North Dakota regulators say some oil companies may have ignored their warnings to protect oil waste pits from spring flooding and failed to take action that could have prevented 32 spills in recent weeks.
Glenn Wollan, a field supervisor with the North Dakota Oil and Gas Division, says waste ponds in five counties were swamped by meltwater from one of the state's snowiest winters on record.
Runoff from the waste pits can contain oil, diesel, drilling muds and chemicals. State health officials say the spilled waste has not threatened drinking water sources but have reached a lake.
The state oil and gas agency warned companies in a March 11 letter to take precautions to prevent overflow at the pits. Wollan says some companies may not have done enough.