Passive Polyethylene Sampling in Support of In Situ Remediation of Contaminated Sediments
The Department of Defense (DoD) currently manages hundreds of contaminated sediment sites. The objectives of this project are to demonstrate that (1) the polyethylene (PE) passive sampling technology accurately measures "mobile and bioavailable" (=porewater) concentrations of hydrophobic organic compounds (HOCs) like PCBs, (2) PE is performance- and cost-effective for characterizing the extent of HOC contamination in sediments, (3) PE sampling is suited for long-term monitoring (LTM) programs associated with in situ sediment remediation, and (4) the PE sampling and associated laboratory analyses are commercially viable.
The PE passive sampling approach, recently developed under the SERDP project Using Passive Polyethylene (PE) Samplers to Evaluate Chemical Activities Controlling Fluxes and Bioaccumulation of Organic Contaminants in Bed Sediments (ER-1496), utilizes an inert medium to accumulate organic contaminants from its surroundings, such as in contaminated sediment beds, to an extent that reflects the relevant concentrations that drive transport, bioaccumulation, and biodegradation. The passive samplers are sheets of low-density polyethylene held in an aluminum frame. Performance reference compounds (PRC) are impregnated into the polyethylene before use to allow evaluation of each PE deployment. The PE strips are inserted into the sediment and retrieved at a later date. Their extraction by soaking in a small volume of organic solvent is trivial, and subsequent analyses via gas chromatography/mass spectrometry (GC/MS) can be done without extract cleanup since the polyethylene does not accumulate significant interfering materials. Using the PRC recovery data in each case, the sediment-equilibrated target compound concentrations in the polyethylene are inferred. Using corresponding PE-water partition coefficients, each contaminant's porewater concentrations are deduced. These data show HOC concentration variations at centimeter scales (indicating burial of previously contaminated sediment), bed-water column gradients (enabling estimation of continuing contamination to overlying ecosystems), and bioavailable contaminant levels (needed to evaluate prospective bioaccumulation and biodegradation).
If commercially developed and accepted by regulators, the PE sampling technique could be cost-effectively employed at virtually all DoD-contaminated sediment sites. When comparing traditional sediment site characterization costs to PE sediment site characterization costs, the PE technology provides a cost reduction in manpower, number of days in the field, equipment, and shipping costs and is overall a safer procedure than traditional sediment sampling techniques. By increasing the data quantity and improving the data quality through the use of PE samplers, it is possible that some sites that would otherwise undergo dredging or ex-situ remediation could be directed to a more cost-effective in-situ remedy, resulting in potential cost savings on the order of millions of dollars. For those sites already in the remedial action process, reduction in LTM costs could be significant if PE samplers are implemented. In addition to life-cycle cost reduction, risk is substantially reduced by the increase in certainty derived from more representative samples and improved understanding of the bioavailability of contaminants in the sediments. (Anticipated Project Completion - 2012)
Points of Contact
Dr. Philip Gschwend
Massachusetts Institute of Technology
SERDP and ESTCP