The Water Research Foundation (WRF) has published a suite of deliverables to help water and wastewater utilities utilize...
Colorado utility nears the end of construction of 50-mile pipeline
Before the end of 2014, Colorado Springs Utilities will lay the final piece of pipe for one of the largest water projects currently being built in the western U.S.
The Southern Delivery System (SDS) is a regional water project in southern Colorado that will bring Arkansas River water stored in Pueblo Dam to Colorado Springs, the state’s second largest city, and its partner communities, Fountain, Security and Pueblo West. Colorado Springs Utilities is completing SDS at a time when the frequency and volatility of drought is growing in the arid American West, while the economy is improving and water demand is increasing.
Fifty miles of predominantly 66-in.-diameter welded steel pipe serve as the artery of SDS, travelling up 1,500 ft in elevation via three new pumping stations and eventually arriving at a new water treatment plant north of the dam.
To finish SDS on time and under budget, the municipally owned utility and its program manager, MWH Global, divided the pipeline into several different work packages. Separate packages facilitated competitive private industry bidding, which is among the reasons that the project is projected to come in significantly under budget at completion, reducing the final projected cost from almost $1 billion to $841 million.
“The program team has been innovative in how we have approached SDS—starting with the design and engineering to contracting and construction,” said John Fredell, SDS program director. “We also have extended this ‘outside the box’ approach to how we communicate and inform interested stakeholders, local residents and businesses impacted by construction activities.”
The following are a few highlights of the creative approaches the SDS team used to install the pipeline in often challenging physical and social conditions.
Ascending From Pueblo Reservoir
The southernmost section of the pipeline, a 4.3-mile section known as South Pipeline 1 (S1), stood out as one of the most difficult sections to construct due to technical and geological conditions.
Much like a stair step, S1 needed to rise 150 feet from the reservoir basin and surmount the surrounding embankment in order to level out and begin its gradual ascent northward. This journey was complicated by the presence of a railroad line cut into the surrounding bluff.
The design engineer chose a route between a drainage way on one side and two 80-ft hills. After examining multiple options, the SDS project team determined that the best design was a 308-ft-long, 10-ft-diameter tunnel at an approximately 3% slope underneath the railroad. A 90-ft vertical riser shaft situated within the bluff supported the pipe and tunnel.
Subsurface conditions proved complicated. The bluff is located just a few hundred yards from one of the globally recognized sections of the Cretaceous-Paleogene boundary, the marker bed of the geologic period approximately 65.5 million years ago. Geologically, the bed hosts layers of limestone and shale, providing both very strong and very weak subsurface soils.
Construction engineers began work by drilling a vertical tunnel and installing a riser shaft, resting it in sand bedding. Then came the arduous work of digging through limestone. Because of the slope, tunnel methods such as auger boring and jack and bore were ruled out. Methods that called for conveyor discharge or muck cars also were not practical due to the slope.
Instead, the main tunnel was completed with the use of a 27-ton road header. Mucking was completed using a skip bucket attached to a tracked skid-steer loader.
At the opposite end of the tunnel, engineers constructed an approximately 12-ft-wide final cavern section in the shale, and supported it using rock bolts at a staggered pattern, steel mesh and shotcrete. The roof of the cavern intersected the previously installed sand bedding of the north riser pipe.
Despite such difficult soil and technical conditions, the S1 tunnel crossing was completed successfully, on time, under budget and to the railroad owner’s specifications.
Traversing an ATV Area
After leaving Pueblo Reservoir, S1 pipeline traverses through one of the most well-used motor sports areas in southern Colorado. Construction was underway during spring and summer—prime season for motor sports enthusiasts to ride.
The conventional approach would have been to establish a linear work area multiple miles long, stage the pipe sections (66 in. in diameter and 50 ft long) end to end, and fence off the linear construction site. That approach would have prohibited the public from using the many ATV trails that traversed the pipeline alignment. But because the SDS team sought to minimize disruption to local residents, they took a different approach.
Prior to the two-month-long trenching project, the SDS public involvement team distributed informational materials to enthusiasts who frequented the area, and coordinated with both the city of Pueblo Parks and Recreation Department and State of Colorado Division of Parks and Wildlife—the two agencies that co-manage the area. Then, rather than laying one continuous line of pipe, the contractor staged the pipe above-ground in islands and then built several crossings using gates and fences between the islands of pipe to allow safe passage through the construction zone.
These passageways were left open until the actual pipe laying was at each crossing and construction was too intense to keep them open. Signs were put up encouraging individuals to use the crossing, but to stay out of the construction areas. This gave off-road motorists the opportunity to enjoy the area. As a result, there were no complaints from ATV enthusiasts, and the measures helped protect public and worker safety by creating designated safe corridors to cross through the construction zone.
Engaging Residents in Pueblo West
Another community engagement challenge arose in Pueblo West, a community of 30,000 residents. The 6.4-mile South Pipeline 2 (S2) section needed to travel through 125 residential yards and required the purchase and removal of six houses and the relocation of their owners.
To keep residents safe and informed and minimize disruption, SDS staff aimed to be good neighbors.
Two full-time “construction facilitators” continuously were on site at the construction areas and served as daily touch points for residents and businesses. Through door-to-door visits, meetings and a 24-hour staffed hotline, the facilitators explained the project and occurrences that residents could expect. As work progressed, residents received ongoing visits, letters, e-mails and newsletters to keep them apprised of issues ranging from road closures to plans for yard revegetation.
Even the six homes acquired for demolition became a community asset. After the project paid for the owners to relocate, the SDS team offered reusable items—such as plumbing fixtures, cabinets and doors—to the local Habitat for Humanity office to resell or install in their homes. Local fire and police departments were invited to use the houses to conduct drills and practice simulated firefighting.
By utilizing creative approaches to construction, coupled with a commitment to communication and community relations, SDS is advancing a critical water infrastructure project for four southern Colorado communities, creating a more certain water future for its customers.