Aug 16, 2002

Maintaining Water Service During Emergencies, Rebuilds


Baltimore County recently reconditioned nearly 100,000 feet of cast iron water mains at a cost of $2.3 million, saving taxpayers 75 percent of the cost of total pipe replacement. In addition, there were virtually no service disruptions during the 12 months it required to complete the project.
Like water lines everywhere, the underground piping in Rogers Forge, Md., had deteriorated over time. Corrosion had pitted the inside walls of the pipe and mineral deposits formed over the pitting, resulting in a phenomenon known as tuberculation. Varying with water acidity, tuberculation causes a host of problems, including discoloration of the water, capacity and pressure losses, undesirable taste, water leaks, and burst mains. Moreover, corrosion deposits in pipelines harbor bacteria that consume disinfectants before they reach the ends of the system, posing a public health hazard.
To eliminate these problems without extensive and costly replacement of pipe, the county called on Mainlining Service, Inc., Elma, N.Y., which specializes in trenchless rehabilitation.
"Water authorities generally choose to work on areas that are experiencing a high rate of consumer complaints," said Paul Hahn, head of engineering for Mainlining Service. "Testing for low Hazen-Williams `C' values helps determine the scope of the problem."
After the problem areas in the system were isolated, Mainlining Service set about cleaning and applying a cement mortar lining to the inside walls of the piping using a procedure known as the Perkins Process. At the outset, the company surveyed the project to determine where it would gain access to the system which was reconditioned in 500-ft. sections to minimize disruption to users.
After surveying, Mainlining Service installed a temporary bypass system of 2" and 4" piping to provide a continuous supply of water for residents and fire protection. The company used a PVC piping system manufactured by Aquamine®, LLC, a unit of Victaulic® Company of America based in Bristol, Tenn., for this bypass.
"The bypass system must be lightweight, quickly installed and removed, and approved for potable water use," explained Mainlining Service's Hahn.
"Because it is installed along the curbs, it must be robust enough to withstand the pounding of crossing traffic," he added. "And since it is not buried, it must be able to contain the internal thrusts due to water pressure.
"A key part of its usefulness is its adaptability to Victaulic fittings and valves needed to connect to hoses, fire hydrants, and to control the system," added Hahn.
The Aquamine system of high-impact resistant, reusable PVC pipe, fittings and accessories combines corrosion resistance, strength, flexibility, and fast, easy assembly. It incorporates rubber O-rings for positive sealing, and a nylon spline provides a self-restraining joint by engaging into grooves in both the coupling and the pipe. SDR-sized pipe in 2" through 12" sizes provides consistent pressure class and rating through- out the system. Pressure ratings range from 160 psi to 350 psi depending upon the size and type of coupling used.
After Mainlining Service completed the bypass work and excavation of access pits, work crews proceeded with cleaning and lining the pipe. The pipe cleaning process involves steel scrapers to loosen deposits from the pipe walls. Squeegees follow the scrapers to remove any remaining debris and standing water.
For lining the 6", 8", 10" and 12" cast iron pipe, cement mortar was batched on the surface and pumped to a remote-controlled, high-speed centrifugal lining machine. The machine projects the mortar uniformly onto the interior wall of the clean, dry pipe in compliance with AWWA specifications. A cone-shaped trowel is towed behind the lining machine to produce a smooth finish, restoring the pipe to as-new condition and preventing future corrosion.
With its resilient physical properties, the lining maintains a zone of alkalinity at the mortar-metal interface that serves as a chemical barrier to corrosion. Forming a continuous self-supporting ring within the pipeline, the lining bridges holes, leaking joints, and abandoned services to reduce water loss.
For further information, contact Aquamine, LLC,, 247-A Vance Tank Road, Bristol, TN 37620. Phone: 423-652-1576; Fax: 423-652-7338.