After coal is burned in a fossil fuel power plant, the remains are pumped through pipelines into huge ponds. The ponds are used as a landfill to prevent the release of ash into the atmosphere. Ash ponds use gravity to settle out large particulates from power plant wastewater. Often, the ash is mixed with chemicals to support neutralization, that's where the vivid colours come from. Although the use of ash ponds in combination with air pollution controls decreases the amount of airborne pollutants, the structures pose serious health risks for the surrounding environment as chemicals in the ash can leach into groundwater and surface waters.