Bagley Wastewater Ponds
The addition of a fourth cell to the city’s existing three-cell pond created the capacity to store 210 days of wastewater at an average flow of 263,000 gallons per day. A network of subsurface drainage pipes keeps the groundwater at least four feet below the pond bottom, in accordance with Minnesota Pollution Control Agency (MPCA) requirements, and a PVC liner prevents seepage through the pond bottom.
To address water quality problems in Clearwater Lake, the MPCA established a 1.0 milligram per liter phosphorus discharge limit for the system. Committed to being a good neighbor to its downstream residents, the City worked with WSN to explore spray irrigation disposal of the treated wastewater on farmland to the east of the pond system. After a year of studies, soil borings, and groundwater measurements, the MPCA determined this was not feasible due to soil conditions. The ultimate solution was to add liquid aluminum sulphate (alum) directly to the ponds to chemically remove the phosphorus prior to discharge. A pontoon equipped with a 200-gallon tank navigates the ponds injecting alum in front of the motor propellers, which mix it with the wastewater. The City now has plenty of storage capacity for the next several years and is meeting the discharge limits required in its NPDES Discharge Permit.