ABSTRACT
Throughout the 1990s, the scientific understanding of natural attenuation processes evolved rapidly to the point where monitored natural attenuation evaluation now receives attention as a cost-effective means of restoring contaminated ground water once immediate threats to public health from drinking contaminated ground water are not considered as an environmental issue. Natural attenuation is being used at sites with a wide range of contaminants, including chlorinated solvents; benzene, toluene, ethylbenzene and xylene (BTEX) compounds; polycyclic aromatic hydrocarbons; phenols; polychlorinated biphenyls; pesticides; and inorganics. The use of natural attenuation at underground storage tank sites with petroleum releases increased significantly in the early 1990s. As of 1995, natural attenuation is the second most popular option for sites with contaminated soils; it is being used at roughly 29,000 sites or at 28% of the active contaminated soil universe. Natural attenuation is the most common treatment option at sites with contaminated ground water; it is being used at 17,000 sites or about 47 % of the active contaminated ground water universe.
