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Table 4 Calculation of Risk-Based Screening Levels for Ground Water <br /> (Construction Worker Scenario) <br /> 1325 and 1515 West Weber Avenue,Stockton, California <br /> Target Level Screening <br /> Constituent H' Da Dw Deff(cap) Deff(soil) Deff(ws) VFwamb in Air Level <br /> (dimensionless) cm2 cm cm2 cm2 cm2 mrr-air (Construction) (Construction) <br /> sec sec sec sec sec mg/1-water (t g/-3 (µg/1) <br /> Benzene 2.00E-01 8.80E-02 9.80E-06 2.09E-05 6.87E-03 1.25E-04 2.74E-05 1.79E+02 6.5E+06 <br /> "toluene 3.00E-01 9.00E-02 9,00E-06 1.75E-05 7.02E-03 1.05E-04 3.45E-05 2.81E+04 8.2E+08 <br /> Ethylbenzene 3.00E-01 7.50E-02 7.80E-06 1.47E-05 5.85E-03 8.87E-05 2.91E-05 7.41E+04 2.5E+09 <br /> Xylenes 3.00E-01 7.00E-02 7.80E-06 1.41E-05 5.46E-03 8.48E-05 2.78E-05 5.11E+04 1.8E+09 <br /> 1,2-DCA 4.00E-02 1.00E-01 1.00E-05 6.15E-05 7.81E-03 3.61E 04 1.58E-05 2.56E+02 1.6E+07 <br /> 1,3,5-TMB 3,00E-01 7.50E-02 7.10E-06 1.43E-05 5.85E-03 8.60E-05 2.82E-05 4.34E+02 1.5E+07 <br /> 1,2,4-TMB 2.00E-01 750E-02 7.10E-06 1.66E-05 5.85E-03 9.97E-05 2.18E-05 4.34E+02 2.0E+07 <br /> Model Parameters <br /> volumetic air content(capillary fringe) eacap= 3.80E-02 (dimensionless) (ASTM,1996) <br /> volumetic air content(vadose zone) eas= 2.60E-01 (dimensionless) (ASTM,1996) <br /> total soil porosity ototal= 3.80E-01 (dimensionless) (ASTM,1996) <br /> volumetric water content(capillary.fringe) Owcap= 3.42E-01 . (dimensionless) (ASTM,1996) <br /> volumetic water content(foundation cracks) ewcrack= 1.20F,01 (dimensionless) (ASTM,1996) <br /> volumetic water content(vadose zone) ows= 1.20E-01 (dimensionless) (ASTM,1996) <br /> thickness of capillary fringe heap= 5.00E+00 cm (ASTM,1996) <br /> thickness of vadose zone by= 2.55E+01 cm (site-specific,based on a Lgw.of 30.5 cm and heap=5 cm) <br /> _ depth to ground water(=hcap+hv) Lgw= 3.05E+D1 cm (site-specific,based on a Lgw of 1 foot) <br /> Henry's Law Constant(dimensionless form) H'= chemical specific (ASTM,1996;USEPA Region 9,1999) <br /> Diffusion coefficient(au) Da w chenucal specific (ASTM,1996;USEPA Region 9,1999)_ _ . <br /> Diffusion coefficient(water) Dw= chemical specific _ (ASTM,1996;USEPA Region 9,1999) <br /> Deff(cap)=[Da x(eacap3'33)/(etctal2)]+[Dw x(1/H')x(owcap"3)/(ototal2)] (ASTM,1996) <br /> Deff(soil)=(Da x(oas3-'I3)/(ototalz))+[Dw x(1/H')x(ows3'33)/(etota1z)] (ASTM,1996) <br /> Doff(-s)_(h-p+hv)/[(hcap/Deff(cap))+(hv/Deff(soil))] (ASTM,1996) <br /> VFwamb=(H'x 10001/m3)/{1+[(225 cm x 200 cm x Lgw)/(1500 cm x Deff(ws))]) (ASTM,1996) <br /> Target level in air: from Table 2 <br /> Screening level=target level in air/Vfwamb (ASTM,1996) <br /> Notes: <br /> 1. Screening level=risk-based screening level for ground water <br /> 2. 1,2-DCA-1,2-dichloroethane <br /> 3, 1,3,5-TMB-1,3,5-trimethylbenzene <br /> 4. 1,2,4-TMB-1,2,4-trlmethylbenzene <br />