In 2007, engineers realized the stadium's concrete base was buckling due to the rusting of structural steel supporting the foundation. Stadium designers and constructors had failed to account for a need to waterproof the structure when it was built, assuming a stadium in the desert would not need hydrophobic concrete. However, they did not take into account that the cleaning/maintenance crews for ASU (and later, the Cardinals) would use pressure washers, along with chemicals, to clean the seats and rows of the stadium after every game and event. The 1958 designers had also not foreseen the stadium, thought to be only used for a number of Saturdays and limited college events per year in what was then a small market, would be the home of an NFL team and the site of a major college bowl game and multiple concerts by the early 90s as Metro Phoenix's growth exploded. This introduced substantially more water to the stadium than the designers had ever envisioned. Engineers estimated $45 million in repairs would be needed to maintain the stadium beyond 2010.