Homeowners Guide to Lagoons

lagoon requirements

What is a lagoon?

• A lagoon is a small pond that receives wastewater from a home for treatment. The lagoon is three to five feet in depth and the size is determined by the number of bedrooms in a home. A lagoon works to treat domestic sewage by a biological process.

How does a lagoon work?

• The sewage from the home enters the lagoon on the bottom. The solids stay on the bottom and become sludge. Algae, a microscopic plant that lives in the lagoon, works with carbon dioxide and sunlight to produce oxygen. Other microorganisms use this oxygen to digest the sewage. This is why sunlight and good wind action are essential for a lagoon to work properly. Trees must be cleared around a lagoon for this reason. The lagoon should also be mowed frequently to make sure the lagoon gets plenty of sun and wind.

What should be done to maintain a lagoon?

• A properly built and maintained lagoon should have little to no odor. The lagoon may "turn over" in the spring and in the fall and have some odor for a few days. If the lagoon has an odor at other times there may be another problem. If a lot of leaves fall into the lagoon, they can cause the lagoon to smell. When the leaves begin to decompose they produce tannic acid which lowers the pH of the lagoon. This kills the algae and upsets the biological process that is treating the sewage. If this occurs, trim or cut the trees that are causing the leaves to fall into the lagoon. The water in the lagoon can be treated with 2 pounds of ammonium or sodium nitrate per day until the odor dissipates. Odors can also be caused when something is put down the sewer that upsets the natural process in the lagoon such as a large amount of chemicals or lack of sunlight as in extended cloudy weather.
• If the home has a garbage disposal, it is best to have a properly sized and constructed septic tank preceding the lagoon. The tank should have at least 1000 gallons of capacity. This will reduce the fats and solids that will overload the lagoon.
• The lagoon should be filled with water prior to operation. No additives will be necessary to start the biological process. The bacteria from the sewage will be sufficient for this.
• The lagoon banks and area around the lagoon will need to be kept mowed and free of trees. The banks should be mowed to the water’s edge. This will prevent tall grass from drooping into the lagoon where it provides mosquito breeding areas and could contribute to premature filling. Mowing debris should not enter the lagoon.
• Remove trees within 50 feet of the lagoon to keep leaf debris from entering, avoid shading the surface and help control tree roots. Remove any other vegetation or trees which shade the lagoon, especially during the winter months. Watch for damage to the banks, especially from burrowing animals. Repair any damage immediately and reseed with grass as needed. Remove cattails and other vegetation including duckweed and floating algae masses from the lagoon immediately to minimize mosquito breeding and excess organic loading and to improve oxygen transfer. To help reduce damage to the banks, keep the fence in good repair so animals cannot get on the banks.

Return to the Environmental Health Division Homepage or return to the Columbia/Boone County Health Department Homepage