In 2008, the Metropolitan Council Environmental Services (MCES) in Saint Paul, Minnesota must meet new requirements for effluent phosphorus discharges at two large wastewater treatment facilities. To meet these standards at current flows, MCES staff searched out a cost effective solution and retrofitted both plants with air mixed selectors. However, it was unclear how the air mixed selector configurations would perform under increased future loadings. By conducting systematic stress testing of future flow and loading conditions, it was demonstrated that the air mixed selector configuration with minor modifications would provide reliable phosphorus removal eliminating the need for a mechanically mixed selector configuration. Implementing the air mixed selector configuration will save MCES $1.5 million in capital expenditures and reduce annual operating costs by roughly $60,000 per year.