This Mining Series webinar presents two case studies that highlight the treatment potential for mercury methylation at mining sites. Methyl mercury (MeHg) is a toxic and bioavailable form of mercury. The first case study will document results of a treatability study conducted at the Formosa Mine Superfund site to assess the influence of sulfate-reducing bacteria on the production of MeHg during the treatment of mining-influenced water. The results are being used to inform the design, application, and assessment of sulfate-reducing biochemical reactors. The second looks at the impact of water level fluctuation on sediment in the Cottage Grove Reservoir, located downstream from the former Black Butte mercury mine of the Black Butte Superfund site. Results suggest that exposure of sediments to air while water levels are lowered may replenish the supply of sulfate (and/or other electron acceptors) needed to stimulate microbial production of MeHg mercury when the reservoir level is raised.