The 1-ha site, within the California Gulch Superfund area near Leadville, Colorado, contained elevated Cd, Cu, Fe, Pb, Mn, and Zn soil concentrations due to historic mining operations in the area. In 1998, the site was amended with biosolids and lime at rates of 224 Mg ha-1 each. In October 2006, soil sampling occurred on a 10 m x 10 m grid to a depth of ~30 cm across the site. In June 2007 soil microbial samples were taken at each grid point to a depth of ~30 cm across the site. In August 2007 bulk plant samples were taken at each grid point using a 0.5 m2 quadrat, and individual plant species were collected on 12 transects across the site for plant tissue metal analysis. Plant cover was also estimated along the same 12 transects.
Overall, it was found that contour mapping was a good tool to identify specific locations within the study site that may require additional remediation efforts. Over most of the site, reclamation efforts were successful for immobilizing soil heavy metals, improving microbial activity and community structure, reducing plant metal concentrations and uptake to at or below those levels considered hazardous to animals, and thus reducing the risk for foragers on the site. This study could be strengthened if a control sample was taken at one of the bare spots at the site. This would have allowed us to determine metal contamination at the site in an area where biosolids and lime had not been applied.