HDD Proves Tricky in Colorado National Park
June 2, 2011A massive horizontal directional drilling project was just completed in a historic national park in Colorado, involving more than 35,000 ft of boring to replace aging and deteriorating water lines with 6-in. stainless steel pipe.
The extensive design-build project involved four expert HDD contractors, who have experience in large HDD projects: Triad Western Contractors Inc., Cortez, Colo., Polaris Drilling Inc., Loma, Colo., Petty Construction Co., Grand Junction, Colo., and Laney Directional Drilling, Humble, Texas. The goal was to replace an aging and deteriorating aboveground water line in a highly sensitive environment. Preplanning and coordination would be the keys to making this pipe replacement happen.
Mesa Verde National Park was created in 1906 to protect some of the best preserved cliff dwellings in the world. Located in Montezuma County in southwestern Colorado, the park occupies 81.4 sq miles and features numerous ruins of homes and villages built by the Ancestral Puebloan people, sometimes called the Anasazi, which inhabited Mesa Verde anywhere between 550 and 1300 AD.
The ancient Anasazi ruins draw hundreds of thousands of visitors to the park each year and give a glimpse of what Native American life would have been like hundreds of years ago. The mesa top within the park rises 1,200 lf above the floor of the adjacent San Juan Basin to an elevation of a little more than 8,000 lf. At one time, there were more Anasazi Indians living in Montezuma County than there are people living in the same county today. As such, the park is covered with old rock ruin walls, huts, kivas and artifacts. Approximately
600 of the 4,700 archeological sites found in Mesa Verde National Park are cliff dwellings.
“Thus the park has to be extremely careful with the manner it chose to replace the old water lines supplying the park and within the park,” explained Triad Western Contractors project manager Jason Umberger. “[Mesa Verde] is definitely a very cool place. The cliff dwellings and the ruins are the most spectacular part of the park.”
All of this made for a challenging project in its pre-planning and execution for the contractors. The project was divided into two sections: The Escarpment and the Chapin Mesa Alignments.
The Escarpment waterline supplies water from the Mesa Verde Water Treatment Plant to the Navajo Hill Water Tank, which is the primary water supply tank for the park. The Chapin Mesa water line supplies water from the Navajo Hill Water Tank to the Chapin Mesa Tanks, which provides potable water for drinking, as well as for the fire suppression system down at the Mesa Verde museum and associated buildings.
The Escarpment Alignment covered 10,000 lf and was subcontracted by Triad to Laney Directional Drilling, which had larger and more powerful drills in its fleet to handle this section. This section was also riddled with varying slopes, jagged cliffs, archeological sites and rough terrain. Laney used its custom-built LDD 750 drill, with 753,000 lbs of pull force; pilot bore and backing reaming took place in September and October 2010. Pullback was completed in two segments, with the lower escarpment covering 5,150 lf and the upper escarpment over 4,850 lf.
The Chapin Mesa Alignment was drilled by the prime contractor, Triad Western, along with two of its subcontractors and covered some 25,000 lf. Triad used its Vermeer D100x120 drill (100,000 lbs of pull force) with R300 Reclaimer. Triad Western did the pilot bore and back reaming between July 2010 and February 2011. This section of the project was pulled back in 21 1,200-ft segments and faced its own set of challenges.
“The Chapin Mesa section had a larger footage, smaller drills and more confined space,” Umberger said. “The rock also ended up being harder than was expected so production was lower and we got into the winter months [where temps reached -20 F].”
To expedite the construction process, project owners decided to use the design-build method of design. The design-build engineering firm for the project was Briliam Engineering. “The luxury of using design-build is that you get the baseline project and then you can start working the different phases and start construction work ahead of having a completed set of drawings and specs. This project was by far the largest design-build project we have worked on,” said Umberger.
The first three months of the project (March, April and May 2010) were spent solely on the design phase, without any physical construction taking place. Actual physical construction onsite began that June. The HDD work didn’t begin until the latter part of July, as sufficient pipe had to be welded out in front of the HDD operation.
This project is unique as well due to it being funded through the federal government’s American Recovery and Reinvestment Act (ARRA) program, which brings with it a whole-lot of rules and regulations; for example all project materials had to be American-made. For instance, finding the proper Schedule 80, 6-in. stainless steel pipe for the project was not an easy purchase. In the end, the pipe supplier was McJunkin Red Man.
“There are only two American manufacturers of Schedule 80 stainless steel pipe,” Umberger said. “Adding to the heart-burn, the cost for nickel used in producing the stainless steel strip is a material whose cost is controlled by the worldwide market… In the end, we ended up having to buy some of the stainless steel pipe when the prices were outrageously expensive in order to get the pipe on time and not hold up production.”
Another challenging aspect was the sandstone that was encountered, mainly because the psi turned out to be much harder than originally planned for. “Sandstone in southwestern Colorado can drill like butter or can be typical of other hard-rock formations,” Umberger said. “As it turns out, the rock within Mesa Verde National Park represented the latter.”
The sandstone on the Chapin Mesa section was 3,000 to 5,000 psi and was 8,000 to 12,000 psi for the Escarpment Alignment. Drilling in hard rock is always challenging but dealing with the archeological significance of the park and the many twists and turns, made this even more difficult. Mud motors were used by all drills on the project due to the significant quantity and hardness of the rock. “Using mud motors slowed down the entire HDD operation,” Umberger said. “A recycler has to be used to reclaim and reuse the drilling fluid and pumps and hoses have to be used for pumping drilling fluid to the desired locations, there’s additional time required for setup and takedown operations.”
The cliff dwellings and ruins posed a challenge because they limited the space available for Triad Western to setup and drill, thus slowing production. “For Chapin Mesa, we were limited to a 14-ft by 80-ft work area from which to directionally drill our 1,200-lf runs. The park did allow us to use one-lane of the two-lane paved roadway located adjacent to our work pads,” Umberger said, noting occasionally that crews were forced to the second lane, limiting traffic. “Most of this work was performed in the height of tourist season.”
In that small 14-ft by 80-ft work area, Triad Western had to fit the following: HDD rig, mud pump/recycler, boom truck/accessories, water truck/accessories, vacuum truck/accessories, generator, drill steel racks, mud pit and one pallet of drilling fluid stacked near the reclaimer.
“With such a small entry pit and recycling area, the recycler wasn’t able to be as efficient,” Umberger said. “So we had to use more drilling fluid, actually doubling the amount of drilling fluid that we would need under normal conditions. Equipment had to be constantly moved when needed due to accessibility issues.”
The use of HDD for this project wasn’t a slam dunk when decisions were being made as to how to upgrade the water lines. Park officials were extremely concerned about disturbing the natural resources of the park and they weren’t initially convinced the new water line could be built.
“Archeological and natural resource preservation was a challenge on this project,” Umberger said. “Each work area had to be cleared by both the park service archeological and natural resource departments. This required numerous onsite planning and layout meetings… Thus our HDD design changed numerous times before the team was able to finally agree on the location of the work areas.”
The park supplied a full-time construction manager to monitor the day-to-day project operations. “The park’s archeological staff was a pleasure to work with,” Umberger said. “They have a job to do and are limited by the parameters of the environmental assessment set for this project. Natural resources are as important within the park as the ruins. Threatened and endangered species of plants are well mapped and protected as well.”
The result of all this planning and coordination between all parties was a successful line installation. “Many of the park service staff never thought this project would be completed in their lifetimes, due in part to economics and technology,” Umberger said. “Though difficult, this project is something we can be proud of.”
Sharon M. Bueno is managing editor of Trenchless Technology.