NASHVILLE, TN (AP) _ A new report by an environmental group says the Tennessee Valley Authority has polluted groundwater supplies at all its coal-fired power plants nearly five years after a massive coal ash spill at its Kingston power plant.

The report by the Washington-based Environmental Integrity Project says TVA could be doing more to protect drinking water supplies from harmful substances. The ash is a byproduct of burning coal at power plants, and the EPA is currently considering whether to classify it as a hazardous material.

The group's report was based on data from TVA monitoring wells, the Tennessean reports. It identifies toxic pollutants including arsenic, boron and sulfate.

TVA said in a statement it was moving aggressively to prevent future damage to water supplies from coal ash.