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
• Additional Resources

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For purposes of this webpage natural sediments are defined as the organic and inorganic materials found at the bottom of a water body. Sediments may include clay, silt, sand, gravel, decaying organic matter, and shells among other things, but exclude anthropogenic debris, such as vehicle tires.

Sediments can become contaminated in a number of ways. Urban runoff that discharges to surface waters often contains polycyclic aromatic hydrocarbons (PAHs), oil and grease, and heavy metals. Agricultural runoff may contain nutrients and pesticides. Industrial spills and releases, especially those that occurred before controls were in place, can put product into the water. Chemicals that are denser than water, such as polychlorinated biphenyls (PCBs) and some pesticides like DDT, will sink to the bottom of water bodies and directly contaminate sediments. Atmospheric deposition of substances such as mercury is another source of sediment contamination as is the discharge of contaminated groundwater through the sediments to the overlying surface water (USEPA 1999 and USEPA 2005).

The classes of contaminants that are most common in sediment contamination are pesticides, PCBs, PAHs, and to a lesser extent dissolved phase chlorinated hydrocarbons. With the right geochemical conditions heavy metals and metalloids can also occur in sediments or precipitate into them. The sediments of many marinas are contaminated with tributyltin, an organo tin compound that was used as a biocide in marine paints (USEPA 1999).

Sediment investigations are generally conducted in two parts. The first uses common sampling and analytical procedures to determine if the total concentrations of contaminants are high enough to warrant concern. The underlying assumption is that all the contaminant is bioavailable. If the data indicate there may be a problem, then the second part of the investigation is done. This part focuses on bioavailability and determining whether there is physical evidence of an impact such as less biodiversity in the impacted sediments and the presence of the chemicals in the tissue of flora and fauna (USEPA 2005).

In addition to evaluating contaminant concentrations, the site investigation needs to develop a very complete conceptual site model. Unlike conventional soil and groundwater investigations, where rapid change in the site conditions is not expected, sediment systems can be very dynamic and it is important for both the risk assessment and remedy selection to have a full understanding of potential changes in site dynamics. A fuller discussion on investigation techniques is found in the Site Characterization section (USEPA 2005).

The risk assessment estimates the potential impacts of the contaminated sediments on human and ecological receptors. Many common organic sediment contaminants are suspected carcinogens and some, such as PCBs and mercury, bioaccumulate in the food chain. Risk assessors have developed a triad, or weight-of-evidence approach, that integrates sediment chemistry, laboratory toxicity testing, and community structure indices to assess risk (Pinkney et al 2005). A more complete discussion of sediment risk assessment and related guidance documents can be found in the Risk Assessment section.

OSWER Directive 9285.6-08 is the main policy guidance for managing contaminated sediments in the Superfund and solid waste programs. Since Superfund responses are subject to other laws and regulations that may be applicable or relevant and appropriate, the directive discusses them and additional related guidance documents. More information can be found in the Policy and Guidance section of this webpage.

OSWER Directive 9285.6-08 emphasizes that remediation at sediment sites generally fail if the source of the contamination is not remedied first. It makes little sense to remove contaminated sediments if an active source will recontaminate the clean sediments. Even innovative technologies like reactive barriers have a finite treatment capability if the active source is not removed. Removal of active sources would include moving upland DNAPLs such as creosote and heavy metals deposition from mining site run off.

The most common sediment treatment technologies are monitored natural recovery, in situ capping, dredging, and excavation (USEPA 2005). Monitored natural recovery takes advantage of natural abiotic and biological degradation processes and includes natural burial of contaminated sediments with clean sediments. Lake Hartwell offers an example of the use of natural burial. The remediation section has a more in depth discussion with examples of these techniques as well as general guidance on sediment site remediation.

In situ capping involves the placement of clean material over the contaminated sediments. When contaminants are relatively immobile in sediment, a cap prevents flora and fauna from contacting them. A relatively impermeable cap can prevent groundwater from discharging through the contaminated sediment. The cap thereby diverts the groundwater away from the contaminated area. Reactive caps are those that use activated carbon mats or organoclays to sorb any contaminants that leave the contaminated sediment pore water (USEPA 2005).

Dredging uses either a hydraulic cutter head or a bucket to directly remove sediment to an onshore treatment and/or disposal area. Both of these techniques produce considerable water that requires treatment before it can be returned to the surface water (USEPA 2005).

Excavation is similar to bucket dredging except that the sediments are partially dewatered by either diverting the surface water from the natural channel or by constructing a coffer dam around them. The contaminated sediments are then removed using conventional construction equipment. This technique has an advantage over dredging in that it produces far less water for treatment (USEPA 2005).

These common sediment treatment technologies are advantageous in highly contaminated source zones where there is a need to quickly reduce the sources. However, in areas of low or moderate levels of contamination an alternative strategy may be more attractive depending on the sensitivity of the ecosystem, and the ultimate goal of the project. Recent research, including limited field studies, has shown the potential for applying amendments which can target certain or a variety of contaminants in effected sediments (Cho, Ghosh et. al. 2009). Strong sorbents, like activated carbon can be amended to sediments to reduce the bioavailability of hydrophobic organic contaminants (PCBs, PAHs, DDT, etc.). Similar sorbents exist for the remediation of various metal contaminants as well.

On this webpage, individual documents specific to a section topic are highlighted in each section with appropriate links. The Additional Resources section is devoted to webpages maintained by EPA and other agencies and groups. These webpages contain several downloadable sediment references.

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Toxicological Exposure of Sediment-Bound Hydrophobic Organic Contaminants as a Function of the Quality of Sediment Organic Carbon and Microbial Degradation
Fredrickson, H.L., J.W. Talley, J.S. Furey, and S. Nicholl

USEPA. 1999. Introduction to Contaminated Sediments. EPA 823-F-99-006, Office of Science and Technology, 24 pp.

USEPA. 2004. The Incidence and Severity of Sediment Contamination in Surface Waters of the United States, Second Edition. EPA 823-R-04-007, Office of Science and Technology, 278 pp.

USEPA. Contaminated Sediments in Superfund: Guidance Documents, Fact Sheets and Policies

USEPA. 2005. Contaminated Sediment Remediation Guidance for Hazardous Waste Sites, EPA-540-R-05-012. Office of Superfund Remediation and Technology Innovation, 236 pp.

Pinkney, A.E., B.L. McGee, P.C. McGowan, D.J. Fisher, J. Ashley, and D. Velinsky. 2005. Using the Sediment Quality Triad Approach to Characterize Toxic Conditions in the Chesapeake Bay (2002): An Assessment of Tidal River Segments in the Bohemia, Elk, Northeast and Severn Rivers, CBFO-C05-01. USEPA, Chesapeake Bay Program Office, 234 pp.

Field Application of Activated Carbon Amendment for In-Situ Stabilization of Polychlorinated Biphenyls in Marine Sediment. Yeo-Myoung Cho, Upal Ghosh, Alan J. Kennedy, Adam Grossman, Gary Ray, Jeanne E. Tomaszewski, Dennis W. Smithenry, Todd S. Bridges, Richard G. Luthy. Environmental Science & Technology 2009 43 (10), 3815-3823

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