MODELING PRECIPITATION OF MINERALS AND WATER CHEMISTRY EVOLUTION IN AN ACID MINE DRAINAGE REMEDIATED STREAM

The Hewett Fork watershed in Southeastern Ohio is impacted by AMD from the AS-14 mine complex in Carbondale, Ohio. In attempts to remediate the stream, the water is being treated with a continuous alkaline input from a calcium oxide doser. While the section of watershed furthest downstream from the doser is showing signs of recovery, the water chemistry and aquatic life near the doser are still impacted. The objective of this study is to examine and model the chemistry of the tributaries of Hewett Fork to see how they contribute to the alkalinity and acidity budgets of the main stem of the stream. By examining the inputs of tributaries into the main stem, the project aims to understand processes occurring during remediation throughout the entire stream system. Chemical analysis of water and sediment samples, XRD identification of minerals and geochemical modeling using the PHREECI program have been applied to understand the chemical processes happening in the Hewett Fork watershed. Results show that the minerals ferrihydrite, goethite, calcite, diaspore, gibbsite, and gypsum form when the acidic waters mix with CaO in equilibrium with CO₂ and O₂ in the air, transferring the contaminants from the water to the sediments. While this contributes to improvements in water chemistry, the precipitation and deposition of metals inhibits biological recovery downstream of the doser. When examining the recovery of an acid mine drainage remediated stream, the inputs of contaminants, the transport of sediments, and the complex reactions between the water and sediments need considered together to understand the variations in stream chemistry.