DNAPL SOURCE ZONE REMEDIATION: HOW MUCH CLEANUP & WHICH PERFORMANCE METRICS?

Several recent field-scale demonstrations have shown that in-situ remediation technologies can extract or destroy a large fraction (50-90+%) of the contaminant mass within DNAPL source zones. Several technical and policy questions are being debated regarding the management of sites contaminated with DNAPLs. Can the spatial extent of the source zone and the total DNAPL mass present within the delineated zone be reliably detected? If so, what fraction of the DNAPL mass needs to be extracted or destroyed? Which cleanup technologies perform the best? What hydrogeologic and other attributes of the site are useful in determining an optimal strategy for source zone management? What benefits in risk or liability reduction are achieved from partial mass removal? Are the benefits accruing from mass removal cost-effective? Are the financial models currently used for cost-benefit analysis appropriate? What is the linkage between site hydrogeologic characteristics; DNAPL properties and distribution; and the remediation technology in achieving the desired risk reduction? Can physical containment, instead of aggressive mass removal, serve the same purpose? What are the appropriate plume management approaches that can be linked to source management (partial mass removal or containment)? What are the impacts (benefits or adverse effects) of aggressive source-removal technologies on biogeochemical processes that govern contaminant attenuation in the dissolved plume? What are the long-term stewardship needs at sites where partial DNAPL mass removal or containment is implemented?? These questions will be explored in the oral presentation. Results from recent theoretical analysis and field data is used to examine potential benefits of DNAPL mass removal from source zones. It is suggested that: (1) contaminant flux-reduction by removing DNAPL mass and altering the DNAPL source architecture should be the goal for source-zone remediation; (2) reduction in contaminant mass and flux to modify dissolved plume behavior should be targeted; and (3) the DNAPL source removal strategy should stimulate contaminant attenuation within the plume.