Follow These Steps to Keep Sewage Lagoons in Good Shape

Following a recent review about lagoon design and construction, let’s talk about monitoring the treatment system for effective performance.
Follow These Steps to Keep Sewage Lagoons in Good Shape
Jim Anderson, Ph.D., is an emeritus professor at the University of Minnesota Department of Soil, Water and Climate, education coordinator for the National Association of Wastewater Technicians, and recipient of the pumping industry’s Ralph Macchio Lifetime Achievement Award. Email Jim questions about septic system maintenance and operation at

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A few months ago I responded to a reader’s question about the use and maintenance of individual sewage lagoons to treat septic tank effluent. I covered lagoon functions, construction and design, and offered some ideas about necessary maintenance. Since then I have looked back at some of the materials available through U.S. Environmental Protection Agency design manuals and some of the Consortium of Institutes for Decentralized Wastewater Treatment (CIDWT) materials developed in 2005. Both address needed maintenance for individual facultative lagoons.

As a refresher, facultative lagoons are 5 to 8 feet deep and designed primarily on organic loading estimates using BOD5. Treatment is accomplished by bacterial action in an upper aerobic layer and a lower anaerobic layer. This explains why they are called facultative lagoons, because both aerobic and anaerobic processes are involved in the treatment of effluent. Oxygen is provided in the upper layer by exchange with the atmosphere through mixing with wind and photosynthesis on the part of algae and other floating organisms at the lagoon surface. They are designed large enough to accommodate organic loading for a long retention time and at a low enough rate for the surface area to ensure the presence of the aerobic condition.


As I indicated in the previous article, lagoons require berms that are at least 2 feet higher than the operating level – and they need a buffer area void of trees and shrubs that would inhibit air movement across the lagoon. This means the area taken up by the system can become quite large. One of the maintenance requirements is to keep the trees and shrubs removed as well as periodically checking to see if there is evidence of seepage or compromise to the berm.

I’ll share a step-by-step approach to lagoon maintenance outlined in the CIDWT Operation and Maintenance manual. If there is more than one cell in the system, each should be looked at separately. For treatment facilities I regularly see multiple cells, while individual residential systems generally have only one cell. Regardless, the cells should be looked at the same way.

As with most onsite treatment systems, our nose and eyes offer some of the best tools to evaluate how the system is working. Strong rotten egg odors would indicate the system is totally anaerobic, which points to a sizing and design problem or perhaps an improper inlet or outlet. Color can also indicate problems but should be considered cautiously because there will be periodic turnovers and algal blooms. Green versus brown color could indicate excessive algae using all the oxygen. Purple colors indicate anaerobic and perhaps toxic bacteria.

The surface should be free of large, floating materials. As outlined in the previous article, prevention of large, floating materials should be taken care of in the pretreatment or septic tank part of the system. If solids accumulate in the lagoon, they will have to be removed by pumping.


Berms should be at least 4 feet wide on top so they can be walked on and inspected for any erosion, leaks or animal burrows. If found, these conditions should be addressed immediately to avoid berm failure. Animals should be removed, leaks plugged and eroded areas replaced and reseeded. Berms should be grass-covered and mowed, both to discourage animals and to make the site more aesthetically pleasing. There should be fencing to keep animals and people out; any gates should be locked and secure. Of course, the fence needs to be maintained.

There should not be any vegetation in the lagoon. There may be cattails or other plants around the edge as long as the surface area is free and the vegetation does not block inlets or outlets.

Lagoon depth and the operating level below the top of the berm must comply with state or local regulations. If the level is too high, outlets should be checked. It is also important to evaluate if there is a structure at the outlet to control the water level. If so, this can be adjusted.

Effluent quality in the surface discharge should be regularly evaluated to determine system performance. This includes looking at dissolved oxygen, pH, clarity and temperature, and any other parameters required by the permit. When samples are taken, it is important to follow the prescribed procedures required by the regulatory authority or the laboratory where they will be analyzed. This may involve understanding and following chain of custody requirements and filing the required reports. Make sure you understand these requirements when evaluating these systems.


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