THE
PURPOSE OF THIS MANUAL In 1881, the septic tank and leach
field were developed, and today over 50 million people in the United
States rely upon this wastewater management system. In spite of
widespread use, approximately one half of the existing septic systems
have extremely high failure rates due to incorrect design, poor
construction, and inadequate maintenance. As more people move out
of urban areas into unsewered rural residential communities, the
potential for septic system failures increases.
The purpose
of this manual is to explain the basic operations of septic tanks
and leach fields to homeowners and residents. In addition, possible
reasons for septic system failures are presented, and several solutions
are recommended. However, this manual should be used only as a general
guide for the operation and maintenance of septic systems. The design
of septic tanks and leach fields and the evaluation of septic system
failures must be completed on a parcel-by-parcel basis. Assistance
is provided by the El Dorado Irrigation District, the El Dorado
County Environmental Management Department, Division of Environmental
Health, local septic system contractors, and local engineers. It
is also important to contact the El Dorado County Environmental
Health Division prior to the construction of a new septic system
or replacement of existing septic systems.
WHAT
IS WASTEWATER? Wastewater, or sewage, is generated through the use of toilets,
bathroom sinks, showers and bathtubs, kitchen sinks, garbage disposals,
dishwashers and washing machines. The average person produces about
50 to 75 gallons per day of wastewater. The wastewater contains
dissolved organic and inorganic materials, suspended and settleable
solids, and microorganisms, including bacteria and viruses. Direct
discharge of wastewater to surface waters, groundwater, or ground
surfaces will result in public health hazards. To protect the environment,
the majority of unsewered homes utilize septic tanks to remove solids
and greases, and leach fields, or other types of soil absorption
systems, for wastewater disposal.
HOW
DO SEPTIC TANKS WORK? In the past, wastewater treatment and disposal facilities for
homes with indoor plumbing consisted of buried bottomless containers,
or cesspools. Discharge of both solids and liquids to the soils
caused the soil pores to clog, and contaminated water entered surface
waters and groundwater. Therefore, to protect the soils and reduce
public health hazards, septic tanks were installed between the houses
and the soil absorption systems. Septic tanks are watertight containers
which remove large solids and greases, provide anaerobic digestion
of the solids, and storage of the sludge
and scum.
Septic tanks do not remove large numbers of bacteria and
viruses.
Septic tanks
are constructed of concrete, bricks, clay, or fiberglass. Baffles
are placed within the tank to improve solids settling and prevent
the scum layer of lightweight solids, fats and greases from floating
out of the tank with the effluent. The settled solids are biologically
digested by bacteria which live in environments without air (anaerobic
bacteria). Some of the products of anaerobic digestion are gases,
including methane, carbon dioxide, and hydrogen sulfide, which has
an odor similar to that of rotten eggs. The gases are vented from
the septic tank through the household plumbing vents. Inorganic
and non-biodegradable materials cannot be digested by the microorganisms
in the septic tank, and accumulate in the sludge or digested by
the microorganisms in the septic tank, and accumulate in the sludge
or scum layers. The sludge and scum layers must be removed periodically
to prevent the accumulated solids and greases from flowing into
the soil absorption system and clogging the soil pores. If washing
machines, dishwashers, and garbage disposals are used, the amount
of sludge will increase and the septic tank will require frequent
cleaning.
WASTEWATER
DISPOSAL BY SOIL ABSORPTION Effluent from the septic tank flows by gravity or is pumped
to a leach field for disposal. The wastewater effluent is absorbed
by soil particles and moves both horizontally and vertically through
the soil pores. The dissolved organic material in the effluent is
removed by bacteria which live in the top ten feet of the soil.
As the effluent moves through the soil, the temperature and chemical
characteristics of the wastewater change and create an unfavorable
habitat for most bacteria and viruses. Therefore, as the septic
tank effluent moves through the soil, organic material and microorganisms
are removed. The wastewater generally percolates downward through
soil and eventually enters a groundwater aquifer. A portion of the
wastewater moves upwards by capillary action and is removed at the
ground surface by evaporation and transpiration of plants.
A leach field
consists of a series of four-inch diameter perforated distribution
pipelines placed in two-to-three foot wide trenches. The perforated
pipe is placed on top of gravel which is also used to backfill around
the pipe. The gravel promotes drainage and reduces root growth near
the pipeline. Untreated building paper or straw is placed over the
gravel to prevent fine soil particles from migrating into the gravel.
The building paper or straw does not reduce the evapotranspiration
of the wastewater. A minimum topsoil cover is placed over the gravel
to protect the leach field, prevent contact with the wastewater
and reduce infiltration from rain and snow.
HOW
DO SEPTIC SYSTEMS FAIL? When sewage collects on the ground surface or seeps from the
side of a bank, or when the household plumbing becomes clogged,
you are probably experiencing a septic system failure. Although
the failure may be caused by the septic tank, usually it is the
leach field which has failed.
Leach field
operation is affected by the soil percolation rates. To ensure that
the sewage is treated adequately, in the soil, minimum separation
distances have been established between leach fields, fractured
bedrock, groundwater, streams, cut banks, wells, water supply pipelines,
houses, and property lines. When adequate soil depth is not available,
untreated sewage seeps from s·ides of sloping cut banks,--enters
streams, or contaminates groundwater. To prevent such failures,
specific design criteria should be used for septic systems in areas
with bedrock and/or steep slopes. These areas in El Dorado County
include lands along the south fork of the American River, lands
to the southeast of Somerset, and lands to the southeast of Latrobe.
The most frequent
cause of sewage ponding on the ground or clogging of household plumbing
is reduction of soil percolation rates. Percolation tests should
be completed on the leach field site prior to construction. The
percolation rate is used to calculate the amount of sewage which
can be applied per square foot of leaching area. If the percolation
rate is slow due to clay particles in the soil, a larger leach field
is needed than if the soil consisted of sand and gravel. Portions
of El Dorado County which may require larger leach fields due to
clay soils include Pollock Pines, Sly Park, land south of Placerville,
Diamond Springs and Shingle Springs.
As the leach
field becomes older, a bacterial slime mat grows in the soil under
the trench. The mat functions as part of the wastewater treatment
process, however, the mat also reduces the percolation rate. Percolation
rates are also reduced by solids which flow from septic tanks that
have not been pumped and by flooding due to high groundwater or
sewage flowing from neighboring leach fields.
HOW
TO REPAIR FAILING SYSTEMS: SYMPTOMS / CAUSES / REMEDIES
Water will not drain in showers & toilets / Ponding
of wastewater over leach fields.
Solids or scum blocking septic tank
inlet and outlet: —Pump septic tank periodically
---Clean effluent filter, if one exists
Roots blocking pipelines: —Contact commercial root remover services. Many chemicals
may harm the septic system.
System hydraulically overloaded: —Reduce water usage through water conservation.
—Reduce landscape irrigation of soils near leach field.
—Increase design capacity of leach field to meet actual use
of septic system.
High groundwater: —Construct surface and subsurface drainage diversion facilities
upstream of leach field.
—Construct new leach field in area without high groundwater.
Gravel clogged with fine soils:
Soils smeared due to obstruction during wet weather:
Damage due to heavy vehicles or objects: —Replace leach field.
Surfacing downslope:
Excessive Slopes
Fractured bedrock
System constructed too close to cut bank
Gopher or rodent activity —Replace leach field.
—Repair suspected area, possible replacement of leach field.
Odors from house vent or leach field:
No Problem —Atmospheric
conditions may prevent dispersion of odors during early morning
and late afternoon.
—Increase height of house vent to provide for better dispersion.
SEPTIC
SYSTEM MAINTENANCE Septic tanks and leach fields are a viable and permanent wastewater
management system if properly designed, constructed, and maintained.
Maintenance of the septic system primarily consists of removing
the accumulated sludge on a periodic basis. Every three years, the
sludge and scum layer depths should be inspected. The septic tank
should be pumped when the bottom of the scum layer is within three
inches of the bottom of the outlet pipe, or the distance between
the top of the sludge and the bottom of the outlet pipe is within
the limits presented below:
Approximate Total Liquid Depth
Volume of
Septic Tank
3ft.
4 ft.
5 ft.
800
gal.
6 in.
10 in.
13 in.
1150
4 in.
6 in.
8 in.
1500
4 in.
4 in.
6 in.
In
addition, users of a septic system must observe the following
basic rules in order to ensure satisfactory operation:
DO... ...inspect
and, if necessary, pump septic tank every three years.
...reduce
the amount of water used during winter and spring when groundwater
levels are high.
...minimize
or eliminate the use of garbage grinders. This appliance adds
extra solids and water to septic system.
...conduct
percolation tests during wet weather season before installing
a new system.
DO
NOT... ...flush
semi or non-biodegradable items into septic tank, including paper
towels, newspapers, writing paper, rags, disposable diapers, or
cat litter.
...wash
down sides of septic tank when it is pumped. The remaining slime
contains bacteria which will be needed to digest the wastewater.
...flush
large amounts of chlorine bleach or lye products into the septic
tank. However, normal household use will not harm the bacteria.
...pour
used motor oil into the septic tank.
...discharge
brine (salt water) waste from self-regenerating water softeners
to the septic tank. The high salt concentrations will clog the
soil pores.
...connect
roof drains and yard drains to septic tanks. Extra water will
flood the tank and the leach field.
...add
sodium hydroxide or potassium hydroxide to the septic tank. These
chemicals will affect solids settling and cause the sludge to
flow into the leach field.
...construct
leach field in close proximity to another leach field. The soil
will become saturated and both systems will fail.
...construct
leach fields in impervious soils, near fractured bedrock, on steep
slopes, or on flood plains.
...plant
small or medium-sized trees within ten feet of leach fields or
large—sized trees within 20 feet of leach fields. Roots will clog
the pipelines.
...plant
vegetation which requires excessive amounts of water on top of
the leach field.
...drive
vehicles or place heavy objects, such as portable swimming pools,
over septic tanks and leach fields. In addition,- stakes-for-plants
and supports for children's’ s swings should not be placed over
septic tanks and leach fields.
...discharge
water from washing machines directly to the ground surface or
leach fields. The wash water contains chemicals and bacteria which
will contaminate surface waters and cause a public health hazard.
The wastewater also contains fine solids and soapscums which will
clog the soil pores. If the existing septic system will not accept
water from the washing machine, a separate septic tank and leach
field must be installed.
COMMON
MYTHS ABOUT SEPTIC SYSTEMS
1. Septic
systems last forever and never need replacement.
Reply: Septic systems require periodic maintenance
including pumping of the septic tank once every three to five
years and periodic replacement of the leach field. A properly
designed, installed and maintained leach field will require replacement
once every 15 to 30 years. However, a leach field that is not
designed and constructed adequately or receives poor maintenance
may require replacement before 15 years of age. This maintenance
requirement is similar to the periodic replacement of a house
roof or water heater. In addition, the leach field must be expanded
if -additional bedrooms are constructed on a house. However, if
the septic tank is pumped more than once every three years or
the leach field requires replacement more than once every 15 years,
the existing septic system is probably failing.
2. Flushing
yeast or buttermilk into the septic tank will eliminate the need
for pumping.
Reply: It has been a common practice to flush additional
organic material into septic tanks that serve vacation homes or
other homes which are used infrequently. The additional organic
material serves as food for the microorganisms during extended
periods when wastewater is not discharged into the septic tank.
This organic material does not help or hinder the operation of
a septic system which is used continuously. However, the addition
of yeast or buttermilk does not cause degradation of non-biodegradable
material which accumulate in the sludge and scum. Therefore, the
septic system must still be pumped periodically to prevent solids
from clogging the leach field.
3. Washing
machine wash water and rinse water should be discharged to the ground
surface to protect the leach field.
Reply: Water from the washing machine contains bacteria
removed from the clothes and will contaminate surface streams.
In addition, the soap residue will clog soil pores and may kill
vegetation. Water from the washing machine is wastewater, and
should be treated and disposed of in the same matter as water
from the sinks and showers.
4. If the
septic system appears to be failing, flush the septic tank with
large amounts of water.
Reply:
Septic system failures are caused by accumulated solids in the
septic tank or clogged soil pores. Flushing the septic tank will
cause the solids to be forced into the soil absorption system
and may cause irreversible damage to the leach field. Flushing
water into a clogged leach field will prolong the saturation of
the soils and prevent oxidation of organic material in the soil
pores.
5. Weekly
use of commercially available lye products will “clean out” plumbing
and the septic tank.
Reply:
The regular use
of lye products will destroy the anaerobic bacteria which digest
solids in the septic tank. Therefore, the septic tank will require
pumping several times each year to prevent solids from flowing
into the leach field.
6.
My septic system is healthy because the grass is bright green over
the leach lines.
Reply:
A bright green leach field area on the surface could be a sign
that the effluent is not percolating through the soil. Look for
clear signs of failure, such as standing effluent above the leach
lines, or marshy areas.
