Passive Polyethylene Sampling in Support of In Situ Remediation of Contaminated Sediments

Dr. Philip Gschwend | Massachusetts Institute of Technology

ER-200915

Objectives of the Demonstration

The overarching objective of this project was to show polyethylene (PE) passive sampling is suited to assessing contaminated sediment sites by enabling the measurement of porewater concentrations of hydrophobic organic compounds, like polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). To this end, the project team sought to demonstrate: (1) the PE technology accurately evaluates concentrations of target contaminants in pore water; (2) PE data can be used to delineate the horizontal and vertical extents of sediment contamination; (3) PE sampling is suited for long-term monitoring; and (4) the PE passive sampling approach is commercially viable.

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Technology Description

The PE passive sampling method involves inserting a strip of low density polyethylene, impregnated with suited performance reference compounds (PRCs), into sediments (and/or surface waters) of interest. After suitable deployment times, the PE strips are recovered and analyzed for the concentrations of the contaminants of concern. The concentrations in the PE may require adjustment based on the PRC losses, to values that would reflect equilibration with the surroundings. This equilibrated result can then be normalized by the contaminant’s polyethylene-water partition coefficient to yield the compound’s porewater (or surface water) concentration.

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Demonstration Results

Laboratory testing showed the PE samplers measured pore waters much more accurately than the common commercial practice of using sediment concentration data. Moreover, the PE data readily revealed the extent of PCB contamination at the demonstration site, both laterally and with depth into the sediment bed. Also, the PE samplers were capable of showing that the demonstration site has concentrations of individual PCB congeners at picogram per liter levels in the uppermost pore waters and the site’s bottom waters. The PE sampler results indicated that the uppermost porewater concentrations were not equilibrated with the sediment solids in which they occurred, perhaps due to significant downward flow of lake water into the bed at the site. Quality assurance/quality control, sensitivity, ease of use, and cost metrics, all supported the conclusion that the PE passive sampling approach is commercially viable.

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Implementation Issues

The development of standard operating procedures and an online calculator suited to using PRC data should enable interested environmental consultants and contract laboratories to implement PE passive sampling. The chief remaining obstacle to widespread use of this PE passive sampling site evaluation approach involves enabling regulatory personnel to relate pore water concentration data with currently available regulatory standards.

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