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~' '1v1s. Debra M. Bloom, P.E. February 12,2001 Page 2 Proposed Conditions Based on information provided by City staff, the peak flow to the station was estimated for full development conditions within the service area. This included flows from existing development and future flows from the following sources: 1. Courtyard by Maniott Hotel (currently under construction) 2. Veritas Building 1 (currently under construction) 3. Proposed 6000 sJ. Restaurant (undeveloped site) 4. Veritas Building 2 (proposed) 5. Veritas Building 3 (proposed) 6. Redevelopment of approximately 5.5 acres of land located east of Cleveland Avenue into medium density residential (identified in Comprehensive Plan) The future peak flow to the station at full development was estimated to be 400 gpm (see Exhibit A for calculations and assumptions). This exceeds the rated pump capacity of 300 gpm. Recommendations 1. Prior to full development of the service area, the existing pump impellers should be replaced with larger impellers. The lift station was originally designed to accommodate a future pumping condition of 400 gpm at 63 feet of total dynamic head. Spare impellers meeting the future pumping condition were furnished to the City when the station was constructed in 1986. Currently, these spare impellers are stored at the City's maintenance facility. The existing 15 H.P. motors will be adequate for the larger impellers. 2. When the impellers are replaced, it is recommended that the City contact an authorized Fairbanks Morse pump representative. The pump curve calls for a trimmed impeller to be used for the future pumping conditions. It is not known if the spare impellers that were furnished in 1986 have been trimmed, or if they are untrimmed. The authorized representative could make this determination and install them. Also, the pumps and motors could be inspected and serviced at the same time that the impellers are replaced. 3. Test pumping should be conducted after the new impellers are installed. The float settings may need to be modified to keep pump run times and pump start frequencies within acceptable ranges. Also, the head loss of pumping through a force mains tends to increase with the age of the force main, and this can decrease the pumping capacity of the pumps. This 6" force main is nearly 40 years old, and it is possible that the higher head loss could cause the pumps to pump at a rate that is less than 400 gpm. (The force main sustained a break during 2000, and this could be an indication that the force main needs to be replaced in the future.) Test pumping after the impellers are installed will confirm actual pumping rates. If the force main is producing higher than expected head losses, the installation of even larger impellers could bring the pumping rate closer to 400 gpm. Larger impellers are currently available for the pumps. The pump representative could assist the City with test pumping, impeller evaluation, impeller installation, float settings, etc. 4. The flow rates at the station should continue to be monitored by the City after the service area is fully developed and the impellers have been replaced. The estimated future peak flow of 400 gpm was based on assumed flow rates, and actual flows may vary. 5. During large rainfall events, it appears that inflow is occuring in the sanitary sewer system. According to City maintenance staff, larger than normal sanitary flows were recorded at the