Crews replaced cracked and aging sewer lines along Narrow Gauge Avenue and beneath the Durango & Silverton Narrow Gauge Railroad depot this spring without digging a trench.
Instead, the city’s contractor broke apart old pipe of clay and iron with a bullet-shaped pneumatic hammer that pulls the new high-density polyethylene pipe behind it, Utilities Director Steve Salka said.
The hammer is driven by a compressor and dragged by a winch in the path of the old pipe. Once broken up, the old pipes stay in the ground around the new pipe.
“It’s an 8-foot-long missile,” he said.
The pipe-bursting technique left infrastructure such as railroad lines undisturbed, saved the city money and allowed the city to maintain sewer service to customers. The technology, while not new, is likely to be used far more often around town, Salka said.
The city expects to spend $600,000 on the ongoing project to replace 2,100 feet of pipe, including a section along Narrow Gauge, from Eighth Street to College Drive and from College Drive underneath the parking lot of the General Palmer Hotel to The Palace Restaurant. The city also replaced pipe in front of the railroad depot to the Gaslight Twin Cinema and underneath the train yard to U.S. Highway 160.
AUI, the contractor from Albuquerque, is scheduled to wrap up pipe-bursting work on Monday, ending the raucous thumping heard downtown in recent weeks, Salka said. In the final stage of the project, crews will clean and refurbish manholes and manhole covers.
The project was not expected to extend under the train yard, but city cameras revealed the pipes, believed to be 80 years old, were deteriorating.
Near the train yard, city staff also discovered small sinkholes caused by pipes deteriorated on the bottom, Salka said. The new inch-thick pipes are expected to last 100 years.
“It will outlive the people that live in Durango,” he said.
Before the city’s sewer rate increases that started in 2015 and were phased in over three years, the city didn’t have the money for pipe replacement, Salka said.
Using pipe-bursting reduced the price of the project by an estimated 25 percent because the city didn’t have to dig trenches or replace any landscaping or pavement above the pipes, he said.
During pipe-bursting, most of the gray water is pumped around the sections of pipe that are being replaced.
Pipe-bursting allows a small amount of gray water to remain in the line, and crews expect a small amount of seepage while breaking up the old pipe and dragging in new pipe, but it’s not a problem because it’s not near the river or a storm drain, Salka said.
Pipe-bursting technology is about 20 years old and the city has used it before, but Salka expects the city to use it much more.
The city has hired AUI to replace the multiple sections of corrugated pipe underneath the dam at Roger’s Reservoir on College Mesa during the summer, Salka said.
Concrete was used to grout together sections of pipe, and because it’s deteriorated, the clay that forms the dam has been leaching through the pipes, he said. The small erosion problem was discovered in 2015.
“The only reason we put it off is we couldn’t get anyone that was qualified to come and do it,” he said.
He also expects to use pipe-bursting to replace sewer lines along busy streets in the next few years.
“When we get ready to do Main Street and Second Avenue, we think this would be an ideal way,” he said.