As part of Nashville’s Central Water Reclamation Facility (WRF) Upgrade project, a ‘green-field’ Headworks Facility was put online as part of their overall plant process in November 2023. This Headworks Facility houses 86 different pieces of major equipment and is a fully automated facility. The 440 MGD Headworks Facility operates as the front line of defense for the entire WRF and consists of both coarse and fine screen systems, as well as a grit removal system. Overall the facility took four years to build with roughly 275,000 manhours over the course of the job. This presentation will detail the facets of the collaborative performance testing procedure that took over two years to develop and work through. The initial phase of testing began with individual equipment checkout, then moved to a dry system check where all automation between equipment was tested prior to introducing flow to the facility. The final phase was to introduce combined sewer flow to the building in order to demonstrate that the complete system would work with live flow. As the Headworks was now connected to a fully operational water reclamation facility, the team committed to responding 24/7 for the duration of the 28 day performance test knowing that any event or failure that wasn’t quickly addressed could cause an overflow in downtown Nashville. Wet weather events during the performance testing raised the intensity to a new level but the presentation will share how the Headworks team rose to the challenge. The CMAR and Engineering team dedicated extensive time to documenting and troubleshooting alarms, issues, and trends for both equipment and system failures. This process allowed the team to identify patterns of failures and ultimately resolve each event. The primary lessons to be taken away for future projects are strong project communication, the importance of a dry system check, and event tracking during testing to identify problems over time. Also, at the core of every project, a strong project team has to be able to communicate effectively at every level because even when equipment and instruments have been checked, wastewater finds a way of creating new issues. The collaborative efforts of the Owner, CMAR team, and Engineer allowed this project to overcome all challenges (even a tornado) and successfully commission the largest Headworks in the state of Tennessee. This presentation will share experiences and lessons learned from the Owner, CMAR team, and Engineer to equip attendees with tools for successful startup and commissioning of treatment facilities.