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Toxics Cleanup Program


Studies of Tacoma Smelter Plume Contamination

The Tacoma Asarco smelter shut down in 1987.  In 1993, the federal Environmental Protection Agency (EPA) began cleaning up soils in yards near the smelter.  The start of cleanup raised interest in arsenic and lead contamination beyond EPA’s cleanup area.

Early studies from before 1987 looked at soils in yards, play fields, forests, and other areas.  However, many of the studies had few samples and only covered small areas.  In 1999, Ecology began working with local health departments on a series of studies to find the full extent of smelter contamination.


Click on map to view larger size.Footprint Studies:


The first phase of studies consisted of “footprint” sampling.  Ecology wanted to find out how far contamination went and how high the levels were.  Summary of footprint study findings

2000 Vashon-Maury Island – Undisturbed Area Study Report
2002 Mainland King County Preliminary Study Report
2004 Pierce County Footprint Study Report
2005 Extended Footprint Study Report


Child Use Area Studies:


The second phase of studies looked at places where children play, such as schools, childcares, and parks.  Summary of child use area study findings.

2001 Vashon-Maury Island Child-use Area Study Report
2002 Dockton Park Resample Study
2003 Mainland King County Child-use Area Study Report
2003 Vashon-Maury Island School District Child Use Area Resample Technical Memo
2004 Pierce County Child-use Area Study Report

Other Studies:


Four other studies helped define the Tacoma Smelter Plume, linked Asarco to the contamination, and explored using ferns to clean up soils.  Read more about how Ecology found Asarco liable for the Tacoma Smelter Plume.  

2001 Survey of Typical Soils Arsenic Concentrations in Residential Areas of the City of University Place
2003 Trace Element Analyses 
2004 Credible Evidence Report
2005 Fern Phytoremediation Study



Summary of Footprint Study Findings

Ecology ended up with 4,175 samples from 851 locations.  They show higher levels closer to the former smelter, but the levels vary greatly, even within a small area.  The Tacoma Smelter Plume map is based largely on data from these studies.

Arsenic was in over 99 percent of all samples, and ranged from 0.48 parts per million (ppm) to 1,050 ppm.  For comparison, natural background levels for the region are around 7 ppm and the state cleanup level is 20 ppm.  Ninety-three percent of samples were higher than natural background and 55 percent exceeded the cleanup level for arsenic.

Lead was in over 97 percent of samples, ranging from 1 ppm to 6,670 ppm.

County Highest arsenic Highest Lead
King 460 ppm 1300 ppm
Pierce 1050 ppm 6670 ppm
Thurston 159 ppm 1110 ppm
Kitsap 37 ppm 198 ppm


Summary of Child Use Area Study Findings

These studies provided Ecology with a better picture of contamination in places where children
might be at risk.  As in the footprint studies, levels are higher closer to the smelter, vary greatly acrosssmall areas, and are higher in the top six inches of soil.  These data helped prompt the legislation that started the Soil Safety Program.

Vashon-Maury Island Child Use Area Study – This study used 1,503 soil samples from 34 play areas at public and private schools, public parks and beaches, childcares, preschools, and camps.    Beach samples had low levels of arsenic and lead.  In non-beach areas, maximum arsenic ranged from 8.9 to 130 ppm and maximum lead ranged from 12 to 900 ppm.  Over 70% of these areas had a maximum arsenic level over the 20 ppm state cleanup level.  

Mainland King County Child Use Area Study - This study used 2,532 soil samples from 97 child use areas at public and private schools, public parks, and childcares.  The maximum arsenic level was 189 ppm and maximum lead was 699 ppm.   However, only four properties had samples above 100 ppm arsenic.

Pierce County Child Use Area Study - This study analyzed 1,211 soil samples from 72 child use areas, including parks, public schools, and childcares.  Arsenic levels ranged from 0.94 to 691 ppm.  Lead ranged from 1.32 to 1,040 ppm.  Twenty-two percent of the samples had arsenic above the state cleanup level of 20 ppm.