Soil removal in Colorado (soil removal is generally deeper in desert climates, since root zone is deeper)

"....soils remedy called for removal and replacement of the top 12 inches of soil, and
18 inches in vegetable garden soils, where metals concentrations exceed 73 parts per million
(ppm) cadmium, 500 ppm lead or 70 ppm arsenic. ...."

from:
Colorado Department of Public Health and Environment
Hazardous Materials and Waste Management Division
Five-Year Review Asarco Globe Site Denver, Colorado