CASPER, Wyo. (AP) — The Wyoming Department of Environmental Quality filed rules recently that would stiffen the state's rules on how coal companies secure the cost of cleaning up any of their mines that close.

The Casper Star-Tribune reports the department unveiled the potential changes to the self-bonding rules recently after an informal proposal that came out last year.

Self-bonding allows companies to promise to clean up their closed mines instead of posting the money up front.

Under the new rules, companies would only be able to apply for self-bonding for mines with more than 10 years of operations left.

No company can self-bond more than 75 percent of its reclamation obligations, and financial liability is tied to the parent company.

The Land Advisory Board will consider the proposed rule changes on March 28.

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Information from: Casper (Wyo.) Star-Tribune, http://www.trib.com