MONITORING SUBSURFACE BARRIER INTEGRITY USING PERFLUOROCARBON TRACERS

Subsurface barriers are an extremely promising remediation option to m any waste-management problems. It is recognized that monitoring of the barrier is necessary to provide confidence in the ability of the barr ier to contain the pollutants. However, the large size and deep placem ent of subsurface barriers make detection of leaks a challenging task. Therefore, typical geophysical methods are not suitable for the monit oring of an emplaced barrier's integrity. Perfluorocarbon tracers (PFT s) have been tested as a means of barrier verification at the Hanford geotechnical test facility, where a soil/cement barrier was emplaced a round a buried drum. PFTs were injected beneath the drum for three day s in the center of the barrier 3 m below grade. The concentration of P FTs in seven external and two internal monitoring wells has been measu red as a function of time over a 17-day period. The data have been ana lyzed through numerical modeling to determine barrier integrity and PF T diffusion rates through the barrier. This paper discusses the experi mental design, test results, data analysis, and modeling of PFT transp ort in the subsurface system.