09/02/2008 Council Packet - Laserfiche WebLink

Home Search

• • • In most of the City the sewer system consists of PVC gravity sewer lines ranging from 8 inches in diameter to 24 inches in diameter. Lateral sewers serving residential areas are typically 8 inches in diameter, and discharge into 10 inch or larger trunk sewers. The City also currently owns and operates 13 sanitary sewer lift stations which are an integral part of the collection system. The locations are also shown on Figure 7 -1 Existing Sanitary Sewer System Map. Descriptions for each station are provided at the end of this section. Trunk sanitary sewers and lift stations were analyzed to determine available capacity for future development opportunities. Existing wastewater flows were estimated by a combination of pumping records, MCES meter records, and counts of existing residential units. The total capacity of each trunk facility was calculated to determine the available capacity for future growth and development. Where estimated future peak flows exceed capacity, reconstruction or upgrading of the system may be required. For those locations likely to experience flows in excess of capacity within the planning period, future upgrades are addressed in the Capital Improvement Plan summarized on Table 7 -3. A discussion of future needs and capacity restrictions in the various Sewer Districts based on the anticipated growth and development plan for the City is presented in the following paragraphs. The plan for phased construction of proposed facilities is also shown on Figure 7 -5, Future Sanitary Sewer System with Utility Staging Map, and Figure 7 -6, Future Sanitary Sewer System with Sewer District Boundaries. The layout of new trunk sewers is greatly dependent upon the existing topography of the areas to be served and the connection locations to the existing sewer system. Gravity flow sanitary sewers are the lowest cost sewer system in urban regions. This is due to their long useful service life and low cost for operation and maintenance. When a lift station is required, additional capital costs are incurred as well as greater operation and maintenance costs. In almost all communities, some lift stations are required as part of the integral sewer collection system. The goal is to carefully plan the overall sewer system in an effort to reduce the total number required. When a lift station is needed, it is important to identify a maximum service area based upon the surrounding topography. It is also important to minimize the forcemain length in an effort to reduce the annual energy costs to pump the sewage to the discharge location. By placing each trunk and lateral sewer at the recommended minimum pipe slope, the service area for that particular sewer is typically maximized and the number of lift stations required throughout the total system is reduced. A second major consideration is to identify the location and available capacity of each connection point to the existing sewer system. It is typically more economical to stage growth contiguous to the existing sewer system, extending incrementally with each new development. Eventually the existing system reaches the extent of its service capabilities. Before additional growth can be added, major infrastructure improvements are then required to extend the system's service area. Immediately following is a description of the existing system for each district and the improvements necessary to accommodate the forecasted growth. Sewer District 1 Sewer District 1 is located in the southwest corner of the City. A significant portion of District 1 is now developed, and contains currently approximately 2060 sewered single family residential units and 350 un- sewered units. There are about 740 developable acres in District 1 currently designated as low density sewered residential, 82 acres designated as medium density residential, 21 acres designated as mixed use - residential, 12 acres designated mixed use - commercial, and 7 acres designated commercial. The residential areas, including undeveloped lots in the existing subdivisions, are projected to accommodate about 2,150 new residential units. At ultimate build -out, assuming existing non - sewered residential areas ultimately receive sewer service, District 1 could accommodate a total of approximately 4,560 sewered housing units. In addition, the commercial and mixed use areas will support approximately 340 new employees. 7 -11