MEMPHIS, Tenn. — The Tennessee Valley Authority says it is installing 24 more monitoring wells at a coal-fired power plant where high levels of arsenic and lead were found in groundwater.

A TVA statement Thursday said it continues to investigate how the toxins ended up in wells that monitor pollution from coal ash ponds at its Allen Fossil Plant in Memphis.

The shallow monitoring wells are near far deeper wells drilled by the TVA directly into the Memphis Sand aquifer, where Memphis gets its drinking water.

The TVA plans to pump fresh water out of the aquifer to cool a natural gas power plant that’s replacing the coal plant next year.

The TVA said it is temporarily limiting the use of the deeper wells at the gas plant during the investigation.