The owners of the Columbia Energy Center are proposing to spend nineteen million dollars to prevent groundwater contamination as they move to close the coal-fired power plant in the next four years. Alliant Energy, the majority owner, had announced earlier that it would retire the plant’s two units in 2023 and 2024, saying it would be more cost effective than keeping the 45-year-old plant running. But federal regulations require a new coal ash handling system designed to prevent toxic chemicals from leaching into groundwater, so the plant’s owners are asking regulators to approve a temporary solution to comply with the law and keep the plant running until they can replace it with clean energy.