ANN ARBOR (WWJ) – Officials say updated test show there’s no threat to human health following a raw sewage overflow in Ann Arbor.
The overflow was discovered Monday in a construction area near the entrance to Gallup Park.
Raw sewage from a broken and then clogged sewer pipe sent sewage into the excavation for a retaining wall, authorities said. On Monday morning, the construction contractor arrived on site and turned on pumps that normally keep the pit free of groundwater. In this case, however, doing so also unknowingly moved sewage from the excavation into the Huron River. Once the city inspector realized what was going on, the pumps were shut down.
The city does not know the exact amount of sewage that was released, though estimates that it was no more than 600,000 gallons.
The small area of land where the sewage overflow ran into the river was treated with lime to inactivate the organic material, and city staff quickly alerted the Michigan Department of Environmental Quality and city parks and recreation, which, in turn, suspended Geddes Pond stillwater paddles and the Argo-Gallup canoe trips.
The Huron River was flowing at approximately 170 cubic feet per second on Sept. 20, equivalent to 110 million gallons per day. Therefore, officials say a 600,000 gallon discharge over 36 hours would constitute less than half a percent of the flow of the river. City staff and the Washtenaw County Health Department continue to monitor the river for bacteria; tests have, so far, indicated no threat to human health.
At no time was this overflow event a threat to the city’s drinking water, as there are no communities downstream of the plant that withdraws water from the Huron River for drinking purposes. The city intends to resume all recreation on the river as of 10 a.m. Thursday, Sept. 22.
City officials say an investigation revealed that the actions of a motorist who broke through numerous barriers may have contributed to the sewer line break. Authorities are following up on information provided by a resident who reportedly observed the incident.
In response to the event, the city has identified improvements to be implemented, both at construction sites and in communications practices, should future sanitary sewer overflow events occur.