Pipeline project options narrowed
By DAN MORIARTY
Staff Writer
WESTFIELD – The Granville pipeline replacement project may involve the use of trenchless technology, as well as traditional trenching methods.
Dave Edson of Hoyle, Tanner & Associates, Inc., the Water Commission’s consultant for the pipeline replacement project, said at the Water Commission’s March 6 meeting that pipe bursting technology may be required in the upper half of Granville Gorge, while traditional trenching may be the more cost-effective approach for the lower half of the project.
The purpose of the project is to replace a 14-inch pipe, originally installed in 1890, with a 16-inch high-density plastic pipe.
The present pipe limits the flow of water and is leaking, while the proposed pipeline is projected to increase flow to the treatment plant, located in Southwick, by a million gallons a day, substantially reducing the demand for well water.
Edson, at the February board meeting, said the Granville Reservoir is the city’s most cost-effective drinking water option because the system is based on gravity flow. Water pumped from wells requires a substantial amount of electrical power.
The consultant has assessed the function of the pipe for more than a decade and observed a drop in the volume of water reaching the treatment facility.
“The (existing) pipeline is losing capacity, which has a real economic impact on the department because this is the least expensive water to produce, because the system is almost entirely gravity fed,” Edson said at the February meeting.
“When you have pipe that is over 100 years old, catastrophic failure is a concern,” Edson said. “The treatment plant has a (treatment) capacity of 2,800 gallons per minute while the pipeline has a capacity of 1,900 to 2,000 gallons per minute.”
The project would be financed through a federal low-interest loan, part of which is forgiven over time, administered through a state revolving fund program. The state has approved $2,357,000 for the project.
However, the Water Department will have to fund the engineering and design work. The state program established a short timetable which requires the city to begin the design process, appropriate funding by June 30, and submit the loan application, with engineering, design and permitting documents in place, by Oct. 15, 2012, with a construction contract awarded by April 2013.
The project is also required to have a “green” energy element. The proposed option to meet that requirement is to install turbines inside the pipeline to take advantage of the “head” of water rushing down through the pipe from the reservoir. The power generated would be sufficient to operate the treatment plant, furthering reducing the cost of producing the city’s drinking water.
The Water Commission considered a number of options, but expressed a preference for replacing the existing pipe. The problem is that the existing pipe was laid by hand along a narrow path cut in the side of the gorge, with ledges above the path and a steep drop below. That topography is not conducive to access by heavy construction equipment.
“This is a very doable project,” Edson said at the March 6 board meeting. “We have a rough construction estimate.”
That estimate, generated by the pipeline construction company of R.H. White, is $2,650,000. However, the state program would “forgive” about $450,000 of the revolving loan, dropping the city’s cost to $2.2 million.
Edson said the project will still include a “green energy” generation component, but that the turbines would be placed inside the basement of the treatment plant at the end of the transmission line.
“You have a high-flow, low-head rate that would require two turbines in parallel,” Edson said. “The electric generation would be sufficient to operated the treatment plant.”
Edson said the project would take a summer construction season to complete, meaning that the department would have to draw water from is aquifers.
“The wells can provide seven to eight million gallons a day,” Edson said.
The upper section of pipe replacement would use technology that expands, bursting the existing pipe, and pulling the larger pipe through the expanded tunnel.
Heavy equipment can access the lower part of the gorge and would allow traditional trenching to remove the existing pipe and replace it with the next line.
Dan Moriarty can be reached at [email protected]
