8.3 SR 02-06-2023 - Laserfiche WebLink

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EXECUTIVE SUMMARY The City of Elk River retained WSB to complete a serviceability analysis of the proposed Northeast and Northwest Urban Expansion Areas in response to the projected growth. The City authorized WSB to proceed with the study in February 2022. As part of this study, WSB evaluated the infrastructure needed to annex the northeast and northwest study areas to the existing sanitary sewer and water distribution systems. In addition, WSB evaluated the adequacy of the existing systems to serve the study areas as well as prepared a financial analysis forthe recommended improvements. A map illustrating the project locations is shown in Figure A1 in Appendix A. An analysis of the projected development densities and topographies within the study areas indicates that trunk gravity sewermain ranging in diameter from 10-inch to 18-inch will be needed to collect and convey the wastewater generated within the study areas. At least six (6) trunk lift stations with firm design capacities ranging from 185 gpm to 4,000 gpm will also be needed. Water service to the northeast areas can be provided by installing a new 12-inch trunk watermain loop through Twin Lakes Road NW, 209th Avenue NW, Quincy Street NW, Smith Street NW, and Tyler Street NW. The 12-inch watermain loop will ensure that the water pressures and available fire flows will be adequate for the projected growth. The northeast areas can be annexed to the system's main pressure zone without the need of installing pressure regulating infrastructure. Water service to the northwest areas will require pressure regulating stations to maintain the water pressures between 40 and 80 pounds per square inch (psi). A combination of 12-inch and 16-inch trunk watermain will be needed to serve the northwest areas. Water storage, supply, and treatment infrastructure is also recommended for both study areas. The recommended infrastructure layouts for the water distribution and sanitary sewer systems are shown in Figures A9, A13, A19, A21 and A22 in Appendix A. The total estimated infrastructure cost needed to serve the study areas over the next twenty years and beyond is $28,478,000 for the sanitary sewer system and $75,612,000 for the water distribution system. Detailed cost breakdowns are shown in Appendix B. A detailed phasing plan to extend public utilities to the study areas cannot be prepared at this time as the construction schedule of individual developments is unknown. However, a preliminary analysis was completed to identify which infrastructure would need to be constructed prior to any developments to provide utility service. This analysis is shown in Section 6 of this report. Overall, it appears that extending water and sewer services to the expansion areas could be feasible as long as leapfrog development is avoided, the areas are not served simultaneously, and the cost is divided over various funding avenues. Promoting leapfrog development will require a considerable amount of infrastructure to be installed initially which could place the City and the ERMU at financial risk if subsequent development is slower than anticipated. Additionally, it is recommended to extend water and sewer service concurrently as this can reduce capital costs. Feasibility Report Northeast & Northwest Urban Service Area Expansion Study City of Elk River, MN WSB Project No. 020010-000 Page 1