Conference on Hazardous Waste Research 1 TARGET CLEAN UP LEVELS AND REMEDIATION

2 Chemical desorption from soil and sediment is of central importance to most environmental concerns including remediation. Des-orption affects chemical fate, toxicity, and associated risk to human and aquatic life as well as the efficiency of most remediation technologies. Desorption is commonly mod-eled as a reversible partitioning process in fate, risk, and remediation models. However, the reversible model has failed to predict the long-term persistent release of contaminants to the environment. Even with the most advanced remediation technologies (physically, chemically and/or biologically enhanced), it is often observed that a fraction of the sorbed contaminant remains in the soil or sediment. The existence of this remaining fraction has hindered the closure of many clean up operations. Knowledge and prediction of desorption is necessary for designing more effective remediation schemes. If it could be shown that pollutants would not be released from sediments in any significant concentrations, either abiotically or via biological means, they would be of little practical concern and could be safely left in place. In this case, the impact on remediation costs could be enormous. The overall objective of this research is to develop a predictive correlation to model contaminant release for both laboratory and field observations. A semi-empirical irreversible sorption isotherm model, based on the laboratory-observed parameters, has been developed and used to correlate most field observations reported in the literature. Chemicals used in this study include an aromatic compound (toluene), halogenated aromatic compounds (1,2 dichlorobenzene), polycyclic aromatic hydrocarbons (PAHs), polychlori-nated biphenyls (PCBs), and a chlorinated pesticide (DDT). Several types of sediments containing various organic carbon contents have been tested This new isotherm has also been incorporated into a transport model to examine the impact on remediation. It has been shown that this two-step desorption often extends remediation time by up to two orders of magnitude and that clean up time is inordinately sensitive to the selection of the target aqueous concentration level; both results are commonly observed in the field. A confidential healthcare client purchased property in eastern Iowa in order to expand its facilities. A Phase I Environmental Site Assessment (ESA) revealed the property purchased was the site of a former dry cleaning operation. A combination of innovative (i.e., direct-push sampling with mobile laboratory) and traditional Phase II sampling, and testing, performed by Howard R. Green Company, confirmed that site soil and groundwater were contaminated with tetrachloroethene (PCE) and trichloroethene (TCE). Maximum concentrations of PCE and …