Million gallon tank and tower takes shape
Posted 12/09/09 (Wed)
By Caroline Downs
Area residents had a clear view on a cloudless day when the tank was hoisted to the top of the pedestal at the Northwest Area Water Supply (NAWS) tower under construction a mile east of Kenmare.
The crew needed an hour and a half to raise the million-gallon, 108-ton steel tank 125 feet to its final position on November 18th, using a series of steel cables and motors powered by a single generator. The project is contracted with Caldwell Tank of Louisville, Kentucky.
“They picked a perfect day for this,” said Kenmare mayor Roger Ness, who was on hand to witness the event.
“There’s no wind,” added Perry Weiner, water resource senior manager with the North Dakota State Water Commission. “How often do we not have wind in this country?”
The tank, composed of sheets of steel welded together around the concrete pedestal, moved steadily up the tower. Members of the Caldwell welding crew scrambled up the ladder built inside the pedestal to climb to the top of the tower and roll up the slack cables as the tank continued its climb.
“Caldwell probably builds 120 of these a year,” said Weiner, adding that the company also makes a two million gallon water tank. “This size of tank, there are only three or four qualified bidders in the country.”
Work started on the tower in June, when excavation began at the site. According to Alan Kemmet, an inspector with the Houston Engineering firm that handles design and engineering work on the NAWS project, the tower is anchored by about 100,000 pounds of rebar and 400 yards of concrete hauled by Sandberg Redi-Mix of Kenmare for the foundation. That concrete extends 20 feet below ground, and was poured and shaped to slope away from the tower and form a firm base.
Approximately 500 yards of concrete were used to pour the 22 rings that form the tower. Each four-foot high ring required 18 yards.
“Most days, they poured two rings of concrete,” said Kemmet. “Everything’s gone pretty smoothly.”
With the tank set in place on a ring of steel brackets at the top of the tower after 90 minutes, the steel was joined to the pedestal by another round of rebar and concrete. The crew estimated 26 yards of concrete would be needed for the ring beam, lifted two yards at time up the side of the pedestal.
“Once that concrete is cured, that makes the final connection,” explained Dave O’Shea, project manager with Houston Engineering. “The crew will weld the roof on, and a quarter-inch thick steel floor has to be welded in place, along with some other piping fabrications. We want to have all the welding operations done so this crew won’t have to come back here next year.”
The steel sheets used to make the tank were fabricated and shop-primed at one of Caldwell’s facilities in the Atlanta, Georgia, area. The tank will be sandblasted and painted with three specialized coatings next spring to minimize maintenance and protect the structure. The final coat will likely be deep blue in color, similar to the color of the NAWS tank built near the golf course at Berthold. Landscaping will also be done on the site next spring.
“There’ll be water in there probably by July of next year,” said O’Shea. “By the time we’re ready to provide service to Mohall, Sherwood and the All Seasons Water District, we will need this tank for storage.”
O’Shea expected this segment of the NAWS project, which includes construction of the storage tank at Kenmare and 63 more miles of pipeline, to be completed by October 2010. While Kenmare area residents may think the tower looks finished now, some interior work will take place next spring. “There’s no piping in the pedestal yet,” O’Shea said, explaining the area was cleared for the welding crew’s use.
Ten-inch pipe was installed for the inlet and outlet, and an overflow pipe was added that can also be used to drain the tank for cleaning or repainting. Connections between those pipes and the NAWS line will be finished next spring.
The interior crushed rock floor of the pedestal will be raised another two feet, and a small two-room building will be constructed inside the base to house equipment used to control and monitor operations and disinfectant levels for the tower’s water supply.
“There are between 60 and 65 miles of pipe from Minot,” said O’Shea. “If the disinfectant level drops in that distance, we can boost it here.”
Vault controls operations
One critical part of the NAWS system at the Kenmare tower remains hidden from the view of most passersby.
Marked only by a small, blue curved pipe emerging from the ground, the underlying concrete room contains what O’Shea referred to as the “brain center” of the system. “This vault costs about $150,000,” he said as he glanced around at the powder blue walls and state-of-the-art electronics. “It’s a good value.”
“Lots of people drive by these things and see the horseheads and don’t realize what’s underneath,” added Weiner.
Work on the vault was contracted with Northern Improvement, with the vault itself pre-fabricated in Mitchell, South Dakota by Dakota Pump, Inc. and delivered to the Kenmare site.
Inside the temperature- and humidity-controlled environment, a series of NAWS pipes are housed with sensors and digitized monitors to track the flow rate. Weiner emphasized how both the number of gallons per minute and the total flow could be determined. “This is how I bill you,” he said, laughing as he said he actually planned to be in the area at least once a week to check the system. “There’s also a radio link back to the central unit in Minot and to the Bismarck office.”
The vault contains the main NAWS line, with additional pipes connected specifically to the storage tank and to the Kenmare system. The NAWS system has eight of the vaults so far, along with four pump stations. “Everywhere there’s a major connection, we put in one of these vaults,” said Weiner.
After Weiner monitors the system for a while, another person will be hired for maintenance on the line. “These are mechanical-type systems,” he said. “They’re complicated, but it’s a super, super reliable system.”
He and O’Shea demonstrated the use of the valves that control flow among the various components of the connection. “It’s a dual system with electric valves, but if that fails, it will default to a manual spring setting,” said O’Shea. “It’s 1920s technology that nobody’s been able to outdo.”
The vault also features a supplemental power system for its computer, should the regular electrical connection go down for some reason. “Everything will still work without power,” Weiner said, adding that water would continue to flow through the system.
In use next summer
The connections between the vault and the new water tower will be completed next summer, when the tower is ready to store water. Until a water intake and treatment facility can be built at Lake Sakakawea to draw Missouri River water into the NAWS system, the city of Minot will supply water to communities and rural water districts along the NAWS line.
The city of Kenmare started receiving water directly through the NAWS line this week from the Minot supply, with a connection made at the south edge of town. Eventually, water will first go to the new NAWS tower and then be piped back to Kenmare, with that infrastructure already in place.
Kenmare will also have its own new water storage tower in the city, with bids scheduled to go out in January or February 2010 for that project.
In the meantime, the skyline east of town has changed, and the new tower stands as a symbol of progress on a water distribution plan that has been in development since the 1980s. “This is another step toward finishing this whole project,” Ness said as he watched the steel tank rise steadily toward the top of the concrete pedestal, “for the whole region.”