THE BROOKHAVEN NATIONAL LABORATORY PERFLUOROCARBON TRACER TECHNOLOGY: A PROVEN AND COST EFFECTIVE METHOD TO VERIFY INTEGRITY AND MONITOR LONG TERM PERFORMANCE OF WALLS, FLOORS, CAPS, AND COVER SYSTEMS.

摘要

Currently, containment system failures are detected by monitoring wells downstream of the waste site. Clearly this approach is inefficient, as the contaminants will have migrated from the disposal area before they are detected. Methods that indicate early cover failure (prior to contaminant release) or predict impending cover failure are needed. The Brookhaven National Laboratory (BNL) Perfluorocarbon Tracer (PFT) technology can measure performance changes and integrity losses as the cover ages. This allows early detection of cover failure or pending failure so that repair or replacement can be made before contaminants leave the disposal cell. The PFT technology has been successfully applied to four subsurface barrier problems, one leak detection problem from underground ducts, and one surface cover problem. Testing has demonstrated that the PFTs are capable of accurately detecting and locating leaks down to fractions of an inch. The PFT technology has several advantages over competing approaches. The ability to simultaneously use multiple PFTs separates it from other gas tracer technologies. Using multiple tracers provides independent confirmation of flaw location, helps to clearly define transport pathways, and can be used for confirmatory testing (e.g., repeat the test using a new tracer). The PFT tests provide a direct measure of flaws in a barrier, whereas other measurements (pressure, moisture content, temperature, subsidence) provide indirect measures that need interpretation. The focus of the six PFT demonstrations has been on engineering aspects of the technology with the intent of finding if a flaw existed in the barrier. Work remains to be done on the scientific basis for this technology. This includes determining PFT diffusion rates through various materials (soils and barrier) as a function of moisture content, determining the effects of barometric pumping on PFT flow for cover systems, and determining wind effects on side slopes of cover systems and their impact on PFT performance. It also includes application of models to assist in the design of the monitoring system and the interpretation of the data. The set of demonstrations was performed on small sites (< 1/4 acre). Future work also needs to consider scaling issues to develop and design optimal techniques for delivery and monitoring of the PFTs.