A Navajo-owned company has acquired a coal mine in northwestern New Mexico, and Arizona’s largest utility is buying more of the power the plant produces. 

Arizona Public Service has completed its purchase of a larger stake in a California utility’s shares of two units at the Four Corners Power Plant, which gets its fuel from the mine. BHP Billiton in the meantime, completed the sale of the Navajo Mine, near Farmington, to the Navajo Transitional Energy Company on Monday, and in a related deal, APS finished buying Southern California Edison’s ownership of the newer units 4 and 5. That purchase, for about $182 million, is expected to cost APS customers, nearly $3 a month.

As part of the previously announced plan to bring the plant into compliance with federal clean air standards, APS on Monday closed the coal-fired units 1,2 and 3. Those older units would have cost much more to bring into compliance with EPA regulations.