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existing and short-term development conditions, it is recommended not to upsize this lift station right away and to monitorthe peak hourly flows as development increases. Consideration to increasing the lift station's pumping capacity by installing larger pumps should be given if the peak hourly flows reach approximately 200 gpm. The existing 6-inch HPDE forcemain can safely flow up to 360 gpm. Consequently, submersible pumps with individual pumping capacities of up to 360 gpm could be installed at the Windsor Lift Station in the future without having to upsize the lift station's wet well, internal piping, or forcemain. As shown in Table 4.5, the peak hourly flow for the entire northwest area under the 2040 development timeframe is projected to be 1,498,434 gpd (or 1,041 gpm). Given that the entire area will require a regional lift station in the future, the actual peak hourly flow leaving the northwest areas will equal the regional lift station's firm pumping capacity (proposed to be 1,500 gpm). The way the City's sanitary sewer system is currently operated, wastewater flow generated in the existing northwest developments is pumped by the Jackson Lift Station and by the Evans Lift Station before arriving at the wastewater treatment plant. The Jackson and Evans Lift Stations have firm pumping capacities of 700 gpm and 2,300 gpm, respectively. Additionally, unlike with the TH 169 Lift Station, neither Jackson nor the Evans Lift Stations have space available to install additional pumps. Given that both the Jackson and the Evans Lift Stations do not have space for additional pumps, increasing their capacity to serve the northwest areas long term would require a significant capital expense. Larger pumps could be installed (similar to the Windsor Lift Station). However, this would only be a temporary solution as there isn't space available to install additional pumps. Therefore, it is recommended that the proposed northwest Regional Lift Station pumps directly to the City's VWVfP. Given the City's estimate of the current wastewater flow treated at the plant, it appears that the existing treatment plant will have sufficient residual capacity to treat the wastewater flow generated in the northwest areas alone. However, flows will need to be closely monitored at the wastewater plant as both study areas (northeast and northwest) approach the 2040 development projections, precisely given that the plant's existing headworks infrastructure is not sized for a wastewater flow of 4.5 MGD. 4.7 Recommended Sanitary Sewer Infrastructure for the Northwest Areas The recommended sanitary sewer collection system layout to serve the northwest study areas is shown in Figure A21 in Appendix A. The sanitary sewer layout for the northwest areas was preliminary designed following the same criteria of the northeast areas — see Section 4.5. A summary of the recommended sanitary sewer infrastructure is listed below: Trunk Sewermain (gravity flow): It is recommended to install trunk sewermains ranging from 10- inch to 12-inch diameters along 205Th Avenue NW up until the intersection with Proctor Road NW as shown in Figure A21. Eight-inch sewermains can be extended beyond the trunk mains to serve the remaining portions of the study area. Lift Stations (pressurized flow): At least three (3) lift stations will be needed to serve the study area. Additional smaller lift stations or small low pressure systems may be needed to serve minor portions of the study area as indicated in Figure A21. A summary of the recommended lift stations is shown in Table 4.10. Each lift station's wet well depth is the minimum recommended depth to serve the lift station's service areas identified in Figure A21. Deeper wet wells can be installed if a more conservative design is desired. Future developments located west of the proposal Regional Lift Station can be served by the existing Windsor Lift Station and 6-inch forcemain. These areas are highlighted in Figure A21 as Wndsor's LS proposed sewershed. Because the Windsor Lift Station can serve the majority of the northwest study areas, the northwest Regional Lift Station will not be needed until the mining areas begin developing. Feasibility Report Northeast & Northwest Urban Service Area Expansion Study City of Elk River, MN WSB Project No. 020010-000 Page 20