Serving nearly 1.8 million residents and maintaining more than 5,500 miles of fresh water pipeline and nearly 5,400 miles of sewer pipeline in the Maryland suburbs of Washington, D.C., Washington Suburban Sanitary Sewer Commission (WSSC) is the eighth largest water and wastewater utility in the nation.
With the congested population and affluent neighborhoods in its service area, the WSSC is constantly looking for new ways to minimize disturbance to traffic and private residences during water and sewer main maintenance. The traditional open-trench method of replacing water and sewer pipe in urban and suburban areas often tears up landscaping, uproots trees, blocks driveway access and sometimes forces the closure of multiple traffic lanes on busy roads. It was factors like these that drew the WSSC to the less-invasive trenchless pipe replacement method of pipe bursting a few yearsago.
“We’re currently under a mandate to take care of a lot of problems in our water and sewer systems before 2015, and part of that involves pipe replacement,” says Mike Trail, construction manager forWSSC.
“We have an abundance of 70-year-old clay pipe that has simply outlived its useful life. One of the biggest complaints we were getting about our water and sewer projects was the footprint that they were leaving on the community. Since we started using pipe bursting on our projects, it’s helped minimize thatfootprint.”
With pipe bursting, contractors can burst water and sewer mains under roads, sidewalks, backyards, creeks, groves of trees and other congested or sensitive areas without disturbing the surface, except for re-tapping services and excavating pits at the start and finish points. Pipe bursting is more cost-effective than an open-trench installation under asphalt or landscaped areas at any depth. And, it’s inherently more affordable than open-trench any time the depth requires trench safety devices, regardless of surface materials or conditions. Pipe bursting also allows contractors to reduce their carbon footprint, since it doesn’t require nearly as much excavation or disruption of landscaping as open-trench jobs and results in fewer loads of dirt and rock taken to dump sites.
The pipe bursting installation method involves utilizing hydraulically powered machinery to split the existing pipe with a specially designed cutter head while simultaneously pulling new pipe back through the annular space previously occupied by the original pipe. In some cases, including many of the projects being undertaken by WSSC, an expander head is also added to the pull string directly behind the cutter and immediately ahead of the new pipe string. This allows the annular space to be increased during pull back forcing the original pipe fragments out into surrounding soil to make room for the larger diameter new pipe being pulled in behind it.
WSSC started out using static pipe bursting to replace the old clay pipe with high-density polyethylene (HDPE) pipe, but this led to new “footprint” problems. Before each pipe pull, separate lengths of HDPE had to be fusion-welded together into one large 500-foot string of pipe, which got in the way and frustrated homeowners and businesses in the area. Last year, WSSC’s trenchless contractor, Midas Utilities Inc., of College Park, Md., recommended using CertaFlo Greenline, a restrained-joint polyvinyl chloride (PVC) sewer pipe from North American Specialty Products. CertaFlo Greenline pipe is available in 10-foot lengths, as well as standard 20-foot lengths, to further decrease disturbance to surroundings. In addition to the shorter pipe lengths occupying less space, the restrained-joint PVC pipe can be quickly and easily assembled as pipe pullback continues. After observing Midas Utilities do a pipe bursting project with CertaFlo Greenline for another client, the WSSC was convinced that this combo would be a good fit for its own projects.
“We had some areas where we simply couldn’t string out a few hundred feet of HDPE pipe,” Trail says. “For example, we had two project sites in downtown Silver Spring, Md., where that was not going to be possible, since the pipe would cross through a business district and a state highway. In order to string out the pipe, we’d have to go across the highway and you just can’t do that. In areas like that, it’s helpful for the contractor to have the option of shorter pipe lengths and be able to assemble them stick by stick. And, without the need for pipe fusion, the job moves along more quickly.”
So far, Midas Utilities has installed about 1,500 feet of restrained-joint PVC sewer pipe in three projects for WSSC, using a TT Technologies Grundoburst 800G Static Bursting System—an 80 metric-ton machine, with 176,000 pounds of pullback.
The projects have all gone smoothly, and the WSSC has plans for more projects in the near future using pipe bursting with restrained-joint PVC sewer pipe. Most importantly, the feedback from homeowners is becoming much more positive.
“We had one recent job, where we were going under people’s yards, mature trees and a slate driveway and retaining wall that we would have had to tear out if we hadn’t used pipe bursting,” says David Ventresca, owner of Midas Utilities. “The homeowners were all thrilled when we got the project done with a minimal amount of digging. It worked out great for everybody.”