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Tacoma Smelter Plume
  Tacoma Smelter Plume ó Study Summary  
  Background  l  Thurston County Study Area  l  Conclusions  

The former Asarco copper smelter in Ruston, Washington, operated for almost 100 years. The copper smelter's smokestack released arsenic, lead, and other harmful chemicals throughout the Puget Sound region.

Some of these chemicals, particularly arsenic and lead, settled into the upper layers of the dirt in Thurston County. The levels of arsenic and lead in Thurston County are not an immediate public health threat; however, people should limit the amount of dirt they contact and accidentally eat.

Thurston County Health Department was part of a study of the Tacoma smelter. The study was funded by the Washington State Dept of Ecology. Soil from north-eastern Thurston County was collected and tested for lead and arsenic content (see map of study area [PDF]). The following information provides some background on the study.

Map of Thurston Co study area
Thurston County Study Area

Click map for larger view[PDF]


Arsenic, lead, and other metals were released into the environment from the Asarco copper smelter, which operated from 1890 to 1986 in Ruston, in north Tacoma. The air pollution that came out of the smelterís smokestack traveled with the wind and settled onto the soil in much of the Puget Sound area.

The Tacoma Smelter Plume studies conducted between 1999-2003 tested soil from King and Pierce counties. These soil samples were found to have levels of lead and arsenic above naturally occurring background concentrations. In 2004 the study area was broadened to include Thurston and Kitsap counties to further define the area impacted by the smelter.

Thurston County Study Area

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In Thurston County, 204 soil samples were collected from the upper six inches of undisturbed soil at 51 sites. Because the smelter ash was deposited onto the ground from the air, the samples were collected in areas believed to have the least soil disturbance. Undisturbed soils were expected to have the highest concentrations of arsenic and lead from the smelter ash, so most of the sample locations were in undeveloped forested areas.

The state's soil cleanup standard for arsenic is 20 parts per million (ppm); for lead, it is 250 ppm. Of the 51 sites where soil was sampled in Thurston County, 32 fell within the state standard for arsenic and 50 were within the standard for lead. Further analysis of the soil will be done at the one site that tested high for lead, to see if the pollution is from the smelter or another source.


Arsenic and lead levels in some of the soil samples were higher than those naturally occurring in the Puget Sound area. There is no health emergency from concentrations measured at any of the sites.

Lead and arsenic are naturally occurring in dirt, food, and water. Although lead and arsenic levels in some of the Thurston County study area soils were higher than natural, they are not an immediate health risk. However, ingesting these metals at concentrations above those naturally occurring for a long period of time may cause an increased risk of developing adverse health effects. People can lower that risk by washing hands, removing shoes before going indoors, and taking other steps to limit the amount of soil they accidentally swallow. Viruses, bacteria, and other metals are also naturally occurring in dirt and even further strengthen the advice to avoid eating dirt.

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This page last updated: 01/28/22