Mont. Code Ann. § 75-10-416

The department may issue a cleanup order to any person who has discharged, deposited, or spilled any used oil or hazardous waste into or onto any land or water in an unlawful or unapproved manner or who has discharged, deposited, or spilled any material or substance into or onto any land or water so as to result in unlawful or unapproved disposal of used oil or hazardous waste. The order must direct the person to clean up and remove the used oil or hazardous waste, to treat the used oil or hazardous waste so as to render it nonhazardous, or to take other actions as may be considered reasonable by the department.