It’s been a decade of growth for the Green Bay (Wis.) Water Utility. The economy may have curtailed that some, but even now, the utility maintains an aggressive program of rehabilitating water mains.
Whether installing new lines or repairing old ones, the work usually gets done the old-fashioned way — by digging a trench. In recent years, though, the utility has used trenchless techniques at times. Sometimes it’s to avoid disturbing environmentally sensitive areas and the regulatory red tape involved with open digging in such places. Other times it’s because nature herself simply gets in the way.
As a result, Green Bay has gained experience with horizontal directional drilling, and with it, the use of various pipeline systems. The technique costs about two to three times that of conventional trenching, says Brian Powell, water utility distribution engineer. But in view of the much more extensive permitting required for open-trench projects in delicate situations, HDD is a reasonable trade-off.
In 2008, the city completed the first project in which it used fusible PVC pipe in an HDD project. The pull crossed a wetland in which open-trench installation would have been impossible.
Decades of growth
Green Bay draws its water from Lake Michigan, taking in up to 42 mgd. Over the last 50 years, the city has tripled in area, to 46.1 square miles. The service area extends beyond the city limits to the neighboring Town of Scott and Village of Ashwaubenon.
Annual water pumpage through the utility’s 456 miles of distribution mains hit nearly 7.2 billion gallons in 2007, and the two largest categories of customers, residential and commercial, have been slowly but steadily rising since 1998.
For much of that time, the system grew by up to 10 miles per year. “Five years ago we were putting in close to 40,000 to 50,000 feet a year of brand new water main,” says Powell. The economic slowdown has reduced new construction to 5,000 feet or less per year, but rehabilitation continues on 10,000 to 15,000 feet of mains per year.
As a city department, the water utility can coordinate water main repair and replacement closely with the city’s street repair program. Green Bay has a street work agenda planned several years in advance, and the water utility follows suit. “They give us a list of streets coming up for repair,” Powell says. “We look at the age and conditions of our water mains on those streets, then base our decision on that.”
All water main complaint calls and repairs are logged into a GIS-linked city database. The list of streets due for repair is checked against that database. “If a street’s being redone and we’ve had water line maintenance problems in the past, then we’ll replace the line in the year the street’s going to be redone,” says Powell. “But if everything’s fine, we’ll leave well enough alone.”
Cast iron to PVC
Green Bay’s original water lines, some dating back to the late-1800s, are traditional cast iron. Corrosion from age and especially from exposure to the area’s highly acidic soils have led to rot, causing leaks, and the area’s cold winter climate produces its share of water main breaks from deep frost.
So about five years ago the city began using PVC pipe almost exclusively when replacing water mains throughout the system. “PVC won’t corrode,” Powell says. “It’s also cheaper to buy and cheaper to install.”
For most open-trench replacement projects, the city uses conventional PVC sections connected by slip joints. It buys the product from a variety of manufacturers based on material price quotes.
In summer of 2008, however, the city turned for the first time to fusible PVC provided by Under-ground Solutions of Poway, Calif., for a project that required HDD.
HDD, widely used in the water industry since the early 1990s, was an established technique for the Green Bay utility when Powell joined six years ago. “It comes in handy where you have environmentally sensitive areas, whether you’re crossing a wetland or a navigable waterway, whether it’s a stream, a creek or a river,” he says. “These are areas where you can’t really open cut without causing environmental damage.”
In some situations, it’s not just a matter of damage. About three years ago, the utility needed to cross under the Fox River with a 2,400-foot-long, 36-inch steel pipe. Trenching in that case was out of the question. That HDD project took nearly two weeks. The pipe sections were welded on site into a single pipe while the drillers bored and reamed a hole to the proper dia-meter to pull the pipe back through.
When the time came to pull the pipe, “They started pulling at 7 in the morning and they got done close to midnight,” Powell recalls. Such jobs are rare. Smaller installations, replacements and repairs in sensitive areas come up every few years.
On the scene
The 2008 project was an example. The task was to connect two dead-end water mains on opposite sides of a small, marshy ravine off of Remington Road on the city’s east side. “It’s a delineated wetland area with a navigable waterway running through it,” Powell says.
The city needed fusible pipe to create a single pipe that could be pulled through the opening created by HDD. “You can’t really pull regular PVC pipe because it doesn’t lock,” Powell says.
Green Bay has used locking PVC piping satisfactorily in previous HDD situations, but fusible PVC was something new. “We heard about it and kind of liked the idea and said, ‘Let’s give it a shot,’” Powell says.
Work on the Remington Road project began on a Wednesday with the arrival of 360 feet of 8-inch PVC pipe. Utility crews dug an entry pit on the east end of the run while employees of Under-ground Solutions prepared the pipe. Matthew Berenson of Under-ground Solutions used a diesel-powered TracStar II 500 fusing machine from McElroy Manufac-turing Inc. to connect seven lengths of pipe.
With each length, Berenson carefully trimmed the ends so that they would join without leaving air pockets. Using a heating coil powered by an electric generator, he heated a metal disk to several hundred degrees, slid it into place on the machine and pushed the two pieces of pipe to be fused against it, under pressure, until they melted.
When the heat caused the rims of each pipe end to curl outward into a bead, he whisked the disk out, pressed the softened ends together, and held them in place under pressure until they cooled and formed a solid weld. “When it’s cool, it’s as strong as the rest of the pipe,” says David Silvernail, director of field operations for Underground Solutions.
Drilling the hole
As the Underground Solutions crew finished fusing the pipe on a hot, humid Thursday, on the other side of the marsh a crew from Ramco Services Inc. was preparing to drill the hole. That morning, Powell and Jim Daubner, the utility’s construction manager, had walked across the marshy ravine in high boots, marking the desired path of the new main at regular intervals with bright pink spray paint.
Ramco’s Andy Vickman maneuvered a DitchWitch 4020 directional drilling unit into place to begin the dig. The drill head bit into the ground at a low angle, spewing a slurry of water and bentonite.
The ratio of water to the pulverized bentonite had been calibrated precisely to provide the necessary support and lubrication for the drilling. No-Sag, a gel product, was added to the mix to help cake the walls of the hole and prevent it from collapsing, explains Ramco Services president Robert Foeller. As Vickman operated the drilling rig, Ramco employees Micah Frost and Glen VandeHey tracked its progress across the ravine, using a locator to follow a sonde in the drill head.
The drilling took about four hours. Ramco and Green Bay crew members then attached a conical pulling head to the plastic pipe. (Copper wire duct-taped to the entire length of pipe would enable crews to detect the pipe in the future.) On the west side of the marsh, Vickman used the drilling rig to pull the reamer head and the pipe back through the hole to the other side.
Often, HDD requires more passes through the hole to ream it out to the desired diameter — in this case, 12 inches, 1.5 times the pipe diameter. That wasn’t required on this project because the sandy clay soil made the hole stable. As the pipe was pulled back, the machine reamed the hole in a single operation.
Once installed, the fusible PVC could be matched up precisely with the existing PVC line at either end using conventional slip joints.
Other options
So far, says Powell, Green Bay’s only trenchless technique for water main installation is HDD. The agency remains open to other methods, such as pipe bursting or various pipe-lining technologies. “We’re always looking into it,” says Powell. “At some point in the future, I would foresee us doing some of those.”
As HDD jobs go, the Remington Road extension was relatively easy, recalls Ramco’s Foeller. “The ground was really muddy, but it was a typical job, with no problems,” he says.
Ramco does about 200 drilling jobs per year, covering nearly all of Wisconsin. The sandy clay soil of Green Bay made this one of the easier jobs. “You can get into some really dense sand,” Foeller says. “With smaller rigs, sometimes dense sands pose a problem. And if you get rocky conditions or boulders, those present problems.”
Silvernail of Underground Solutions noted that in many projects, the drill is done the day before the pull. The Green Bay project stands out in his mind for “how smoothly it went,” he says. “It just pulled a lot easier than everyone expected it to.”
