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US Army Corps of Engineers
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Dredging with Turbidity Tests and the EPA in Green Bay Harbor
Michael Staal, E.I.T.
Civil Engineer
U.S. Army Corps of Engineers
Detroit District
Lake Michigan Area Office –Kewaunee Sub-Office
October 24, 2012
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Detroit District
Covers 82,000 square miles of land
4,000 miles of Great Lakes shoreline
Maintain 94 harbors Primarily a civil works
district, including navigation, flood control beach erosion, etc.
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Green Bay, WI
N
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History of PCBs in Green Bay
In 1954, paper companies started using PCBs to make carbonless copy paper
Nearly 700,000 lbs of PCBs were released into the Fox River between 1954 and 1971
The use of PCBs was officially prohibited by federal environmental regulations in 1976
*Data from WDNR
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Green Bay PCB Concentrations
*Data from WDNR
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History of PCBs in Green Bay
In 2007, a Record of Decision and a Unilateral Administrative Order required the primary responsible parties to initiate clean up of the Fox River
EPA and USACE entered into a IA to set monitoring requirements for dredging in Green Bay
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2010 Dredging Map
Area 1
Area 2 Area 3Area 4
Mod. Area
Option 2 Area
Turbidity Testing Required
Total Volume Dredged 173,755 CY
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Turbidity Testing Requirements
►1 week of background testing, 8 hours a day, 1 test each 15 min.
►2 assessments every work day, at least 4 hours apart
►Take initial test 500 feet upstream of dredge►Then take a downstream test 250 ft -500 ft
from the dredge►Downstream test – Upstream test < 80 NTU
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14 CY Dredging Bucket
A Cable Arm Bucket with Seals and Baffles
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Steps the Contractor took to reduce Turbidity
Scows were sealed with spray foam insulation
Dredge material loaded in scows was controlled
Speed of dredging bucket was controlled.
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Turbidity Testing
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Turbidity Testing Results
Maximum Difference 54 NTU(after a 50 year storm)
Minimum Difference 0 NTU
Average Difference 17 NTU
Average Distance from Crane 399 feet
The EPA has decided that turbidity monitoring no longer be used for those areasof Green Bay and Fox River Dredging as long as the Corps operates in a similar manner of dredging.
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Fox River Dock
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Bayport Disposal Facility
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Lessons Learned Switching up testing times keeps
contractor honest Mechanical dredging can be used in a
manner that does not cause large increases in turbidity
Background testing is important. Knowing how the Fox River turbidity reacts to rain events, ships, etc. helped us understand the turbidity in the river better.