Originally Published on mlive-com >
ANN ARBOR, MI — Ann Arbor officials resolved three years ago to launch a $34,000 odor study to further investigate a stinky street.
That was after several years of complaints from residents desperate for a solution to the lingering stench of sewage along Arborview Boulevard, particularly during warm months. “It is a problem for all my neighbors and makes it very unpleasant to walk in the area,” one resident complained to the city in June 2015. “The smell is very strong and noxious and seeps into houses. Neighbors report having been told various explanations but the fact is that it’s unacceptable. Is this problem being worked on? Is anyone paying attention to this?”
After recently completing a major street repair project on Arborview that included new zigzag sidewalks the city plans to undo, some may wonder: What ever came of the odor issue?
It was not a focus of the recent street project, but officials report a special oxygenation system installed a few years ago seems to be effectively controlling odor now.
The city had long suspected the unpleasant smell was coming from hydrogen sulfide venting out of manholes along a sewer line near where a township sewer pipe connects to the city’s sewer system. Scio Township installed the oxygen system to help reduce odor formation and has been collecting odor data to evaluate the system’s effectiveness.
“The odor, as you know, was coming from Scio’s pipe that runs through the neighborhood,” city spokesman Robert Kellar said last week, reporting progress on the issue. “The city of Ann Arbor asked Scio to study the problem and find a solution. This was a few years ago. The system they installed seems to be working — we continue to monitor it and work with them if there is an outage that may cause odors to spike.”
The city had long suspected the unpleasant smell was coming from hydrogen sulfide venting out of manholes along a sewer line near where a township sewer pipe connects to the city’s sewer system. Scio Township installed the oxygen system to help reduce odor formation and has been collecting odor data to evaluate the system’s effectiveness.
“The odor, as you know, was coming from Scio’s pipe that runs through the neighborhood,” city spokesman Robert Kellar said last week, reporting progress on the issue. “The city of Ann Arbor asked Scio to study the problem and find a solution. This was a few years ago. The system they installed seems to be working — we continue to monitor it and work with them if there is an outage that may cause odors to spike.”
When Scio Township’s sewer system along Jackson Road was created in the 1980s, an agreement between the city and the township specified the township would maintain the outlet line until it discharged into a gravity sewer in the city. The township’s pump station at the northeast corner of Zeeb and Jackson roads discharges into a force main sewer that is a little over three miles long and outfalls into a gravity sewer near the intersection of Dexter and Maple roads in the city.
“The force main sanitary sewer runs intermittently and is designed to discharge via pumps when a wet well has reached a certain depth of sewage,” OHM reports. “Therefore, it does not flow constantly. This lack of consistent flow can create conditions that allow the formation of hydrogen sulfide (H2S), which is a colorless gas known for its pungent ‘rotten egg’ odor.”
It is flammable and toxic and tends to form more easily when the sewage stream is warm and the odor is more noticeable during warm weather, according to OHM, explaining why there have been occasional complaints near the outfall and in the neighborhood along Arborview, under which the city sewer travels after taking in the township’s sewage.
For many years, the township treated the sewage discharge with a calcium-nitrate chemical to prevent formation of sulfides, but it was corrosive, dangerous to work with for utilities staff and prohibitively expensive, according to OHM.
Due to the challenges, the township stopped treating the sewer discharge around 2010-2011, according to OHM, and over the coming years odor complaints went up, culminating with the city asking the township do something about it. OHM launched an odor-control study in 2015 that explored options and recommended the oxygenation solution that was implemented and calibrated in late 2019 and early 2020.
OHM also worked with the township in 2021-22 to complete projects to improve overall air intake into the system.
The new system involves injecting oxygen into the waste stream using a special “Speece Cone” system made by ECO Oxygen Technologies in Indianapolis. “Since that time, the system has been relatively effective in reducing H2S along with the odor complaints,” OHM reports, noting the township has a monitoring device that tracks hydrogen sulfide levels on a weekly basis and maintains the device monthly to ensure levels stay low.
“There have been intermittent disruptions due to maintenance issues or running out of oxygen,” OHM reports. “When these disruptions have occurred, the resulting H2S levels have spiked. Once the necessary remediations are complete and the system operations are restored, the system tends to get back to equilibrium within a day or two.”
Like any sewer, the system operates in an equilibrium where abrupt changes can create impacts, but overall there has been a significant improvement and downstream odor complaints have been all but eliminated, OHM reports.
