LFA Helps Mishawaka Move Closer to Separated Sewers

The City of Mishawaka is in the process of implementing projects that will satisfy the city’s Long Term Control Plan (LTCP) for reducing combined sewer overflows (CSO) to the St. Joseph River. One of the requirements of the LTCP is to separate approximately 152 acres in the Linden Area that contribute stormwater runoff to the combined sewer system. Linden Division M is one component of the plan to allow the existing Byrkit Street 60 / 66 inch diameter combined sewer to be converted to a storm sewer. All sanitary flows that discharge to the 60 / 66 inch Byrkit Street sewer will be redirected to a new 30-inch diameter sanitary sewer that will ultimately discharge to the city’s combined sewer system at Fourth Street and Mason Street. In addition to contributing to the LTCP required separation activities in the Linden Area of the City, the conversion of the 60 / 66 inch Byrkit sewer will provide a stormwater discharge location for areas south of the Norfolk Southern Railroad.

The first phase of the Linden Division M project, Phase IA, required the new 30-inch diameter sanitary sewer to cross perpendicularly beneath the existing Norfolk Southern Railroad, west of Byrkit Street. Since railroad traffic needed to be maintained during the sewer construction activities, the 30-inch diameter sanitary sewer was placed via jack and bore methods. Jack and bore is a trenchless method of horizontal boring sewer construction and this construction procedure requires significant coordination and planning, such as:

• • • • • • • Geotechnical investigations to determine the soil conditions beneath the railroad that the Contractor can reasonably expect to encounter.
            • Soil stabilization activities within the limits of the jack and bore activities beneath the railroad to minimize risk of settlement.
            • Dewatering activities to lower the existing groundwater table and provide a dry working environment within the jack and bore construction limits.
            • Settlement monitoring to ensure that the integrity of the Norfolk Southern track rail elevations are maintained throughout the jack and bore activities.
            • Development of contingency plans should any cobbles or boulders be encountered during trenchless construction activity.
            • Consistent communication with Norfolk Southern representatives to ensure that rail traffic is not hindered in any way during construction.

In late 2021, the city’s construction contractors began the 24-hour jack and bore operation and were able to complete it prior to the end of 2021. The placement of the sewer was significant milestone for the City as they continue to implement LTCP projects. Construction of Phase IB of the Linden Division M project is scheduled to begin in summer 2022 and will result in full conversion of the 60 / 66 inch diameter Byrkit Street sewer to a storm sewer.

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