NOONKESTER, Jay V., Dennis G. JACKSON, and Roger M. WHITE, SRTC-Environmental Sciences & Technology, Westinghouse Savannah River Co., Aiken SC

Diffusion samplers are currently being used for two applications in the Southern Sector of A/M Area at the Savannah River Site.  These applications include: 1) Monitoring the effects of remedial activities on VOC concentrations in the Lost Lake aquifer and 2) determining if the VOC plume is discharging into a downgradient stream, Tim’s Branch.  Diffusion based sampling techniques are an alternative to conventional purge and/or grab sampling.  Diffusion samplers are made of polyethylene bags filled with deionized water.  They work on the principle that VOCs diffuse through a semipermeable membrane, such as polyethylene, until concentrations inside the sampler reach equilibrium with concentrations in the surrounding environment.  Current studies use both water-to-water and water-to-vapor diffusion samplers as the basis for characterization
    Water-to-water based samplers have been deployed in four Southern Sector wells to evaluate their performance as an alternative to the traditional method of purge and sample.  One significant advantage of the diffusion samplers is the elimination of the cost of collecting, managing, and treating two to four well volumes of purge water per well per sampling event.  If diffusion samplers produce reliable results in the Southern Sector wells, the problem of hazardous purge water disposal can be greatly reduced
    Water-to-water and water-to-vapor based samplers are also being used as a reconnaissance tool to identify the lateral extent of the outcropping VOC plume from the Lost Lake aquifer into Tim's Branch.  Diffusion samplers have been placed along the stream just below the bottom of the streambed in the area where the VOC plume may emerge.  Because the diffusion samplers are buried below the streambed, they should provide a more accurate sample of the discharging ground water before it has been diluted by the stream flow.  The resulting data will guide future characterization and placement of monitoring wells along Tim’s Branch.  This methodology will allow a more comprehensive, cost-effective survey of the seepline area.