Off the Grid Sustainable Housing Options

Common Technologies for Off-Grid Living: Septic System

While in some rural areas you can get away with the gray water system for sewage treatment most cities and places in the U.S.  require a septic system.  Septic systems are relatively inexpensive and provide the optimum say safe and effective way for waste disposal for Off-Grid Living.

Good soil facilitates treatment and disposal of septic system wastewater. Soil profiles made of sand, silt and clay work best. If there is too much clay in the soil, the waste may percolate poorly. If the soil contains too much sand and large particles, wastewater may pass through to the groundwater without being treated by soil microbes. Soil treatment occurs best when above the water table and the soil is relatively dry with oxygen present. Septic systems need space as proper design and use is important. Septic systems are designed to treat and dispose of a specific volume and type of wastewater in the conditions found at the site. The system must not be overloaded. Hazardous chemicals or large amounts of grease should not be disposed in septic systems.

Kitchen grease should be place in the garbage, not the septic tank. Water conservation extends the life of the system and routine maintenance is critical. Septic tanks must eventually be pumped. Sludge and scum accumulate and, if allowed to remain, will eventually cause the tank to overflow and clog the drain field. Good judgment in planning and design and diligent maintenance are the most important aspects of an effective septic system management program.

Sewage or untreated household waste will quickly clog all but the most porous gravel formations. The septic tank conditions sewage to allow percolation of the liquid portion into the subsoil. The most important function of septic tanks is to protect the absorptive ability of the subsoil. In doing this, the septic tank does the following three things. Removes solids from liquid. As sewage enters the tank, the rate of flow is reduced and heavy solids settle, forming sludge. Grease and other light solids rise to the surface, forming a scum. Natural processes break down the solids and liquids by bacterial action. Areas with warm climates, such as the southern United States, allow more complete breakdown of solids and scum than in the cooler climates of the North. For this reason, tanks in warm climates do not usually need to be pumped or cleaned out nearly as often

as those in cold climates. Regardless of climate, a non-volatile residue of material remains in the tank. Sufficient volume for the solids must be provided in the tank between pumping or cleanings. If the solids fill the tank and enter the drain field, the solids can clog the soil in the drain field.

Once the percolation rate is known, the drain field trench bottom area can be found. Drain fields should be at least 100 feet from the closest well or spring, at least 10 feet from water supply lines, and not closer than 50 feet to a pond or stream. Drain field trenches should normally be level and not less than 25 inches or more than 36 inches in depth. In rare cases, trenches will be deeper and filled with several feet of gravel to obtain acceptable percolation. The tile drain must have at least 12 inches of soil over the tile. The aggregate should be a minimum of six inches deep under the drain tile. The drain field trenches should not exceed 36 inches in width.

Septic tanks must provide at least 24-hour retention time or at least 750 gallons for a one- or two- bedroom house, 900 gallons for a three-bedroom house and 1,000 gallons for a four-bedroom house. Add 250 gallons for each bedroom exceeding four. Septic tanks must have access openings over inlet and outlet baffles. Access location should be marked and visible for easy inspection.

Here are important points for selecting a site:

• Stay at least 100 feet from drinking water sources

• 50 feet from streams or ponds and 10 feet from water lines.

• Slope drain fields away from houses, buildings and the water supply.

• Keep drain fields unshaded and free from trees and shrubbery.

• Allow sufficient space to enlarge the drainfield if it becomes necessary.

• Keep septic tanks or drainfields uncovered by driveways or concrete.

• Locate septic tanks and drainfields away from drainage areas and waterways.

• Never use an open flame or matches to inspect a septic tank.

•Sewer gases may explode violently.

Drainfields consist of two or more trenches not more than 100 feet in length. Each trench

contains sections of open-jointed four-inch drain tile or perforated plastic drainpipe laid with

the holes down. The pipe is level to disperse effluent evenly over the soil area. The percolation

rate indicates how fast water will penetrate the soil and sizes the drainfield. Some counties

require additional soil analysis.

Properly designed and installed septic tanks can function for many years. Annual inspection

is desirable to prevent tank solids from overflowing and sealing the soil in the drainfield.

Minimize the amount of grease from the kitchen and garbage disposal solids going into septic

tank. Water conservation reduces the loading and saturation of the drainfield.

Check with your local health department for specific requirements in your county before

purchasing lots or beginning construction. Septic tank permits may be subject to additional

restrictions in groundwater recharge areas.

Figure 1: Septic Tank System (“www.thenaturalhome.com/img/septicdesign.pdf ” nod., Para 1-5)