Recovered mine drainage passive treatment residuals address legacy sediment pollution: A field mesocosm study at Grand Lake o' the Cherokees, Oklahoma

Abstract

Grand Lake o' the Cherokees, Oklahoma is a large multipurpose reservoir that receives both elevated metals concentrations from the upstream Tri-State Lead-Zinc Mining District (TSMD) and excess nutrients from its agricultural watershed along with significant internal phosphorus (P) legacy loads. Mine drainage residuals (MDRs), amorphous iron oxyhydroxides recovered from passive treatment systems, may serve as phosphorus sinks. To evaluate the role of MDRs on reservoir sediment dynamics, a field mesocosm study (20-L vessels) was designed with four different mine drainage residuals (MDR) treatments: sediment control (no addition), mixed (MDR mixed with sediment), layered (MDR on top of sediment, no mixing) and bagged (MDR inside a fine mesh bag on top of sediment, no mixing) with phosphorus-spiked water. Soluble reactive P (SRP) concentrations demonstrated decreasing trends and the control treatment showed greater concentrations than all MDR treatments. P adsorption capacity (PAC) was determined to be approximately 0.7 mg/g and > 30 mg/g for sediments and MDRs, respectively. At Day 135, SRP reached >99% removal for all four treatments. Aqueous lead and cadmium concentrations were below detection limits and zinc concentrations were below the National Recommended Water Quality Criteria. Sediment lead, zinc and cadmium concentrations were below the TSMD-specific sediment quality guidelines, except for final Mixed MDR treatment sediment with 16.7% of samples exceeding both Cd and Pb criteria. Results showed that MDRs removed excess P from the water column and by using the recommended bagged addition method, trace metal release to both the water column and sediment layer were minimized.