Framework to Calculate TMDL of Acid Mine Drainage for Cheat River Basin in West Virginia

The Watershed Analysis Risk Management Framework (WARMF) was enhanced to calculate the total maximum daily load (TMDL) of acid mine drainage for the Cheat River Basin in West Virginia. The framework divides the river basin into catchments, river segments, and lake layers. Some catchments have deep mines and/or surface mines. These catchments have a soil layer that contains pyrite (FeS₂), calcite, and other minerals. The oxidation of pyrite requires molecular oxygen. The framework tracks the concentration of atmospheric oxygen in soil macropores by the advection due to earth breathing and by the sinks due to organic matter decay and pyrite oxidation. Pyrite oxidation produces Fe²⁺, Fe³⁺, SO₄<sup arrange="stagger">2– and H⁺. These by-products are leached and carried by groundwater to rivers as acid mine drainage (AMD). In surface mines, the AMD is carried by the lateral flow in saturated soil. In deep mines, the AMD is leached down to the tunnel for exit through a portal. Due to low pH, the AMD also dissolves other weathering by-products (Al³⁺, Zn²⁺, and Mn²⁺). Upon entry to surface water, insoluable metals can precipitate as hydroxides. For TMDL determination, the designated use is for aquatic life. To protect this use, the State of West Virginia has specified the water quality criteria for pH, Fe, Al, Zn, and Mn. To calculate the TMDL, WARMF steps down the loading of individual constituents in AMD until the water quality criterion is met.