Lagoons Study

Research on the operation of the Noelville lagoon has been ongoing and the French River Stewardship Council has developed relationships with other groups to share our findings and recommendations.

The Noelville Lagoons – how they operate?

There are two lagoons that service the Town of Noelville. These are called facultative lagoons based on the way they operate. The process requires two lagoons one in operation and the second lagoon, which has just been filled, should be sitting to allow the various bacteria processes to do their work.

The bacteria processes take place in three different levels of the Lagoon.

  1. In the top section we find Aerobic Bacteria which needs oxygen to complete its work.
  2. In the middle section we find facultative bacteria which can survive with oxygen present or not.
  3. In the bottom of the lagoon are anaerobic bacteria which require an oxygen depleted environment.

The top and middle sections of the lagoon operation are the most important to ensure good quality discharge. The bottom anaerobic activity is important to ensure solids are fermented and released as gases, this conversion from solids to gas allows longer operation of lagoons before dredging is needed.

During the winter months, once ice cover is established, the Aerobic bacteria become inactive as oxygen is now depleted, as a result, spring discharges should be held off as long as possible.  In off ice conditions lagoons are provide with much needed sunshine which provides the ultraviolet light needed to kill the e-coli. The open surface now also allows the lagoons top surface to draw oxygen from the air to oxygenate this section giving the Aerobic bacteria the conditions it needs to thrive and complete its work of further cleaning the lagoon prior to discharge.  It is for these reasons that lagoon holding times become so critical.

There are simple analyses that can be made to determine how effectively a lagoon system is operating. Some of the more critical include

  • Testing for dissolved oxygen to ensure a healthy environment for the aerobic bacteria.  Target 5 to 20mg/L
  • Testing for suspended solids to ensure both proper settling and digestion of solids. Target less than 250mg/L
  • PH to ensure a healthy environment for bacteria. Target 6.5 to 9.5

There are other analyses required to ensure optimum health of a lagoon system but these are critical.

In addition to these tests the water color and appearance of the lagoons is an important monitoring tool.

  • Good – sparkling green
  • Might be okay monitor for 2-3 weeks – tan to brownish
  • Testing is needed – dull green to yellow and blue green algae present
  • Bad needs attention – grey to black.

The health of a Lagoon should be monitored twice annually and prior to any discharge of the lagoon to receiving waters. The results and any corrective action needed or taken should be reported to the Municipality.

Over time lagoons will eventually require dredging of solids. A determination of sludge depth should be completed after ten years of operation and every 5 years thereafter. Most will operate for 20 to 30 years depending on design and loading.

Facultative lagoons are usually not designed to handle a large volume of sewage pump outs.