First at bat: regional sewer repair

Ballpark, rail construction in Minneapolis accelerate sewer project

Long before a Twins clean-up hitter parks a hanging curveball in the sun-splashed, left-field bleachers, and even before dignitaries turn over the ceremonial first shovels of dirt at the new Twins ballpark in Minneapolis, there’s work to be done to get the site ready for construction.

Construction began on Fifth St. N. in downtown Minneapolis in early May. Workers will dig as much as 50 feet below street level to reach the 119-year-old sanitary sewer and install new pipes on the inside.

Under the Fifth St. bridge, workers used shovels and a small backhoe to dig carefully around a manhole and the sanitary sewer below. This is one of as many as seven access shafts that will be dug down to the old pipe.

Among the preparations is work on a 1,400-foot stretch of a Met Council regional sanitary sewer, running under Fifth St. N. just beyond left and center fields. The sewer was built of brick and rock masonry way back when Grover Cleveland was President of the United States (during his first term, which started in 1885).

The 90-inch-diameter pipe is still in full service today, part of a longer network of pipes that convey about 21 million gallons of wastewater daily from northwest Minneapolis, Golden Valley, Medicine Lake, Plymouth and New Hope, and parts of Robbinsdale and St. Louis Park to yet more pipes en route to the Metropolitan Wastewater Treatment Plant in St. Paul. But it’s beginning to show signs of its 119 years of service, with cracking and sagging showing up at various points.

Project accelerated for ballpark, rail construction

Major rehabilitation of the sewer would have been scheduled about 10 years out because the pipe is still serviceable, according to Bill Moore, general manager of Metropolitan Council Environmental Services (MCES), the Council division that operates the regional wastewater collection and treatment system. However, MCES accelerated that schedule because of other major construction scheduled to begin this summer, including the new ballpark, Northstar commuter rail, the extension of Hiawatha light-rail, and the new intermodal (train, bus, and light-rail) station adjacent to the ballpark.

Three key factors were at play in the decision:

Stabilizing the sewer so it can withstand the vibration and loading from construction above.
Building alternate manholes and access shafts for ongoing operation and maintenance of the sewer — in places that won’t be covered by new structures.
Getting a jump start on the work to avoid delaying ballpark and other construction.

“Council staff and consulting engineers went down into this stretch of sewer during the winter to get a first-hand look at what already had been documented on videotape with a remote-operated camera,” Moore said. “Given the deteriorating conditions that we saw in the sewer and the various construction projects planned for the area, we’ve been able to expedite planning, design and contracting for the project, and we began the restoration work in late April.”

Service seamless during construction

The $3.5 million project involves digging up to seven access shafts of 30 to 50 feet deep to reach the old pipe. Permanent access structures will be built at three of these locations, consisting of concrete underground vaults, with only a manhole cover visible at street level. At each access shaft, workers will lower sections of 72- and 78-inch-diameter fiberglass pipe into the existing pipe and join them together — all while wastewater flows non-stop through the existing pipe. Once the pipe sections form a continuous length of pipe, concrete will be injected into the space between the old and new pipes to stabilize them.

“We’ve done this type of construction on other regional sewers, but it is difficult in that it involves very deep shafts that have to be braced with heavy, wood-and-metal pilings to keep from caving in or causing damage to nearby structures,” Moore said.

“It also involves relocating other utility lines and coordinating with other construction that needs to occur in the same place at the same time or soon after,” he explained. “Our goal is to get in, get the job done, and get out as quickly as we can so that other aspects of the larger projects can fall into place.”

The umpire’s call to “Play ball!” is still nearly three years away, but the construction players are already stepping up to the plate.