Manholes are a critical part of every sewer system as they provide necessary ventilation and an access point for cleaning and inspecting sewer lines. The EPA estimates that there are about twenty million manholes in the United States—one manhole for every 400 feet of pavement. Many of these manholes are seriously decayed or in need of immediate rehabilitation or replacement. Manholes generate a disproportionate amount of inflow and infiltration (I&I) and play a unique role in the structural integrity of roadways. From an operational standpoint, inflow and infiltration of groundwater reduces capacity of the collection system as a whole. From a structural standpoint, deterioration and corrosion within a manhole can cause cave-ins (Water World).