Polypropylene Pipe Used For Maine Combined Sewer Overflow Project

January 2012, Vol. 67 No. 1

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."