A Midwest environmental group has followed through on its promise to formally challenge Peabody Energy's ability to guarantee it has enough money for future cleanup of its Illinois and Indiana coal mines. The Environmental Law and Policy Center asking regulators to stop allowing the St. Louis-based company to use the process known as self-bonding instead of posting conventional bonds for mine remediation. Peabody has pledged that it has adequate assets to pay for the estimated $92 million needed to reclaim three southern Illinois mines once there's no coal left to extract, or if the company shuts down. Its Indiana mine remediation costs are estimated at $163 million. Another environmental group last week formally challenged Peabody's self-bonding in Wyoming and other Rocky Mountain states.