The company says the board did not have enough evidence to order it to pump water from the Schwartzwalder Mine shaft and to impose fines for failing to do so, The Denver Post reports. The lawsuit was filed in District Court in Denver.
State inspectors say water contaminated with uranium in the mine is rising and threatening to spill over into Ralston Creek, which flows into a reservoir used by Denver Water, which supplies water to 1.e million people in the region.
"We continue to be very concerned over Cotter's failure to address the serious problems at Schwartzwalder," said Bob Randall, deputy director of Colorado's Department of Natural Resources. "We're monitoring the situation closely to ensure that the public's drinking-water supply is safe."
Cotter has been pumping water from surface ponds but says the water in the shaft is contained and will not seep into groundwater or spill over into the creek.
The state has already ordered Cotter to pay a $55,000 fine and is trying to increase the penalty.