In 2022, BCUA conducted investigations to determine the condition of the Primary Settling Tanks (PSTs) for all four batteries A, B, C, and D. The investigations, conclusions, and recommendations were published in an engineering report titled “Primary Settling Tank Rehabilitation and Upgrade Facilities Assessment and Planning Report’ dated December 19, 2022 (Exhibit A). The report identifies a number of upgrade projects necessary to improve treatment performance and resolve maintenance issues. The investigations concluded that the Battery A PSTs (PSTs 1 through 4) as well as a portion of Pipe Gallery A-2 (PG A-2) have undergone significant settlement which impacted the performance of the PST Battery. Settlement was attributed to the construction of PG A-2 which increased the loading on the western Battery A wall (PST-4 west wall) without the installation of additional foundation wall support as well as the degradation of the existing timber piles which support the Battery. Previous modifications to the tanks, including the installation of helical piles in the southwestern portion of PST-4 in 2009, were constructed in an attempt to limit the settlement of the tanks and pipe gallery, however, settlement continued to increase. A complete demolition and reconstruction of Battery A was considered, however, removing the entirety of Battery A from service for a significant period of time would greatly reduce the hydraulic capacity of the treatment facility and was not considered feasible. As such, a phased rehabilitation of the existing battery was chosen as the desired solution.
