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Under the Boise River: deep drill Solves city's water main crisis.

On Sunday, April 8, a water main beneath the Boise River near East 52nd Street burst when a dislodged tree floating in the river' crashed into it. Immediately, water to supply hundreds of homes in the Plantation neighborhood of Garden City, a suburb of Boise, ID, was disrupted. The city worked quickly to patch the damaged pipe, which was originally installed in the riverbed during the 1970s, but knew a more permanent solution was needed.

Although the river is cleaned out regularly when water levels are low, drifting debris has eroded the riverbed over the years, leaving the older pipe buried just a few feet under the ground. As crews raced to get water flowing back to the residents, city leaders worked on a proposal for the installation of a new water main.

According to local news sources, the proposed line would be 16 inches in diameter or greater to accommodate the city's current residents and future growth. City leaders also proposed that the replacement line would run along Remington Street and be buried deep under the river to prevent future debris snags. Finally, the proposal called for the line to connect to another water source on the southwest side of the river bank, upstream from the broken pipe, where it would tie back to the city's public works facilities. The entire project was estimated to cost approximately $700,000 and would be paid for out of the city's emergency funds, which are set aside for such events.

As city leaders worked out the details of the project, it was decided that the final project would be a 20-inch water main, with two-inch thick walls, installed 50-feet below the river's surface. To make sure that water service disruptions would be minimal, the city mandated that the project needed to be completed in one month.

To the rescue

To accomplish this feat, the city hired Shane Mace and his directional boring crew at Track Utilities to handle the 650-foot bore underneath the river with their Vermeer D80x100 Series II Navigator horizontal directional drill. Established in 2002, Track Utilities' crews have extensive experience in all types of utility installation, maintenance and repair, making them the ideal contractor for the job.

"We started in business 10 years ago with the idea that we could take care of our customers better than larger companies could," says Mace, Track Utilities president. "We work with customers such as Idaho Power, CenturyLink, Frontier Telecom as well as a number of small rural utility services.

"The Boise River water main install is probably the most challenging bore that we've been contracted to do so far," says Mace. "We recently completed one with the same drill, a couple weeks before, that was installing 1,100 feet of six-inch conduit. Being only a 650-foot install, this project is shorter, but a 20-inch water line brings its own unique set of issues."

Because the project went under the Boise River, there were some environmental concerns, as well as the depth and the size of the water line. "It's not too common to pull back something of that size at that distance, particularly with all the backreaming we needed to do and in the rocky riverbed conditions that we're working in," he says.

According to Mace, Track Utilities role was to get the new water line installed underneath the Boise River. The entry and exit pits were designated in the city's project plan, so Mace and his team knew where they had to go into the ground and where they had to come out. The city's plan also required the crew to set up close to the banks of the river to prevent traffic and pedestrian concerns.

"It was a fairly technical bore," says Mace. "To get the right arc on the line, we had to bore deep in the middle of the river, about 50-feet down.

"The ground and terrain conditions on this bore were also extremely tough," he continues. "There were lots of big rocks and pit run to bore in and through. The city's mandates on certain elements of our setup and operations really helped us build our profile and understand what we were going to be working in to begin with."


Because the project commenced during the spring plus the depth the line needed to be installed, one of the major challenges of the project was that the water levels were extremely high on the Boise River. Track's crew could not locate the bore with a locator from the top of the ground like they would normally do. "To locate, we brought in a wire line system to guide us through and under the river," says Mace.

On this project, Mace and his crews employed their D80x100 Series II drill, one of five Vermeer horizontal drills they currently have in their equipment fleet. "We chose this drill because it's the biggest one that we have, and with our operator's ability, we were pretty comfortable that it would shoot 650 feet across that river and be able to pull back the 20-inch water line," says Mace.

"Jeff Sorenson is a very capable bore operator. He's shot a lot of tough bores all over the country, including under rivers in Alaska, which gave us the confidence that it could be done," Mace pointed out.

After reviewing the city's project plan and consulting with the team, Sorensen and Mace decided to take a little longer approach with the bore. "Even though it was a rush project," says Mace, "it's not something that we wanted to rush into--skipping a bunch of steps just to get it done fast. For example, we didn't know what would happen if we pulled back a 10-inch backreamer and then went straight to a 30-inch reamer. We agreed that it would be better to take it in progressive steps and allow a little more time to get the project done right the first time."


Mace explains that the city dictated that the project's completion deadline was four weeks. To meet their deadline, Mace says the crew had a week of setup and a week to bore across the river with the wire line. Sorensen and the drilling crew used a single roller cone pilot bit and bentonite quick gel to make the initial bore. "We had some pretty good-sized boulders we had to get through," adds Mace. "And it's extremely important on a bore like this one to keep the hole open and get the cuttings back out of the hole, so we didn't have any hang-up when we pulled the final pipe through."

Once they shot through, the crew had to backream seven to eight times, starting with a 10-inch backreamer, then going to a 14-inch and progressively getting larger, finally ending with a 30-inch backreamer to make sure they could get the product across and not lose their hole. Mace says that the backreaming process took about two weeks. "We actually trailed steel through the hole behind the backreamer to make sure that the opening stayed steady and made a nice hole through the riverbed for the new 20-inch water line."

As Track Utilities prepared for this project, Mace points out some specific elements of the company's processes that were critical to their success. "The biggest thing we do to prepare for our projects is to know what ground and site conditions we are going into," says Mace. "It is important to know the soil conditions, how the locating will be done and what tools were needed to complete the project. Being prepared up front made sure we had what we needed to complete the project, on time, on budget and to the client' satisfaction."

After four weeks on the job, the new water line was installed, allowing Garden City to connect customers to the city's water supply.


Track Utilities

(208) 362-1780,

Vermeer Corp.

(888) 837-6337,
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Publication:Underground Construction
Date:Dec 1, 2012
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