NASHVILLE, Tenn. (AP) -- A former federal mining regulator contends small leaks years earlier were advance warnings of a coal ash pond collapse that flooded a Tennessee neighborhood.

Jack Spadaro, a retired mining engineer who investigated a 1972 coal waste dam break that killed 125 people in West Virginia, says states have done a poor job monitoring huge ponds of coal ash.

The federal government does not regulate the ponds.

Three homes were destroyed and 42 parcels of land damaged after the Dec. 22 collapse at the Tennessee Valley Authority's Kingston Steam Plant. A billion gallons of sludge poured into the neighborhood.

Meantime, a coalition of environmental groups has notified TVA of a planned lawsuit on behalf of 40 families. The suit will argue that TVA did not fully disclose the extent of spill contamination.

Ash ponds are a mix of water and fly ash, a byproduct of coal-fired power plants.