Sediment Quality Criteria

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Sediment Quality Criteria

• William Fish
• Civil Engineering
• Environmental Sciences And Resources

2
Introduction

• Sediment disposal options often depend on the
  chemical and biological quality of the materials
• Sediment Quality Criteria hinge on composition
  and chemistry of sediments

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Sediment Characterization
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Major Contaminants of Concern in Sediments

• Persistent toxic organics (pesticides, PCBs,
  PAHs)
• Heavy metals (lead, mercury, cadmium, etc.)

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Reference Approach

• Earliest
• Compare to natural or background levels and
  clean up accordingly
• But what to compare with and how?

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Sediments Strongly Bind these Pollutants

• Sediments carry high contaminant load because
  pollutants stick to them
• If pollutants bind extremely well to sediments,
  they may pose little or no risk
• So, how strong is the binding?

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Equilibrium Partitoning

• Whats actually in the interstitial water is in
  proportion to whats on the solids
• Must assume chemical equilibrium, not always
  achieved
• Interstitial water is not always the main pathway
  of biota exposure

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Asdorption ModelingOrganics like Organics

• Sediments typically contain some natural organic
  matter (humus-like material)
• Organic contaminants bind strongest to natural
  organic matter in the sediment
• Binding strength depends on compound AND on
  organic content of the sediment

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Predicting Binding of Organic Contaminants

• Kp overall partition coefficient
• Sed. Conc. Kp x Water Conc.
• Koc generic coefficient for compound
  (tabulated)
• Kp foc x Koc
• foc is the fraction of organic carbon in sediment

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Example

• PCB Typical Koc 200,000 L/kg
• Sediment with 2 organic content
• Ratio of Water Conc/Sed Conc 1/(0.02)(200,000)
  0.00025
• Virtually ALL PCB stays with sediment, not water

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Columbia Slough

• Sediment PCB 30 ug/kg
• foc 0.02
• Calculated water PCB lt15 ng/L (parts per
  trillion below detection)
• But bioconcentration occurs Carp tissues
  contain up to 850 ug/L

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Metals and AVS

• AVS Acid Volatile Sulfides
• Easy measure of natural reactive sulfides in
  sediments
• AVS combines with toxic metals and renders them
  insoluble
• AVS thus immobilizes metals, protects biota

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AVS and Sediment Quality Criteria

• If AVS gt Total Toxic Metals, then assume they are
  all immobilized
• If Metals gt AVS, reduce the metal mobility in
  proportion to the AVS
• Unfortunately AVS may break down if sediments are
  disturbed and exposed to air

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Interstitial water Approach

• Directly sample and measure interstitial water
• But does not work for sediments above waterline
  (tidal)
• Very hard to do outside a research settling

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Pathways for Contaminant Transport

• Desorption during dredging sediment --gt
  water
• Mobilization of non-settling particles during
  dredging
• Desorption or mobilization during
  handling/dewatering
• Desorption or mobilization during final
  confinement

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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