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Plan of Study for City of North Olmsted Phase I by Floyd Browne Group January 4, 2006 soils and shallow rock elevations, the ground water table must be somewhat high and contributing inflow through foundation drains on a daily basis. The pump station is being evaluated in a separate section within this report. The Clague Road trunk and service area experienced only a few isolated problems during the August 20th storm. However, the Walter Road trunk experienced multiple problems and by-pass pumping was required in five (5) locations within the system. From a review of the by-pass pumping records for the last seven years, only 1-2 storm events each year required by-pass pumping (normally at two locations) to protect the residents from basement flooding and in two of those years, no pumping was required. The sewer maintenance crews have elevations marked in the manholes indicating the level of the lowest basements. Until the August 20tH storm, no one in this area has experienced basement flooding for almost eight (8) years due to a wet weather sanitary sewer surcharge. From testing performed on the by-passed flow, the results indicate a large volume of clean water mixed with dilute sanitary sewage. From discussions with the sewer maintenance staff, the storm sewers are usually not flowing full which indicates that much of the storm water is not reaching its proper destination. This issue is discussed further in the section on Storm Water. Over the past twenty (20) years, the City of North Olmsted has made many improvements to its sanitary sewer system that is within the public right-of-way such as joint sealing, pipe replacement, manhole rehabilitation, and equalization of peak wet weather flows. Manholes in low-lying areas that may be subject to flooding have been protected from inflow using a plastic manhole insert. In addition, many sanitary laterals have been inspected, grouted to repair leaks, or replaced. The mainline sanitary sewer system appears in good condition with one (1) exception. After discussion with the sewer maintenance staff and a review of the internal televising log (see Appendix E) performed in 1990 by United Survey (Reel #60J), it appears that there is a severe belly or sag in the Walter Road trunk sewer from Manhole 1-8201 at the intersection of Walter and Marie/Deerfield to Manhole 1-8102 at the intersection of Walter and Beech. The sag occurs in numerous spots in the 12-15-inch trunk with 4-10-inches of standing water. This sag can cause a significant reduction in capacity and will be analyzed in the next paragraph. It is important to note that this deficiency occurs just downstream of the three most utilized manholes for by-pass pumping. Further investigation is needed on the 18-inch trunk sewer on Beech and LeBern as well as the 12-inch trunk upstream of these manholes. The ninety-degree turns in the four-foot diameter manholes may also be causing some hydraulic losses during high flows that would decrease capacity in this line. In analyzing the capacity of this system, it is important to note that most of the pipe is laid at minimum grades with a few exceptions. If the grade is steeper, then more flow capacity is available, but if it is a flatter slope or there are bellies or sags in the line, then flow capacity is decreased. The 12-inch trunk sewer on Clague Road can convey approximately 1.0 MGD when flowing full. This trunk sewer has approximately 900 residential equivalent units (REUs) connected to it or an ADF of 0.36 MGD and a peak daily flow (PDF) of 0.9 MGD. The 18-inch trunk sewer on LeBern can convey approximately 2.25 MGD when flowing full. This trunk sewer has approximately 1,300 REUs connected to it or an ADF of 0.52 MGD and a PDF of 1.3 MGD. Under surcharged conditions, the system can convey more flow as experienced at the LeBern Pump Station where flows peak at 3.8 MGD. In the Walter Road trunk sewer, the 15-inch line should be able to convey approximately 1.7 MGD, but the sags in the line could reduce this capacity to 0.6-0.9 MGD which is about 50%. This restriction has a big effect on draining the upstream areas. 12