On the shores of Puget Sound

CalPortland’s Washington-based DuPont Pit delivers high-quality gravel to ports as far away as Alaska.

By Kerry Clines, Senior Editor

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.

The deposit

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.”

Material 1½ inch and finer goes through the wash plant.

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.

The location

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.