New Study Examines Naturally Occurring Asbestos Carried in Sumas River Sediment

TACOMA, Wash. — The Sumas River, in northwest Washington, contains sediment that carries naturally occurring asbestos. This week, scientists at the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, released a report detailing new and publicly available information about the asbestos in the water and sediment. 

A large active landslide on the western flank of Sumas Mountain in Whatcom County, Washington, is a significant source of sediment to Swift Creek and the salmon-bearing Sumas River, especially after heavy rains. The landslide contains naturally occurring asbestos and elevated levels of metals. Naturally occurring asbestos is described as asbestos found in-place in its natural state, such as in bedrock or soils. Although the landslide has been active since the early 20th century, a 2006 analysis of the sediment revealed a high asbestos content, leading resource managers to treat the sediment with caution.

During a two-year study, USGS scientists measured the amount of sediment carried by the Sumas River during normal and wet years and assessed the settling and transport characteristics of asbestos fibers in river water. Heavier sediment such as sand and gravel settle out quickly, but finer sediment including silt, clay and asbestos fibers settle out more slowly and travel farther downstream.

In water, asbestos fibers can form bundles that are visible when in high concentrations and, when seen up close, give water a miso soup-like appearance that, under most river flows, does not settle out. The study found that the river transported 24,000 and 54,000 tons of suspended sediment in 2012 and 2013, respectively, and observed that samples of river sediment were up to 37 percent asbestos by mass. 

Results from the USGS will help guide agencies managing sediment, and flood and health risks in the Sumas River watershed.  

The report, "Transport and Deposition of Asbestos-Rich Sediment in the Sumas River, Whatcom County, Washington," by Christopher A. Curran, Scott W. Anderson, Jack E. Barbash, Christopher S. Magirl, Stephen E. Cox, Katherine K. Norton, Andrew S. Gendaszek, Andrew R. Spanjer, and James R. Foreman, is published and available online as U.S. Geological Survey Scientific Investigations Report 2015-5177.