Adopt Resolution #18-264 Approving West Riverdale Study as Official Planning Document

The purpose of this case is to approve the attached study to be utilized as a continued planning document and continue conversations with area Property Owners to develop an appropriate cost-distribution model for infrastructure needs for future development. Nothing in this document is binding; it simply allows Staff to utilize as a planning tool and have productive conversations with area Property Owners about requested development potential.

Alternative 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.

Alternative 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.

Alternative 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. Additionally, this allows for each developable area to proceed independently. Under the Comprehensive Sewer and Water Plans, development would have required impacts to the existing neighborhood (Alpaca Estates) and negotiating with an adjacent Property Owner potentially unwilling to negotiate for easement.

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.

Staff recommends that the City Council adopt the attached study as an official planning document.

Motion to adopt Resolution #18-264 approving West Riverdale Study as an official planning document.