An international group of researchers and engineers discuss using natural attenuation to degrade contaminants and thereby remediate soils and groundwater. This volume describes laboratory studies and field demonstrations in support of subsurface remediation at military, manufactured gas plant, landfill, petroleum spill, and other sites. The contaminants of concern include benzene, toluene, ethyl-benzene, and xylenes (BTEX); naphthalene; trichloroethene; trichlorethane; and perchloroethylene. Analytical methods for assessing the potential for natural attenuation (passive bioremediation) at a given site and for confirming and documenting efficacy are discussed.