Launch Slideshow

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End of the Line

End of the Line

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    It's not illegal to install new asbestos-cement pipe — just impractical. Photos: TT Technologies

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    The bladed cutter head of a static pipe-bursting machine enters the host pipe at McGuire Air Force Base in New Jersey. More than 8,250 linear feet of 3- through 12-inch asbestos-cement water main was replaced with HDPE. The project was specified as trenchless pipe bursting so the pipe could be replaced without removing it from the ground. The Water Research Foundation is seeking agencies for pilot studies of less than 260 linear feet to help develop a “consolidating mud” that can serve as a lubricant and that conglomerates the soil, mud, and broken fragments into a single material; this mud could make fragments left behind more acceptable because they'd be less likely to be disturbed during subsequent excavation. Contact Jian Zhang at 800-666-0206.

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    Hot spots

Disposal is limited to 260 linear feet, or 35 cubic feet, of broken pipe. These days pipe removed during short spot repairs to correct breaks is commonly — and legally — crushed and mixed with backfill material. Pipe that's crushed and left in place and is more than 260 linear feet long, or has a total volume of 35 cubic feet, is considered a regulated asbestos-containing material — essentially making it hazardous waste.

Cutting, grinding, or crushing the pipe must be performed while water is sprayed directly on the work area to control dust. Broken pieces must be wrapped in water-tight bags and handled and disposed of as hazardous waste.

Unbroken segments aren't classified as friable material and may be disposed of at Class II facilities. Workers must receive special training, but special licenses aren't required.

Regulations control cutting into the pipe to make spot repairs or to install new connections, as well as to remove, dispose of, and rehabilitate pipes using bursting and reaming trenchless construction technologies.

COST CONSIDERATIONS

The Water Research Foundation has commissioned a study of 17 public agencies throughout North America to determine the long-term performance of asbestos-cement pipe and when it should be replaced. The study is expected to be completed by March 2011.

Meanwhile, if your system contains asbestos-cement pipe, start thinking about how to fund replacement.

Unfortunately, two of the best alternatives — and the only ones that provide increased capacity — are severely restricted by NESHAP. In most cases the EPA has ruled that bursting and reaming render the pipe friable, so using those methods to replace more than 260 linear feet of pipe creates an active hazardous-waste site.

In many areas, the agency has delegated enforcement of asbestos programs to local air quality control boards that have more stringent policies. San Francisco's Bay Area Air Quality Management District, for example, limits replacement length to 100 linear feet.

With pipe bursting, broken pipe fragments are pushed into the surrounding soils, and a new, often larger, pipe is pulled into the opening. Bentonite is usually added to reduce friction on the pipe and help hold the tunnel open. Excavations are typically required at pulling and receiving pits and for reconnecting each service.

Reaming uses specially adapted horizontal directional drilling equipment. Although similar to pipe bursting, the host pipe is ground into small particles, many of which are removed with the surrounding soil to create space for the new pipe.

Sliplining, cured-in-place lining, fold-and-form lining, and similar techniques can be used, but beware: Lining is appropriate only when the hydraulic capacity of the existing pipeline can be reduced to accommodate the resulting smaller cross-sectional diameter. The smooth pipe interior presents challenges for methods — such as fold-and-form lining and sliplining without grouting the annular space — that don't involve mechanical bonding to the host pipe.

Every project is different. But generally, lining is more cost-effective than bursting and reaming; and both rehabilitation methods are less expensive than open-cut construction, assuming the replacement of an existing utility pipe in urban environments requiring traffic control and bypassing, at depths of 5 feet or more, and with a moderate number of service reconnections.

In addition, unlike bursting and reaming, lining doesn't render the material friable, leaving both public works directors and the public at ease.

— Kent Von Aspern is the business class leader for pipelines and pump stations in Northern California for HDR Inc.

Source: Compiled by Kent Von Aspern