September 21, 2016 - On the morning of Monday, Sept. 19, a discharge of untreated sewage was discovered on a section of the Geddes Avenue project (http://www.a2gov.org/news/pages/article.aspx?i=308). Raw sewage from a broken and then clogged sewer pipe sent sewage into the excavation for a retaining wall. Since Monday, the city has determined that the actions of a motorist who broke through numerous barriers may have contributed to the sewer line break. The city is investigating information provided by a resident of the area who reportedly observed the incident.
On Monday morning, the construction contractor arrived on site and turned on the 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. Later investigation revealed that sewage had overflowed the excavation into the 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, 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.
The city is often asked why these discharges aren't detectable outside of sight or odor. The wastewater treatment plant is not able to detect such flows because they make up such a very small part of the overall flow into the plant. In addition, significant rainfall can make flows into the plant fluctuate.
In response to the event, city staff acted as quickly as possible with the information available and met all regulatory reporting requirements. After a review of events, the city has identified improvements to be implemented, both at construction sites and in communications practices, should future sanitary sewer overflow events occur. These improvements are to include enhanced internal training regarding construction site release protocols as well as expanded notifications. Additional notifications are not required by MDEQ and may lack the detail available in later releases, but in doing so, the city would aim to give the community peace of mind that everything possible is being done to keep the public informed.
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