8.3 SR 02-06-2023 - Laserfiche WebLink

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Table 4.2 — Existing Wastewater Flows Parameter TH 169 Lift Evans Lift Windsor Lift Station Station Station Average Daily Flow (gpm) 335 370 11 Peak Hourly Flow (gpm) 700 — 800 800 44 Firm Pumping Capacity (gpm) 1,660 2,300 240 Residual Capacity (gpm) 860 — 960 1,500 196 City staff also reported that the City's wastewater treatment plant treated an average daily flow of 1.35 MGD in 2021. Based on a biological treatment capacity of 4.5 MGD, the wastewater treatment plant has 70- percent biological residual capacity. It is unclear how much capacity is remaining at the headworks portion of the plant. Both the lift stations shown in Table 4.2 and the wastewater treatment plant are adequately sized to convey and treat the existing wastewater flows. 4.3 Wastewater Flow Projections Wastewater flows for the study areas were projected using the unit wastewater flows shown in Table 4.3. These unit wastewater flows were calculated based on city-provided lift station runtime data for the Windsor Lift Station, the proposed land use densities for new developments, and industry-standard wastewater generation rates. Lift station runtime data for the Windsor Lift Station indicated that, on average, residential dwellings in Elk River generate approximately 83 gallons per day (gpd) of wastewater. In order to conservatively estimate average wastewater flows for new residential dwellings in the study areas, a 50- percent safety factor was applied to the Windsor Lift Station data resulting in an average wastewater flow of 124.5 gpd per dwelling. This residential average wastewater flow is still below industry-standard rates. Table 4.3 — Wastewater Generation Assumptions Land Use Type Density Residential Unit Average Unit (units/acre) Flow (gpd/unit) Flow (gpd/acre) Single Family Residential — Northeast Areas 2 124.5 250 Single Family Residential — Windsor LS Homes Varies 83 - Single Family Residential — Northwest Areas 3 124.5 375 Mixed Residential 5 124.5 625 Neighborhood Commercial - - 800 Highway Business - - 800 Public/Semi Public - - 0 Open Space/Parks - - 0 unit — residential dwelung; gpd/acre — Gallons per uay per Hcre The projected wastewater flows calculated for the study areas are summarized in the tables below. Table 4.4 — Projected Wastewater Flow for Northeast Areas Land Use Type Net Developable Average Unit Wastewater Wastewater Acres Flow (gpd/acre) Flow (gpd) Single Family Residential 1,012 250 253,000 Mixed Residential 307 625 191,875 Neighborhood Commercial 9 800 7,200 Total Average Wastewater Flow (gpd) 452,075 Peak Hourly Flow Peaking Factor�'► 3.5 Peak Hourly Flow (gpd) 1,582,263 (1) Source: Metropolitan C;ouncil tnvironmental Services Flow Vanation ractors tor Sewer Uesign. Feasibility Report Northeast & Northwest Urban Service Area Expansion Study City of Elk River, MN WSB Project No. 020010-000 Page 16