Columbus, Ohio, was founded in 1812 at the confluence of the Scioto and Olentangy rivers. Ohio’s capitol, as well as the state’s largest city, Columbus was named after Christopher Columbus and has grown to become the fifteenth most populous city in the United States. Unlike other cities in the Midwest, Columbus continues to expand both in area and in population, making it one of the fastest-growing large cities in the country. The city is right in the thick of things by being centrally located in the state and by being within 550 miles of one-half of the nation’s population. Due to its forward-minded approach to wet weather management, it is among the busier tunneling cities in the country as well.
Water Water Everywhere
Before Columbus was Columbus, water management was a prominent issue. In 1797, a young surveyor from Virginia named Lucas Sullivant founded a settlement on the western banks of the Scioto River. Sullivant named his settlement Franklinton, as he was a great admirer of Benjamin Franklin. In 1798, Franklinton was wiped out by a great flood. Sullivant stayed firm and rebuilt the settlement. He was a key figure in the founding of Columbus as the state capitol a decade later, on the opposite bank of the Scioto.
Roughly 100 years later, in March 1913, Franklinton (now a neighborhood of Columbus) was again devastated by a flood that killed nearly 100 residents and left thousands homeless. The U.S. Army Corps of Engineers was brought in to prevent future flooding. The Scioto River was widened through downtown, with new bridges constructed and retaining walls lining its banks.
In the 1950s, Columbus adopted an annexation policy, which meant that in order for water and sewer service to be extended to outlying areas, they needed to become part of the City. This policy has been credited with keeping Columbus’ tax base strong in the later 20th century era of suburbanization. Rather than independent suburbs with independent tax bases ringing Columbus and draining it of residents and resources, annexation has meant that the City has seen its population and tax base grow at a time when similarly sized cities faced the opposite.
Wet Weather Management Plan
When the sewer system was built decades ago (portions are better than 100 years old), wet weather capacity issues were handled much differently. It was acceptable, for example, for sewers to overflow into existing bodies of water when sewer capacity was unable to keep pace with volume. The federal EPA issued new guidelines for sanitary sewer overflows (SSOs) and combined sewer overflows (CSOs) and the City of Columbus signed consent agreements with Ohio EPA to address overflow issues. Specifically, the 2002 agreement requires the cessation of SSO into rivers and streams and the 2004 agreement calls for the stoppage of CSO overflows into rivers and streams.
The City committed $2.5 billion (in 2005 dollars) to a 40-year plan to comply with the consent agreements with capital improvements to capacity and treatment. Along with the capital improvements, an existing program will improve and rehabilitate the existing sewer system.
Big Walnut Augmentation/Rickenbacker Interceptor (BWARI)
As part of the first major undertaking by the City as part of the Wet Weather Management Plan, BWARI, along with sister project BWOAS, will increase the wastewater capacity of the collection system that serves the areas along the Big Walnut, Blacklick and Alum Creek basins in eastern Columbus as well as a connector line from the Rickenbacker Airport.
BWARI’s scope includes four miles of 14-ft diameter lined interceptor sewer between the Alum Creek sanitary trunk sewer and the Southerly Wastewater Treatment Plant, as well as seven access shafts and several hundred feet of 14-ft square box tunnel connecting the sewer with the new headworks of the Southerly plant.
Working primarily below the water table, the Jay Dee/Michels/Traylor joint venture employed a 16-ft diameter Lovat EPB TBM to push through the glacial and glacio-fluvial terrain, comprising layered, dense glacial tills and water-bearing sand and gravel outwash deposits. Designers considered a few TBM options to tackle the soil and groundwater conditions, including an open-face TBM and full dewatering, but city officials were concerned that such methods would compromise the water quality of private wells in the area.
Mining began in late 2004 and encountered early setbacks due to flooding of the area surrounding the main shaft. Crews quickly made up any lost time, though, and finished the drive ahead of schedule.
The TBM broke through on October 15, 2006. Lining work began in early 2007 and is scheduled to complete in June 2008.
Big Walnut Outfall Augmentation Sewer (BWOAS)
The second phase in the City’s sewer improvement project, BWOAS began construction in mid-2005 with shaft and slurry wall work and began mining in late summer. A joint venture of McNally/Kiewit is overseeing the project.
A Lovat EPB TBM was selected for the 13,200 lf drive and was assembled in the shaft, with some sections suspended in place as assembly continued due to the absence of a tail tunnel. The bore path is primarily through glacial clay, tills and sands with boulders. The TBM bored a 167-in diameter tunnel, concrete segment lined to 144-in. diameter 60-ft below the surface.
Also included in this project were five shafts (one working shaft and four access shafts), 5,000 lf of surface sewer and two 400-lf lengths of pipe jacking. The surface sewer work was completed by mid-2006 by open-cut method. Sub-contractor Complete General trenched 4,600 lf, 7-ft wide and 25-ft deep, to install the Hobas 42-in. pipe.
Tunneling halted approximately 2,500 lf along in order to maintain the TBM and replace the seal on the articulation seals. During this break, the Lovat machine from BWARI holed into the working shaft on BWOAS. Once the BWARI TBM was clear of the shaft, the BWOAS machine was able to continue on its drive.
On August 1, 2007, the TBM broke through into the recovery shaft, completing tunneling work on BWOAS. Lining work is under way and expected to complete in November 2008.
Big Walnut Sanitary Trunk Sewer Extension (BWSTSE)
Tunnel boring is currently under way on BWSTSE, roughly 6,000 lf into the 10,000 lf drive. The bore path, which is on a gentle downward slope to allow it to pass safely beneath the Big Walnut Creek, passes primarily through Ohio shale. Ohio shale is prevalent in the Eastern part of Columbus as is particularly tunnel-friendly, with the Lovat EPB TBM advancing between 90 and 100 ft per day.
BWSTSE will provide sanitary sewer service to the rapidly developing area between the Hoover Reservoir and the village of New Albany. A joint venture of Kassouf, Mole, Murray Hill and Jay Dee is the contractor on the project, with design features provided by DLZ and Jenny Engineering. In addition to the 10,000 lf of tunnel, the project includes four shafts between 60- and 175-ft deep and connecting structures.
Construction began in 2007 with shaft work primarily utilizing a 30-ft diameter vertical boring machine developed by Kassouf. Mining operations commenced in October 2007 and has proceeded smoothly. An anticipated encounter with gas led to a one-day evacuation of the site but crews were able to resume work quickly. Concrete pipe with T-Lock liner is put in place behind the TBM as it advances.
The final 600 lf of the drive will encounter soft ground and was originally designed for pipejacking installation methods. The on-site design team is exploring alternatives to tackle this portion of the drive.
In all, BWSTSE is an anticipated two- to three-phase project. The remaining 10,200 lf will be constructed in one or two phases. If divided, Phase 2 would be 5,720 lf through Ohio and Bedford shales, while Phase 3 would be 4,500 lf through similar soils.
Around the Bend
In December 2007, Columbus Mayor Michael B. Coleman cut the ribbon on the new $106 million Headworks Facility at the Southerly Wastewater Treatment Plant. The improvements boost treatment capacity by 50 percent, which will be needed as the Big Walnut sewer projects come on line. Six additional projects at the Southerly plant will further increase capacity from 260 to 330 mgd. City officials are confident that these improvements, along with the $100 million in improvements to the Jackson Pile Wastewater Treatment Plant, will serve the City and the central Ohio sanitary sewer district for 100 years.
Columbus’ Wet Weather Management Plan is on a 40-year construction schedule. Several more tunnels are planned to handle CSOs and SSOs, including the Lockbourne Intermodal Subtrunk (currently in design), Olentangy and Alum Creek Relief Tunnels (proposed 11- and 18-mile tunnels, respectively, for SSO storage and transport) and OSIS Augmentation and Relief Tunnel (proposed 4.8-mile tunnel for CSO storage and transport).
By 2010 as more and more of the WWMP components become operational, residents will not only benefit from fewer flooded basements, but will benefit from a vastly improved ecological environment. As the saying goes as found peppered throughout Columbus WWMP literature, “We All Live Downstream.” Thanks to WMMP, it will be a great place to live.
Greg Thompson is assistant editor of Tunnel Business Magazine. Special thanks to the City of Columbus, DLZ and URS for assistance and guidance in compiling this article.
