This is the story of how public agencies can collaborate to resolve environmental challenges in ways that are acceptable—and cost-effective—for both.
The Pennsylvania DOT (PennDOT) is adding two lanes to four miles of state highway in Northampton County, a stretch that includes a bridge over Saucon Creek in the City of Bethlehem. Widening the bridge required more than 900 lineal feet of city-owned sanitary sewer to be relocated.
The plan was to bury 48-inch steel carrier pipe beneath the creek bed and run the 30-inch sewer pipe through it. However, the creek is considered a high-quality watershed and home to native species of trout. Construction calendar restrictions for spawning had to be observed.
At bid time, engineers expected to install the pipe via trenchless jack-and-bore construction consisting of two large pits made of steel sheet piling. Though effective, it was also one of the most expensive installation options. Any unanticipated challenge, such as encountering bedrock, would further complicate and delay the work. Other trenchless methodologies, such as directional drilling, were also cost-prohibitive.
There was one other option: Temporarily move the water out of the way to provide a dry work space and bury the pipe via traditional open cut construction.
Divide and conquer
“We’ve physically moved a creek before, but not to this scale,” says City of Bethlehem Engineering Assistant Bob Deutsch. The crossing was 150 linear feet.
Project owner: Pennsylvania DOT
Sewer pipeline relocation: HRI Inc.
Cofferdam design and installation: Portadam Inc.
Dewatering: Rain for Rent
Timeline: Sept. 1–15, 2013
HRI Inc., the State College, Pa., contractor that oversaw the project for PennDOT, invited Portadam Inc., Williamstown, N.J., to visit the site. The company, which designs and installs cofferdams for in-water construction and aboveground storage, recently partnered with Rain for Rent, a provider of liquid-handling systems based in Bakersfield, Calif. The two companies’ 65 U.S. locations serve construction, remediation, rehabilitation, flood protection, and inspection projects in rivers, streams, lakes, and reservoirs.
After being brought up to speed on project specifications, contractual requirements, in-stream calendar restrictions, design and permitting requirements, and constructability concerns, Portadam provided HRI with schematics for configuring the coffer dam.
The pipeline would be buried in two phases: A cofferdam would provide a dry worksite for installation halfway across the creek; then dismantled and reconfigured for the other half. Rain for Rent would dewater the cofferdam and ensure the worksite stayed dry.
Even though it was only an idea on paper, HRI decided to implement the concept.
“We envisioned building a three-sided box,” says Portadam National Sales Manager Gerry Mann. “We’d go 60% to 70% out across the stream and run parallel 35 feet to 50 feet.”
Large frames for the boxes had to be floated out and placed into position in the streambed.
“It was sort of like building an erector set while floating around in the water,” Mann says. “Rocks and debris on the streambed had to be cleared before construction of the cofferdam to ensure a sound seal, so we sent in divers.”
Rain for Rent’s biggest challenge was managing 197,000 gallons more per minute than expected. The company provided 4- and 6-inch Power Prime diesel-powered, trailer-mounted pumps, but submitted a change order for another 6-inch pump and extra hoses to dewater in five to six hours.
Time constraints were tight, but the project was completed within the anticipated two-week time frame.
“The options were essentially renting or buying steel sheet piling and installing a coffer dam,” says HRI Senior Project Manager Eric Klimas, PE. “Portadam was by far much faster to install and remove. Since we only rented for a short period of time, the cost of performing this work was drastically decreased by minimizing labor, equipment, and materials. This application may not be best suited everywhere, but this instance made me realize that a coffer dam is a viable, cost-effective alternative to more traditional construction methods.”
“It was a very interesting solution and did a great job of keeping water out of the area we needed to work in,” says the City of Bethlehem’s Bob Deutsch. “From an engineering point of view, any time you have to divert a body of water that’s been flowing for a number of years, and do it without disrupting or disturbing anything, it’s an amazing feat.
“This solution was well-coordinated, constructed efficiently and, overall, very impressive.”
Kathryn Caggianelli is a freelance writer based in Albany, N.Y. E-mail [email protected].