An aging sanitary pump station and 4-inch force main convey wastewater five miles from the Rainbow Casino in the town of Port Edwards, Wis., to the Nekoosa wastewater treatment plant. Concerns about the station’s reliability and capacity, and pending casino expansion, prompted Ho-Chunk Nation leaders to contact engineer Scott Chilson of MSA Professional Services in Baraboo, Wis.

Chilson recommended replacing the pump station and doubling the diameter of the force main. A site for the new facility was available, but the privately owned force main was in a public easement controlled by Wood County, the Town of Port Edwards, and the City of Nekoosa. Those entities granted permission to install a larger force main so long as construction methods minimized surface disturbance.

Chilson worked with Bill Brennan of TT Technologies Inc. in Aurora, Ill., to develop the best approach. Their solution, involving 20,000 feet of static pipe bursting and 4,000 feet of horizontal directional drilling (HDD), became one of the largest projects of its kind in the Upper Midwest.

By invitation only

Allen Steele Co., Lake Delton, Wis., won the invitation-only bid. The firm had done HDD for several years, but this was its first bursting job. Therefore, Brennan helped Richard Steele and pipe bursting foremen Paul Glavan operate the self-contained hydraulic Grundoburst 800G static pipe bursting system from TT Technologies.

Brennan selected a specially designed quad cutter to split the relatively new 4-inch force main. He also recommended using bentonite slurry during the bursting runs to restrain the sand from caving in and blocking the pullback. The slurry also lubricated the path for the 8-inch replacement HDPE pipe. A Grundomudd DS 500 mixing system from TT Technologies delivered the slurry through a manifold and hose to the pipe.

The route of the 6- to 7-foot-deep force main crossed a trout stream, two high-pressure crude oil pipelines, two county highways, and a heavily-traveled county road. In one instance, a fiber optic communication line lay above the pipe. “The project had a little bit of everything,” says Steele.

Because the job involved the worst sands the men had ever seen, they divided the 1,000-foot static pulls in half. The exit hole was dug at 500 feet, with launch pits at either end of the run. Exit pits were shored with four 5-foot spreader bars in a 25-foot steel box. Launch pits required only 8- by 20-foot steel enclosures. “Constructing the trench boxes and maintaining safety were the project’s most time-consuming aspects,” says Steele.

Efficient work plan

Once the bursting unit was in the exit pit, the crew linked Quicklock bursting rods together until they reached the first launch pit. Then they removed the guide rod and attached the pipe bursting components which, under 100 tons of pullback force, split the host pipe, displaced the fragments into the soil, and pulled in the fused replacement pipe.

As the rods appeared at the exit pit, workers fed them into the next length of pipe. When one section was completed, the crew lifted and turned the machine 180 degrees and prepared for the next run.

“Not having to unlink and reconnect the rods sped up the process and improved efficiency,” says Steele. “The setup enabled us to pull 500 feet in two to three hours. During our best week, the crew pulled 1,000 to 1,100 feet in a nine-hour day and installed more than 6,000 feet of pipe.”

The crew, however, initially resisted the trenchless technology, being accustomed to open-cut techniques. “By the end of the 10-month job, they had the system down pat and enjoyed the bursting process,” Steele says. “They can see the benefits of it now.”

Time for HDD

The two high-pressure crude oil pipelines presented a hazard. “Our initial plan was to burst the force main, but we found that it was too close to the pipelines,” says Steele. “Switching to directional boring required permits, and getting the paperwork took longer than the 400-foot job.”

The biggest challenge was boring 600 feet up a 50-foot grade change. Water, hauled from a casino hydrant in a 6,000-gallon tanker, was mixed with bentonite at the bottom of the hill, then fed into a Vermeer D36x50 Series II Navigator HDD unit with 50 gpm mud pump. Its 140-hp engine delivers 4,928 foot-pounds of rotary torque and 33,000 pounds of thrust with 36,000 pounds of pullback.

“The sand kept trying to cave in and block the pipe during the pullback,” says Ron Demlow, directional boring foreman. “We went through 17,000 gallons of mud and never could have completed the pull without it.”

Seven men worked a 14-hour day to finish the job. Except for the sand, none of the directional bores presented any unusual problems.

The new pump station and enlarged force main enabled Ho-Chunk Nation leaders to proceed with casino expansion plans, and the construction methods met the needs of the land owners. Trenchless technology turned out to be a good ­bet for all concerned.