND HAZARD INDICES <br /> VAPOR PATHWAY ANALYSIS <br /> EXPOSURE: POTENTIAL EXPOSURE TO CHEMICALS IN SUBSURFACE SOIL <br /> RECEPTOR: RETAIL FACILITIES NORTH WEST OF SITE <br /> SITE CONDITION: FENCED, UNPAVED AND UNDEVELOPED <br /> ' EXPOSURE SCENARIO: REASONABLE MAXIMUM EXPOSURE <br /> ENDPOINT: CALCULATION OF MOISTURE CONTENT BY WET WEIGHT <br /> EQUATIONS: <br /> Mwet = 1/(1/Mdry + 1) <br /> SYMBOLS AND DESCRIPTIONS UNITS <br /> VALUE RATIONALE <br /> Mdry = Average Moisture Content of Soil by Dry <br /> Weight Determination dimensionless <br /> ' Mwet = Wet Weight Moisture Content of Soil 0.080 (maximum expected value) <br /> dimensionless 0.074 (by equation) <br /> ENDPOINT: CALCULATION OF DRY SOIL BULK DENSITY AND AIR-FILLED SOIL POROSITY <br /> EQUATIONS: <br /> � Pa = Pt-(Mdry*Sb) <br /> SYMBOLS AND DESCRIPTIONS UMTS VALUE RATIONALE <br /> ' sb = Dry Soil Bulk Density /cm3 <br /> g 2.13 (95% UCL, Alton, 1990) <br /> Mdry = Moisture Content by Dry Weigh[Determination dimensionless <br /> Pt = Total Soil Porosity 0.080 <br /> dimensionless 0.276 (95% UCL, Alton, 1993) <br /> Pa = Air-Filled Soil Porosity dimensionless <br /> 0.106 (by equation) <br /> ENDPOINT: CALCULATION OF CHEMICAL CONCENTRATION IN SOIL GAS <br /> EQUATIONS: <br /> FROM HENRY'S LAW <br /> Csg= Csoil* H*0/Mwet) *Dw*cfl <br /> f , SYMBOLS AND DESCRIPTIONS UNITS <br /> VALUE RATIONALE <br /> Csoil = Concentration of Chemical in Soil <br /> H = Henry's Law Constant see below (Highest Detected Concentration) <br /> dimensionless see below (EPA, ]990) <br /> t Mwet = Wet Weight Moisture Content of Soil dimensionless 0.074 <br /> Dw = (by previous equation) <br /> Density of Water <br /> kg/cm3 !E-03 (average value) <br /> cfl = Conversion Factor <br /> Csg = Chemical Concentration in Soil Gas g/mg 1 E-03 (by definition)/cm3 <br /> 1 g see below (by equation) <br /> 1 Chemical H Csoil CsE <br /> Benzene 0.23 6.6 2.05E-05 <br /> 1' Toluene 0.26 2.4 8.42E-06 <br /> Ethylbenzene 0.27 17 6.20E-05 <br /> Xylenes 0.29 6.3 2.47E-05 <br />' RSKCALC4 ; <br />