A residential septic system works on the same principal as a large municipal system. It takes in the waste product from your home and bacteria in the system breaks down the waste to a liquid form. This liquid is then dispersed over a large area of field line where the liquid is either absorbed into the soil or evaporates into the atmosphere. These systems are very simple in design and concept, and if properly installed and maintained can provide many years of efficient service.
The septic system has three components. The septic tank itself, the distribution box, and the field lines. The vast majority of septic systems are gravity systems which means each component is lower than the previous one, thus allowing gravity to do all the work of moving the waste product from one section to the next.
The septic tank should be located a minimum of ten feet from the foundation of the home. Most septic tanks are buried no more than 24 inches below the surface. In most areas of the country regulations require a minimum tank size of 1,000 gallons. You should check your local codes to determine if there are any size limitations. Most states require you to receive a permit to install a septic system. This is to insure the project is done correctly since the system will be underground and all but impossible for any future owners to inspect. Get all permits and review all codes before starting work.
Dig the hole for the septic tank. The floor of the hole needs to be perfectly level to insure the tank functions as designed. Have the hole dug before the septic tank is installed. This way, the delivery company can generally place the tank directly into the hole. These tanks are made of concrete and can weigh several thousand pounds. Not something you want to be man handling if you don’t have to. If you have rented or hired a backhoe to perform the digging, it is also important to have the entire system marked off so all of the digging may be done at once.
Dig a ditch from the house foundation to the septic tank hole, then continue the ditch on the opposite side of the tank hole to the planned location of the distribution box. This box should be placed at the beginning of the field lines. A separate ditch will need to be dug from the distribution box to the beginning of each field line. The field lines need to be a minimum of 24 inches up to a maximum of 365 inches. These lines should be a minimum of 36 inches apart. All field lines must be of the same length and should be a minimum of 29 inches deep. Once all of these components are dug, you are ready to begin assembling the various components.
Once the septic tank is placed into the hole, connect the house drain to the inlet port of the tank using 4 inch PVC pipe. Continue to use this same pipe from the outlet port to the distribution box. The concrete distribution box will have a single inlet port from the septic tank and a separate outlet port for each of the field lines. The distribution box must be level so the waste water will be evenly distributed between each of the lines. Use silicone caulk to seal around the pipe and the tank to insure a watertight connection. Continue on to the head of each field line with 4 inch PVC pipe. Secure each connection with PVC pipe cement.
Each field line should be filled with gravel to a minimum depth of 12 inches. Atop this bed of gravel lay 4 inch perforated PVC pipe. This pipe should be connected to the solid 4 inch pipes coming from the distribution box. Once these pipes are in place add more gravel to each field line until the pipe is covered by 1 to 2 inches of gravel. Atop this gravel lay out a layer of geotextile material to prevent dirt and other debris from filtering down and clogging the pipes.
The system is now assembled and all ditches and holes may be back filled. Be certain to mound the dirt over each area to allow for settling. If you will not be using the septic tank right away it should be filled with water. In the event there is heavy rainfall before the tank is in use this will prevent the tank from floating out of the ground should the ground water rise too high. This would result in serious damage and major re-work.
Be certain to install an above ground access port on the tank and at least every 100 feet of solid pipe you install. This will make routine maintenance much easier and far less expensive. Do not allow any vehicle traffic over the septic system. The weight of a vehicle can crack septic tanks, crush pipes and smash distribution boxes. You should also never plant large trees or shrubs over any portion of the septic system.