5.2. SR 08-08-2011 - Laserfiche WebLink

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data for the years from 2005 through 2010, the WWTF currently receives an annual average daily wastewater flow of 1.23 MGD. The highest annual average daily flow was in 2005 and was 1.419 MGD. The estimate average daily wastewater flows projected from the proposed development area range from 0.135 MGD for Scenario 1 to 0.375 MGD for Scenario 3. The estimated peak hour wastewater flows from the proposed development area range from 0.526 MGD for Scenario 1 to 1.351 MGD for Scenario 3. The existing eastern area wastewater collection and the existing WWTF have capacity to provide wastewater service for the proposed development area under all three scenarios. However, under Scenario 3 hour, 85% to over 90% of the capacity of sections of the existing trunk sewer system along Twin Lakes Road from 179th Avenue NW to 171St Avenue would be utilized during estimated peak hour flow conditions. Also under Scenario 3, approximately 97% of the current pumping capacity of the TH 169 Lift Station would be utilized during estimated peak hour flow conditions. To address the needed infrastructure to accommodate the sewer system, wastewater from the west side of TH 10 would be conveyed north through a new sanitary sewer line to the existing 15-inch sewer that crosses TH 10 just north of 170th Avenue. Under Scenarios 1 and 2 a 10-inch diameter gravity sewer line would have sufficient capacity to carry the projected peak hour wastewater flows from the portion of the study area west of TH 10, plus potential flow from future development south of the study area. Under Scenario 3 a 15-inch gravity sewer line would be required. For Scenario 1 a 10-inch diameter sewer would be recommended to serve the area along the west side of TH 10. For Scenarios 2 and 3 a 15-inch gravity sewer line would be needed to carry the projected flows west of TH 10 to allow for potential future development south of the study area. Wastewater from the east side of the study area between TH 10 and the Burlington Northern Railroad could be conveyed north and connected to the existing 15-inch sewer just south of 171St Avenue that extends north to 173rd Avenue. For all three scenarios, a 10- inch gravity sewer would be large enough to convey the estimated peak hour flow from the portion of the study area between TH 10 and the Burlington Northern Railroad. However, because the current urban service area boundaries extend beyond the limits of the study area, a 12-inch sanitary sewer is recommended to provide additional capacity for future development. Storm Water Management (Item 17) Approximately 15 acres of the study area is within subwatershed ER02 and drains to the Rum River. The remaining area is within subwatershed ER01 which drains to the Mississippi River. The portions of the Mississippi River and the Rum River which are downstream of these subwatersheds are classified as Outstanding Resource Value Waters (ORVW). Both rivers are listed as impaired by the Minnesota Pollution Control Agency for mercury (Mississippi and Rum Rivers) and PCB's in fish tissue (Mississippi River). Scenario 1 represents the development conditions with the least amount of impervious surfaces. Much of the agricultural and open space land uses are preserved under this scenario with the majority of the remaining area being developed to 75% impervious. City of Elk River Draft Alternative Urban Areawide Review July 2011 Page 6 of 84