AbstractNatural microbes living in contaminated subsurface media can be enhanced to degrade large concentrations of contaminating compounds at a faster rate than the microbes could degrade under natural conditions. A feasibility study demonstrating this principle was performed on‐site in southern Louisiana to evaluate the effectiveness of two microbial degradation remediation methods used to decrease the human carcinogenic risks associated with exposure to ethylene dichloride and vinyl chloride concentrations in contaminated clay and sludge soils at the site. The results of the study are compared to an acceptable Louisiana Department of Environmental Quality closure level to evaluate in‐situ microbial enhancement in chlorinated aliphatic‐contaminated sludge and clay soils as a remediation/cleanup alternative in similar industrial situa