Wastewater from septic tanks

(The information below was taken from the Florida Department of Health Environment, Division of Environmental Health, Bureau of Onsite Sewage Programs Web site.)

A properly located, designed, constructed and maintained septic tank system can serve a home as efficiently as a central sewer system, but a system that does not receive proper care and attention can be a financial burden and a potential health threat.

In Florida, approximately 33 percent of the population is served by an estimated 2.5 million on-site sewage treatment and disposal systems (OSTDS). These systems discharge over 750 million gallons of treated effluent per day into the subsurface soil environment.

Though central sewer systems serve much of the Jacksonville area, more than 650,000 septic tanks are in use throughout the 18-county St. Johns River Water Management District, including more than 120,000 septic tanks in use in the northeastern region of Florida as of 2007.

Frequently asked questions

How do septic systems work?

A septic tank system consists of a large, watertight tank that receives wastewater from the home plumbing system. The tank is followed by an underground drainfield consisting of a network of perforated pipe or chambers for distributing partially treated water from the septic tank to the soil for final treatment and disposal.

Septic tanks contain bacteria that grow best in oxygen-poor conditions. These bacteria carry out a portion of the treatment process by converting most solids into liquids and gases. Bacteria that require oxygen thrive in the drainfield and complete the treatment process begun in the septic tank.

If the septic tank is working well, the wastewater which flows out of the tank is relatively clear, although it still has an odor and may carry disease organisms. It should flow only into the drainfield — never onto the ground surface or into Florida waters. 

While bacteria can be harmful, they occur naturally in all ecosystems. Humans can increase the number of bacteria present in these ecosystems. A septic system that is not properly located, designed, installed or maintained can allow liquid wastes to pollute nearby surface waters and groundwater, as well as providing a breeding ground for mosquitos.

Contaminants can travel long distances in some soils. Therefore, drinking water wells should be located at least 75 feet from any part of a septic tank system.

With certain exceptions, septic tanks and drainfields must be located at least 75 feet away from the high water line of ponds, rivers and lakes. Also, the drainfield should be located so that it will not be saturated by surface water drainage or runoff from roof gutters or the water table. The bottom of a drainfield should be located 24 inches above the estimated seasonal high water table to allow for effective pathogen, bacteria and some virus removal. High water tables result in the mounded systems often seen in Florida.

How do I maintain my septic system?

After the septic tank system is placed in service, proper operation and maintenance of the system will ensure continued efficient service and prevent sudden replacement expenses.

The septic tank and drainfield are designed and installed to handle a maximum calculated daily sewage flow. Consistently exceeding the design flow will eventually overload the system and cause failure. The tank may receive new solids faster than it can treat them and the drainfield may become saturated from excessive water use.

Various products are on the market that are said to start, accelerate or improve the action in the septic tank. Since all necessary bacteria are already present in the sewage entering the system, such products are not recommended.

Maintenance of a septic tank will depend largely on the daily sewage flow and individual household wastewater characteristics. With ordinary use and care, a septic tank should not require pumping out more than once every three to five years. It should, however, be inspected to determine the depth of accumulated sludge and grease.

Waste from kitchen garbage disposal units puts an extra load on a septic tank system. If a disposal is used, the capacity of the tank should be increased to handle the increased solid wastes. The tank may also require more frequent pumping to remove accumulated solid waste buildup.

Failure to pump out a septic tank system when indicated will result in solids or greases overflowing into the drainfield, which in turn may become clogged and stop functioning. In this event, not only will the tank have to be pumped out, but the drainfield may also have to be replaced.

Septic tanks can be cleaned by contractors permitted by the county health department. This type of work should be done only by experienced professionals who will pump the entire contents of the tank into a tank truck and dispose of the contents in an approved, sanitary manner.

What would cause my septic system to fail?

Septic tank systems fail when the drainfield does not dispose of sewage as rapidly as it is being added to the system. Thus, improvements that reduce the amount of incoming water or improve the quality of wastewater passing through the system will increase the system’s longevity. Other important considerations include the following:

A drainfield can be damaged by compaction due to vehicular traffic and can be blocked by excessive shrubbery or tree root growth. The drainfield should be unobstructed and seeded with grass. Grass and sunlight aid evaporation.

Washing machines are responsible for large volumes of water entering the septic tank. The surge of wash water can create turbulence in the tank which increases the amount of solids flushed into the drainfield. Space washings throughout the week rather than doing many loads at a time, or, install a separate system for washing machine water (“gray” water).

Cooking oils and grease are troublemakers. The types of bacteria found in septic tanks and drainfields do not survive or function well in solidified grease. Grease and cooking fats should never be washed down the sink drain. Save grease in jars or cans for disposal in the garbage.

When buying a home that is not on a central sewer system, you will want to know the age and capacity of the septic tank and drainfield. Obtain a copy of the permit and the as-built plans from the county, if possible. You also should know if the system’s location endangers the water supply and if the drainfield and soil will work properly year-round under all weather conditions.

What agencies regulate septic systems?

The Florida Department of Health Bureau of Onsite Sewage Programs and county environmental health units regulate the use of septic tanks in Florida.

In addition to state and local government Web sites and contacts, the U.S. Environmental Protection Agency’s (EPA) Office of Water offers information on septic systems to homeowners, state and local governments, and industry professionals.

Its updated Web site, www.epa.gov/owm/septic, provides guidance, technical information, management guidelines, and a variety of other information to help citizens manage their septic systems and to help state and local officials strengthen their regulation and management of these potential sources of water pollution.

Tips

(from the Florida Department of Health)

Do
  • Know the location and capacity of your septic tank system
  • Have a licensed contractor inspect the tank at least every three years
  • Have the tank pumped when the combined depth of the sludge and scum equals one-third of the tank liquid volume
  • Install the system so that rainfall and surface water will flow away from the drainfield and at an appropriate distance from nearby waterways
  • Grow grass above the system
  • Install water conservation fixtures or devices to reduce the total volume of water entering the system
  • Keep plumbing fixtures such as toilets and faucets in good repair to prevent leakage and wasting of water
Do not
  • Flush paper towels, newspapers, wrapping paper, rags or sticks into the system
  • Allow large, irregular, intermittent or constant volumes of clear water into the system, as with a leaking toilet or faucet
  • Overuse ordinary household cleaning chemicals that will be flushed into the system
  • Pour out or empty hobby or home industry chemicals into the system
  • Allow grease or other bulky waste to enter the system
  • Flush toxic materials such as pesticides into the system
  • Plant trees or shrubbery in the drainfield
  • Allow vehicles to drive across or park on the drainfield — protect it from being crushed
  • Waste water
  • Use chemical solvents to clean plumbing lines or a septic tank system