Polypropylene Pipe Used For Maine Combined Sewer Overflow Project

The West Side Interceptor sewer replacement project in Portland, ME, utilized a 60-inch diameter, high performance polypropylene pipe to increase conveyance capacity, replacing a smaller 100-year old vitrified clay line and separating a parallel 10-foot diameter combined sewer, which now solely conveys storm water.

Completed in October 2010 after just five months of construction, the combined sewer overflow (CSO) abatement project used some 5,600 feet of 60-inch SaniTite HP pipe from Advanced Drainage Systems Inc. (ADS). The $4 million project replaced runs of 24-inch and 30-inch diameter pipe from Congress Street to Lucas Street with a single larger diameter pipeline to eliminate combined sewer overflows at Capisic Pond Dam and stop untreated wastewater from flowing into the Fore River Estuary.

Last summer, the city of Portland was awarded first place for this project in the Public Works Excellence Competition from the Maine Chamber of the American Public Works Association (APWA) in recognition for efforts performed demonstrating excellence, quality, innovation, value and community satisfaction.

The design, by engineering consulting firm Woodard & Curran Inc. (Portland, ME) specified several pipe options such as epoxy coated, reinforced concrete (RCP) and centrifugally-cast glass fiber reinforced polymer pipe. The critical requirements were that the pipe provide a watertight joint and meet the city’s standard for pipe stiffness of 46 PII.

“Aside from being rugged, one of the reasons we went with the ADS pipe was because we could set it in place simply with our backhoes and wouldn’t need cranes,” explained Ken Grondin of R. J. Grondin & Sons, Inc. (Gorham, ME). “Plus there were logistic issues. If we used concrete pipe that comes just in eight-foot lengths, we’d have nearly 200 truckloads that we’d have to coordinate to the holding site and then move again piece by piece to the trench. That’s a lot of extra handling and traffic control. So with the 20-foot lengths of the ADS pipe, instead of the eight footers, there are essentially three times fewer trucks required, and it worked out pretty well.”

Grondin and his crew buried the line at depths ranging from eight to more than 20 feet. “We basically followed the line of the old pipe, but we did have some challenges. The last half of the project was through a park with a wetlands complex and ecological features that required close attention. In that area, we were limited to a 30-foot wide travel corridor to install the line where it could be as much as 22-feet deep.”

Due to the tough Maine bedrock, blasting was also required which added more complexity to the project.

SaniTite HP pipe manufactured in diameters from 12-inches to 30-inches (300-750mm) meets ASTM F2736 and is made with dual-wall construction to provide performance ratings that exceed many of today’s industry standards for gravity flow sanitary sewers. The 60-inch diameter SaniTite HP pipe is available in 20-foot and 16.3-foot standard lengths from ADS to accommodate various trench box dimensions.

Another 200 feet of ADS SaniTite HP pipe was used in diameters ranging from 24 to 48 inches for laterals which were connected to the main trunk using Inserta Tee fittings and fabricated fittings. Inserta Tee provides a method of water-tight lateral service connection for waste water and storm water pipe systems. Inserta Tees fit ADS pipe and can be used to connect corrugated, solid wall, profile wall and concrete pipe regardless of manufacturer. ADS acquired the Inserta Tee product line in June 2010.

Determining the flow
“To determine the necessary conveyance capacity of the pipe, we put in flow monitoring equipment on the existing line to determine what flow rates we could be looking at during different storm events,” explained Dave Senus, P.E. of Woodard & Curran. “This effort told us what size pipe would be needed when considering factors associated with pipe hydraulics, such as slope and roughness coefficients.”

“We went through a several year effort of working with the city on flow monitoring and looking at different design alternatives and options.”

Monitoring was done during a continuous year-long flow recording period and supplemented with previously collected data.

The new system was designed around true rainfall data using several large scale storm events, not a predicted 25 or 100 year storm event model, but actual storms that occurred while the flow monitoring was in place. The biggest storm was Sept 6-7, 2008, during which 5.46 inches of rain fell with the maximum intensity reaching almost an inch an hour.

The city of Portland collected flow data from a number of monitoring sites within the project area in 2004 and 2005. This data was supplemental to data collected as part of project specific analyses from September 2007 to 2008.

“Our analysis of the flow monitoring data determined that the main line would require a 60-inch diameter pipe to handle the peak flow rate anticipated for the system of 70 million gallons a day along its one mile length.”

The sanitary manholes (SMH) from ADS were fabricated at the factory using the 60-inch SaniTite HP pipe with a 48-inch riser. Once in place, each was encapsulated in concrete with a field-placed steel reinforcing cage. Each of the 21 structures was individually designed for an H-20 load rating and fill heights. The alternative was to use eight-foot precast concrete structures that would have been heavy and cumbersome to move especially in some areas.

“We had low clearance under an electrical transmission lines and had to maintain the required separation that the local utility required. And that went well. The shorter pipe lengths and the fact that the pipe is easy to move made it possible. We were able to use small machines and worked a little slower,” stated Grondin.

“And for this project we used their T-base as well instead of concrete access manholes. This made it possible to maintain the alignment and be in the same trench, rounding the corners, etc.

“For us it was ideal to use T-bases because essentially you plug them in and at the end of every night you can open up the line installed that day and go home, not worry about flows or your bypass pump as opposed to a precast concrete structure,” he continued

But there was a greater challenge that awaited the R.J. Grondin crew. The last half of the pipeline would go through a park with a wetland complex and ecological features that required close attention. “In that area, we were limited to a 30-foot wide travel corridor to install the line where it was as much as 22 feet deep,” Grondin stated.

Another local company, Everett J. Prescott, Inc. (Gardiner, ME) provided logistics and system design support.

Gorrill-Palmer Consulting Engineers, Inc. (Gray, ME) was selected to perform construction monitoring services and provided continuity between the city and R. J. Grondin and Woodard & Curran.

The project started June 2010 and had to be completed in five months. Bedrock, terrain, low power lines plus an ecologically delicate wetland all presented time barriers.

The Capisic Pond area is an inland wading waterfowl habitat, as identified by the Maine Department of Inland Fisheries and Wildlife and the Department of Environmental Protection, which limited construction to starting no earlier than Aug. 1 and ending no later than Oct. 15.

With the park deadline fast approaching, R. J. Grondin brought in another crew, basically splitting the park segment in half, one crew starting upstream, the other downstream and meeting in the middle.

The Grondin crew had to be a little creative in making the connection because it was a very tight fit. They picked up both pipe sections, let them touch and then lowered both into place. They used a steel band coupler and did a concrete collar around it.

To backfill the trench, most of the material used was existing native soil. Crushed stone was laid as a bed for the pipe and about a foot of cover directly over the top the pipe.

Advanced Drainage Systems Inc., (419) 424-8275, www.ads-pipe.com
Woodard & Curran Inc., (800) 426-4262, www.woodardcurran.com
Gorrill-Palmer Consulting Engineers Inc., (207) 657-6910, gorrillpalmer.com
R. J. Grondin & Sons Inc., (207) 854-1147, grondinconstruction.com
Everett J. Prescott Inc., (207) 582-1851, ejprescott.com

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