On the Fast Track

April 2, 2018

About the author:

Carroll Hunnewell is a regional manager with Baker Pumps. He can be reached at 508/987-0034 or via email at [email protected].

When the Massachusetts Bay Transportation Authority (MBTA) decided to extend the existing commuter rail line down the south shore, from Braintree all the way to Scituate, it became evident that the master plan would involve far more than simply laying down 18 miles of new track. The $250 million project, referred to as the Greenbush project, faced a variety of challenges almost immediately.

One of many concerns was a decision regarding the functionality of a stretch of 48-in. pipe that belonged to the Massachusetts Water Resource Authority. As it turned out, the pipe was positioned at the exact point where a portion of the extended rail line was planned. This stretch of pipe was part of a combined sewer line, a system that allows general public and industrial waste to be combined with groundwater runoff when conventional sewer systems are at capacity during times of heavy rainfall.

In order to complete the rail extension as planned, the sewer line would have to be bypassed and rebuilt at a lower elevation without disturbing the local population of the area or causing environmental impact. There was a tremendous amount of water that would have to be re-routed before re-construction of the pipe could begin. Cashman/Balfour-Beatty (CBB), the company entrusted with completing the massive undertaking, contacted Baker Pumps.

Potential issues with pumping also put fiscal responsibility of the project in danger. Julie Power, a project engineer who worked on the Greenbush project for CBB, said, “It was an active construction site. Any problem would have been a big mess to clean up. And with the environmental issues at stake, we could have faced fines for any violation.”

Making tracks
The project team chose to use The Gorman-Rupp Co.’s Prime Aire pumps, which operate with a patented priming system engineered to eliminate weep-age. They also feature a dual-suction side capability, a compressor-over-pump and an abrasive handling seal.

To execute the pumping operation, Baker Pumps designed a siphon to direct the water down and then back up a 5-ft elevation. The operation implemented seven, 12-in. pumps (six primaries and one backup) that attached directly to seven, 14-in. suction lines, with water being discharged 750 ft away into a 2-18” and 1-27” siphon chamber. Baker Pumps also had to deal with a 22-ft lift in elevation from the water level to the centerline of the pump at its highest point, a considerable increase from the 10- to 15-ft lift found on average in the New England region.

The first obstacle in the pumping stage came courtesy of Mother Nature. With the pumps selected, the plan in place and the project team ready to go, the Boston area suddenly found itself in the midst of back-to-back, 100-year storms, periods of rainfall that have just a 1% chance in any given year of being equaled or exceeded. Luckily, the Gorman-Rupp pumps were equipped to handle the increased flow. Baker Pumps’ original design featured safety margin so that even when the operation exceeded expected flow by upwards of 10 million gal per day, the pumps continued to work flawlessly. Later, when the weather once again changed, the pumps continued to demonstrate the ability to effectively operate in periods of extreme dryness.

CBB was most pleased, however, with the project’s cost efficiency. Based on past experience, Baker Pumps and Gorman-Rupp anticipated that the authority would burn 3 gal per hour per pump, but in the end, the bypass used 1.5 gal per hour per pump, a 50% reduction in fuel cost. This amounted to savings of nearly $15,000 to the Greenbush Bypass Project’s bottom line.

About the Author

Carroll Hunnewell

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