your consulting firm found that the source of benzene is a subsurface zone spanning over 500 yd3. by treating the source with the bioremediation method, the overall groundwater cleanup cost can be reduced in the long term. the porosity and bulk density of the soil is 0.4 and 1.6 g/cm3. the relative saturation of the soil is 20%. the concentration of benzene in groundwater is 1 mg/l.