Beneficial Use of Dredged Material in Brown County, Wisconsin
A problem is becoming an opportunity when one considers what's happening
to dredged material in Wisconsin's Brown County. The county is utilizing
a straight forward process to dewater dredged material from the Port
of Green Bay and make it available as a resource for agricultural and
transportation purposes. This action may eliminate the need to build
future disposal capacity.
Dredging and Disposal Situation
The United States Army Corps of Engineers (USACE) dredges approximately
150,000 cubic yards of sediment annually to maintain an 18 mile long
shipping channel in the Port of Green Bay at the designed depths of
22-26 feet. In the early 70's, a majority of the sediment was dredged
hydraulically and pumped to the Bay Port disposal facility. After it
was filled to its initially proposed elevation, Brown County received
authorization to additionally fill within a 160-acre area of the 400
acres with sediment hauled by truck. Also an in-water confined disposal
facility (Renard Island also known as Kidney Island CDF) received 1.2
million cubic yards of sediment under the Public Law 91-611 enabling
As the island CDF was nearing capacity, the Brown County Harbor Commission
accelerated its search for disposal alternatives. The desirable option
of continued use of the Bay Port facility would require periodic removal
of material, preferably for beneficial use. Such an action would require
a part of the facility to be designated as a landfill. The Wisconsin
Department of Natural Resources (DNR) and the County worked together
to expedite the landfill approval process and construction began in
Bay Port Landfill Design
Before the harbor commission could implement beneficial use options,
it was necessary to find an economic method to dewater the sediments.
The result was a design that used four cells for dewatering and two
for storage or disposal of the dewatered sediments. With funding support
from Wisconsin's Department of Transportation ($1.3 million) and U.S.
EPA's Great Lakes National Program Office ($150,000), a facility was
built which occupies 110 acres and is designed to accept over 200,000
cubic yards of wet sediment yearly, with a total dry sediment capacity
of 2 million cubic yards. The dewatering cells range from 7 to 20 acres
in size, with perimeter berms that are up to 15 feet high. The perimeter
berms are constructed with a clay core with the remainder of the berm
constructed of on-site soils. There are 1 to 3 off-loading ramps per
cell depending upon the size of the cell.
The base of each cell is graded to one corner where a gravel dewatering
infiltration bed and discharge piping drain off carriage water. The
off-loading ramps are constructed on the high corners of each cell so
that the sediment can flow across the cell, creating a slope on the
surface of the sediment that allows precipitation to drain to the low
corner. The infiltration bed is covered with coarse sand to prevent
the sediments from draining through the gravel, yet permit the gradual
drainage of water. This water leaves the cell through a pipe that drains
into ditches that connect to a series of sedimentation ponds, and eventually
to the waters of Green Bay. The DNR approved a stormwater pollution
prevention plan that includes monthly monitoring for total suspended
solids and phosphorus and quarterly monitoring for PCB's.
In general, the facility will operate on a three year cycle, with 150,000
cubic yards deposited in the first cell in year one and the dewatered
sediments removed after two years. The dewatered sediments will be excavated
with conventional earth moving equipment and transported to one of two
storage/disposal cells where it will be stockpiled, graded, and vegetated.
The two storage/disposal cells can hold 600,000 cubic yards of dewatered
and compacted sediment, which is equivalent of 12 years of dredging.
The facility can operate for an additional 38 years by over-filling
the storage cells and then filling the dewatering cells with this soil.
Beneficial Use Opportunities
Brown County is confident that the facility will never fill because
they have embarked on an aggressive program of developing beneficial
use options. In 1995, two-year-old sediment from Bay Port was used in
a greenhouse study. This project included a bulk analysis of the sediment,
leaching tests, and plant growth and chemical uptake analysis. The data
was compared to the various standards for groundwater, hazardous waste,
wastewater solids, and fertilizer value. Except for an elevated concentration
of nitrogen, the soil passed all of the other standards. Because of
the increased nitrogen, the study measured a 50% increase in plant weight
over plants grown on a control plot. This attribute will be used as
a selling point for the use of this material as a soil amendment and
Another beneficial use opportunity studied was to use the soil as general
fill, in cooperation with the county and state transportation departments.
This study, funded through Wisconsin's Coastal Management Program, evaluated
the practicality of dewatering the sediment and using it in a road embankment.
The study showed that it was not necessary to actively dewater sediments
that had been deposited four years previously. Instead, the contractor
was able to scrape 6-12 inches of soil off the fill periodically to
generate a 10,000 cubic yard stockpile of suitable soil. Some additional
work remains, however, to determine whether the sedminent typically
dredged from Green Bay harbor is structurally suitable for road construction
and at a cost that is competitive with other alternatives.
A project the county is currently working on with the USACE is composting
sediment with cow manure and chipped shipping pallets. The work is a
continuation of a composting project that the USACE conducted at the
Milwaukee harbor in 1998 with funding support from EPA's Great Lakes
National Program Office. The Corps project will include an extensive
greenhouse study and chemical testing. The goal of the composting project
will be to determine how composting degrades PCB's that are contained
in the sediments.
The Brown County Harbor Commission has aggressively pursued unique
solutions to sediment disposal. The commission's attitude has always
been that the sediment is a resource that should be used, not buried.
A practical goal of the commission is to reuse every cubic yard of sediment
dredged from the river. Everyone acknowledges that the ultimate goal
though would be to be to drastically reduce the need to dredge by eliminating
upstream soil erosion.
Note: This case study was prepared during the summer of 1999.
For further information:
Port Manager Brown County Port and Solid Waste Dept.
2561 South Broadway
Green Bay, WI 54304
Donald L. Miller, P.E.
Robert E. Lee & Associates, Inc.
2825 South Webster Avenue
Green Bay, WI 54302
Phone: (920) 336-6338
Fax: (920) 336-9141
Great Lakes Commission
Eisenhower Corporate Park
2805 S. Industrial Hwy, Suite 100
Ann Arbor, MI 48104-6791