Septic Systems: What you need to know
Published by: North Carolina Cooperative Extension
Publication Number: WM-1
Last Electronic Revision: March 1996 (JWM)
What are the parts of a septic system?
In North Carolina, most septic systems are the conventional
type, consisting of a septic tank and a drainfield. The
tank, which usually has a capacity of about 1,000 gallons,
is buried in the ground along with a number of gravel-filled
trenches. Either the front yard or the backyard of a home
must be large enough to accommodate the tank and drainfield.
Generally, at least 1 acre of land is needed for a properly
functioning septic system. The cost of installing a
conventional septic system ranges from $1,000 to $2,500.
How does each part of the septic system function? How can I
tell if my septic system is not functioning safely or
Household wastewater from the kitchen, bathrooms, and
laundry area flow into the septic tank. Solids remain in the
tank, and the liquidcalled septic tank effluentflows out of
the tank to the drainfield where it leaches through the
soil. In a properly functioning septic system, the germs
(bacteria and viruses) in the septic tank effluent are
removed in the soil treatment zone by filtering and by soil
microorganisms before reaching the groundwater. Some
chemicals such as nitrates, however, are not typically
removed in the soil treatment zone.
Not all soils, however, are capable of absorbing and
purifying septic tank effluent. An odor of sewage and a wet
area around the drainfield are signs that the septic system
is not functioning properly. Also, contaminated well water
may be a sign that your septic system is not doing its job.
If you suspect a problem with your septic system, call your
local health department immediately.
FIGURE 1: (Not Shown) The conventional septic system usually consists of
a septic tank and a soil drainfield.
What maintenance does a septic system need?
The biggest maintenance task is pumping the solids from the
tank. After a few years, the solids that accumulate in the
tank need to be removed and disposed of properly If not
removed, the solids will spill over into the drainfield and
clog the soil. With proper maintenance, a septic system can
work efficiently for many years.
These factors determine how often your tank will need to be
- the size of your tank;
- the volume of your wastewater;
- the amount of solids in your wastewater.
Extension publication AG 439-13, Septic Systems and Their
Maintenance, gives guidelines for pumping.
Seasonally used systems, such as those of vacation homes and
summer cottages, will not need to be pumped as often as
year-round residences. The use of a garbage disposal,
however, doubles the amount of solids in your system, and
your tank will need to be pumped more often. Here are some
tips for proper maintenance:
- Limit the use of garbage disposals.
- Do not use too much water. (A good limit is 50 gallons per
person per day.)
- Do not add materials such as facial tissues, hygiene
products, or cigarette butts to wastewater.
- Do not pour cooking oils or grease down the drain.
- Maintain a grass or other vegetative covering over the
- Keep autos and heavy equipment off of the system.
What should not be flushed through a septic system?
The following substances should not be put in the septic
- cooking grease, oils, or fats;
- paint thinners;
- disinfectants; and
- other household chemicals.
Cooking grease, oils or fats should be placed in a container
and put in household garbage that will be landfilled.
Pesticides, paints, paint thinners, solvents, disinfectants
and other household chemicals are toxic substances that
threaten ground water quality. They may also kill the
microorganisms that help purify the sewage. For information
on safe disposal of these chemicals, contact your county
office of the N.C. Cooperative Extension Service.
What is in the effluent from my septic system?
The effluent contains all of the liquid from your
wastewater, which often includes bacteria, viruses,
chemicals, and other contaminants. The septic tank removes
some wastes, but the septic tank effluent may still contain
bacteria, viruses, chemicals and other contaminants. The
soil drainfield provides further absorption and treatment.
If effluent is not treated adequately, its contaminants may
threaten ground water quality.
Can my septic system contaminate my well?
If septic tank effluent flows into an area with a shallow
water table, it might not be adequately purified before
entering ground water. A similar problem can happen where
the soil is too thin over rock to treat the septic tank
effluent well. If inadequately treated septic tank effluent
enters groundwater, your well water supply and that of
others nearby can be contaminated. In this case, you might
unintentionally "recycle" this poorly treated septic tank
effluent into your home with your drinking water supply.
With proper safeguards, recycling of untreated sewage can be
greatly reduced or avoided.
Figure 2: (Not shown)The soil must be able to both absorb and purify
the wastewater if a septic system is to work properly.
How does the location of my septic system affect my water
To avoid problems such as recycling untreated wastewater,
location should be the first consideration when installing a
septic system. A septic system usually requires 1 acre of
land or more and should be at least 100 feet from any wells.
The ability of the soil surrounding the drainfield to absorb
and treat the effluent is an important concern in regard to
water quality. Signs of soil problems or site limitations
that could affect the septic system include gullies,
ravines, excessively steep slopes, or other land
characteristics that would make installation difficult. The
system should not be installed in land that is wet or
swampy, designated wetlands, or land near streams or rivers
that could flood. It has also been found that septic systems
constructed where the water table is too shallow do not
provide effective treatment in the drainfield .
Often the most suitable soil for a septic system is on the
highest ground on the site. Under ideal conditions, however,
the septic system should be located lower than your well,
but good soil is most important. Also, the deeper your well,
the less likely it is to draw in sewage effluent.
What are the rules and regulations governing septic systems?
State law requires a comprehensive soil and site evaluation
by your local health department to determine the suitability
of your soil and land site. Before construction begins on
your home or septic system, you must receive an improvement
permit from the health department. Permits for septic
systems are valid for no more than five years. Beginning in
July 1992, state regulations will require a septic system
maintenance contract between homeowners and management
organizations for certain types of alternative septic
The size of the septic system that you install is legally
determined by the number of bedrooms in your home and the
type of soils at the site. Once installation is complete,
the system must be approved by the health department before
electrical service can be permanently connected to your
What are the alternative types of septic systems?
The conventional septic system is the most widely used and
least expensive. Alternative types of septic systems include
low-pressure pipe systems, fill systems and aerobic
treatment units. These cost a great deal more to install
than a conventional system, and the low-pressure system
needs to be inspected every 6 months. The aerobic treatment
unit must be inspected 4 times a year.
Other possible options for on-site wastewater disposal
include cluster systems, sand filters, mound systems, and
spray irrigation systems.
What interest do banks and mortgage companies have in my
water and septic systems?
Some banks or lenders require that the prospective buyer or
seller furnish proof of a bacteria-free water supply before
they will issue a mortgage. Also, some will not issue a
mortgage for homes with a failing septic system. Thus, it
pays to be concerned about your water from well to wash to
This publication was supported in part by the U S.
Department of Agriculture, Extension Service, under special
project number 91-EWQI- 1-9274.
Distributed in furtherance of the Acts of Congress of May 8 and June 30,
1914. Employment and program opportunities are offered to all people
regardless of race, color, national origin, sex, age, or disability. North
Carolina State University, North Carolina A&T State University, U.S.
Department of Agriculture, and local governments cooperating.