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DREDGING OF CONTAMINATED SEDIMENT AT BADGER ARMY AMMUNITION PLANT,
GRUBER'S GROVE BAY IN LAKE WISCONSIN 
by Bay West, Inc.

Aerial view of 
Badger AAP Site
(Photo courtesy Bay West, Inc.)

Under the U.S. Army Corps of Engineers' Omaha District's Total Environmental Restoration Contract (TERC) 5, for which Bay West, Inc. is a team subcontractor to Stone & Webster, Inc., Bay West was contracted to dredge sediments from Gruber's Grove Bay, located off the Wisconsin River near the Badger AAP site (vicinity of Baraboo, Wisconsin), where munitions components were formerly manufactured up until 1972.

Initial Investigation & Winter Sampling
Bay West initiated work at the site in the winter of 1999 by performing an investigation of sediments in the frozen 20-acre bay to identify the extent of mercury-impacted sediments. Sediment probes were used to determine the thickness of sediments at more than 500 locations. As a cost efficient approach, work was completed in the winter when the lake was frozen; this way, surveyors could stake sample locations and the sample crews could move easily between areas, in comparison to using boats. Using a combination of geoprobing for discreet core sampling, and hand-operated grab and core samplers, Bay West collected and sampled sediment cores at 1-foot intervals. The crews were able to complete each location in less than half the time originally estimated. As a result, Bay West saved the client nearly $50,000.

Dredging Activities
Dredging of the impacted sediments took place throughout the spring and summer and fall and is scheduled to be completed late November 2001. Utilizing an Mud Cat Mud Cat™ MC-2000 hydraulic auger dredge, Bay West dredged approximately 90,000 cubic yards of impacted sediments.  The Mud Cat™ MC-2000 utilizes a 24-inch (609 mm)  diameter, 22,000 pound torque horizontal auger to combine sediments and water into a slurry that will be hydraulically pumped through 4,500 feet (1,372 m) of 10-inch (254 mm) pipeline. The dredge was able to take 2 foot depth cuts in the forward direction and 1.5 foot cuts in the reverse operation.  Aerial surveillance of the dredge showed virtually no turbidity plume. This is typical when using the MC-2000 in fine, colloidal sediments.

Mud Cat™ MC-2000 Dredging Mercury-Contaminated Sediments
from Gruber's Grove Bay - Making Final 5 Passes to Complete Project

Samples of the water taken at the sprayheads showed only 5 parts per billion of mercury, and well below the Wisconsin DNR design parameters.

North end of lay down area, 
geo containers stacked 3 high

The ability of the MC-2000 to cut out sediment while operating in the reverse direction reduced dredging site time considerably.  Approximately 105 of the tubes were filled, a larger amount than planned, and the MC-2000 pumped in excess of the 90,000 cubic yards.  Even with the excess yardage the job was completed on time during 2001. 

Mud Cat™ MC-2000 Dredging at Badger Army Ammunition Plant
Gruber's Grove Bay in Lake Wisconsin
(Photo courtesy Bay West, Inc.)

Dewatering/Disposal
The sediments were dewatered through the use of large geotextile fabric containers (geotubes) placed in a lined and bermed dewatering basin, called a Laydown Area. The 105 geotubes, each 200 feet (61 m) long and 20 feet (6 m) in diameter, were pumped full of slurry at a rate of 1,500 gpm, until the tubes were full of sediment. Water from the sediments was pumped through another pipeline and discharged over 20 acres of pastureland via spray irrigation techniques.  Tests indicated less than 5 PPB of mercury in irrigation water which is below WDNR State standards.

Filled Tubes with Pinch System Inset

Spray Irrigation System for
water collected from geo containers

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