The state Oil and Gas Conservation Commission approved Monday new groundwater protection rules that it said were among the strongest in the nation, though both industry and environmental interests said they were unhappy with the regulations.

The new rules require that operators sample nearby water wells before and after drilling activities to ensure that oil and natural-gas development does not harm water supplies and to identify potential problems.

"This new set of groundwater monitoring rules once again puts Colorado in the forefront of thoughtful and progressive regulatory oversight of energy development," commission Director Matt Lepore said in a statement. "We worked earnestly with many stakeholders to develop a groundwater rule that provides strong protections and that we believe strikes the right balance among many interested parties."

Only two other states have mandatory groundwater programs in place, according to the commission. No other state requires operators to collect water samples after drilling.

Colorado's rules will require sampling as many as four water wells within one-half mile of a new oil and gas well before drilling. Two more samples of each well must be taken between six and