Work Begins on Deep Rock Tunnel Connector

By Jim Rush

After years of planning, Indianapolis recently marked the start of its largest-ever public works project. On April 25, officials including Indianapolis Mayor Greg Ballard and Citizens Energy Group president and CEO Carey Lykins gathered at White River State Park to commemorate the start of the Deep Rock Tunnel Connector (DRTC), a $180 million, 7.5-mile tunnel project that is a major component of Indianapolis’ $1.7 billion long-term control plan to reduce sewer overflows.

The long-term control plan is part of a consent decree with the U.S. EPA and Indiana Department of Environmental Management that is to be completed by 2025. When completed, the program will improve water quality and protect public health in the Hoosier State’s capital and beyond by capturing, storing and conveying sewage and stormwater to treatment plants. The overall tunnel storage system will extend approximately 25 miles and store 250 million gallons of sewage and stormwater during rain events.

Digging Deep

The DRTC is the first phase of the tunnel program. Originally designed as the Belmont-Southport Interplant Connection intended to divert flows from one watershed to another, the tunnel was redesigned as a deep storage and conveyance tunnel.

In the initial concept, the 12-ft ID tunnel would have been constructed in soft ground under high groundwater conditions 35 to 75 ft below the ground surface. Under the redesign, the DRTC will be constructed in limestone more than 250 ft below surface with an internal diameter of 18 ft. The larger diameter allows for more storage while the deeper design reduces surface disruption and avoids areas of contamination discovered along the project route.

Increasing the capacity of the DRTC also allowed planners to reduce the diameter from 27 to 18 ft for tunnels planned upstream, thereby expanding the potential pool of bidders. Ultimately, the DRTC project came in about $100 million below the engineer’s estimate of $280 million. “The new approach allowed us to spread out the storage throughout the system and hit the sweet spot in terms of the tunnel diameter that would be the most economical and allow for the most competition,” said John Morgan, Manager of the
Special Projects Group for Citizens Energy.

The change in approach led to a fast-track design to keep the program moving toward meeting the milestone dates identified in the consent decree. “The design was quite a technical challenge,” said Alex Varas, vice president for project designer Aecom. “We had less than 16 months to create the 100 percent design in advance of the December 2011 award date.”

In December 2011, the DRTC was awarded under a design-bid-build contract to a joint venture of Shea-Kiewit. The project includes the construction of launch and retrieval shafts, approximately 35 ft in diameter and 280 ft deep, which are being constructed by slurry wall to bedrock. Additionally, three access shafts and three diversion structures will be built along the alignment. Bencor is currently constructing the slurry walls for the launch shaft at the Southport Advanced Wastewater Treatment Plant under a subcontract. The arrival of the Robbins TBM is expected in late August and boring is expected to begin in early 2013. Construction is expected to last until 2017.

Utility Transfer

Interestingly, the redesign from a shallow inter-connection tunnel to a deep storage tunnel wasn’t the only major change associated with the tunnel program. The project owner also went through a major transformation.

In March 2010, Mayor Ballard and Citizens Energy announced a plan to transfer Indianapolis’ water and sewer utilities to Citizens Energy, a charitable trust established in 1887 to operate the gas utility. City Council approved the transfer in July 2010, and the $1.9 billion transfer was completed on Aug. 26, 2011. As a result, the water and wastewater systems, which billed customers under the Indianapolis Water name, are now operated as Citizens Water.

The transfer is expected to result in $60 million in annual savings that will help Citizens Energy reduce projected water and wastewater rate increases 25 percent by the year 2025. The City also received $425 million from the transfer to fund its Rebuild Indy initiative that is making much needed repairs to parks, bridges, streets, and sidewalks, while removing hundreds of abandoned homes throughout the city.
In addition to assuming responsibility for the long-term control plan, Citizens Water assumed operations of the water utility from Veolia Water Indianapolis (Veolia) and also assumed the City’s contract with United Water to operate the wastewater system.

“The utility transfer is complete and has been a big improvement,” said Morgan, who previously worked for the city’s Department of Public Works. “It has taken the politics out of managing the water and sewer system and allows us to focus on doing the right thing.”

Future Works

Four other tunnel projects are planned that will have staggered start and completion schedules. “We won’t have more than two rock tunnel projects taking place at the same time,” Morgan said. “We feel that this will help us obtain competitive pricing from the tunnel contractors. As one projects gets near completion another will be bid.”

The remaining tunnel components include:

  • The Pleasant Run Deep Tunnel (PRDT), which will be an 18-ft finished diameter tunnel, nearly 34,000 ft long and approximately 250 ft deep. PRDT is anticipated to be constructed in limestone and dolomite using a main beam TBM. The tunnel alignment will have two 35-ft finished diameter shafts, one tunnel working shaft and one TBM retrieval shaft. The upstream reach is expected to include a 6-ft finished diameter soft ground microtunnel, nearly 6,000 ft long and an average of 35 ft deep. Up to eight drop shaft vortex structures will be constructed to drop flows into the tunnel capable of conveying combined sewer overflows up to 260 mgd.
  • The Lower Pogues Run Tunnel (LPgRT), which will be a deep rock tunnel in limestone and dolomite, and approximately 11,000 ft long, 250 ft deep and 18-ft finished diameter. The project will use trenchless technology to install 20 to 50 ft deep consolidation sewers approximately 8 ft in diameter. Three drop shafts that will convey flow into the tunnel from eight combined sewer overflows that currently discharge into Lower Pogues Run and ultimately into the White River are also anticipated.
  • The Fall Creek/White River Tunnel System (FCWRTS) is anticipated to be an 18-ft finished diameter tunnel approximately 46,000 ft in length. FCWRTS consists of two segments: 1) Fall Creek Tunnel Segment, length approximately 27,000 ft; and 2) White River Tunnel Segment, length approximately 19,000 ft. The tunnel will be an average of 270 ft deep and is anticipated to be constructed in limestone and dolomite using a main beam tunnel boring machine (TBM). Deep tunnel access shafts are anticipated to be up to 35 ft finished diameter. Twenty drop shaft vortex and baffle structures will be constructed to drop flows into the tunnel capable of conveying combined sewer flows up to 400 mgd.

“The start of DRTC construction is the beginning of a long path ahead of us,” Varas said. “We are all hopeful and enthusiastic that we will have a successful project.”

Jim Rush is editor of TBM.

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