Combining Mass Balance Modeling with Passive Sampling at Contaminated Sediment Sites to Evaluate Continuing Inputs and Food Web Responses to Remedial Actions

Dr. Philip Gschwend | Massachusetts Institute of Technology



Given the need for tools to guide site assessments and remedial design, especially when there are ongoing, low-level, contaminant influxes, this project will investigate the utility of the following coordinated modeling and passive sampling measurement objectives:

  1. Develop a contaminated sediment site mass balance model (MBM) that calculates the expected water column concentrations assuming only one source (diffusion from sediment bed) and one sink (flushing of the contaminants of concern from the aquatic site of interest). Hydrodynamic information will be used to estimate bottom boundary layer thicknesses, and a polyethylene (PE) passive sampling-based method will be used to characterize bed-to-water contaminant concentration gradients.
  2. Develop a PE passive sampler-based method to quickly sample the freely dissolved concentrations of low-solubility contaminants like polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in the overlying water column, allowing assessment of the accuracy of the initial water column estimates using the MBM. This sampling method can also be used to evaluate ongoing inputs of contaminants from upstream contaminant sources.
  3. Develop a PE passive sampling method to map sediments from which groundwater is exfiltrating and carrying contaminants like PCBs and PAHs.
  4. Develop PE passive samplers suited to assessing episodic, short-lived sources such as combined sewer overflow (CSO) and storm drain discharges, even allowing such inputs to be “fingerprinted.”
  5. Integrate the use of a Food Web Model (FWM) to demonstrate the impact of surface water and porewater data derived from combined MBM and PE measuring to evaluate potential improvements in exposure characterization for FWMs. 
  6. Exercise the mass balance and food web models to assess the impacts of “what if” scenarios resulting from continuing low-level contaminant inputs after targeted sediment hot spots are remediated.

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Technical Approach

Variations in PE passive sampling will be used to obtain key data. In order to capture water column concentrations and potential upstream inputs, the samplers can be made to work quickly (hours) using suitable performance reference compounds (PRCs) and very thin PE sheets. In order to map groundwater sources, the PE must remain thick enough to allow insertion into the sediment, but must have relatively rapidly exchanging PRCs. Finally, in order to evaluate time-varying inputs from point-sources like outfalls, the PE samplers must have properties (thickness, PRC choice) that are tuned to the hypothesized frequency of input events.

The MBM and FWMs must be set up to take advantage of passive sampling data; this involves working at a suitably complex site where ongoing, low-level inputs are expected. The Lower Duwamish Waterway in Washington is such a site. For the MBM, contaminant concentrations will be tracked at this site; and for the FWM, calculations will be driven by measured porewater concentrations rather than values calculated from sediment concentration data and assuming sorption coefficients given by the product of the sediment's organic carbon content and the compound's organic carbon-normalized partition coefficient (focKoc). These models need to handle specific PCB congeners so exposures to the particularly toxic ones are estimated well. 

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Successful development of this integrated modeling-measurement system will allow Department of Defense remedial project managers to: (1) identify their data needs, (2) synthesize the data in terms of time- and space-varying exposures, (3) estimate how those exposures translate into different food web responses for scenarios ranging from monitored natural recovery to targeted site clean-up, and (4) evaluate potential improvements in FWMs seeking to predict organism concentrations given a more refined exposure field. (Anticipated Project Completion - 2018)

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Apell, J. N. and P. M. Gschwend. 2016. In situ Passive Sampling of Sediments in the Lower Duwamish Waterway Superfund Site: Replicability, Comparison with Ex situ Measurements, and Use of Data. Environmental Pollution, 218:95-101.

Apell, J.N. and P.M. Gschwend.  2017. The atmosphere as a source/sink of polychlorinated biphenyls to/from the Lower Duwamish Waterway Superfund site.  Environmental Pollution, 227:263-270.

Apell, J.N., D.H. Shull, A.M. Hoyt, and P.M. Gschwend.  2018. Investigating the Effect of Bioirrigation on In Situ Porewater Concentrations and Fluxes of Polychlorinated Biphenyls Using Passive Samplers. Environmental Science Technology, 52(8):4565-4573.

Jonker, M.T.O., S.A. van der Heijden, D. Adelman, J.N. Apell, R.M. Burgess, Y. Choi, L.A. Fernandez, G.M. Flavetta, U. Ghosh, P.M. Gschwend, S.E. Hale, M. Jalalizadeh, M. Khairy, M.A. Lampi, W. Lao, R. Lohmann, M.J. Lydy, K.A. Maruya, S.A. Nutile, A.M.P. Oen, M.I. Rakowska, D. Reible, T.P. Rusina, R. Smedes, and Y. Wu. 2018. Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison. Environmental Science Technology, 52(6):3574-3582.

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Points of Contact

Principal Investigator

Dr. Philip Gschwend

Massachusetts Institute of Technology

Phone: 617-253-1638

Fax: 617-258-8850

Program Manager

Environmental Restoration