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New Diffusion Samplers Track Contamination Entering Lakes and Ponds

Close up of diffusion sampler
Close-up of passive-vapor-diffusion sampler
(Click on photo for larger version)

USGS scientists developed, tested, and demonstrated the effectiveness of a new passive-diffusion sampler to delineate where plumes of contaminants are discharging into ground-water-fed lakes and ponds. The diffusion samplers are composed of glass vials surrounded by a permeable membrane. They have many advantages over conventional ground-water sampling methods because they are made of readily accessible and inexpensive materials, are simple to deploy, and do not require time-consuming well purging procedures. The sampler is left in place long enough for contaminants dissolved in the ground water flowing past the sampler to diffuse through the membrane into the water enclosed in the vial; thus, concentrations inside and outside the sampler become equal. This provides a simple way to analyze ground water that is discharging to a river, lake, or other surface water body for the presence of selected contaminants.

Map of Snake Pond
Location of diffusion samplers in Snake Pond, Cape Cod, Massachusetts used to delineate contaminated ground-water discharge areas (Click on diagram for larger version)
Modified from WRIR 03-4133
The samplers were recently deployed by USGS scientists to delineate where contaminated ground water is discharging to John's Pond and Snake Pond on Cape Cod, Massachusetts. The studies were conducted on separate plumes of solvents and explosive chemicals, demonstrating the broad applicability of the samplers. Delineating discharge areas is important for characterizing potential adverse effects on aquatic ecosystems. Organic contaminants often are biodegraded by microorganisms present in bottom sediments of lakes and ponds; delineating the discharge area enables scientists to understand and quantify these natural processes.

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