A Cost-Effective Approach to In Situ Bioremediation in Fractured Bedrock

摘要

Fractured bedrock aquifers commonly display dual-porosity characteristics, preferred flow paths, and heterogeneities that increase the difficulty of contaminant remediation. Extraction and treatment approaches are limited in effectiveness by the rate of diffusion of contaminants from microfractures into the preferred flowpaths, and in situ treatment approaches are limited by the inefficiency of introducing additives through injection wells. Delivery of nutrients to enhance biodegradation of organic contaminants via shallow subsurface infiltration galleries can be an efficient, cost-effective alternative to wells and trenches. The case history program described here has continually evolved since its initiation in response to monitoring results, and has continued to show increases in effectiveness and efficiency as those modifications have been enacted. The approach provides an inexpensive nutrient application to a larger bulk volume of fracture pore space than could be accomplished through injection wells. The result has been an abrupt and significant enhancement of an anaerobic environment and reductive dehalogenation of the source contaminant. This is confirmed by biogeochemical conditions in the aquifer, sharp reduction in concentration of the source contaminant (1,1,1-trichloroethane), and increases in concentrations of breakdown compounds at the margin of the anaerobic zone.