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DRAFT <br /> D of = Effective diffusion coefficient for soil between groundwater <br /> WS <br /> and soil surface(cm2/sec) <br /> ' heap = Height (thickness) of capillary zone (cm), site-specific <br /> ' h, = Height (thickness) of vadose zone (cm), site-specific <br /> D eP = Effective diffusion coefficient through capillary zone (cm2/sec) <br /> D Sff = Effective diffusion coefficient in soil based on vapor phase <br /> 1 concentration (cm2/sec) <br /> — Dair x n3.33 Dwat x n3.33 <br /> DefT acap + wcap 11'4) <br /> cap nT H x nT <br /> where: <br /> D eff = Effective diffusion coefficient through capillary zone (cm2/sec) <br /> cap <br /> Dair = Diffusivity in air (cm2/sec), chemical-specific <br /> Dwat = Diffusivity in water (cm2/sec), chemical-specific <br /> nacap = Volumetric air content in capillary zone soil (cm3 air)/cm3 soil), <br /> EPA (1992) <br /> 3 <br /> nwcap - Volumetric water content in capillary zone soil (cm water)/cm3 <br /> soil), ASTM E 1739-95 <br /> SOMA 99-2218 8 12/10/99 <br />