The septic-tank-soil-treatment system (also called a septic system) is an effective, long-standing method for collecting, treating, and disposing of sewage from rural and suburban homes. Septic systems are used in every county in North Carolina: more than 50 percent of the homes have them, and new systems are being installed at a rate of 40,000 per year. This fact sheet will answer some typical questions about septic systems and septic pumping in Hampstead NC.
Septic systems are used when sewage treatment plants are not accessible. They safely treat and dispose of wastewaters produced in the bathroom, kitchen, and laundry. These wastewaters may contain disease-causing germs and pollutants that must be treated to protect human health and the environment. Although septic systems are usually a permanent solution to wastewater treatment and disposal, they sometimes serve as a temporary solution until sewer lines are installed.
There are a number of different septic systems, each with its own design. The conventional system is the one most commonly used in North Carolina (Figure 1). It consists of three main parts: the septic tank, the drainfield, and the soil beneath the drainfield.
The septic tank is a watertight concrete box about 9 feet long and 5 feet tall. It is buried in the ground just outside the home. The tank is usually precast from reinforced concrete and can be purchased from concrete manufacturers. While typically designed with a 1,000-gallon liquid capacity, the size of the tank is legally determined by the number of bedrooms in the home. The tank temporarily holds household wastes and allows a small amount of pretreatment to take place (Figure 2).
The tank is connected to the drainfield by a buried pipe. A typical drainfield consists of two to five trenches excavated into the subsoil. In many systems, a distribution box or a flow divider helps move wastewater to each trench. In most conventional septic systems, the trenches are 3 feet wide, 2 to 3 feet deep, and 9 feet apart. In each trench, a 1-foot thick layer of washed gravel or stone is placed around a 4-inch-diameter perforated distribution pipe. After the trenches are covered with soil, the area must be landscaped to keep surface waters from ponding over the drainfield.
The drainfield has also been called the nitrification field or the soil absorption field. The sole purpose of the drainfield is to deliver wastewater to the soil. The soil purifies the wastewater by removing the germs and chemicals before they reach the groundwater or any adjacent surface waters such as rivers, lakes, and estuaries.
All credit for this content can be found here: http://www.soil.ncsu.edu/publications/Soilfacts/AG-439-13/