Predicting aqueous metal species in a stream impacted by mining activity

The impact of mining activity in the Tri-State Mining District of Missouri, Kansas, and Oklahoma has resulted in continual exceedance in water quality standards in many surface waters including Short Creek in Galena, Kans. Critical heavy metals detected in Short Creek have been lead, cadmium, and zinc. Water column samples were collected at each of seven sites from May 1992 to May 1995 and were analyzed for temperature, pH, conductivity, and total PO^3-₄, CO^2-₃, Ca²⁺, Mg²⁺, SO^2-₄, Ba²⁺, Cd²⁺, Pb²⁺, Mn²⁺, Fe²⁺, Ni²⁺, Al³⁺, and Zn²⁺. Using MINTEQ (a geochemical equilibrium speciation model for dilute aqueous systems that can be used to calculate the equilibrium composition of dilute solutions in laboratory or natural aquatic systems), probable concentrations of metal species were predicted to evaluate the potential for metals to be in a bioavailable form. The MINTEQ predictions demonstrated the presence of dissolved metals, including a dominant free metal ion. Aqueous components within the dissolved fraction predicted using MINTEQ offered a unique understanding of the critical factors that may determine toxic aqueous conditions.