Mechanisms of coal ash release and transport into lakes with coal-fired power plants based on sediment records from the Southeastern USA

This study investigates 210Pb- and 137Cs-dated sediment records to connect hydrologic drivers to mechanisms of coal ash release from waste storage ponds into three lakes in North Carolina. Originally constructed to provide cooling water for power plants, these lakes have evolved into recreational resources and drinking water supplies for urban populations. Ash ponds are designed to release excess stormwater to protect the integrity of their earthen dikes, however this process chronically contaminates the lakes with both effluents and ash. Our analysis shows that elevated ash content and trace element concentrations (arsenic and selenium) in sediment cores are associated with both long periods of rainfall and high magnitude rainfall events driven inland by hurricanes. Peak trace element concentrations in Hyco Lake sediments occurred between 1980 and 1994 after the Clean Air Act restricted emissions of fly ash and led to onsite storage in ponds. Core samples show that sorting of this ash by size and type during transport through the lake increased concentrations of As and Se near the dam. Use of ash in structural fill during plant construction contributed ash to Hyco and Mountain Island Lakes. Nonpoint sources of coal ash including agricultural soil amendments and construction materials contaminated upstream cores in Mayo Lake. Although these activities occurred in the past, coal ash is continually eroded and transported into the lakes. Our study shows that coal ash ponds contaminate adjacent waterways. This threat is expected to increase with higher intensity rainfall and flooding, as projected from climate changes in the southeastern U.S.