What is happening at the Tavistock lagoons?

    Oxford County is upgrading and performing maintenance on Lagoon Cell 1 at the Tavistock Wastewater Treatment Plant. This includes: 

    • removing and disposing of biosolids and sludge that have built up in Lagoon Cell 1;
    • upgrading the submerged aerators that are there now;
    • repairing erosion to the slide slopes; and
    • adding stone berms to reinforce sewage containment. 

    This is necessary work that keeps the lagoon system operating well and helps protect the local ecosystem.

    Why was odour from the lagoons stronger over spring?

    A lagoon system does not usually release strong odours, except during some temporary circumstances like season changes or construction. 

    Odour was more noticeable in May and June because water levels for Cell 1 were deliberately lowered for construction work, which exposed biosolids and sewage to the air. Biosolids need time to naturally dry out and stronger odours can be present when biosolids are first exposed to air. This timing also coincided with some high temperature days, which can heighten odour, and with manure spreading in rural areas. 

    After the strong community feedback about odour, construction was temporarily paused and the lagoon's cell levels were fully restored in order to help contain the exposed sludge biosolids (and odour). As a result, higher than normal raw sewage odours were also being released during the time it took for microbes in Cell 1 to manage and break down the incoming sewage. It can take three to five weeks to restore a lagoon cell's natural microbial biological action, which is needed to treat sewage and return the cell back to its normal operating performance capacity. 

    Unfortunately, it is not possible to eliminate odours during construction work.

    What is the County doing about smell?

    We are taking the community's concerns about smell seriously. This is what we have done so far:

    • Reassessed and updated the construction work plan. We temporarily returned Cell 1 to its normal operating capacity to manage odours to the degree possible. We used Bioxide (calcium nitrate) and hydrogen peroxide to more quickly restore the natural microbial biological action that is needed in the lagoon cell to most effectively break down sewage.

    • Installed new vapour pipeline system. In July, we expanded our odour control system to include a new vapour pipeline system along the lagoon property line that blows a dry mist odour neutralizer through pipelines and into the air to bind with odourous materials. This expanded system is intended to provide a more effective and longer lasting odour neutralizer that can cover a wider area around the lagoon cells.

    • Continue to use an odour counteractant. This is an additive that neutralizes smells through a chemical reaction. The County has been using AirSolution™ 9312 Odor Counteractant, a non-toxic, non-corrosive additive that is safe to use in areas where there is human activity. We are also exploring other options.

    • Increased monitoring. We have been monitoring conditions on-site at the lagoon more frequently so that we can adjust lagoon operating conditions where possible and if needed.

    • Took preparations for construction restart. All sewage flows to the Tavistock WWTP are now being diverted into Cell 2. We have relocated surface aerators from Lagoon Cell 1 to Cell 2 to boost performance of this cell to prepare to restart construction on Cell 1. We’ve also set up an automated dosing system for Bioxide for Cell 2 to enhance its biological performance (and odour management capacity) during peak times. We've also left extra aeration time for sewage to break down in Lagoon Cell 1 before resuming construction.

    • Provided more information. This project website has been set up to give residents access to information, documents, and the project timeline.

    Why does this work have to take place in the summer when people are outdoors more often?

    To install the new aeration system and repair erosion along the sides of Lagoon Cell 1, we must remove the sludge biosolids from the bottom of the lagoon (Cell 1). To do this, the lagoon cell must first be drained so that the biosolids can be pushed up the sides of the lagoon (dewatering) to  dry naturally in warm weather conditions. Once the biosolids have been dried, they can be removed. 

    In addition to the seasonal needs for this type of construction work, lagoon outflow operations are typically limited during late fall and winter months. This is because freezing conditions do not allow us to discharge treated wastewater from the lagoons into the permitted receiving water course in a manner that complies with Ministry of Environment, Conservation and Parks conditions.

    Should I worry about health impacts from the odour?

    Wastewater emissions like hydrogen sulfide have a very low olfactory detection limit (smell) and are detectable at very low levels. This can make them a nuisance and inconvenience; however, they do not pose a health risk.

    Who is carrying out the engineering and construction work for this project?

    Oxford County has contracted the maintenance and upgrades to Lagoon Cell1 at the Tavistock WWTP to Birman Excavating Ltd. The County is also consulting with the engineering firm CIMA+ for this project. 

    Oxford County engineering staff are involved at each phase of the project and are on site during construction work.