The Arizona Department of Environmental Quality says that it stands by permits it has issued for a copper mine in Tonto National Forest about an hour east of Phoenix.
The statement comes as conservation groups consider a legal challenge to those permits.
ADEQ monitors stream health under the Clean Water Act, with oversight from the Environmental Protection Agency.
But Roger Featherstone of the Arizona Mining Reform Coalition says it's difficult for the federal agency to monitor every stream, even those with headwaters near mining claims.
The coalition has given it 60 days to look into dissolved copper and lead levels in the Queen Creek watershed. ADEQ said in a written statement that Resolution Copper's discharge permit for the Oak Flat mine "already has strict limits that are over 1,000 times more stringent than the federal drinking water standard for copper." The agency added that because the discharge will likely be used for crop irrigation, it may never enter the streambed.
It also said that the dissolved copper could come from a variety of sources.
EDITOR'S NOTE: This story has been updated to clarify ADEQ's statement about the projected discharge from the Oak Flat mine. A previous version that indicated the discharge will exceed drinking water standards intended to convey that the limits set forth in the discharge permit exceeded federal standards in that they are more stringent.
