The landfill beneath Monona Terrace presented both environmental and stability issues. The building is supported by 1,735 steel piles driven through the landfill and the lake to solid ground, some as deep as 85 feet. All existing landfill material removed during excavation had to be trucked to a licensed landfill, and water pumped out of the site had to be filtered first and then discharged into Madison's municipal sanitary sewerage system for treatment. Concern about view preservation meant the building had strict height limitations, which in turn led to structural design challenges. Convention facilities need long, open spaces with no load-bearing columns to interrupt the span of ballrooms and exhibition halls. In the case of Monona Terrace, the problem was compounded by the rooftop gardens, with their engraved concrete roof tiles and planters heavy with soil. The typical solution is deeper, hence taller, trusses to carry the weight, but in this case, taller was not an option, and designers drew the line at lowering ceilings in the ballrooms or exhibition hall. That meant shallower, heavier and more expensive trusses.