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On August 27, the Detroit Water and Sewerage Department’s 11-foot-diameter sanitary and storm sewer interceptor in Macomb County failed. Normal dry weather flow through the interceptor is 50 cubic feet per second. During a storm it rises up to approximately 100 cubic feet per second, or 45,000 gallons per minute. The interceptor services approximately 600,000 people.

“We needed to stabilize the soil and get an emergency bypass to ensure that we would continue to have service to our customers,” Victor M. Mercado, Utilities operations chief for the Detroit Water and Sewerage Department (DWSD), said.

“We’ve stabilized several of the holes near the failure; we have stabilized the sinkholes so that we do not lose anymore ground in that area; and we have the permanent bypass working. We are pumping sewage from upstream of the break to downstream of the break.”

“There was an emergency that was created here with the collapse, which meant the immediate mobilization of a variety of contractors to stabilize the situation, protect the area, and to try and figure out what we were going to do to remedy the situation,” Walter Rozycki, account executive for Inland Waters Pollution Control, Inc., of Detroit, said. Inland Waters is the prime contractor on the project.

A relatively new method of installing grout was used, in order to prevent the sinkholes from migrating around the pipe. The ground was drilled with a 6-inch-diameter drill string and the cement grout was injected with high pressure.

Subcontractors on the project include L. D’Agostini & Sons, Inc. (earthwork), of Macomb Township; Mersino Dewatering, Inc., of Davison; and Thompson Pump Midwest.

Mersino has had a dewatering system in place with a little less than 12 deep wells, ranging from 80 feet to 100 feet deep. Mersino has been using multiple generators and high volume, in-ground pumps to pump water out. Mersino was a first responder on the site.

Contractors worked 24 hours per day, seven days per week, in order to install an emergency bypass pumping system.

Originally, diesel driven centrifugal pumps were thought to be a viable solution to handle the flow in the tunnel. The critical point in the sewer surcharge would have been reached before a centrifugal pump would have been effective. Centrifugal pumps cannot prime greater than approximately 28 feet.

Per Inland Waters instruction, Thompson Pump Midwest brought triple-stage 30-inch and triple-stage 24-inch axial flow pumps to support the temporary bypass. These pumps were able to handle the volume required, preventing the possibility of breaching the 35-foot flood mark. Each triple-stage unit contains three large propellers driven by an individual hydraulic motor. (THESE PUMPS ARE MWI HYDRAFLO PUMPS. THEIR UNIQUE DESIGN ALLOWS THEM TO BE QUICKLY SET UP AND TO BE JOINED IN SERIES TO MEET THE REQUIRED HEAD AND FLOW) This allowed Thompson Pump Midwest to work with the design engineers to formulate the permanent bypass plan.

During and after the emergency bypass was installed, engineering firm NTH Consultants, Ltd. was called upon, along with some of its subconsultants including Lakeshore Engineering Services, Inc. and Spalding DeDecker, to develop a more permanent bypass, until the interceptor is repaired and can be used again. The permanent bypass system was installed within four weeks.

“It’s been a very concerted effort by everyone involved to put this together within four weeks. It was done by holding daily meetings with all of the contractors and consultants involved. We put our heads together and worked out a viable solution to whatever work activity was there,” Rozycki said.

“We have to reduce the levels of flow in the line enough so that L. D’Agostini & Sons, Inc. can go in and put two bulkheads in to isolate the damaged area so that they are able to get in there to begin excavation with an earth retention system with auger piles in order to get access to the pipe and find out what its condition is. The pipe will have to be removed. Material in the pipe that has fallen from the sinkhole will have to be removed.” It is anticipated that a maximum of 250 feet of reinforced precast concrete pipe will replace the existing poured-in-place concrete pipe. Northern Pipe will manufacture the pipe.

“The soil is very wet and there is a lot of dewatering that needs to occur in order to bring the water table below the invert of the pipe,” Gino D’Agostini, of L. D’Agostini & Sons, Inc., said.