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Infrastructure Reinvestment Yields Dividends for Detroit Area

 

 
Continued investment in our water and sewer infrastructure is critical to maintaining the level of service customers expect. Water main breaks are inconvenient and sewer overflows from infrastructure failure damage the environment. Both require costly repairs. Focusing investment where it is needed most and following through on long term rehabilitation programs is key to gaining traction in the continuous process of infrastructure renewal.

Infrastructure needs to be upgraded for a variety of reasons – expected life time has passed, environmental factors shortened the life expectancy, or new technology can better manage the task. Annual capital improvements targeting problem areas help communities focus their efforts and make progress over the long haul. These programs, paid by system users, increase system reliability and lower risk of future problems. This article focuses on the valued reinvestment projects being undertaken in the Detroit Water and Sewerage Department (DWSD) service area that are extending the life of our water and sewer infrastructure.

Joining Forces to Tackle a Major Sewer Rehabilitation
Regional sewer systems develop in response to land development patterns and frequently cross jurisdictional boundaries. The 21-mile-long Oakland-Macomb Interceptor Drain (OMID) was constructed in the early 1970s to provide wastewater service to growing areas in Oakland and Macomb Counties. Beginning near the intersection of 23 Mile and Dequindre Roads, and extending down to the Wayne County line, the OMID ranges in diameter from more than 9 feet to nearly 13 feet. The interceptor connects to the Northeast Pump Station in Wayne County where sewage flows are lifted into one of the main interceptors that goes directly to the Detroit Wastewater Treatment Plant (WWTP).

When the OMID was constructed, DWSD’s bonding capacity was used to secure favorable project financing and DWSD became the owner. Oakland and Macomb Counties’ customers were responsible for paying back the bonds as well as future maintenance costs since they were the only customers using the OMID. When a second collapse occurred along the OMID in 2004, a detailed inspection revealed costly repairs were needed for more than seven miles of pipe. Seeking the most cost-effective rehabilitation alternative, Oakland and Macomb Counties agreed to create an intercounty drainage district to assume ownership of the OMID.

Intercounty drainage districts are formed to maintain sewers or drains that cross county lines. The districts have the authority to issue bonds, apply for grants and loans, and impose taxes to repay the bonds. Through Chapter 21 of Michigan’s Drain Code, the Oakland-Macomb Interceptor Drain Drainage District (OMIDDD) was created as a separate public corporation. Additional funding sources could be tapped for the OMID, and the District could select the preferred rehabilitation method and oversee its completion. With the OMIDDD in place in 2009, a plan of action was undertaken to reduce the estimated $200 million rehabilitation price tag.

The 2004 collapse was the result of silty soil conditions around the pipe. Sand and silty sand made its way into the interceptor through tiny openings, leaving voids in the supporting soil around the pipe. Once support under the pipe was lost, the load of the soil over the pipe cracked it circumferentially. Investigations revealed that a 4.3-mile downstream segment of the OMID was in the same type of soils and at risk for a future failure. Complicating the situation was the fact that this was in the deepest part of the interceptor where pipe reaches depths of 110 feet.

A solution was needed to strengthen the soil around the pipe, and repair the deteriorating pipe interior. First, a plan was developed to maintain flows during construction since the OMID is the sole conveyance conduit that transports sewage for more than 830,000 people.

“Six gates were added along the OMID to manage the flow diversions required to rehabilitate the soil and pipe,” explains Mark Steenbergh, Operations Manager, Wastewater Services Division, Macomb County Public Works. “These were installed first so flows could be held back during the day when contractors are performing work.”
 

   
 The OMID was repaired by installing sections of new HOBAS pipe lining (left). Prior to installing pipe, soils surrounding the sewer were stabilized with grout (above).
 
 
 
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