Soil Remediation Index

Heavy Metals and Youth

The purpose of this analysis was to identify areas within Pierce County, Washington where the remediation of toxic soils would have the greatest impact.

The Asarco copper smelter operated for almost 100 years in Tacoma, leaving a toxic legacy behind in the soils of Puget Sound. Arsenic and lead are by-products of smelting, and a plume of these and other toxic heavy metals spread via the smelter’s 571 foot tall stack. Arsenic and lead pose health risks if inhaled or ingested, particularly during development causing children to be increasingly susceptible to exposure.

A Priority Remediation Index was created based on the ranking of:

•Density of children 10 and under

•Arsenic soil concentrations

•Lead soil concentrations

An Index for Priority Remediation of Toxic Soils in Pierce County, Washington

Click the map for a printable version of this analysis

The EPA monitors arsenic and lead soil concentrations throughout Washington, and site remediation continues in conjunction with the Department of Ecology.

To learn more visit ecology.wa.gov, or clicking the image below

Combining EPA Monitoring Sites

ICP-MS determined 2002 and 2004 EPA replicate soil sample arsenic and lead concentrations for depths ranging from 0 to 6 inches were aggregated by averaging values.

Replicate sample information was dissolved into single sites and the averaged concentration of arsenic and lead used as proxies for total heavy metal concentrations.

Surface Metal Concentrations

Kriging was used to interpolate the surface concentrations and spatial distribution of arsenic and lead concentrations between sites.

Arsenic concentrations ranged from 5.3 to 139.6 ppm.

(mean: 17.9 ppm, standard deviation: 10.9 ppm)

Lead concentrations ranged from 20.7 to 362.9 ppm.

(mean: 57.6 ppm, standard deviation 29.3 ppm)

Metal concentrations were reclassified based on the standard deviation of metal concentrations into ranks.

Possible errors in estimation due to the unavailability of data for areas with low or no heavy metal concentration.

Density of Young Children

The density of children 10 and under per square mile was calculated using 2010 US Census data.

A continuous surface of children 10 and under was interpolated using Inverse Distance Weighted (IDW) and reclassified using standard deviation into ranks. Child density ranged from 0 to 49,519 children 10 and under per square mile.

(mean: 92, standard deviation 377)