Management’s principal concern is whether pollutant disposal complies with applicable city requirements. An assurance engagement is therefore appropriate because internal audit can objectively evaluate evidence and determine whether the organization’s practices conform to established regulatory criteria. The objective is compliance rather than determining the least costly disposal method. A due diligence engagement is normally associated with evaluating a potential transaction, third party, investment, or other decision before commitment. A performance engagement emphasizing financial regulations would not address the environmental compliance concern described. Internal audit’s assurance role includes evaluating compliance exposures when they could affect organizational objectives, reputation, or legal obligations. Consequently, an assurance engagement assessing whether pollutant disposal practices comply with city regulations directly addresses management’s stated concern and provides an objective basis for determining whether controls are adequate.