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(P194) Delineating Chlorobenzene in Sediment Using Passive Vapor-Diffusion Samplers.
Barnes, Charles*,1, Koll, Caron2, 1 BBL Sciences, Syracuse, NY, USA2 Blasland, Bouck & Lee, Inc., Syracuse, NY, USA
ABSTRACT- The potential for ground-water discharges to affect surface water quality is a significant issue at many hazardous waste sites, but one that has been difficult to evaluate quantitatively in many cases. This paper describes how a passive collection technique was successfully used to evaluate a chlorobenzene plume suspected of entering a gravel-bed river in New England. Bed porewater concentrations were determined using an innovative, cost-effective sampling procedure [passive vapor diffusion (PVD)] recently developed by the USGS. This reconnaissance tool avoids use of more invasive and costly sampling procedures, and compares favorably with sediment sampling in terms of lower quantitation limits and cost. Sixty PVD samplers were constructed and installed in a systematic grid pattern in the river bed. Upon retrieval two weeks later, only 4 of 60 samples contained detectable chlorobenzene concentrations [> 0.02 milligrams per cubic meter (mg/m3)]. Three of the four detections were clustered in an area bounded by the limits of the suspected plume. The highest reported PVD vapor-phase concentration was 5.5 mg/m3. The vapor-phase results require conversion based on Henry's Law to determine the equivalent equilibrium porewater concentration to compare with available standards. The maximum 5.5 mg/m3 vapor-phase concentration corresponds to an equilibrium porewater concentration of 50 ug/L. This concentration is an order of magnitude below the state standard of 500 ug/L for chlorobenzene in groundwater discharging to surface water and significantly below surface water quality criteria for chlorobenzene. The results indicated the discharge of chlorobenzene to the river did not constitute a significant environmental risk. These results precluded the need for a more extensive investigation of the ground water plume and its potential impact on the river.
Key words: pore water, VOCs, hyporheic zone, monitoring
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