AWWA DSS63724

The Philadelphia Water Department (PWD) employed divers and a remotely operated underwater vehicle to inspect, diagnose, and repair the polyethylene liner of a 150- million gallon water storage basin without draining the basin or removing it from service. Inspection of the basin was triggered when residual chlorine values in the basin effluent samples were unexplainably lower than normal. Using a camera mounted on a remotely operated underwater vehicle inserted through a hatch in the floating cover, it was determined that the polyethylene liner was torn in three critical locations. At the influent end of the reservoir, water was seeping under the bottom liner due to a large tear. At the two effluent locations, water underneath the liner was being drawn into the effluent piping through two additional tears. Divers made repairs quickly with the reservoir still in service to safely and effectively meet system water demands. Includes figures, appendix.