Under-Harbor Project

Digging Deep to Protect Milwaukee's Waterways

by Elaine Schmidt

The $138 million Harbor Siphons project in Milwaukee involves laying two 17-ft-diameter tunnels beneath the city's harbor to help reduce the overflow of untreated wastewater into local waterways.

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Bill Graffin, spokesperson for the Milwaukee Metropolitan Sewerage District, says the project is "part of a court-stipulated agreement between the MMSD and the state's Department of Natural Resources."

Currently, the city's Deep Tunnel system feeds untreated storm and sanitary wastewater from 28 Milwaukee-area communities to the South Shore plant in Oak Creek and the Jones Island Wastewater Treatment Plant in Milwaukee. The Deep Tunnel was designed to hold wastewater for treatment at peak usage times.

But overflows occur due to the lack of capacity, says Larry Ellis, senior project manager for MMSD on the Harbor Siphons project. The existing siphons that run beneath the harbor to Jones Island were built before the Deep Tunnel was added in the 1990s.

"The existing harbor siphons can't deliver plant capacity," he adds.

Calling the existing siphons a "known bottleneck in the system," Graffin says that once wastewater enters the sewer system, there's nowhere for it to go except to the plant, the tunnel or basements of buildings and homes on the system. Rather than flood businesses and homes in times of heavy rain, overflows have to be released into the waterways.

The answer is to create new underground connections between the tunnel and the Jones Island plant.

"If we can move more wastewater to the plant during a storm, the tunnel can store more," Ellis says.

One tunnel will stretch north from the Jones Island facility to Erie Street, near the Marcus Amphitheater. The other will reach from the plant to Scott and Barclay streets, to the west of the facility. Both have to pass under the harbor.

The project is part of the $1 billion Overflow Reduction Plan to reduce overflows of untreated wastewater into local waterways. Work within the Overflow Reduction Plan covers rehabilitation of older portions of the city's sewer system. Some of Milwaukee's downtown sewers are between 90 and 115 years old.

The Harbor Siphons project got under way in May 2006 and is slated for completion in 2009. The project has crews of 15 people for each tunnel covering three shifts every weekday, and 10 of those people are underground every day.

Freezing Soil

Poor soils adjacent to and beneath the harbor are a major issue on the project.

"This whole valley used to be a marsh, so it's not real good soil," Ellis says.
"We have three shafts that are almost 300 ft deep to get down to bedrock."

Since water is easier to control when it is in its solid form, the project is making use of a fairly unique method of freezing the soil before digging.

"We freeze a big donut in the soil, all the way down to bedrock so there is no water moving at all," Ellis says. "It's like ice."

Workers can excavate within that donut without danger of it falling in on them, says Martin "Dutch" Vliegenthart, vice president and Midwest project director for California-based J. F. Shea Co., a part of the Shea-Kenny venture formed for this project. The other team member is Wheeling, Ill.-based Kenny Construction Co.

"Once we are down to bedrock we can shut off the freeze plant, and it is safe to go through the rock," Vliegenthart adds.

The freeze work is being done by the Kansas-based Layne Christensen Co., one of only two contractors in the United States that do that type of work, Vliegenthart says. The other is Freeze Wall in New Jersey.

To freeze the ground, crews drill down 10 ft and insert pipes that are connected to an enclosed system. The pipes circulate cold brine that lowers the ground temperature, freezing it solid. Then the unfrozen center of the donut can be removed and concrete poured. Then another 10-ft section can be frozen.

Even with the freezing technique in place, water has been an issue on the project. "We lost two months on the first shaft," Ellis says. "We were down 60 ft when water started coming up. It was following fissures."

The solution is to drill before you dig and try to push grout into the fissures, Ellis says. "We were dealing with vertical fissures, so we filled the shaft with sand [for stability] and pushed about a thousand bags of grout into one of the fissures," he adds. When the water stopped coming in, the sand was removed and the digging could continue, Ellis says.

Limited Space

The limited amount of space available at the sewage treatment plant for the project-related equipment and activities is another headache, but the solution benefits both MMSD and the Port of Milwaukee.

"The treatment plant didn't have a lot of room for what we were trying to do, so we obtained two acres from the Port of Milwaukee," Ellis says.

In return, the project will create two acres for the port by building a new dock wall where the old car ferry terminal and some deteriorating dock wall was located. Overburden from the bedrock below the harbor is being used as fill behind that wall.

"It's saving money because we don't have to haul our spoil away, and they get a frontage to anchor another boat," Ellis says.

With protection of the local waterways at the center of this project, four pipes ranging in size from 48 in. to 96 in. in diameter will be run through the under-harbor tunnels. Once those are in place, the tunnel will be back-filled with concrete to ensure no leakage.

Even though the bulk of the work-the freezing, digging and tunnel blasting-is going on below ground, crews on the Erie Street side of the harbor are trying to be sensitive to the neighborhood of condos that has gone up there in recent years. No surface work can take place there during the overnight hours.

Many of the rehabs can be accomplished by inserting liners into existing sewers. The liners are held in place by a resin that cures into an extremely hard, durable substance.

Like the work on the harbor siphons, much of the liner installation work can be accomplished underground, with a minimum of disruption to roadways and neighborhoods.

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