QUESTION: What do I need to do to maintain my sewage lagoon system?

ANSWER: A few months ago, a visitor to the Pumper website wrote to me about the individual lagoon system serving a residence. The writer’s family had just moved out from the city and they wondered how to take care of the system.

Personally, I don’t have experience with lagoon systems; it’s a technology not routinely used in my state. Over the years, though, I served on various committees and task forces reviewing individual sewage treatment systems and had varying levels of discussion with colleagues from Missouri, North Dakota and a couple of other states where these systems are allowed in less densely populated areas. In Missouri, they also looked to this option in areas of the state where the soils were very slowly permeable (clay) and, in their view, difficult to have soil-based systems perform well.

In most cases, an individual lagoon system has a septic tank between the house and the lagoon to capture the large solids and scum. Effluent flows by gravity from the tank to the middle of the lagoon where it discharges. Most – but not all – states require septic tanks in front of the lagoons. Having a septic tank in front of the lagoon reduces odor problems and prevents floating solids on the surface.

SIZE MATTERS

The lagoon itself can be circular or rectangular in shape. Sizing is dependent on the flow from the house and the local climatic conditions; the differences between precipitation and evaporation over the year; and the length of the winter season without significant evaporation. These factors lead to significant differences in size requirements among states and regions.

For instance, Missouri requires 440 square feet per bedroom, and North Dakota 1,000 square feet per bedroom. The square footage is the working area of the lagoon. Typically lagoons will have a 3-foot working depth with the dikes built with a 3-to-1 side-slope ratio. So the actual area required for the lagoon is much larger, which is one of the drawbacks for using lagoons for individual houses. Setback distances from neighbors’ property lines also vary widely, with 100 feet required in Missouri and a quarter of a mile in North Dakota.

The lagoon is not meant to be an infiltration pond; it is meant to act as a container in which the facultative, aerobic and anaerobic processes can take place to break the waste down. At a minimum the lagoon needs to be lined with a clay bottom that is never allowed to dry out. In most areas, a synthetic liner is now required to ensure the lagoon does not leak out the bottom. A grassy area is usually provided to deal with times of lagoon overflow due to excessive precipitation. Each state has its own requirements for how overflow situations are handled.

TAKING CARE OF BUSINESS

With that background about lagoons, what about the maintenance question? The inquiry came from Michigan, where the lagoon is located on a farm and the nearest neighbor is a quarter mile or more away. So it fits the overall rural location criteria.

As with any onsite system, maintenance begins with household use patterns and the septic tank. Levels of scum and sludge accumulation should be monitored regularly and the tank cleaned when those levels exceed 25 percent of the tank’s operating depth. For example, a tank with a 60-inch operating depth needs to be cleaned when the depth of the scum and sludge total 15 inches. For a typical residence in Minnesota, this occurs every three to five years.

This is why a number of states and local counties have programs requiring systems be evaluated on three-year intervals. When the tank is cleaned, it should be evaluated for the baffles and effluent screen being in place, overall tank condition and watertightness. Any defects or problems should be fixed. 

Lagoons need to be in direct sunlight and open to the atmosphere and breezes to operate most efficiently. There should not be any trees or brush located near enough to the lagoon that it is shaded or interfering with wind patterns across the lagoon. Part of the treatment process requires oxygen mixing, and wind is the primary way for this to happen. Also, when trees or brush are too near the lagoon, falling leaves can create additional organic solids that contribute to excessive sludge accumulation.

BE A STEWARD

Lagoons need to be fenced to restrict access to individuals or animals that may wander into the area. The fence and gates need to be maintained to prevent entry to animals and, more importantly, children.

Berms should have a grass cover, which should be periodically clipped during the growing season. This is to discourage burrowing animals from setting up their homes in the berm, which may lead to berm failure and sewage discharges. Dikes should be periodically walked to inspect for animal damage.

Similarly, if cattails or other plants become established inside the berms, they can help with the treatment processes, but their roots can also provide channels for seepage through the dike. Checking the dikes periodically and solving any seepage problems before they become failure points is important.

Overflow areas are usually provided into a grassed waterway. The waterway should be maintained with a good stand of grass vegetation. Making sure this is in place is important to protect other areas and other properties during periods of excessive rain.

Finally, even though lagoons are not supposed to accumulate sludge if designed properly, sludge sometimes accumulates and needs to be removed. This requires a professional just as with the septic tank. The sludge needs to be removed and disposed of according to state regulations. This may require dewatering or other treatment.