METHODOLOGY FOR THE EVALUATION OF ENGINEERED IN-SITU BIOREMEDIATION -LESSONS FROM A CASE-STUDY

Engineered in situ bioremediation is an economically and ecologically sound technology for the clean-up of contaminated soils and aquifers. However, a successful bioremediation requires solid evidence for the d etoxification of the contaminants, preferably proven by complete miner alization. This paper discusses a stepwise evaluation leading to the d emonstration of successful engineered in situ bioremediation. Five maj or evaluation steps assess whether: (1) the contaminants can be minera lized by the indigenous microbial population (2) the mineralization ra tes can be increased (3) the remediation concept can be simulated unde r continuous flow conditions (4) the increase of mineralization rates can be achieved at the field site (scale-up), and (5) complete mineral ization to harmless end products is achieved at the field site. For th ese evaluations, the applicability of four experimental approaches (fi eld investigations, laboratory aquifer columns, microcosms and microbi al cultures) and the relevance of various microbiological or chemical monitoring parameters are discussed. The evaluations are illustrated u sing a specific engineered in situ bioremediation of a diesel fuel-con taminated aquifer in Menziken, Switzerland. The case study demonstrate s that microbiological and chemical monitoring parameters as well as f ield tracer studies and stable carbon isotopes should be combined for the unequivocal evaluation of engineered in situ bioremediation. (C) 1 998 Elsevier Science B.V.