“A 350-horsepower drive keeps the conveyor from overrunning,” Nicholson says. “With all that weight and momentum going down the hill, that conveyor would just take off if you had a small motor. We use about 125 horsepower to start the conveyor, and then it settles back to about 75 horsepower in an empty condition. When the material hits the belt, it actually goes into negative horsepower and regenerates power back into the grid. It’s a pretty unique conveyor system.”
It takes one operator in the tower on the dock and one person handling barge lines to control the loading of the barge. The operator can move the barge wherever he wants it during the loading process with the winch system. The conveyor will luft, extend, retract, and swing to reach all areas on the barge. The tug boats that bring the barge to the dock simply tie up to the barge and wait until loading is complete.
“We do 3 million tons per year, which sounds like a lot, but it’s 50 percent of what we’re used to doing,” Nicholson says. “In 2005, we did 6.2 million. We typically load 24/7, but we’re down to two shifts now, five days a week.”
Both Nicholson and Tweedy agree that the best part of DuPont Pit is the employees. “We have really high-quality employees here,” Tweedy says. “The current average tenure is 10.4 years for plant employees. They really take a lot of pride in what they do. We do most fabrication in house. We built all our own conveyors, feed distributors, chutes, and structural supports. The employees come up with many of the ideas, and we have our in-house engineer do the design drawings.”
One employee, Randy Davis, does all the programming for the plant’s automation system. “Randy started with us as a plant mechanic at Steilacoom in the mid ’80s,” Nicholson says. “In the ’90s, when we were getting ready for the DuPont Pit, we switched one of the towers at Steilacoom over to PLC control. Randy took an interest and had the knack, so he’s our programmer now.”
The programming is all Web-based. It can be accessed at the office or at home, so if there are any issues, they can be handled quickly, even at night. “The system is really reliable,” Tweedy adds.
As the economy improves, CalPortland plans to have DuPont Pit ready for it. “When we get so busy, as the industry did before 2008, we were able to have additional resources,” Tweedy says. “With this down economy, the real trick is trimming back while maintaining the assets and keeping safety and the environment at the forefront. That’s something that’s a priority here. The plant’s got to be ready to go all the time.” AM
From Aggregate Mine to Public Park
Steilacoom Mine opened in the 1890s and was rich with a deposit of fine, clean sand. “Originally, Steilacoom sluiced material using pumps in Puget Sound,” says Scott Nicholson, director of aggregates, Materials Group, Northwest Division of CalPortland. “They would bring barges in and put them up on the beach. They would, basically, sluice the material and bury the barges with sand and gravel. Then, when the tide came in, they’d tow it up to Seattle and manufacture concrete with unprocessed sand and gravel right off the pit face. At the time of its close, about 90 percent of the Seattle skyline had come from materials mined at our old Steilacoom plant.”
In the early 1990s, the mine entered into negotiations with Pierce County, and the county bought the property. The plant continued to operate, paying royalties to the county, until 2002 when it closed and locked its gates for the last time.
“Extensive construction work began on the Steilacoom plant right away after we left,” Nicholson says. “We had done some reclamation, but Pierce County had a vision of turning it into a huge park. The old mine site is now a park and a world-class golf course.”
The park includes walking trails that weave in and out of parts of the old mine that were left in tact for their historical value. Some of the old concrete stanchions that the plant was built on remain in the park, as well as the pond that supplied wash water for the old plant. The U.S. Amateur Championship was held at the Chambers Bay golf course this year, and the U.S. Open is scheduled to take place there in 2015.
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