Pam Radtke Russell/ENR Gas-line replacement project aims to limit disruptions.

The system is still sound, but the New Orleans-based utility, a subsidiary of Entergy Corp., also headquartered in New Orleans, has only about 10 years to replace 844 miles of pipe. Total project cost is expected to be $465 million.

While the type of work isn’t unusual, the pace and scope is, says Fred Harrah, vice president of A&L Underground, Memphis, Tenn., one of two firms doing the work. “They are doing everything at once,” he says. At Entergy’s normal pre-Katrina pace of replacing three to four miles of pipe per year, the work would have taken more than 100 years.

To minimize disruptions to residents and improve the overall system, Entergy is abandoning its old low-pressure steel and cast-iron pipes under the streets. Contractors are using directional boring to run a replacement network of high-pressure, polyethylene pipes under sidewalks instead.

“Here in New Orleans it’s absolutely the only way to go,” says Harrah, of directional drilling. “People here have been damaged enough. We need to try to save as much of their yards and sidewalks as possible.”

Relocating to the sidewalks should also minimize disruptions when construction crews come later to fix flood-damaged roads and sewer and water lines, says Perry Dufrene, Entergy’s manager of the gas rebuild. A&L and Houston-based Quanta Services have the first 3-year, $74-million, fixed-price contract to rebuild 130 miles of gas service. A&L is doing about 70% of the work, and Quanta the remainder, Dufrene says. Work started last summer and contractors replaced about 33 miles of pipe. The utility chose to limit the first contract to three years because it is reevaluating the pipe condition and the city’s repopulation patterns.

Dufrene says Entergy considered other options, including running the polyethylene pipes through the existing metal pipes, but directional boring was seen as causing fewer disruptions and being most cost-effective. Because of the old system’s twists and turns, it isn’t likely it will be used as a conduit for anything else, such as for fiber-optic or other cables, Dufrene adds.

The new high-pressure system should be less vulnerable to future flooding. In New Orleans, it only took 7 in. of water over a line break in the low-pressure, .25-psi system to enter the pipes. It would take 215 ft of water over a break in the high-pressure, 99-psi system for the water to infiltrate, according to Entergy. “We’ll have bigger problems if that happens,” Dufrene says.