The dreaded lagoon, most people do not like this option when it is given to them. Most people feel that the lagoon will smell and the thought of open water is unattractive feature. The lagoon can be a person's best friend or the worst enemy to some. The positive points of the lagoon are there is no smell if the work is done correctly. The way the lagoon is designed the effluent leaves the home to the septic tank where it gets pre-treated, then passes through a filter to the bottom of the lagoon. The reason this pipe exits on the bottom of the lagoon is the gases that you would smell get trapped in the water of the lagoon keeping the system from smelling. If the water does reach the overflow point it leads to overflow chambers (most of the time) to keep the system underground. If your ground has high clay soils or massive clay, the lagoon is perfect for those types of soil. If you have a large lot the lagoon can be hidden from site and will not need much maintenance (out of site out of mind). Most commonly the lagoon is one of the most inexpensive types of systems (cheaper the better). Now the bad part of the lagoon, if you have a small lot it will be very close to the home. It requires a 6' fence around the lagoon to keep animals and kids from getting in the water, (very steep slope on sidewalls) if they get in they may not get out. Also the lagoon may be difficult to put in on rocky lots, due to the depth required to place the lagoon.