September 10, 2015
On the shores of Puget Sound
By Kerry Clines, Senior Editor
Editor’s Note: This article originally appeared in the August 2010 issue of Aggregates Manager.
CalPortland’s DuPont Pit, located near the small town of DuPont, Wash., was ranked number 2 in sand and gravel production in 2009. What makes DuPont Pit successful? Actually, there are several keys to its success, including a unique deposit of material, a great location, and dedicated employees.
DuPont Pit sits on top of what CalPortland claims is some of the highest quality gravel in the world. “This is a really unique deposit,” says Jim Tweedy, plant superintendent at DuPont Pit. “The material was deposited here during the last Ice Age, which most geologists say was around 14,000 years ago. This was the recessional outwash — in other words, this material was carved from the mountains by glaciers as they advanced from Canada into the Puget Sound area and was deposited by water flowing from glaciers as they melted. The material, ground and sorted by the glaciers and washed by the glacial melt-water, comprises a world-class deposit of sand and gravel.”
The deposit is split into two veins. DuPont Pit sits atop one vein, and Steilacoom Mine, which was located several miles further north on the coast of Puget Sound until it closed in 2002, sat atop the other. Both mines shared the same basic deposit, but Steilacoom Mine, which had been in operation since the late 1800s, was renowned for its fine sand, while the DuPont material is a coarser deposit.
“Steilacoom was rich with fine, very clean sand, but we have a deficit of fine sand at DuPont,” says Scott Nicholson, director of aggregates, Materials Group, Northwest Division of CalPortland. “At the time we moved from the Steilacoom deposit, we applied for permits to reactivate the existing dock at our mine on Maury Island in Puget Sound. This mine is rich with fine sand and, if made available to the market, would balance the DuPont deposit well. Despite the fact that the Maury Island site is an existing mine and designated under local land use codes as a mineral resource of long-term significance, permit issues have held up construction of the dock and access to the sand for over 12 years.
“During this time, we have looked for alternative sources of sand to balance DuPont, including an extensive study on crushing the DuPont gravel to make sand,” Nicholson adds. “As part of the study, a test was used to compare the crushability of the DuPont material on a crushability index. We sent 50,000 pounds of gravel to Metso’s test center in Milwaukee. They told us if you score in the high teens, you have a very hard gravel. They did 10 tests on our gravel that averaged a score of 30. They said it was the hardest gravel that had ever come through their test center.”
The hardness of the gravel may not allow DuPont Pit to manufacture fine sand, but it does make the gravel highly desirable for projects that require high-strength durable aggregates. For example, in Alaska, where studded tires tear up the roads every winter, they use a test called the Nordic Abrasion Test to determine whether aggregates will resist studded tire wear. There are very few mine sites that can supply material that scores high enough on the test to supply material for surfacing major roadways in Alaska.
DuPont Pit is located on the shore of Puget Sound, which provides a type of transportation that most aggregate plants don’t have — marine transportation. “About 80 percent of our material goes out by barge,” Nicholson says.
About 98 percent of the material produced by the plant is used within the Puget Sound Region including Seattle, Tacoma, and Everett. The remaining 2 percent is used for special projects in other areas like Alaska. “A typical barge transports about as much material as 186 truck and trailer loads, reducing traffic congestion and the overall carbon footprint, and it is safe,” Nicholson says. “Ready-mix and asphalt producers in the greater Puget Sound Region depend on DuPont to supply their aggregates. Of the four ready-mix companies in the Seattle area, including us, only one doesn’t use DuPont aggregate.”
It wasn’t all roses to get DuPont Pit approved, however. The permitting process took 10 years.
“We were very forthcoming about everything with the community — what we’re going to do and how we’re going to do it,” Nicholson says. “We have 114 special conditions that were set forth during permitting. One of the requirements is that we can’t disturb the bluffs along Puget Sound. So, from the Sound, the only thing you see is a cut in the bluff. We have a large tube that comes down to the dock with a conveyor in it, but our mining area can’t be seen.”
Another requirement was that DuPont had to have regular biannual monitoring of noise at the loading dock. People living on Anderson Island, just across Puget Sound from the dock, were very concerned about the level of noise that would be generated during the loading of barges. The regulation only allows the noise level on the shores of Anderson Island to be 5 dB above ambient. A third party chooses the time to test the noise levels and doesn’t notify the plant until after the test has been completed. They then ask what the plant was doing at the time of the test.
“Of course, it’s always the same,” Nicholson says. “There’s virtually no impact, no noise from our dock. One day, I got a call from someone who had been one of our biggest opponents during the permitting process. He said, ‘I just want you to know that I was wrong. I can’t hear anything and, in fact, I really enjoy watching the marine traffic.’”
In addition to Mine Safety and Health Administration noise standards, CalPortland has a very strict company hearing-protection policy. “Basically, the rule of thumb is, if you can’t have a normal conversation with someone, you’re required to wear hearing protection,” Nicholson adds. “We’ve got just a couple of places that we don’t require hearing protection, and one of them is the dock. There’s really no noise.”
DuPont Pit has been reaching out to educate the community and to, hopefully, improve people’s opinions of the aggregate business. “Recently, we’ve been doing a lot of field trips with grade schools,” Tweedy says. “They have a required curriculum where they have to study rock and minerals. So, at the end of the terms, the classes come out. We talk about concrete and the different things we make out of our materials, and where they see and use it in their daily lives. It’s a lot of fun.”
“In 1997, when the plant was built, it was probably one of the most automated plants in the country,” Nicholson says. “Of course, it’s not that now, but it’s still pretty impressive.” Many improvements have been made since then.
The whole system is designed around 2,400-ton-per-hour production out of the mine, while shipping is typically about 2,000 tons per hour. The material is mined in a simple scoop and dump fashion. A dozer maintains a workable slope in the mine to ensure safe working conditions for the loader operators. Two wheel loaders scoop up the sand and gravel and dump it into a feeder over a conveyor system that carries the material up to a fractionated processing plant. No processing is done in the mine itself.
“We bring it in to the primary screening plant and sort it off into three raw surge piles, two different sizes for the crushers and one for the wash plant,” Tweedy says. “We wash everything 1½ inch and finer through the wash plant. Out of the wash plant, we make four different sizes of washed gravel and one size of coarse sand. All the fines are pumped over to our sand house where we have four classifiers that sort off three more sizes of fine sand. On the crushed side, we feed the crushers from the surge piles. The material comes through the crushed/screening house, where we make four sizes of crushed gravel. Out of those 12 basic sizes of materials, there are few limitations on how many different blends we can make.”
The plant is designed with two parallel 1,500-foot-long tunnels running under the stockpiles. The stockpiles on one side are all washed sand and gravel and the other side contains crushed gravel. The processing plant runs right between the two rows of stockpiled materials, which helps contain the noise inside the processing plant. Quality control (QC) monitors material gradations in the stockpiles continuously to ensure consistency.
Two feeders under each product stockpile enable the plant to produce different blends. “When a customer wants a certain product, our QC lab analyzes what the customer wants in their specifications and selects, proportionately, the blend he needs to pull to make those specifications,” Tweedy says. “Then he designates that blend a product number and it goes into the data base. When an order is entered in the system, the product number dictates which feeders are activated to make that blend and ensures they are the only feeders that will open. It’s timed so that, no matter where you’re pulling from, when the material hits the shipping belts, all of it is perfectly blended. We currently run about 350 different blends on our data base.”
While barging is the primary method of transport for DuPont’s material, trucks transport the remaining 20 percent. The plant simply flips a gate to change loading from the shipping dock to the truck lines, and vice versa.
A series of two conveyor belt systems carries material to the loadout dock on Puget Sound. The first conveyor in the journey is covered. “Once the material is on the loadout conveyor belt, the only place for it to go is on the barge,” Nicholson says. “It’s about a 3,100-foot conveyor and is covered for two reasons. The primary reason is that we can’t discharge a drop of anything into Puget Sound. The Sound is downhill, so if it rained on the conveyor, it would discharge material into the water. The other reason is that this is a long, flat conveyor. If the power went out during a storm and the belt sat in the rain with material on it, it would get pretty sloppy.”
The second conveyor goes down the bluff to the dock on Puget Sound at an extreme angle and is completely enclosed in a tube to prevent any spills. This conveyor has a very large drive motor and gear box with a hydraulically controlled clutch and large disk brake, so that if there’s a problem on the barge, the conveyor can stop quickly.
“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.
Svedala 5×12 scalper
Svedala 8×24 double-deck screens (4)
Svedala 8×20 triple-deck screens (4)
McLanahan 12×48 classifiers (4)
McLanahan 66×36 double screws (2)
McLanahan 66×36 single screw
Conn-Weld 6×12 dewatering screens (2)
HP-500 Nordberg standard cone crusher
HP-400 Nordberg cone crusher (2)
ISC-82 vertical impact crusher
Barmac/ISC-82 vertical impact crusher
JCI 6×16 double deck for the standard crusher
8×20 Svedala SH double-deck screens (8)
85-foot High Flo thickener
Phoenix 3-meter belt presses (4)
Caterpillar 992 loaders (2)
Caterpillar 990 loader
Caterpillar 988 loaders (3)
Caterpillar D10 dozers (4)
Caterpillar 40-ton articulated haul trucks (2)
Caterpillar Challenger 45 tractor
Caterpillar D6 dozer
Tiger 690 wheel dozer
To see a short video of CalPortland’s barge loading operation, visit this article in our digital edition at www.aggman.com.