the Montana Supreme Court, answering a certified question from a federal district court, concluded that migrating groundwater contamination fell within the “continuing tort exception,” thus tolling the statute of limitations on the theory that each migration of contamination onto the plaintiffs’ properties constitutes a new tort. Hence, the tortious conduct does not cease merely because the defendant has ceased the activity that created the contamination or because the contamination has stabilized in terms of concentrations beneath a plaintiff’s property. The court noted that the nuisance would be considered temporary and ongoing – and thus not subject to the statute of limitations – so long as it is “reasonably abatable.” Conversely, if the contamination was not reasonably abatable, then the harm would be complete and the nuisance permanent. A permanent nuisance would be subject to the statute of limitations. However, Montana follows the discovery rule, and the court stated in dicta that “a plaintiff would be required to bring an action within the limitations period when the plaintiff knows, or reasonably should know, of a permanent injury.” Hence, mere knowledge of the existence of contamination may be insufficient to trigger the running of the limitations period, instead requiring actual or constructive knowledge that the contamination is not reasonably abatable. The court determined that whether contamination is reasonably abatable is generally a question of fact for the jury. Thus, a defendant litigating a contamination case in Montana is likely to have to proceed through trial in order to establish its statute of limitations defense. The court also concluded that contaminated property may be reasonably abatable even in cases where total decontamination and restoration of the property to its pre-contamination state is not possible. Mitigation that reduces property damage could qualify as reasonable abatement. The court purported to adopt the standard set forth in the Restatement (Second) of Torts § 839 to determine whether a reduction or decrease in the contamination would be reasonable. It stated that the trier of fact should consider the ease with which a tort feasor could abate the harm, and additional factors, such as: (1) the cost of the abatement; (2) the type of property affected; (3) the severity of the contamination; and (4) the length of time necessary to remediate the pollution.