U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Sediments

Remediation

Monitored Natural Recovery

Monitored natural recovery (MNR) is a risk reduction approach for contaminated sediment that uses ongoing, naturally occurring processes to contain, destroy, or reduce the bioavailability or toxicity of contaminants in sediment. Not all natural processes result in risk reduction; some may increase or shift risk to other areas. Therefore, to use MNR successfully, it is necessary to identify and evaluate the natural processes that reduce risk. MNR usually requires assessment, modeling, and monitoring to demonstrate that risk is actually being reduced. Natural processes that can reduce risk include the following, in order of preference:

  • Processes that convert contaminants to less toxic forms (e.g., biodegradation)
  • Processes that bind contaminants more tightly to the sediment (e.g., sorption)
  • Processes that bury contaminated sediment beneath clean sediment (e.g., sedimentation)

MNR is most effective in bodies of water that are relatively deep and slow moving. It is not recommended for use where local cultures subsist on fish or shellfish because it is generally a slow process. MNR may be recommended for some sensitive environments depending on the type of contaminant in the sediment. For instance, MNR may be suitable for certain wetlands when disturbing the sediment could cause irreversible damage to the ecosystem.

Monitoring of the ecosystem during MNR ensures that the conditions needed for MNR to take place haven't changed and that progress is being made towards cleanup goals. Testing may include water and sediment sampling, and tissue sampling of birds, fish, shellfish, and other bottom dwelling organisms.

General site conditions that are especially conducive to MNR include:

  • Risk is low to moderate
  • Anticipated land uses or new structures are not incompatible with natural recovery
  • Natural recovery processes have a reasonable degree of certainty to continue at rates that will contain, destroy, or reduce the bioavailability or toxicity of contaminants within an acceptable time frame
  • Expected human exposure is low and/or reasonably controlled by institutional controls
  • Site includes sensitive, unique environments that could be irreversibly damaged by capping or dredging
  • Sediment bed is reasonably stable and likely to remain so
  • Sediment is resistant to resuspension, e.g., cohesive or well-armored sediment
  • Contaminant concentrations in biota and in the biologically active zone of sediment are moving towards risk-based goals
  • Contaminants readily biodegrade or transform to lower toxicity forms
  • Contaminant concentrations are low and cover diffuse areas
  • Contaminants have low ability to bioaccumulate

Text adapted from USEPA. 2004. Presenter's Manual for: Remediation of Contaminated SedimentsAdobe PDF Logo. Office of Solid Waste and Emergency Response, 58 pp.

Determination of Rates and Extent of Dechlorination in PCB-Contaminated Sediments during Monitored Natural Recovery
EPA 600-S-08-012, 8 pp, 2008

Data generated during field studies at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell Superfund Site in Pickens County, South Carolina, are used to show how reductive dechlorination can be identified by the historical transformation of higher-chlorinated PCB congeners with sediment depth and time, and through the preferential loss of meta and para chlorines and the conservation of ortho chlorines.

Adobe PDF LogoEnhanced Monitored Natural Recovery (EMNR) Case Studies Review
K. Merritt, J. Conder, V. Magar, V.J. Kirtay, and D.B. Chadwick.
SPAWAR Technical Report 1983, 55 pp, May 2009

This report presents detailed EMNR case studies for Wyckoff/Eagle Harbor Superfund Site in Bainbridge Island, WA; the Ketchikan Pulp Company Site in Ketchikan, AK; and the Bremerton Naval Complex in Bremerton, WA. Overall remedies at these sites also variously included dredging, construction of confined disposal facilities, isolation capping, debris removal, and monitored natural recovery. Other sites are discussed briefly for additional information on EMNR, including a site where a landslide created conditions similar to the placement of a thin layer cap, sites in which thin layer cap placement constituted a pilot project with monitoring goals focused on implementation rather than demonstration of long-term stability or risk reduction, and sites in which limited placement and/or monitoring data are available for assessing progress toward meeting site-specific remedial action objectives. This report also has been published by ESTCP as Demonstration and Validation of Enhanced Monitored Natural Recovery at DoD Sites: Case Study ReviewAdobe PDF Logo.

Long-Term Recovery of PCB-Contaminated Surface Sediments at the Sangamo-Weston/ Twelvemile Creek/Lake Hartwell Superfund Site
Brenner, Richard, et al.
Environ Sci Technol 2004, 38, 2328-2337

Discussion of natural recovery by burial of contaminated sediments in Lake Hartwell.

Methods and Tools for the Evaluation of Monitored Natural Recovery of Contaminated Sediments: Lake Hartwell Case Study
U.S. EPA, National Risk Management Research Laboratory, Cincinnati, OH.
EPA 600-S-10-006, 24 pp, 2010

As part of EPA research to develop methods and tools for the evaluation of MNR of sediments contaminated with PCBs, PAHs, and mercury, a multiyear, interdisciplinary research project was conducted at the Sangamo-Weston, Inc./Twelve-Mile Creek/Lake Hartwell PCB Contamination Superfund Site in Pickens County, SC. The methods and tools described in this summary comprise quantitative approaches for characterizing naturally occurring mechanistic processes relevant to MNR. This information is expected to provide a reference case study for managers considering MNR as a site remedy or monitoring the progress of MNR in contaminated sediments.

Adobe PDF LogoMonitored Natural Recovery at Contaminated Sediment Sites
Blackman, T., M. Martin, G. Braun, S. Ozkan, and E. Ashley.
Lockheed Martin Middle River Complex Feasibility Study Team, Project Note 2, 34 pp, 2013

To provide background for future sediment remediation at the Middle River Complex site, this Project Note gives a general description of MNR, a partial list of sediment remediation projects where MNR has been applied, and several case study reviews of projects that utilized MNR as a component of the remedy.

The Role of Monitored Natural Recovery in Sediment Remediation
Magar, Victor S. and Richard J. Wenning
Integrated Environmental Assessment and Management, pp 66-74, 2006

Adobe PDF LogoTechnical Guide: Monitored Natural Recovery at Contaminated Sediment Sites
Magar, V.S., D.B. Chadwick, T.S. Bridges, P.C. Fuchsman, J.M. Conder, T.J. Dekker, J.A. Steevens, K.E. Gustavson, and M.A. Mills.
Environmental Security Technology Certification Program (ESTCP), Project ER-0622, 276 pp, May 2009

This technical guide focuses on the role of natural recovery processes in the remediation of contaminated sediments. Case studies and generic examples are provided to demonstrate concepts at work in real-world situations. No one-size-fits-all approach exists for monitored natural recovery (MNR), capping, or dredging at contaminated sediment sites. Thus, conditions at actual contaminated sediment sites vary, and actions to be taken are necessarily site- and contaminant-specific. This document provides a step-by-step conceptual primer for applying MNR at sediment sites. It covers the integration of MNR into conceptual site models, lines of evidence, numerical models, the remedy selection process, and monitoring. The appendices contain case studies, contaminant-specific considerations for natural recovery processes, and a summary of relevant models commonly used or applicable to MNR.

Use of Sediment Core Profiling in Assessing Effectiveness of Monitored Natural Recovery
EPA 600-S-08-014, 8 pp, 2008

Evaluation of the natural recovery process at two study sites--the Wyckoff/Eagle Harbor Superfund site and Boston Harbor/Mystic River--relied on vertical contaminant profiling and age dating of sediment cores to assess the history of contaminant accumulation, measure the extent of natural sediment capping, and document contaminant accumulation, compositional changes, and sources over time and space.



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