WINONA, Minn. - Police arrested 35 people for trespassing Monday during a protest of frac sand mining in Winona.

More than 100 people split into two groups and gathered at the city's commercial dock, where frack sand is shipped out on barges, and at a sand processing plant on the city's west end.

Officers asked protesters several times to leave both sites, then began arresting them, the Winona Daily News (http://bit.ly/14IqP0C) reported. Police arrested 19 people at the dock and 16 people at the plant, according to the Winona Police Department. All were arrested without incident.

Winona Catholic Workers organized the protest. Protesters say their goal was to halt business operations at each site.

"I think people see that the issue of silica sand is something affecting the entire region," protester Molly Greening said. "They've come to stand in solidarity with this issue."

Opponents of frack sand mining have raised environmental concerns.

The energy industry uses the sand in fracking, a technique used to extract oil and gas from rock. Fracking uses high-pressure mixtures of water, sand or gravel and chemicals.

Dan Nisbit, owner of CD Corp., which leases the commercial dock, says the protest created a distraction for workers and temporarily slowed operations at the facility. Daily activities at the dock were interrupted for close to two hours, Nisbit said.

"Obstructing business isn't the right way to go about things," Nisbit said.

Monday's protest was part of an annual celebration of the regional Catholic Worker community. Volunteers from Iowa, Missouri, Wisconsin, Michigan and other states in the Midwest traveled to Winona to participate.

"As Catholic Workers living with the poor and marginalize, we come to this land to prevent the desecration of this land and the health of this community," they wrote in a statement Sunday evening. "We declare Monday to be a moratorium of business as usual at the sites of production of silica sand to eliminate a necessary component of fracking."

Catholic Workers and others in the Winona area have protested the industry for more than a year. They have blocked a rail loading terminal, demonstrated at the steps of the Winona City Hall prior to a City Council meeting on frack sand regulations, and held other rallies.

During one rally at City Hall in May 2012, a protester was cited for littering after he threw a handful of frack sand on the front steps.

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Information from: Winona Daily News, http://www.winonadailynews.com