A SEMIPASSIVE NUTRIENT INJECTION SCHEME FOR ENHANCED IN-SITU BIOREMEDIATION

A permeable wall injection system is capable of introducing dissolved substances into an aquifer in a manner which minimizes the displacement of naturally present ground water, and maximizes the potential for dispersive mixing. The system operates predominantly in a passive mode, and should require relatively little power and small amounts of chemicals. The injection wall is a permeable cutoff wall installed across the path of a contaminant plume. The ground water can be amended with the desired nutrient solution using pumping and injecting wells within the wall. The high permeability of the wall ensures that the injection-withdrawal operation causes flow which is primarily confined to the wall itself. Thus, only a minimal disruption of the ambient flow need result from a nutrient injection. After the nutrients have been introduced to the wall, the pulse is permitted to drift into the aquifer under natural gradient conditions, spreading longitudinally as it goes. Theoretical calculations and preliminary results of a field trial indicate that if this pulsing cycle is repeated at intervals of weeks to months (site-specific), a stable microbial population can be supported at some distance downgradient from the wall. The advantages of this system include the predominantly passive nature of its operation, the effective use of longitudinal dispersion to maximize the mixing of added substances with contaminated ground water, and the flexibility of the system with regard to the types of biodegradation reactions which it can promote.