Certain septic tank designs include siphons or other devices to increase the volume and speed of output to the drainage field. This helps fill the discharge pipe more evenly and extends the life of the drainage field by avoiding early blocking or biocoupling. Wastewater can leave the septic tank in a more traditional drainage field consisting of a series of gravel or stone branches where the wastewater separates before the wastewater enters the ground. Alternatively, there may be a drop distribution system consisting of a series of small tubes approximately half an inch in diameter, which treat wastewater and drip into the ground for further treatment.
Bacteria break down solid waste into mud through a process called “anaerobic digestion,” which occurs in the absence of oxygen. Excess mud can overflow in the second compartment, but cannot escape the tank through a T-shaped exhaust . To prevent mud from accumulating and the system from failing, homeowners are expected to pump their septic tanks every three to five years, depending on the amount of use and soil conditions on site. Spray irrigation is an efficient way to feed plants and apply recovered wastewater to the soil; However, to protect public health and reduce odors, wastewater must be treated at a very high level before it is used in this type of system.
A low level of effluents may be a sign that a plug has been released at the bottom of the tank. Even if the effluent level is normal during pumping, any plug after pumping has yet to be manually inspected. While plastic septic tanks are more resistant to the natural chemical processes of a septic system, the lighter weight makes it more susceptible to structural damage. The lighter can also cause the tank to move to the ground during periods of wet soil. Along the way, a plastic septic tank can be raised from pipes that break the ground.
An anaerobic septic system is a relatively simple type of septic system consisting of a tube that leads from the facility to the tank, and a branched tube that comes from the tank to the discharge field. Anaerobic septic systems depend on anaerobic bacteria (aversive oxygen bacteria) whose presence promotes the decomposition of waste in the septic tank. Anaerobic septic systems are usually much cheaper to install than the more complex aerobic system. Septic tank systems are underground on-site wastewater treatment systems dedicated to individual properties.
The treated liquid effluent is generally drained in a septic discharge field, providing additional treatment. Because successful septic treatment depends on this soil filtration process, the design of the drainage field depends on the depth of the seasonal groundwater level and the characteristics of the soil at the site. In a standard septic system, the wastewater is discharged into a discharge field through pipes nested in excavated trenches filled Wastewater Design Expert Witness with clean, porous gravel and then covered with landscape material. Some drains see trenches in favor of a shallow drain field bed filled with the same clean, porous gravel. For areas with a shallow groundwater table, rooms or even hill systems are preferred because they create more space for wastewater to seep through the ground before connecting groundwater. Read more about alternative drainage fields on the EPA septic system types page