You may have noticed cranes and barges at work along Milwaukee’s port, just north of the Lake Express Ferry terminal. When it’s done, it will be a watertight storage space that will hold vast amounts of contaminated sediment slated to be removed from Milwaukee’s rivers and estuary.
“We started the DMMF (Dredged Material Management Facility) project back in 2020. We finished the design in 2023 and construction started in 2024,” Bridget Henk explains. She’s a senior project manager with the Milwaukee Metropolitan Sewerage District.
READ: Groups for to remove contaminated sediment from Milwaukee estuary, aim to engage public
The sound of pounding fills the air.
“Right now you’re hearing some of our pipe piles going in. Those are circular piles that are part of the perimeter of the DMMF. There are more than 950 of those piles as part of this facility,” Henk says.
Two parallel walls of sheet piling will surround the facility.
The lakebed serves as its foundation. “But each of those piles that we’re putting in goes about 50 feet into that lakebed. So that’s a pretty significant depth to be able to get underneath that. In the case when they have a rock or an obstruction that’s blocking the way, they may need to use a hammer ... to get past that obstruction,” Henk says.
She points to another crew placing sand that's delivered by barge between the 50-foot-wide walls.
"Once they're done, another crew compacts that sand. Their equipment vibrocompacts and shoots water into sand to make it settle," Henk explains.
Beyond that crew, another is tying the two walls together. "It's called a tie rod," Henk says. "It basically acts like a large screw holding the two sides of the wall together, making it structurally sound."
An additional 2.5- to 3-foot wide wall will hold the contaminated sediment within the DMMF.
Henk describes it as a soil mix: “Bentonite, blast furnace slag and fly ash. That’s combined with the sand and water to create that cementitious mixture that creates the wall."
She says coming up with the right proportions of each ingredient took months of meetings, laboratory tests and finally testing in the field. “That whole testing period was about nine months."
Henk calls the soil mix one of the greatest outcomes of the design process. "Because it is simplistic in in execution and its operation and maintenance. If there is a problem, it can be easily fixed."
While MMSD constructs the DMMF, the EPA is puzzling out how to deliver the vibrosediment to the facility.
“The intent is that all of that material is going to be removed by something called the hydraulic dredge, which would pump that material from the bottom of the river all the way over here. And the biggest benefit of doing it with that method is that you don’t have trucks going back and forth from our waterways downtown to the DMMF and filling it. The hydraulic dredge is faster, it’s cleaner,” Henk says.
As the sediment enters the storage space, water will be removed. That means the DMMF will need its own water treatment facility.
“Since the water is going right to Lake Michigan, the DNR is actually the main reviewing entity,” Henk says.
Henk says partnering agencies meet every week to keep this $150 million project on track. “Because there’s so much happening here and so much coordination that needs to happen when you’re working on something of this magnitude, and it’s partnerships like I’ve never seen."
She calls the work a once-in-a-generation opportunity to do better with our waterways.
“It makes me feel real good,” Henk says.
The Milwaukee Metropolitan Sewerage District is hosting one-mile walking tours of the DMMF on Wednesday, Sept. 24 between 5 and 6 p.m. You can find more information here.
And, another opportunity to learn about the DMMF initiative is coming up. The EPA is hosting a public meeting at Discovery World on October 8.
