Your Household Septic System
Extension, College of Agriculture & Life Sciences, The University of
Elaine Hassinger, Assistant in Extension, Water Quality Education
Kitt Farrell-Poe, Water Resources , Specialist
As long as people have lived in communities there has been a need for
sanitary disposal of human wastes. About three thousand years ago, homes
in the Indus Valley had bathrooms with water-flushed latrines that emptied
into pits similar to modern septic tanks. In contrast, many Europeans
were still dumping human wastes into the streets a little more than
two hundred years ago. In the United States, early sanitation consisted
of outhouses with earthen-pits. Later, flush toilets were added to homes,
but they emptied directly into surface waters, not into sewers. Today,
most homes have the convenience of being connected to public sewer systems.
Homes not connected to public systems usually have separate on-site
treatment systems to handle household wastewater.
This fact sheet is one in a series concerning domestic wastewater treatment.
It gives a brief overview on how septic systems work. Knowing how your
on-site septic system functions will help you understand how to care
for the system to maximize its ability to treat your households
How a Septic System
Septic systems are designed to hold, treat, and dispose of household
wastewater. The liquid portion of what goes into the system will leave
the system and may eventually reach groundwater or surface water. Household
wastewater contains bacteria, viruses, household chemicals, and excess
nutrients such as nitrates, all of which can cause health problems.
Therefore, household wastewater must have adequate treatment to prevent
Your septic system has two major parts: a septic tank and a soil absorption
system. Wastewater from toilets, sinks, showers, and other drains, flows
from the household sewer drain to an underground septic tank. There,
waste components separate--the heavy solids settle on the bottom, forming
a sludge layer, while grease and fatty solids float to the top, forming
a scum layer. Bacteria in the tank partially decompose the solids.
Solids will build up in the tank and must be removed periodically by
a professional contractor. The relatively clear layer of wastewater
in the middle is called effluent. Effluent flows from the septic tank
outlet to the soil absorption system where most of the treatment process
The Soil Absorption System
The soil absorption system, also known as the drainfield, leach field,
or disposal field, consists of gravel-filled trenches containing plastic
chambers or perforated plastic pipe. This underground portion of the
system accepts effluent from the septic tank outlet. Effluent moves
through the pipes and seeps into surrounding soil for final treatment.
Soil particles filter out small suspended solids and organic matter,
while soil bacteria break down harmful microorganisms and other organic
components. Viruses adhere to clay particles in the soil and eventually
die. The now treated effluent continues its downward flow through the
Managing Your System
As long as your septic system has been properly designed and installed,
there are some things you can do to keep it functioning well.
- protect the system from being overloaded with water
- improve the quality of your wastewater
- protect the soil absorption (drainfield) portion of the system
Less water entering the system means better treatment and longer system
life. Keep in mind that as water enters the septic tank, an equal amount
is displaced and released into the drainfield. When excess wastewater
enters the septic tank, settling time is reduced, enabling some solids
to enter the drainfield area. Excess solids in the drainfield can cause
the system to fail by clogging the soil pores. Clean water from heavy
rains or too much lawn watering can also negatively affect the drainfield
area. Because it is designed to treat wastewater, any excess clean water
that enters the drainfield makes the system work more than is necessary.
You can improve the quality of your wastewater by reducing the amount
of suspended solids that go into the system. Suspended solids include
grease and fat particles and ground-up foods from the garbage disposal.
These small particles dont settle out well in the tank and can
end up in the drainfield reducing its useful life-span.
Since the drainfield area is where most of the treatment occurs, its
very important to protect this portion of the system. Soil compaction
is a major hazard to the operation of the drainfield because compacted
soil cannot treat wastewater. Once compacted, soil cant be restored;
the installation of a costly new drainfield is the usual solution to
the problem. Examples of things that can cause soil to become compacted
include vehicle traffic, heavy objects, and buildings.
A properly designed, installed, and maintained septic system should
protect the environment and give your household many years of good service.
For more information on household septic systems, visit the University
of Arizona Extension publications web page at ag.arizona.edu/pubs.
The University of Arizona is an Equal Opportunity/Affirmative
Action Employer. Any products, services, or organizations that are mentioned,
shown, or indirectly implied in this publication do not imply endorsement
by the University of Arizona.
Document located http://ag.arizona.edu/pubs/water/az1158/
Published February 2000
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