Remediation of Lead in Mine-Contaminated Wetland Soils Using Phosphate Amendment.

Early mining activities in Northern Idaho have left thousands of acres of contaminated soil and sediments in the Coeur d’Alene River Basin. Contamination includes elevated concentrations of Pb, Zn, Cd, and As that present toxicity risks to humans and animals. The amount of contaminated soil is massive, and cannot be feasibly removed. Therefore, alternative in-situ remediation strategies are essential. This study investigated the use of phosphorus for lead remediation of two Coeur d’Alene soils. The aim of this strategy is to produce lead phosphate minerals in teh soils, which have low solubility and pose a lesser threat of mobility and thus toxicity. However, amending soil with phosphates creates several challenges that must be addressed. One of the most problematic issues is the movement of phosphorus into surface water, which in turn could lead to decreased water quality and potential eutrophication. Along with the concern of P loading, there is an additional threat of mobilization and increased solubility of other contaminants.

Conclusions from this research suggest that P remediation can be implemented at sites along the Coeur d’Alene River with phosphorus amendment rates that will keep Bray extractable P below the P threshold recommended for agricultural fields. However, before other sites int eh CDA Basin undergo P application, prior investigation of the soil’s physiochemical properties should be done to determine the correct P application rate. Addiitonally, post-phosphate amendment, potential for As release needs to be considered.