At approximately 11 a.m. on Tuesday, Feb. 20, 2018, the City of Ann Arbor staff observed flow from an overflow pipe between the north and south interceptor chamber at the Wastewater Treatment Plant (49 S. Dixboro Road). This discharge of sanitary sewage occurred for approximately four hours with an estimated 180-300 gallons flowed directly into the Huron River.
Within 20 minutes of locating the leak, plant staff immediately went to work to stop the flow. This was accomplished at 3:05pm.
The flow within the Huron River for the time over which the discharge occurred was approximately 10,472 gallon per second; therefore the estimated sanitary sewage overflow was diluted by a factor of 630,000:1. There are no communities downstream of the plant that withdraw water from the Huron River for drinking purposes. In addition, there are no health risks posed by this overflow to those using the Huron River for recreational purposes, due to the dilution effects.
In accordance with regulatory protocols, the City of Ann Arbor Wastewater Treatment Plant contacted the Michigan Department of Environmental Quality and the Washtenaw County Health Department to inform them of this unfortunate incident.
Plant staff is commended for demonstrating clear thinking and fast action, which prevented this situation from becoming any worse. Additionally, actions to avoid similar circumstances are being evaluated by plant staff.