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- FORMER MOBIL BULK TERMINAL 04-333, 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: BUSINESS POPULATION ONTOP OF SITE <br /> SITE CONDITION: PAVED AND DEVELOPED COMMERCIAL AREA <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 DESCRIP'T'IONS UNITS VALUE RATIONALE <br /> Mdry = Average Moisture Content of Soil by Dry <br /> Weight Determination dimensionless 0.080 (maximum expected value) <br /> Mwet = Wet Weight Moisture Content of Soil dimensionless 0.074 (by equation) <br /> ENDPOINT: CALCULATION OF DRY SOIL BULK DENSI'T'Y 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 glcm3 2.13 (95% UCL, Alton, 1990) <br /> Mdry = Moisture Content by Dry Weight Determination dimensionless 0.080 <br /> Pt = Total Soil Porosity dimensionless 0.276 (95% UCL, Alton,1993) <br /> Pa = Air-Fillad Soil Porosity dimensionless 0.106 (by equation) <br /> ENDPOINT: CALCULATION OF CHEMICAL CONCENTRATION IN SOIL CAS <br /> EQUATIONS: <br /> ' FROM HENRY'S LAW <br /> Csg = Csoil*H*(1/Mwet)* Dw *cfl <br /> SYMBOLS AND DESCRIPTIONS UNITS VALUE RATIONALE <br /> Csoil = Concentration of Chemical in Soil mg/kg see below (highest detected concentration in soil) <br /> H = Henry's Law Constant dimensionless see below (EPA, 1990) <br /> Mwet = Wet Weight Moisture Content of Soil dimensionless 0.074 (by previous equation) <br /> Dw = Density of Water kg/cm3 lE-03 (average value) <br /> cfl = Conversion Factor glmg 1E-03 (by definition) <br /> Csg = Chemical Concentration in Soil Gas g/cm3 see below (by equation) <br /> Chemical TTI Csoil C8 <br /> Benzene 0.23 6.6 2.05E-05 <br /> 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 /> 6 <br /> j .. <br /> k <br /> RSKCALC4 <br />