Recontamination of Waterway Cap Thea Foss Waterway What has been learned

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Recontamination of Waterway CapThea Foss
Waterway(What has been learned?)

• Matthew G. Dalton
• (Dalton, Olmsted Fuglevand, Inc.)

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Types of Stormwater Pollution

• Dissolved
• Biologic
• e.g. fecal coliform
• Nutrients
• e.g. nitrogen
• Chemicals
• e.g. zinc, benzene,
• solvents

• Particulate
• Physical
• turbidity
• Nutrients
• e.g. phosphorus
• Chemicals
• e.g lead, PAHs,
• PCBs

Dalton, Olmsted Fuglevand, Inc.
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Stormwater Sediment ContaminationHydrophobic/Par
ticulate Contaminants of Most Concern

• Organics (koc ml/g)
• (organic carbon-water)
• Benzene - 22
• PCE (PERC) - 265
• Naphthalene 1,191
• Bis(2-ethylhexyl)
• phthalate 111,123
• Aroclor 1260 822,422

• Metals (Kd l/kg)
• Copper - 22
• Zinc - 62
• Total Cr 1,000
• Lead 10,000

Partitioning Coefficients
Source WAC 173-340-900
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Contaminants of Concern(mostly hydrophobic in
nature)

• Sediment/
• Stormwater
• Metals
• PAHs
• Phthalates
• PCBs
• Pesticides

• DNAPL Seep
• Visual Sheens
• PAHs

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Site Vicinity
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Remedy Features
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Hybrid Cap
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Post Remedy Conditions
4,600 Acres
Stormwater Outfalls
181 Acres
45 Acres
Sheet Pile Wall
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Twin 96 OutfallsHead of Thea Foss Waterway
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Monitoring Approach
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Monitoring

• February 2004 to May 2009
• (Five Years)
• What Happened?

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Sediment Accumulation(2004 to 2009)
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Surface Sediment Above Cap

• FINES CONTENT

• ORGANIC CARBON

Cap lt4
Cap lt0.5
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Surface Sediment Above Cap
SQO 17,000 ug/kg
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Surface Sediment Above Cap
SQO 1,300 ug/kg
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Stormwater Relationship(in sediment)
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Historic Stormwater Relationship

• 2004
• 2006
• 1984

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Sediment Trap Sediment Comparisons
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Sediment Trap Early Warning Sediment Sample
Comparisons 2008 Data
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Conclusions

• Bottom-up and top-down monitoring is working.
  Early warning samples were successful in
  identifying recontamination.
• Sediment core data, suite of contaminants
  detected, correlations and trends indicate
  recontamination has occurred from top-down
  sources, primarily stormwater.
• In-line (pipe end) sediment traps were effective
  in providing data to assess stormwater
  recontamination.
• Monitoring of hydrophobic (particulate)
  recontamination is most effective in bottom
  sediment of the receiving water body.

Dalton, Olmsted Fuglevand, Inc.