LEAD AND ARSENIC CONTAMINATION IN SOILS IN TOOELE, UT: AN EVALUATION OF CONCENTRATION PATTERNS, MOBILITY AND THE NEED FOR REMEDIATION

Anthropogenic lead (Pb) and arsenic (As) contamination in Tooele, UT has caused levels to reach >500 Pb and >100 As ppm locally in soils, which is above the US EPA’s action limit for residential property in this area. Agricultural property in Tooele, Utah, which may be developed in the near future as residential property, is being evaluated for Pb and As concentrations in soil to determine whether remediation will be needed.

Located downhill of historic waste ponds associated with ore milling, episodic overflows contaminated the soil of these properties. X-ray fluorescence (XRF) results show many areas with >1,000 ppm Pb and >100 ppm As. These data complement and are consistent with prior studies when the property was initially characterized as agricultural land. However, a greater sample density combined with a strategic choice of sample locations permits the application of spatial statistics to better define sub-regions within a larger property that require remediation for housing development.

Strong positive correlations of Pb, As, Cu, and Zn with S suggest that these metals are associated with very fine-grained sulfides mobilized during past overflow events. X-ray diffraction (XRD) experiments establish a soil mineralogy of quartz, feldspars, halloysite, and ferrihydrite, where sulfide minerals occur in such low abundances that they are obscured within XRD backgrounds and peak overlaps. Halloysite and ferrihydrite suggest that some heavy metals may be sequestered or retarded through mineral surface--solute interactions.

Planned SEM analysis, in particular X-ray maps, should determine which minerals host Pb and As, having a direct bearing on their mobility and bioavailability. Toxicity characteristic leaching procedure (TCLP) experiments indicate that Pb, As and Cd concentrations greater than EPA primary drinking water concentrations, indicating additional concern for heavy metal mobility in the soil column.