<p>Passive treatment of mine drainage effectively decreases the concentration of ecotoxic metals in impacted water and sequesters the metals in residual solids, the composition of which vary depending on the biogeochemical process in use. Mine drainage passive treatment systems must undergo rehabilitative maintenance to continue functioning over decadal time scales. This maintenance includes removing residuals from the system, creating large amounts of potentially hazardous waste. In this study, two types of residuals from two passive treatment systems were amended with biochar, biosolids, and coal combustion residuals, to increase retention of ecotoxic metals in hard rock mine drainage treatment residual solids. Three leaching tests were used to determine whether the retention of metals was increased by the addition of these amendments. The amendments were intended to act as low-cost materials that decrease metals leaching in tests simulating landfill disposal and open-air application of the residual solids. Although the amendments had neutral to basic pH, large surface areas, and cation exchange capacities that were hypothesized to increase sorption of trace metals, the concentrations of most metals were statistically similar or elevated compared to the control. Although these amendments were ineffective in decreasing metals leaching, further research may show that using other materials or a mixture of amendments may decrease the concentration of metals available to the environment.</p>