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 displacemen t of naturally present ground water, and maximizes the potential for d ispersive mixing. The system operates predominantly in a passive mode, and should require relatively little power and small amounts of chemi cals. The injection wall is a permeable cutoff wall installed across t he path of a contaminant plume. The ground water can be amended with t he 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 w all itself. Thus, only a minimal disruption of the ambient flow need r esult from a nutrient injection. After the nutrients have been introdu ced to the wall, the pulse is permitted to drift into the aquifer unde r natural gradient conditions, spreading longitudinally as it goes. Th eoretical calculations and preliminary results of a field trial indica te that if this pulsing cycle is repeated at intervals of weeks to mon ths (site-specific), a stable microbial population can be supported at some distance downgradient from the wall. The advantages of this syst em include the predominantly passive nature of its operation, the effe ctive use of longitudinal dispersion to maximize the mixing of added s ubstances with contaminated ground water, and the flexibility of the s ystem with regard to the types of biodegradation reactions which it ca n promote.