http://www.ohm-advisors.com. An American Council of Engineering Companies National Finalist project, this presentation features a breakthrough new hydrologic model for sanitary collection systems. The i3D model more accurately accounts for the antecedent moisture that enters a sewer system through inflow and infiltration. The outcome? Using i3D, engineers can determine the right system size, without overbuilding or risking unhealthy SSOs and CSOs.