Resolution - #18-264 - 12/11/2018

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a.Trunk & Lateral Sanitary Sewer Extension Alternate 1 The sanitary sewer improvements associated with Alternate 1 are based on discussions with City staff. The alternative is intended to provide sanitary sewer service to a smaller area of the City at reduced capital costs. While technically feasible, this alternative has relatively high capital costs compared to the area that can be served. This is primarily due to lack of depth achievable in the sanitary sewer main. See Figures 3 and 4 for depictions of Alternate 1. b.Trunk & Lateral Sanitary Sewer Extension Alternate 2 Alternate 2 is based on the City’s Sanitary Sewer Comprehensive Plan. A lift station is proposed at the intersection of 142nd Street and Armstrong Boulevard to a depth needed to service the areas within Sewer District M3. Two options were reviewed, as extra depth will be needed to service to the western City limits with gravity sewer (see Figure 5). The lift station is proposed to discharge to an existing sanitary sewer manhole located at the intersection of Armstrong Boulevard and Riverdale Drive. Construction of a force main from the lift station to the discharge location will be required along Armstrong Boulevard. Trunk sanitary sewer mains and lateral lines are proposed to direct flow to the lift station as shown in Figure 6. The capacity of the 18” sanitary sewer main (downstream of the receiving manhole) was reviewed against the anticipated land use described in the City’s August 2018 Zoning Map, along with flow rates set forth in the Sanitary Sewer Comprehensive Plan. Based on our analysis, adequate capacity exists in the sanitary sewer system to allow for this alternative to be considered feasible. c.Trunk & Lateral Sanitary Sewer Extension Alternate 3 Alternate 3 was developed as a potential modification to the Sanitary Sewer Comprehensive Plan layout. See Figure 7 for the Alternate 3 lift station location. This location is more centralized within in the sewer district, and allows for the same capacity via conventional gravity sewer, but at a shallower depth. For this alternative, a crossing of TH 10 is required to allow for connection to the receiving manhole located at the intersection of Bunker Lake Boulevard and Puma Street. A more detailed analysis of the sanitary sewer system capacity should ultimately be conducted for the area within Sewer District M3. Our analysis of this area assumes 100% developable acreage, and that all land will be fully developed. If this scenario were to occur, with the flow rates detailed in the Sanitary Sewer Comprehensive Plan, the system would be approximately 2% over capacity. Further analysis, using actual developable acreage, would likely reveal the sanitary sewer system’s capacity could accommodate this area. d.Trunk & Lateral Sanitary Sewer Extension Alternate 3 - Interim Because Alternative 3 will most likely be found to be feasible as a long term means of providing sanitary sewer service to District M3, we reviewed a potential interim solution to serve the Riverdale Drive area proposed for immediate development. Alternate 3 Interim improvements are depicted on Figures 8 and 9. The improvements consist of installation of the long term sanitary sewer improvements (for future use) along the Riverdale Drive Extension, extending gravity sanitary sewer mains across Trunk Highway 10, and connecting to the existing system at the intersection of Bunker Lake Boulevard and Puma Street. The crossing of Trunk Highway 10 and the BNSF railroad will require the sanitary sewer main to be placed in casing pipe. Prepared by: Bolton & Menk, Inc. West Riverdale Drive Roadway & Utility Extension – City of RamseyPage | 3