Arsenic Contamination in Pierce County Soil: Is
Environmental Justice Present?
Temre Smith, Elizabeth Kalama-Wojtowicz, Erin Campbell
Dec 1, 2010
This study was done to determine whether or not arsenic levels in the soil effect home values. By
using random cluster sampling to find the mean home values in five different contamination levels, we
discovered that the contamination levels had no significant impact on home values.
The soil in Pierce County contains arsenic at levels up to 50 times higher than allowed by
the state. The most likely source of the contamination was Asarco’s copper smelting plant in
Ruston, near Tacoma. From 1890 to 1986, emissions from the plant, which included arsenic, lead
and other heavy metals, were probably carried by wind and deposited over Vashon and Maury
islands as well as mainland King and Pierce counties. The widespread soil contamination left by
the smelter is called the Tacoma Smelter plume site. In this study, we will be focusing on the
home values in some of these affected areas. We intend to determine if there is a connection
between home value and the level of arsenic contamination so we will be able to conclude if
people of lower incomes are subjected to more dangerous conditions. The study will be based on
assessments of property values taken randomly from the Pierce County Assessor’s Website in
October of 2010, http://www.co.pierce.wa.us/pc/abtus/ourorg/at/at.html, by using the parcel
numbers. To see if environmental justice is apparent within the areas contaminated with arsenic,
we will use home value as criteria to determine if there is a pattern between contamination levels
and level of income.
Our study was conducted by examining the assessed property values for homes in North
Tacoma that were listed on the website for the Pierce County Assessor’s (PCA) office. These
samples were determined first by dividing a map provided by the Washington State Department
of Ecology that showed the different regions that were sampled during a study conducted in
2000. In this study there were soil samples taken from 59 residential yards. The 195 samples
were analyzed in a state Ecology Department-funded study to learn the extent of arsenic and lead
contamination around the now-closed Asarco copper smelter in Ruston. The average arsenic
concentration was 26.4 ppm, slightly above the 20-ppm cleanup standard. In 60 percent of the
yards sampled, average arsenic concentrations were over 20 ppm. However, in 80 percent of the
yards sampled, arsenic was below 40 ppm. The highest level measured was 1,050 ppm at a
The map used was of North Tacoma and represented all five contamination levels that
were indicated in the 2000 study. We divided each area into a section approximately one square
mile and numbered them. After a single area was selected randomly from each of the five
contamination levels, those areas were then divided again into one block radiuses. That block
was then sampled on the PCA website. We divided the value of each house by the square
footage to obtain a value of each square foot. This was done to eliminate any bias that may have
been formed by comparing a three bedroom to a one bedroom ext.
In the five contamination levels there were seventy-one homes sampled. The median
range for all five levels was approximately the same ranging from 117 and 132 value per square
foot in dollars. The distribution of all the home values in the box plot below overlapped, showing
that the ranges are similar for all contamination levels.
The mean home values are provided below:
Level of Contamination Mean Home Value Standard Deviation
`Supersite 123.48 23.32
Greater than 100. ppm 137.63 28.12
40.00 to 100.00 ppm 129.55 8.01
20.1 to 40.00 ppm 133.03 16.25
Not detected, < 20.0ppm 129.5 32.42
A sample mean was used to determine if there were differences in property values in the
various arsenic contamination levels. Initially, we expected to find evidence that property values
in the areas most contaminated with arsenic would be lower than the property values in the areas
least contaminated with arsenic. However, there was not enough evidence to show that property
values were different. (p-value = 0.785924, F-value = 0.430736).
When we first began to examine the North Tacoma area and the different property
values, it was our belief that there would be a difference of the housing values in the different
contamination levels. We were pleasantly surprised to discover that the hypothesis test indicated
that there were no clear differences of housing values in the areas of contamination. Because of
this, the results clearly show that environmental justice is present in North Tacoma.
Background on Tacoma Smelter Plume. (2010). In Public Health- Seattle & King County.
Retrieved September 15, 2010, from
Dirt Alert- Tacoma Smelter Plume Interactive Map. (2010). In Department of Ecology State of
Washington. Retrieved September 18, 2010, from
Parcel Search. (2010). In Pierce County Assessor's Treasury. Retrieved October 15, 2010, from
Home values and listings. (2010). In Zillow.com. Retrieved November 6, 2010, from