During extremely high inflows to the Fountain Valley Treatment Plant subsequent to a January storm, a situation developed where the five 100 mgd booster pumps began vibrating significantly. Vibrations were so severe that the acceleration sensors on some of the pumps forced them to shut down. Flow Science determined that the cause of the problem was that the pumps had insufficient NPSH available when operating high on the pump curve (they also could experience the same problem when operating low on the curve). The operation of multiple pumps within the pump station therefore required careful adjustment to the flow rate and the number of pumps in operation. Flow Science recommended a revised training program for operators to address this potential problem in pump station operation.