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Assessing and Cleaning Up Contaminated Sediments

Assessing and Cleaning Up Contaminated Sediments. ESR 410/510 Environmental Cleanup and Restoration. Introduction. Sediment contamination problems have been recognized for many years Widespread concern did not appears until 1970s Sediments of virtually all active harbors are contaminated

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Assessing and Cleaning Up Contaminated Sediments

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  1. Assessing and Cleaning Up Contaminated Sediments ESR 410/510 Environmental Cleanup and Restoration

  2. Introduction • Sediment contamination problems have been recognized for many years • Widespread concern did not appears until 1970s • Sediments of virtually all active harbors are contaminated • Also, many other major waterways such as the Great Lakes, Puget Sound, the Hudson River

  3. Early Evidence of Sediment Contamination

  4. Replicate studies reveal widespread problems

  5. Sediment Characterization • Grab sampling at low tide • Sediment surface showing biological activity

  6. Sediment Dwelling (Benthic) Organisms • Eel Grass Zostera marina Requires abundant light and clear water. Excess algae kills it off.

  7. Sediment Dwelling (Benthic) Organisms • Polychaete worms Burrow to 20-30 cm into sediments, mixing shallow and deep sediment material and associated contaminants. (Bioturbation)

  8. Sediment Dwelling (Benthic) Organisms Nereids (Polychaeta)

  9. Sediment Dwelling (Benthic) Organisms • Burrowing shrimp, Callianassa californiensis • Southern rock lobster, Jasus novahollandiae • Mole crab, Emerita analoga

  10. Sediment Dwelling (Benthic) Organisms • Mole crab (Emerita) • Horseshoe crabs (Limulus polyphemus)

  11. The Benthos We Eat • Rock sole • Softshell clams • Blue crab • Mussel

  12. Major Contaminants of Concern in Sediments • Persistent toxic organics (pesticides, PCBs, PAHs) • Heavy metals (lead, mercury, cadmium, etc.)

  13. Van Veen Hand Dredge

  14. Ponar Box Corer

  15. Ekman Box Corer

  16. Large, Ekman-type Corer

  17. Sediment Sampling:Mackereth Pneumatic Corer

  18. Multi-Corer Array

  19. Benthic Biota Samplers (sleds)

  20. What Constitutes “Contaminated Sediments” • ALL sediments contain at least traces of metals, including some very toxic metals • Many persistent organic compounds like DDT and PCBs are globally distributed at low levels • So the mere presence of “contaminants” does not mean a sediment is contaminated by local sources or to a worrisome level.

  21. Defining problem Contamination: The Reference Approach • Earliest scientific approach • Compare levels in site samples to “natural” or “background” levels • Background levels drawn from what are believed to be relatively “pristine” locations • If samples > background, clean up accordingly • But what to compare with and how? • Also, the method does not account for mixtures of chemicals nor the “bioavailability” of the chemical

  22. Bioavailability • Just because a chemical is found in the environment does not mean it is available for uptake by organisms (bioavailable) • E.g., toxic metal ions trapped inside rock particles (like ore) are not bioavailable unless the ore dissolves • Many other natural processes limit the bioavailability of certain forms, particularly with metals and with hydrophobic organic compounds

  23. Bioavailability of Pb (thanks Mark)

  24. Sediments Strongly Bind Many Pollutants • Sediments carry high contaminant load because pollutants “stick” to them • If a contaminant has little tendency to “stick”, then of course, it probably will not end up or persist in the sediment • But, if pollutants bind extremely well to sediments, they may pose little or no risk • So, how strong is the binding?

  25. “Partitioning” of Contaminants Between Sediments and Water Dissolved chemical (mobile, available) Sediment particles Interstitial or Pore Water Adsorbed chemical (immobile, less available)

  26. Equilibrium Partitoning • What’s in the interstitial water is in proportion to what’s on the solids • E.g., suppose100 molecules on the solid and 10 in the water. Double the contamination and its 200 on the solids and 20 in the water

  27. Asdorption Modeling:“Organics like other Organics” • Sediments typically contain some natural organic matter (“humus”-like material) • Organic contaminants bind strongestto natural organic matter in the sediment • Binding strength depends on compound AND on organic content of the sediment

  28. Predicting Binding of Organic Contaminants • “Kp” = overall partition coefficient • Sed. Conc. = Kp x Water Conc. • Koc = “generic” coefficient for compound (tabulated) • Kp =focx Koc • focis the fraction of organic carbon in sediment

  29. Example: • PCB: Typical Koc = 200,000 L/kg • Sediment with 2% organic content (foc = 0.02) • Sed Conc = 0.02(200,000) x Water Conc • Ratio of Water Conc/Sed Conc = 1/(0.02)(200,000) = 0.00025 • Virtually ALL the PCB stays with the sediment, not in the water

  30. PCB in the Columbia Slough • Sediment PCB: ~30 ug/kg • foc = 0.02 • Calculated water PCB: <15 ng/L (parts per trillion; below detection) • But bioconcentration occurs later: Carp tissues contain up to 850 ug/L (magnification of 57,000X !!)

  31. Interstitial water Approach • Directly sample and measure interstitial water • But does not work for sediments above waterline (tidal zones, floodplains) • Very hard to do outside a research settling

  32. Sediment Bioassays • Various means of testing in lab the organisms with sediment samples • Costly, but useful • Hard to say connection to actual system in some cases

  33. Pathways for Contaminant Transport • Desorption during dredging: sediment --> water • Mobilization of non-settling particles during dredging • Desorption or mobilization during handling/dewatering • Desorption or mobilization during final confinement

  34. Sediment Cleanup Options • No action: Let nature cover over or dilute contaminated sediments with fresh sedimentation • Works only if all sources of contaminant are shut off, so some “action” often required • Good only if natural processes fast enough to mitigate danger • Not good if severe imminent harm

  35. Dredging as a Remediation Method • Appropriate where environmental impacts are severe • Where physical disruptions like strong currents, flooding, navigational dredging are likely to occur • Biggest problems are • Resuspension of dirty sediments • Severe disruption of the benthos • Where to put the spoils?

  36. Quantities of Dredged Sediments in the Northwest Alone • 250 million cubic yards from 25,000 miles of navigation channels • 75 million cubic yards from permits • 325 million cubic yards each year

  37. How Much Dredged Material? > 5½ feet deep over Washington, D.C. > 1½ feet deep over Chicago

  38. Authorization • Rivers and Harbors Act of 1899, • Section 10 • Clean Water Act • Section 404 • Marine Protection, Research, and Sanctuaries Act • Section 103

  39. Regulatory Authorities • U.S. National Marine Fisheries Service • U.S. Fish and Wildlife Service • U.S. Environmental Protection Agency • State Fish and Game Agencies • State Water Quality Certifying Agencies • State Coastal Zone Management Agencies • Other Federal and State Agencies

  40. TIER I • Existing • Data TIER II INCREASING COMPLEXITY/ COST ENHANCED RESOLUTION • Physical/Chem. data • Screening Tests • Predictive models TIER III • Toxicity Tests • Bioaccumulation Tests TIER IV • Chronic Sublethal Tests • Steady-State Bioaccumulation Tests • Risk Assessment

  41. https://www.nwp.usace.army.mil/ec/h/hr/

  42. Basic Dredge Types • Hydraulic • Pipeline • Hopper • Mechanical • Clamshell • Other / Combinations

  43. Factors in Selection ofDredging Equipment • Physical characteristics of sediments • Quantities to be dredged • Dredging depth • Distance to disposal area • Physical environment of and between areas • Contamination level of sediments • Method of disposal • Production required • Types of dredges available (US or foreign)

  44. Disposal of Spoils • Simple in-water disposal usually not an option for contaminated sediments • Upland disposal gets it safely out of the water but presents many problems

  45. Upland Disposal • If not “hazardous” under RCRA, may be able to just pile it up on the shore • Near-shore upland sites are cheaper and can use a slurry pipeline, but may not be available (NIMBY or other limitations on land use) • If not near the shore, transportation adds big costs (truck or rail; pipeline not usually feasible)

  46. Upland Sediment Disposal: Barview, OR

  47. Barview, OR

  48. Barview • Slurry inlet pipe

  49. Barview • Variable-depth outlet weir

  50. Hazardous Waste Disposal • If sediment fails RCRA test, then must either: • Treat it on-site to make it pass the haz waste test, then ship to disposal • Take it off-site for treatment and disposal • Ship directly it to a Subtitle C (Haz Waste) landfill • For large loads the first is the cheapest, for smaller loads, the last 2 may be best

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