Mont. Code Ann. § 75-10-712

If the department determines that immediate response to an imminent threat to public health, safety, or welfare or the environment is necessary to avoid substantial injury or damage to persons, property, or resources, remedial action may be taken pursuant to 75-10-711 (1) without the prior written notice required by 75-10-711 (3). The department shall give subsequent written notice to a person who is liable or potentially liable under 75-10-715 (1) within 30 days after the action is taken, describing the circumstances that required the action to be taken without prior notice.