Based on the City’s master planning model, the flows into the plant would only reach about 60 percent of the expanded plant capacity by late 2027, the proposed date that the supporting improvements would be brought online. Therefore, ensuring that the supplemental improvements are complete by late 2027 minimizes the time and risks of operations under the initial expansion. The City approved this approach, and in early 2022 the initial capacity improvements project, now referred to as Phase 4A, was initiated. The intent of Phase 4A was to modify the plant with minimal improvements to enable the design, permitting, and construction of the treatment capacity expansion by the third quarter of 2025. The Phase 4A upgrade was centered around the implementation of the new EQ basin and the retrofit of the biological treatment process. However, other improvements, such as the expansion of the influent pumping capacity to accommodate the higher flows, were also necessary to support the treatment capacity expansion. The following is a summary of the improvements and permitting included in the Phase 4A capacity expansion project: ➢ Upgraded plant headworks • Junction box, influent pump station expansion, septage receiving ➢ New influent EQ pump station ➢ Converted EQ with new aeration system ➢ Retrofitted biological treatment system ➢ Additional tertiary filtration ➢ Upgraded solids handling building odor control ➢ New sludge dewatering beds ➢ Upgraded effluent pump station ➢ Permitting • APP permit update for 18-mgd treatment capacity • AZPDES permit update for increased effluent discharge
