The Tennessee Valley Authority is expected to conclude a trial in which environmental groups accuse the utility's power plant outside Nashville, Tennessee, of illegally polluting the Cumberland River with coal ash.
TVA attorneys will likely finish their defense and end the trial Thursday in Nashville federal court.
Tennessee Clean Water Network and Tennessee Scenic Rivers Association claim ash ponds from TVA's Gallatin coal-fired power plant are seeping pollution into the Cumberland River, violating the Clean Water Act and permits.
TVA, a federal utility serving seven southeastern states, says it has followed permits and the law, and environmental groups haven't proven otherwise.
The utility says decades of data show no effect on drinking water sources.
On Wednesday, Judge Waverly Crenshaw told the environmental groups to cite more specific evidence in later filings.