Former Extension Engineer
Contrary to common belief, septic tanks are not maintenance free. However, properly designed septic tanks installed correctly and not overloaded with water or household grease or solids from garbage disposals normally function well for many years.
Typically, septic tanks are made of precast concrete. Some tanks have lids of three or more parts. The baffles (or tees) must be in good condition to keep floating scum and grease from leaving the tank and plugging the soil in the drainfield. In addition to the floating scum, the tanks also contain liquid sewage, which eventually flows to the drainfield. Over a period of time, a sludge layer forms in the bottom of the tank. The sludge consists of the solids that remain after the anaerobic bacteria in the tank breaks down the solid wastes.
The natural process of anaerobic digestion normally does quite well on its own, so no chemicals, enzymes, yeast or other additives should be routinely fed into the tanks. Normal household chemicals and occasional use of drain cleaners will not significantly affect tank operation. Roots that penetrate porous drain lines can sometimes be controlled by adding copper sulfate crystals.
Sludge eventually accumulates in the bottom of all septic tanks. The buildup is slower in warm climates than in colder climates. The only way to determine the sludge depth is to measure the sludge with a probe inserted through an inspection port in the tank's lid. Do not put this job off until the tank and sewer fills and the toilet overflows. If this happens, damage to the drainfield could occur and be expensive to repair.
Once each year, measure the sludge depth with a probe. To measure the sludge depth, wrap a long stick with a piece of rough white toweling (secured with wire, using pliers) on one end. Slowly lower the towel-wrapped end of the stick through the large inspection port or through the outlet tee (to avoid the scum) to the bottom of the tank. After a few minutes, remove the probe slowly. Black sludge particles cling to the towel and indicate the sludge level in the tank. If the sludge layer is within three to four inches of the submerged outlet tee, the tank should be cleaned. Many warm-climate septic tanks that are lightly loaded can serve 20 years or more before cleaning. Nevertheless, tanks should be monitored periodically to prevent sludge buildup and damage to the drainfield caused by plugging of the soil.
The floating scum thickness can be measured with a probe. The scum thickness and the vertical distance from the bottom of the scum to the bottom of the inlet tee can also be measured. If the bottom of the scum gets within three inches of the outlet tee, scum and grease can enter the drainfield. If grease gets into the drainfield, percolation is impaired and the drainfield can fail. If the scum is near the bottom of the tee, the septic tank needs to be cleaned out. The scum thickness can best be measured through the large inspection port as shown.
Tree roots can enter sewage and drainfield lines and cause plugging of the lines. Lines should not be placed near trees, and trees should not be planted near lines. Remove tree roots mechanically or flush copper sulfate crystals down the toilet to help discourage or destroy the roots where the solution comes in contact with them. Some time must elapse before the roots are killed and broken off. Recommended dosage rates are two pounds per 300 gallons of tank capacity. No more than two applications per year are recommended. Time the application of copper sulfate to allow minimum dilution and maximum contact time. Copper sulfate will corrode chrome, iron and brass, so avoid contact with these materials. Used in recommended dosage, copper sulfate will not interfere with septic tank operation. Neither mechanical removal nor copper sulfate contact is a permanent solution for tree roots. Remove the trees for a permanent solution to the problem.
Damage to the septic tank and drainfield can occur from traffic or wheel loads on the system. No vehicles should be driven over septic tank systems. No driveways, concrete surfaces or asphalt should be placed over drainfield lines or the septic tank. If vehicles must cross the drainfield, use cast iron pipe or heavy pipe under the crossing.
It is sometimes easy to tell when the drainfield is not working properly. Failure occurs when the soil is not adequately absorbing the effluent and it comes to the surface as a result. Growth of lush and dark green grass may indicate the point of failure. A black-gray odorous liquid may be seen at the soil surface when failure occurs. If liquid rises to the surface, a health hazard could exist for children, who should be kept away from the area until the problem is solved.
A number of problems can cause failure, including solids filling the septic tank, tree roots, excessive grease from the kitchen, overloading and excessive water. Leaking plumbing fixtures should be repaired immediately, because a continuous leak can saturate the drainfield and cause failure of the system. Water-saving shower heads and plumbing fixtures and other water conservation measures are beneficial. It is a good idea to direct surface water away from drainfields to allow more absorption from the tank. It may become necessary to add a waste pump to pump the effluent to an alternate drainfield in another site.
If through misuse or neglect the drainfield becomes clogged, it may be desirable to install additional drain tile. Some advantages exist in alternating the use of drainfields if a second drainfield can be added. If flow is diverted to another field and the ailing field is rested, the biological substances causing the soil to clog will break down over a period of time. A diversion valve can be used to control flow to the newly constructed field. Allowing six to 12 months of rest for the failing field often allows the biological breakdown of the substances plugging the soil.
Other methods to remedy failing drainfields have been tried. One method is to flush the drainfield with hydrogen peroxide. Studies at the University of Wisconsin show only a partial cure with highly variable results even in sandy soils. Any use of chemicals (such a hydrogen peroxide) should be carried out only by a professional who has experience and can perform the procedure safely. Another method is pressure dosing. Dosing involves flooding the drainfield two or three times a day with large volumes of water. Uniform distribution of the effluent is assured, so the entire field is flooded and the soil gets a short rest between applications. The theory behind dosing involves exposing the entire infiltrating surface to air to improve biodegrading and reduce soil clogging. The practice should be considered marginally successful at best.
Any person who cleans or removes the contents of septic tanks must obtain a septage removal permit, which is renewed annually. Application for permits must be submitted in writing at least 10 days before the cleaning will be done. Disposal and removal methods must be defined. If land application or subsurface land disposal is used, additional information may be required.
- Preventative maintenance is the best approach for septic tanks. Preventative measures include:
- Monitoring sludge and scum levels in the septic tank on an annual basis.
- Minimizing grease, solids from garbage disposals, chemicals and other materials. Discharge from grease traps cannot go to the drainfield unless it goes through the septic tank.
- Reducing water flow into sewers and never emptying water from downspouts into the septic tank. Direct surface water away from the drainfield.
- Planting grass over the septic tank and drainfield to reduce erosion and to absorb moisture and nutrients.
- Avoiding traffic or wheel loads over the septic tank and drainfield. Don't put driveways over drainfields or tanks.
- Removing trees from the drainfield area to avoid tree root problems.
- Getting help when you suspect a problem, to minimize the damage.
- Checking with your local health department before purchasing a lot for home construction if you plan to install a septic tank. This cannot be overemphasized.
The acceptable method of disposal of septage includes processing septage through a wastewater treatment plant, or septage handling facility, or land application. Disposal by any of these methods may require written permission from the appropriate government agency, the local health department and land owner.
Septic tanks require reasonable usage and maintenance to ensure efficient operation. The following suggestions should be followed:
Contact your local health department or county Extension agent for more information.
- Repair leaking plumbing fixtures to avoid complete soil saturation and premature tank failure. Add water-saving fixtures and shower heads to reduce loading on the soil.
- Allow only household waste to be disposed into the system. Put kitchen grease and garbage into the trash, not in the septic tank.
- Septic tanks require periodic cleaning (pumping out) to remove accumulated solids. Do not allow the septic tank to fill with solids and overflow into the drainfield. If this happens, the soil in the drainfield can become sealed (water will not percolate into the soil) and is very expensive to repair.
- The solid level in the tank should be monitored annually and pumped out before overflow occurs. Unfortunately, most homeowners will not do this. If checks are not made on solids levels, the tank should be cleaned every five years or so. It is difficult to predict how fast solids will build up in the tanks because many factors are involved. When you decide to pump out the septic tank, contact your local health department for a list of approved contractors who are permitted to handle this waste.
Grateful appreciation is expressed to Commissioner Tommy Irvin and the Georgia Department of Agriculture and to the U.S. Environmental Protection Agency (Region IV) for financial support of this publication.
The University of Georgia and Ft. Valley State College, the U.S. Department of Agriculture and counties of the state cooperating. The Cooperative Extension Service offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, sex or disability.
An Equal Opportunity Employer/Affirmative Action Organization Committed to a Diverse Work Force
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, The University of Georgia College of Agricultural and Environmental Sciences and the U.S. Department of Agriculture cooperating.
Gale A. Buchanan, Dean and Director