Conducting a “repair, replace, or abandon” evaluation on the rotating biological contactor (RBC) process at this small treatment plant in the Sierras. When the shaft of the existing RBC unit broke for the second time, the Association requested an evaluation of whether it should be repaired or whether some other treatment technology should be selected. Careful attention was given to the limitations of the steeply sloping site, large differences between winter and summer flows, and severe icing problems in winter.