Sections of Poly-Flo pipe were welded onshore prior to being floated on the lake and then installed beneath the lakebed.
FLINT, Mich. - Feb. 9, 2016 -- Due to expected water rate increases of up to 15 percent a year, the Karegnondi Water Authority (KWA) is building a new water supply pipeline from Lake Huron. It is estimated that when completed in 2016, the 74-mile long new water line will save Flint and surrounding communities millions of dollars in increased water rates each year. The first segment of the project, a mile-long, 78-inch diameter intake pipeline from the lake to onshore pump stations, was completed in September. KWA, however, had to find a way to deal with zebra mussels in the lake which adhere themselves to water intake lines, restricting flow and clogging the pipe.
In 1989, Monroe, Michigan lost its water supply for three days due to massive numbers of zebra mussels clogging the city’s water-intake pipeline. Since then, city water suppliers have had to retool their water-intake systems or apply chemical treatment. The U. S. Fish and Wildlife Service estimates the potential economic impact from zebra mussel infestation for U. S. and Canadian water users within the Great Lakes region to be $3 to $5 billion during the next 10 years.
While oxygen deprivation, temperature treatments, exposure and dry-up, passive and barrier filtration, removable substrates, electric currents and sonic vibration have had limited success in fighting the zebra mussel problem, a regular dosing of sodium hypochlorite into the water intake structure has proven to be the most effective way to control zebra mussels and prevent the mussels from clogging up the intake pipe. KWA specified an innovative pipe system that is designed to deliver the sodium hypochlorite solution to protect the water intake line.
Traditional pipe cannot effectively deal with the oxidizing and caustic nature of sodium hypochlorite. Also, the plan was to horizontally directionally drill (HDD) the last 300 feet of pipe 40 feet under the lake bed and shore to the water lift station. These needs would require a pipe with a high degree of structural strength, flexibility and advanced resin characteristics. The Poly-Flo® Advanced Polyethylene (PE) (PE100RC) piping system with four-inch diameter (DR11) carrier pipe surrounded by a six-inch (DR17) containment pipe from Asahi/America was chosen. The pipe's physical properties will allow the plant to treat the water supply line with sodium hypochlorite to prevent mussel infestation and build-up without damaging the pipe, fittings or welds. The double wall pipe design also protects against leaking of sodium hypochlorite into the surrounding waters.
Because of its unitary construction, the Poly-Flo double wall PE pipe system can be installed like a single wall system. This is especially important in installations with fluctuating temperatures, chemical use and applications like this that require directional drilling. According to the company, the Poly-Flo system is not a disk-centric system like traditional double containment systems.
To install the system, sections of the double wall PE pipe were welded onshore into lengths of 200 to 300 feet, floated on the lake surface, then submerged to the lake floor and attached to the top of the 78-inch concrete intake pipe that is buried 44 feet under the lakebed.
