Gov. Mark Dayton said Tuesday he can't personally block the frac sand industry from expanding in southeastern Minnesota, rebuffing a group of mining opponents who delivered a moratorium petition to St. Paul as part of an Earth Day rally at the Capitol.

Bobby King, policy program organizer for the nonprofit Land Stewardship Project, said a rarely-used statute called the Critical Areas Act allows the governor to engage the state's Environmental Quality Board (EQB), without action by the Legislature, in a process that could lead to a two-year moratorium against frac sand development.

The area they seek to protect is the ecologically sensitive limestone and bluffs region stretching south of Red Wing and inland from the Mississippi River.

But Dayton's spokesman, Matt Swenson, issued a statement saying the governor "lacks the authority to unilaterally impose his own moratorium.'' Swenson said the position was based on the advice of Micah Hines, the governor's legal counsel.

Swenson said Dayton supported a moratorium on frac sand mining in southeastern Minnesota during the 2013 legislative session. The proposal died, but lawmakers passed a bill that gives local jurisdictions authority to declare their own temporary frac sand bans. In addition, any company proposing to mine frac sand near a trout stream in southeastern Minnesota must obtain a special permit from the Department of Natural Resources (DNR), as well as meeting other regulations.

Meanwhile, the EQB, DNR and state Pollution Control Agency are developing air quality standards, land reclamation standards and revisions to the environmental review process for frac sand mining and processing in the state.

King was part of a group of 80 to 90 citizens who rallied at the Capitol, calling on Dayton to issue a moratorium. The group's petition, started in mid-January, carried more than 6,000 signatures and was delivered to the governor's office.

"We want the governor to use all the tools he has,'' King said. "We believe he has the ability to act.''

Tony Kennedy • 612-673-4213