FIELD-SCALE EVALUATION OF IN-SITU COSOLVENT FLUSHING FOR ENHANCED AQUIFER REMEDIATION

A comprehensive, field-scale evaluation of in situ cosolvent flushing for enhanced remediation of nonaqueous phase liquid (NAPL)-contaminate d aquifers was performed in a hydraulically isolated test cell (about 4.3 m x 3.6 m) constructed at a field site at Hill Air Force Base, Uta h. This sand-gravel-cobble surficial aquifer, underlain by a deep clay confining unit at about 6 m below ground surface, was contaminated wi th a multicomponent NAPL as a result of jet fuel and chlorinated solve nt disposal during the 1940s and 1950s. The water table within the tes t cell was raised to create a 1.5 m saturated flow zone that contained the NAPL smear zone. The cosolvent flushing test consisted of pumping about 40,000 L (approximately nine pore volumes) of a ternary cosolve nt mixture (70% ethanol, 12% n-pentanol, and 18% water) through the te st cell over a period of 10 days, followed by flushing with water for another 20 days. Several methods for assessing site remediation yielde d consistent results, indicating that on the average >85% mass of the several target contaminants was removed as a result of the cosolvent f lushing; NAPL constituent removal effectiveness was greater (90-99(+)% ) in the upper 1-m zone, in comparison to about 70-80% in the bottom 0 .5-m zone near the clay confining unit. Various interacting factors th at control the hydrodynamic sweep efficiency, and the NAPL removal eff ectiveness during cosolvent flushing in this unconfined aquifer are di scussed.