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,~, Plan of Study for City of North Olmsted Phase I by Floyd Browne Group January 4, 2006 b. There is evidence from interviews with the residents that the local storm drainage infrastructure has been damaged or removed by other homeowners' property improvements. This makes local drainage difficult or impossible. LeBern and Dover Sanitary Pump Station Evaluation Floyd Browne Group also performed a general evaluation to determine the reasons for low pump output at certain wet well levels with three (3) pumps in service for both the LeBern and Dover sanitary pump stations. The study centered around the LeBern pump station due to the fact that both pump stations are constructed identically and that the LeBern station was slightly more critical to reduce flooding. Any solution found at the LeBern station should be equally adaptable for the Dover pump station. The evaluation consisted of an assembly of the pump station history and past performance, an examination of the "as-built" plans for the pump station and associated force main, calculation of the system curve pump curve performance with three pumps in service, and adraw-down test to determine actual performance. LeBern Pump Station History The LeBern pump station consists of three (3) flooded suction pumps rated at an average of 2.6 MGD at 24 psi per pump. The force main is approximately 4,900 feet long and discharges into a manhole on Lorain Road at a static height of approximately 31.0 feet above the pump off level in the LeBern wet well. The station typically operates at a static wet well level of 7.0 feet using one pump and a variable frequency drive. The normal pumping rate of a single pump at 100% speed is approximately 3.0 MGD. When a storm travels through the area and the precipitation is enough to increase the influent flow to the pump station a second pump comes on line to assist. Two (2) pumps working simultaneously can deliver approximately 3.5 MGD to the gravity sewer. In extreme cases a third pump is brought on line and minimal but important flow increases are realized from this pump of about 3.8 MGD. However, when the station's wet well raises to 8.0 feet with three pumps in operation the station pumping rate drops. The low output can be stopped and normal three-pump pumping capacity restored if the permanent by-pass pump (located above the wet well) suction line is placed within the wet well during the event and water is recirculated within the wet well. Both the LeBern and Dover stations are well cared for and maintained and no other problems have been experienced except in that rare condition of three (3) pumps in service and an 8-foot wet well depth. Plan Evaluation The LeBern pump station was designed and built to operate with two (2) pumps in operation. The third pump was designed only for failover and alternation purposes and never intended to become part of the emergency operation of the station. Nothing out of the ordinary was observed with the pump station drawings. The drawings followed good design dimensions in the spacing of the flooded suction intake lines within the wet well as is outlined in the US Army Corps of Engineer's design guide. The recommended submergence is more than sufficient but the flow ratio exceeds 0.4 and is calculated to be 0.82 at 3.0 MGD. This indicates that the pump bell diameter is too small. The optimum bell diameter for this flow would be 1.33 feet or greater. 23