Abstract
Restoration of ground water contaminated from activities at sites for which the United States Department of Energy (DOE) is responsible poses a daunting task. Challenges arise as a result of difficult hydrogeologic settings (e.g., karst, fractured rock, extreme depth), unique contaminants (e.g., tritium, technetium-99, dense non aqueous phase liquids [DNAPL]), and the sheer volume of water and contaminants involved. With remedies selected or proposed for 97 of 134 plumes identified in a recent Departmental survey, the annual cost of operation and maintenance for remedies is estimated to be $78 million per year. When extrapolated across the estimated years of operation, the reported cost exceeds $4 billion. As a consequence, the Department is developing a groundwater restoration strategy to help identify the sequence of activities that will provide the greatest level of risk reduction/resource restoration for a given level of expenditure. The strategy, which is being reviewed by the U. S Environmental Protection Agency (EPA), DOE’s primary regulatory contact, has evolved with experience gained through technical reviews of existing activities at individual sites.
Currently, the greatest cost for restoration of ground water at DOE sites is associated with operation and maintenance of pump and treat systems. Historically, pump and treat has been applied as the default remedy for ground water and is specified as the sole remedy or a portion of the remedy in two thirds of the DOE plumes for which remedies have been selected. Most of these systems were selected with the objective of restoring the aquifer to a quality that would support potable use of water. However, experience has shown that pump and treat remedies cannot achieve such restoration in reasonable time frames in many settings typical at DOE sites. Indeed, in a 1994 review of pump and treat remedies in the U.S., the National Research Council (NRC, 1994) determined that at 69 of 77 sites studied, restoration had not been achieved to date and could take extended periods of performance for contaminant concentrations to be reduced below target levels. In general, once initial concentrations have been reduced, the effectiveness of a pump and treat operation rapidly diminishes as relatively dilute water is pumped and treated, yet little or no substantive reductions in concentration are observed. Thus, the cost/benefit ratio of operating the systems ultimately plummets even when pumping rates and well placement are optimized. The Department’s strategy prescribes a transition to the use of more-cost-effective passive technologies or approaches such as monitored natural attenuation at the point where pump and treat experiences diminishing returns. Transition to these more cost-effective approaches can save substantial amounts of money with no real loss of risk reduction. The strategy is equally applicable to groundwater contamination anywhere, and if applied early in the program, can save significant resources while continuing to ensure human health and the environment are fully protected.
