Merricks said a report issued last week by the state's Uranium Working Group provided the framework for regulations that would need to be in place for the mining to occur, but he said it didn't address all his concerns.
"I'm convinced in my mind that even if you had the best management practices, it doesn't eliminate the risks involved with the mining and the milling," Merricks said.
Milling involves the separation of rock and uranium. Waste rock laced with uranium, called tailings, ultimately must be stored for generations.
Virginia Uranium has pledged to store the waste in secure below-ground containment units to minimize risk.
Locke, an environmental health scientist, has not publicly stated his position on uranium mining, and he didn't budge Thursday. His NAS committee issued a report on uranium mining one year ago that said Virginia faced a tall task before it could regulate mining and milling. The report did not offer a recommendation on the ban.
He agreed that even the most robust regulatory oversight does not ensure that uranium mining would be risk-free.
"It's a very, very, very formidable task," Locke said. "It will require a lot of analysis. We can't give anybody a bullet-proof guarantee."
Locke also said establishing the appropriate controls for mining would require a high level of expertise and resources.
Full-scale uranium mining has never occurred east of the Mississippi River.
Wales said Virginia Uranium welcomed the most stringent regulatory controls. The Pittsylvania County uranium deposit is on property owned by the Coles family, who date back generations and continue to live there.
"We drink the water. Our children play in these fields," Wales said. "We have the highest stakes as well ensuring that this is done in an environmentally friendly way."
Steve Szkotak can be reached on Twitter at https://twitter.com/sszkotakap.