The Town of Greenwich, Conn., part of the tristate area immediately surrounding New York City is an affluent New England town and is home to approximately 60,000 people. The Sewer Division of the Greenwich Department of Public Works is responsible for the construction, maintenance and repair of all sewer and sewerage systems, including the wastewater treatment plant and the 28 pumping stations within the network. Like many towns across the United States, Greenwich has a proactive approach when it comes to its aging infrastructure, with ongoing initiatives to address repairs or upgrades.
“Some components of our sanitary sewer and wastewater system are well beyond their expected useful life,” says Richard Feminella, Wastewater Division manager for the Town of Greenwich. “So each year we budget for ongoing repair, replacement or upgrade projects that need to be addressed.”
As part of its proactive program, Greenwich needed to complete critical sewer line upgrades at multiple sewer manholes along Bruce Park Avenue, a busy roadway in downtown Greenwich that runs parallel to Interstate 95. Given the proximity to the center of town and the volume of traffic on the congested roads, this was a high-visibility and high-profile project. The upgrades included the installation of new cement coatings to deteriorating structures, which required hydro-
blasting before installation. And there was 600 ft of 39-in. reinforced concrete sewer line that was in poor condition that needed to be re-lined, via a cured-in-place pipe (CIPP) liner solution. As is typical with this type of sewer line rehab, the town needed a temporary sewer bypass in place before any of the work
Teamwork and Know-How
The town’s consulting engineer, CDM Smith, worked together with the local Xylem branch to develop a temporary sewer bypass plan, which would facilitate the project and enable the critical infrastructure improvements. The bypass needed to contain combined sewer flow of 16.72 gallons per day (MGD) from three different sewer lines: a 24-in. gravity line and 8- and 24-in. force main sewer lines. The bypass plan called for all three lines to be diverted into a 45,000-gal temporary concrete wet well. A.Vitti Excavators was brought in to do the excavation work and the actual installation of the bypass system.
The bypass design required four Godwin Dri-Prime CD300M Critically Silenced Diesel-Driven pumps with 16-in. suction tubes from the wet well, with flow pushed through four 12-in. HDPE lines to a manifold. From the manifold, there were two 18-in. HDPE discharge lines that ran 2,600 ft downstream of the work area. Xylem had two fusion technicians onsite during the installation to handle all aspects of pipe cutting and assembly. In order to prevent the flow from backing up into the wet well, and for efficient isolation, the system had gate valves off each of the four pumps and check valves on the 12- and 18-in. lines.
The Heart of the Bypass
The four Godwin CD300M pumps were set up sequentially, with the first pump able to handle the bulk of the daily flow; pumps two and three would kick on for high-flow activity; and pump four was in place as a mechanical back-up, should any of the other three pumps fail. The pumps were operated by a Godwin PrimeGuard controller, turning the pumps on and off based on readings from the level transducers, set at pre-determined levels in the wet well. There was an auto-dialer put in place, as an added safety precaution that would notify the Greenwich Sewer Division via cell phone if the back-up pump was activated. Two 500-gal fuel cubes were brought on site to provide fuel for the diesel pumps, which made for easier refueling.
The bypass took three weeks to install and it ran for a total of four weeks while the CIPP installation took place. Given the short timeframe of the project, it made sense for the Town of Greenwich to rent the necessary bypass pumps and accessories from Xylem’s local branch. This enabled the town to utilize Xylem’s expertise and to get the right pumps for the job at a fraction of the cost of buying the equipment.
As part of the bypass plan and due to the high-profile nature of the project, Xylem provided the Town of Greenwich with 24/7 pump watch for the duration of the bypass, with two factory-trained service mechanics on site each shift to make any necessary field repairs, ensure pump efficiency and oversee the bypass operation.
Continues Feminella, “The whole project was pretty complex, given the different structures and lines we had to upgrade, and the three lines we had to divert into the wet well. And all of this happening in close proximity to the highway and to the center of town, there were a lot of moving parts. But the collaboration between our staff and the team of contractors, working through all the details and pulling it together, they did a terrific job. We’ve used all three contractors in the past — CDM Smith, A. Vitti and Xylem — so we knew they could make it happen. When a high-profile project like this gets done on time and without incident, then everyone’s happy.”
Molly Russell is a regional applications engineer for Xylem.