DLZ Wins ACEC of OH Award for Columbus Sewer Tunnel

OARS Tunnel breakthrough.

The American Council of Engineering Companies (ACEC) of Ohio awarded DLZ with an Outstanding Achievement Award for the OARS-OSIS Augmentation & Relief Sewer project in Columbus. This prestigious award is given to engineering firms for projects that demonstrate a high degree of achievement, value and ingenuity.

The OARS project consists of the construction of a 20-ft diameter, 170-ft deep tunnel that provides relief to the existing OSIS from just north of the Arena District in downtown Columbus to the Jackson Pike Waste Water Treatment Plant (about 23,300 ft in total length).

The OARS tunnel is sized to provide adequate conveyance capacity through the year 2047 for all storms contained within the typical year as defined in the Wet Weather Management Plan. The sewer will also provide some inline storage during critical periods to eliminate combined sewer overflows from the 12 regulators located along the OSIS in downtown Columbus. The Level of Service will be equivalent to a 10-year level of wet weather flow protection.

Once the OARS is operational, more than a billion gallons of combined sewage overflows will be treated instead of discharged to the Scioto River each year.  The 170-ft depth allows for the tunnel to be constructed in competent rock, reducing risks associated with construction. Special drop structures are required to direct flow from shallow sewers to the deep tunnel.

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Tangential inlets with deaeration chambers will be utilized to dissipate energy and minimize air entry into the tunnel. Tunnel surge relief facilities will also be provided at several shaft structures.

In 2012, the 540-ft long tunnel boring machine (TBM) began its journey north from south of Frank Road near the Scioto River to I-670 on the north side of downtown Columbus, averaging about 70 ft a day. On Sept. 4, 2015, the giant TBM broke out into the final shaft at the upstream end of the tunnel, completing a 4.5-mile long adventure. The tunnel is the most expensive public works project ever for the City of Columbus.

Once the entire project is complete, the tunnel will carry wastewater to the treatment plants on the South side of Columbus, where the water will be pumped out and treated. More importantly, the tunnel will hold combined stormwater and sewage to prevent it from overflowing into the Scioto River during heavy rain.

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