Septic systems range from the very simple to the extremely complex. Even on the simplest septic systems there are still many things that can go wrong. If you believe that septic systems are something you bury and forget about, then I guarantee that you will come across many of these problems. There are simple things anyone can do to keep their septic system running properly for decades.
First a general description of a septic system. The system starts where the common drain leaves the house. This drain can go to a municipal sewer or to an individual septic system. The water flows by gravity into the septic system. The inlet to the septic tank is protected by a T shaped baffle. It is open on the top and bottom. It is designed to contain floating debris in a small area and to direct solids to settle down towards the bottom. The water is contained here where solids settle out to form a sludge layer and floating objects form a scum layer. In between there is a clear zone where the water has very few solids. The water in the tank is treated by anaerobic bacteria. The bacteria break down organic compounds in the water until there is almost nothing left.
The water leaves the tank through another T shaped baffle on the other side of the tank. This one goes down to the clear zone and allows clear zone water to exit the tank without coming into contact with the scum layer. Some tanks have a septic pump, the pump is installed on the opposite side of the inlet and at the expected height of the clear zone. Larger tanks might have a dividing wall to keep sludge and scum on one side and clear water on the other side.
The sludge layer if not removed every three to five years can cause a major failure of the entire system. Not everything can be broken down completely. There are always things that either never breakdown or breakdown too slowly and they accumulate. The sludge layer will eventually reduce the capacity of the tank and the solids will block the inlet or the outlet of the tank. The sludge layer will be a rapid problem if the people using the system treat the toilet as a garbage can.
The scum layer is all the floating solids the get flushed into the system. Grease and oils cause a large part of the scum problem. But they are far from the only culprits. Cooking oils and grease coat the walls of the pipes and tanks and slowly reduce the size of the of the inlet and outlet eventually blocking them, and you can see how that is a problem.
The drain field is where the treated effluent gets released back to the environment. It may be called something else like a tile bed or weeping tile. They are usually subterranean but can sometimes be on the surface. Regardless there are still buried pipes and they are easy to collapse if you drive a vehicle over them. Lawn tractors are OK but even compact cars are too heavy for the shallow plastic piping. If the piping becomes cracked or even a section collapses then pipe will become blocked with dirt and your waste water will have nowhere to go except back into the house.
Hydraulic overloading is the technical name for putting too much sewage into your septic tank. This can happen if you have a party and there are more people using the system or if the sludge layer reduces the capacity of the tank. The end result of overloading is that poorly or untreated sewage leaves the system negatively impacting the surrounding area.
Leaks are bound to occur with age. You can also create leaks by driving over the tank and excavating too close to the tank. Leaks are a huge problem once they occur. The groundwater and soil contamination is extremely expensive to clean up. You may also be liable for damage to the neighbor’s water supply depending on the riparian laws where you live. A leaking tank needs to be replaced immediately.
Proper maintenance will prevent most problems. The worst thing anyone can do is to bury the septic system and forget about it.