Sediments

Valence state: The combining capacity of an atom or radical determined by the number of electrons that it will lose, add, or share when it reacts with other atoms.

Source: The American Heritage™ Dictionary of the English Language, Fourth Edition
Copyright © 2000 by Houghton Mifflin Company.

free product: A NAPL found in the subsurface in sufficient quantity that it can be partially recovered by pumping or gravity drain.

aerobic: Direct aerobic metabolism involves microbial reactions that require oxygen to go forward. The bacteria uses a carbon substrate as the electron donor and oxygen as the electron acceptor. Degradation of contaminants that are susceptible to aerobic degradation but not anaerobic often ceases in the vicinity of the source zone because of oxygen depletion. This can sometimes be reversed by adding oxygen in the form of air (air sparging, bioventing), ozone, or slow oxygen release compound (e.g., ORC(r)).

Aerobic dechlorination may also occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. Cometabolic dechlorination does not appear to produce energy for the organism. At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal. For aerobic cometabolism to occur there must be sufficient oxygen and a suitable substrate which allows the microbe to produce the appropriate enzyme. These conditions may be present naturally but often in the presence of a source area oxygen and a substrate such as methane or propane will need to be introduced.

Adapted from US. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites

anaerobic: Direct anaerobic metabolism involves microbial reactions occurring in the absence of oxygen and encompasses many processes, including fermentation, methanogenesis, reductive dechlorination, sulfate-reducing activities, and denitrification. Depending on the contaminant of concern, a subset of these activities may be cultivated. In anaerobic metabolism, nitrate, sulfate, carbon dioxide, oxidized metals, or organic compounds may replace oxygen as the electron acceptor.

Anaerobic dechlorination also may occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. Cometabolic dechlorination does not appear to produce energy for the organism. At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal.

Quoted from US. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites

architecture: "Architecture" refers to the physical distribution of the contaminant in the subsurface. Residuals that take the form of long thin ganglia or small dispersed globules provide a larger surface area that will dissolve much faster than if the same amount of liquid were concentrated in a competent pool.

Sources: For purposes of this discussion, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" of accumulation above confining units. In addition, the DNAPL source zone includes regions that have come into contact with DNAPL that may be storing contaminant mass as a result of diffusion of DNAPL into the soil or rock matrix.

source zone: For purposes of this discussion, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" of accumulation above confining units. In addition, the DNAPL source zone includes regions that have come into contact with DNAPL that may be storing contaminant mass as a result of diffusion of DNAPL into the soil or rock matrix.

focal ulceration: The process or fact of a localized area being eroded away.

metaplasia of the glandular stomach: A change of cells to a form that does not normally occur in the tissue in which it is found.

hyperplasia of the glandular stomach: A condition in which there is an increase in the number of normal cells in a tissue or organ.

histiocytic: Degenerative.

duodenum: First part of the small intestine.

microcytic: Any abnormally small cell.

squamous cell papillomas: A small solid benign tumor with a clear-cut border that projects above the surrounding tissue.

squamous cell carcinomas: Cancer that begins in squamous cells-thin, flat cells that look under the microscope like fish scales. Squamous cells are found in the tissue that forms the surface of the skin, the lining of hollow organs of the body, and the passages of the respiratory and digestive tracts. Squamous cell carcinomas may arise in any of these tissues.

jejunum: The middle portion of the small intestine, between duodenum and ileum. It represents about 2/5 of the remaining portion of the small intestine below duodenum.

ileum: The distal and narrowest portion of the small intestine.

squamous: Flat cells that look like fish scales.

metaplasia: A condition in which there is a change of one adult cell type to another similar adult cell type.

ossification: The process of creating bone, that is of transforming cartilage (or fibrous tissue) into bone.

clastogenesis: Any process resulting in the breakage of chromosomes.

neoplastic: Abnormal and uncontrolled growth of cells.

ulceration: The process or fact of being eroded away.

leucocytosis: An elevation of the total number of white cells in blood.

neutrophils: A type of white blood cell.

chromodulin: A small protein that binds four trivalent chromium ions.

biomagnification: The increased accumulation and concentration of a contaminant at higher levels of the food chain; organisms higher on the food chain will have larger amounts of contaminants than those lower on the food chain, because the contaminants are not eliminated or broken down into other chemicals within the organisms.

exencephaly: Cerebral tissue herniation through a congenital or acquired defect in the skull.

everted viscera: Rotated body organs in the chest cavity.

To Be Considered: Documents, such as federal or state guidances, that are not legally binding but may be relevant to the topic in question.

gaining: A gaining surface water body is one where groundwater flows into it.

losing: A surface water body is losing when there is a permeable sediment bed that is not in contact with the groundwater allowing the surface water to seep through it.

fluvial: Of or pertaining to flow in rivers and streams.

lacustrine: Of or pertaining to a lake as in lacustrine sediments—sediments at the bottom of a lake.

lipid: Any class of fats that are insoluble in water.

lipophilic: Able to dissolve in lipids—in this case fatty tissue.

organelles: A part of a cell such as mitochondrion, vacuole, or chloroplast that plays a specific role in how the cell functions and membranes.

RfD: The RfD is an estimate of a daily exposure of the human population (including sensitive sub-groups) to a substance that is likely to be without "the appreciable risk of deleterious effects during a lifetime." An RfD is expressed in units of mg/kg-day.

autonomic: That part of the nervous system that controls non-conscious actions such as heart rate, perspiration and digestion.

ataxia: Lack of muscle coordination.

funnel-and-gate configuration: A system where low-permeability walls (the funnel) placed in the saturated zone direct contaminated ground-water toward a permeable treatment zone (the gate)

References: ATSDR (Agency for Toxic Substances and Disease Registry). 2015. Draft Toxicological Profile for Perfluoroalkyls. 574 pp.

EFSA (European Food Safety Authority). 2008. Opinion of the scientific panel on contaminants in the food chain on perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) and their salts. EFSA Journal 653:1-131.

Hekster, F.M., R.W.P.M. Laane, and P. de Voogt. 2003. Environmental and toxicity effects of perfluoroalkylated substances. Reviews of Environmental Contamination and Toxicology 179:99-121.

Higgins, C. and R. Luthy. 2006. Sorption of perfluorinated surfactants on sediments. Environmental Science & Technology 40(23):7251-7256.

HSDB (Hazardous Substances Data Bank). 2012 Update. Perfluorooctanoic acid.

Kaiser, M.A., B.S. Larsen, C-P.C. Kao, and R.C. Buck. 2005. Vapor pressures of perfluorooctanoic, -nonanoic, -decanoic, -undecanoic, and -dodecanoic acids. Journal of Chemical and Engineering Data 50(6):1841-1843.

Kauck, E.A. and A.R. Diesslin. 1951. Some properties of perfluorocarboxylic acids. Industrial and Engineering Chemical Research 43(10):2332-2334.

Lewis, R.J., Sr., ed. 2004. Sax's Dangerous Properties of Industrial Materials. 11th ed. Wiley-Interscience, Hoboken, NJ. V3:2860.

Lide, D.R. 2007. CRC Handbook of Chemistry and Physics. 88th ed. CRC Press, Boca Raton, FL. 3-412.

SRC (Syracuse Research Corporation). 2016. PHYSPROP Database. SRC Scientific Databases, Accessed May 2016.

UNEP (United Nations Environmental Program). 2015. Proposal to List Pentadecafluorooctanoic Acid (CAS No: 335-67-1, PFOA, Perfluorooctanoic Acid), Its Salts and PFOA-Related Compounds in Annexes A, B and/or C to the Stockholm Convention on Persistent Organic Pollutants. UNEP/POPS/POPRC.11/5.

USEPA (U.S. Environmental Protection Agency). 2016. Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA).#pdfsmall# Office of Water, EPA 822-R-16-005, 103 pp

• Overview
• Policy and Guidance
• Conceptual Site Models
• Fate and Transport of Contaminants
• Site Characterization
• Risk Assessment
• Remediation
  • Capping
  • Dredging
  • Excavation
  • Innovative
  • Institutional Controls
  • Monitored Natural Recovery
• Additional Resources

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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 Sediments. 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.

Enhanced 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 Review.

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.

Monitored 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

Technical 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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