During the construction phase of the Loudon (Tenn.) Utilities Water Treatment Plant (WTP) expansion in January 2025, three interconnected sinkholes developed beneath the newly constructed filter building which was nearing completion. Over the course of the next 12 weeks, the sinkholes were successfully remediated and construction resumed. During this time period, the production of drinking water from the plant was never interrupted. However, additional investigation revealed that the cast-in-place concrete filter basins settled and were out-of-level by as much as two inches. Three of the six newly constructed multi-media filter underdrains and wash troughs were demolished and reinstalled within the design tolerance. All filters and associated piping were retested before successfully being placed in service. The project team responded immediately to the discovery of the sinkholes by engaging the geotechnical engineer to assess and stabilize the site. The contractor quickly implemented the initial remediation by placing 350 cubic yards of flowable fill into the sinkhole cavities to prevent further settling. Within two weeks, a comprehensive cap and compaction grouting plan was developed, and three weeks later a specialty contractor was on site to begin work. The cap and compaction grouting continued for seven weeks, while concurrent hydro-excavation ensured existing, active utilities within the affected area were protected. The structure and the ground surface were continuously monitored for further movement throughout the process. Twelve weeks after the discovery of the sinkhole, remediation was complete and construction resumed, demonstrating effective risk management and project resilience. The cherry-on-top of this situation was that the builder’s risk insurance ultimately covered a significant portion of the costs associated with this event. The keys to success in this difficult situation included: strong and collaborative relationships between all parties, Construction Manager At Risk (CMAR) delivery method with open-book pricing, engaging technical experts at the right time, and robust contractual provisions. This presentation will walk through the timeline of the sinkhole activities from discovery to production of water through the impacted filters and will include lessons learned through this unique process. This presentation is intended to be followed up by the presentation titled “After the Karst-astrophe: Ensuring Process Reliability in Water Treatment Plant Construction”