 | If not properly
maintained, an on-site septic system could cost you up to $20,000 to repair
or replace. The following provides technical information and tips to help
you avoid such an expense.
|
Septic Tanks:
| All on-site septic systems have a septic tank, a large container that is
buried underground and is made of concrete, fiberglass or polyethylene. The
septic tank protects the absorption ability of the subsoil by: |
| Removing solids from liquid. As sewage enters the septic tank, heavy
solids settle at the bottom and forms sludge, which reduces the flow of
sewage into the tank. While grease and other light solids rise to the
surface (scum), both the sludge and scum are retained and break down while
the liquid (effluent) is passed along to the drain field for absorption by
the soil. |
| Providing biological treatment. Bacterial activity breaks down the
solids and liquids in anaerobic conditions (without oxygen), which are
referred to as “septic,” the name given to the tank. |
| Retaining scum and sludge. Scum, the mat of floating solids and
grease, and sludge, the solids that build up in the bottom of the tank,
are eventually compacted into a fraction of its original volume. Warm
geographical regions of the country allow for a more complete breakdown of
the scum and sludge than cool regions. Hence, tanks in warm climates tend
to not require pumping or cleaning out as frequently as tanks in cold
climates. Note that it is important to maintain a sufficient volume for
solids to accumulate between pumpings and cleanings in order to avoid
having the solids enter the drain field and clog the soil. |
| Septic tanks should provide at least 24-hour retention time or at
least 750 gallons for a one or two-bedroom house; 900 gallons for a
three-bedroom house; and 1,000 gallons for a four-bedroom house. 250
gallons should be added for each bedroom exceeding four. |
| Kitchen grease is generally detrimental to the septic tank’s
operability. Small amounts of kitchen grease can enter the septic tank
without damaging the system. |
Types of Septic Systems:
The following are descriptions of the various types of
septic systems, according to the U.S. Environmental Protection Agency.
Conventional Septic System:
| Consists of a settling or septic tank and a soil
absorption field. The traditional system accepts both grey water
(wastewater from showers, sinks, and laundry) and black water (wastewater
from toilets).
These systems are typically restricted in that the bottom invert of the
absorption field should be at least 2 feet above the seasonally high water
table or impermeable layer (separation distance) and the permeation rate
of the soil should be between 1 and 60 minutes per inch. Also, to ensure
proper operation, the tank should be pumped every 3 to 5 years. Nitrogen
removal of these systems is minimal and somewhat dependent on temperature.
The most common type of failure of these systems is from clogging of the
absorption field, insufficient separation distance to the water table,
insufficient permeation capacity of the soil, and overloading of water. |
Intermittent Sand Filter:
| Used in conjunction with pretreatment methods such as
septic tanks and soil absorption fields. An intermittent sand filter
receives and treats effluent from the septic tank before it is distributed
to the leaching field. The sand filter consists of a bed (open or buried)
of granular material 24 to 36 inches deep. The material is usually 0.35 to
1.0 mm in diameter. The bed of granular material is underlain with graded
gravel and collector drains. These systems have been shown to be effective
for nitrogen removal, however, this process is dependent on temperature.
Water loading recommendations for intermittent sand filters are typically
between 1 and 5 gallons per day/square foot (gpd/ft2) but may be higher,
depending on wastewater characteristics. Primary failure of sand filters
is due to clogging, and maintenance is recommended to keep the system
performing properly—resting the bed, raking the surface layer, or removing
the top surface medium and replacing it with clean medium. In general, the
filters should be inspected every 3 to 4 months to ensure that they are
operating properly. |
| Intermittent sand filters are used for small commercial
and institutional developments as well as individual homes. The size of
the facility is limited by land availability. The filters should be buried
in the ground, but they may be constructed above ground in areas of
shallow bedrock or high water tables. Covered filters are required in
areas with extended periods of subfreezing weather. Excessive, long-term
rainfall and runoff may be detrimental to filter performance, requiring
measures to divert water away from the system (USEPA, 1980). |
Recirculating Sand Filter:
| A modified intermittent sand filter in which effluent
from the filter is recirculated through the septic tank and/or the sand
filter before it is discharged to the soil absorption field. The addition
of the recirculation loop in the system may enhance removal effectiveness
and allow media size to be increased to as much as 1.5 mm in diameter. |
Buried or recirculating sand filters:
| Buried or recirculating sand filters can achieve a very
high level of treatment of septic tank effluent before discharge to
surface water or soil. Dosed recycling between sand filter and septic tank
or similar devices can result in significant levels of
nitrification/dentrification, equivalent to between 50 and 75 percent of
overall nitrogen removal, depending on the recycling ratio. Regular buried
or recirculating sand filters may require as much as 1 square foot of
filter per gallon of septic tank effluent. |
Mound Systems:
| An alternative to conventional OSDS and are used on
sites where insufficient separation distance or permeation conditions
exist. Mound systems are typically designed so the effluent from the
septic tank is routed to a dosing tank and then pumped to a soil
absorption field that is located in elevated sand fill above the natural
soil surface. There is evidence suggesting that pressure dosing provides
more uniform distribution of effluent throughout the absorption field and
may result in better performance. A major limitation to the use of mounds
is slope. |
| Where adequate area is available for subsurface
effluent discharge, and permanent or seasonal high ground water is at
least 2 feet below the surface, the elevated sand mound may be used in
coastal areas. This system can treat septic tank effluent to a level that
usually approaches primary drinking water standards for BOD5, suspended
solids, and pathogens by the time the effluent plume passes the property
line for single-family dwellings. A mound system will not normally produce
significant reductions in levels of total nitrogen discharged, but should
achieve high levels of nitrification. |
Evapotranspiration (ET) and Evapotranspiration /
Absorption (ETA) Systems:
| Combine the process of evaporation from the surface of
a bed and transpiration from plants to dispose of wastewater. The
wastewater would require some form of pretreatment such as a septic tank.
An ET bed usually consists of a liner, drain field tile, and gravel and
sand layers. ET and ETA systems are useful where soils are unsuitable for
subsurface disposal, where the climate is favorable for evaporation, and
where groundwater protection is essential. In both types of systems,
distribution piping is laid in gravel, overlain by sand, and planted with
suitable vegetation. Plants can transpire up to 10 times the amount of
water evaporated during the daytime. For an ET system to be effective,
evaporation should be equal to or greater than the total water input to
the system because it requires an impermeable seal around the system. In
the United States, this limits use of ET systems to the southwest. The
size of the system depends on the quantity of effluent inflow,
precipitation, local ET rate, and soil permeability (Otis, undated).
|
Aerobic Treatment Units:
| Can be employed on-site. These systems require regular
supervision and maintenance to be effective. An aerobic bacteriological
farm can digest 90% to 95% of the solid wastes that are deposited into the
septic tank. Typically, oxygen is supplied to a septic system when there
is a problem with pumping frequency or the overall effectiveness of the
system. The typical design of these systems is such that a small
compressor is located near the sewer line as it exits the house, which
provides oxygen for the tank. |
Disinfection Systems:
| Chlorination, ozonation, and ultraviolet disinfection
are the most common methods of disinfection in the U.S.Chlorine, the most
widely used disinfectant in municipal wastewater, destroys organisms by
oxidizing cellular material. Chlorine can be applied as chlorine gas,
hypochlorite solutions, and other chlorine compounds in solid or liquid
form. |
| Ozone, an unstable gas generated by an electrical
discharge through dry air or pure oxygen, is another oxidizing agent.
Ultraviolet radiation, generated by an electrical discharge through
mercury vapor, is absorbed into the genetic material of microorganisms and
hinders their ability to reproduce. |
Care of Septic Systems:
To maximize the useful life of a septic
system and prevent premature failure, all systems require proper care and
periodic maintenance.
| Inspect your septic tank once every
year and pump as necessary. Solids
will eventually fill the tank and pass them into the drain field, mound or
sand filter, which can lead to expensive repairs. |
| Avoid flushing harmful material
into the septic tank. Never put grease, any
kind of paper (other than toilet paper), cigarettes, coffee grounds,
sanitary napkins, solvents, oils, paint, caustic chemicals or pesticides
into the tank. |
| Avoid the use of any type of chemical
or biological septic tank additive.
Additives do not improve the performance in a
septic tank. They are not a substitute for routine pumping, and some can
be harmful to the system or the environment. |
| Use water wisely.
Keep the amount of wastewater entering the septic system well below the
"daily designed flow," which is the maximum number of gallons the system
is designed to handle per day. For a three-bedroom house, the daily
designed flow in gallons per day (gpd) is 450; for a four-bedroom house,
it’s 480 gpd. A septic system cannot be run at its peak capacity for very
long without problems developing. Using more water than the system is
designed to manage is one of the leading causes of premature septic system
failure.
To reduce the risk of water overloads, use "low flow" fixtures on faucets,
showerheads, and toilets (many newer homes come with low flow fixtures).
Front loading washing machines use considerably less water than top load
models. Do laundry throughout the week, rather than all on a single day.
Promptly repair all leaky faucets and toilets. |
| Limit garbage disposal use.
A garbage disposal can lead to a significant increase
in solid build-up and waste strength problems in a septic system.
Therefore, they are not recommended for use with a septic system. If your
house already has one, limit the amount that it is used. |
| Don't construct patios, carports, decks or use
landscaping plastic over the drain field or septic tank.
The system should be kept accessible for proper
maintenance and repair and the drain fields need oxygen in order to work
properly. When soil is compacted, the drain field paved over or covered,
oxygen cannot get into the soil. |
| Keep all vehicles off the septic tank and drain
field areas. Vehicular traffic is a major
cause of damage to septic systems. Septic tanks are typically not designed
for vehicular traffic and may crack or collapse as a result. Drain field
pipes can be easily crushed by cars being driven over them. Vehicles also
compact the surrounding soil, which prevents proper drainage. |
| Direct water from roof drains and surface
drainage away from the drain field and septic tank.
Additional water from these sources may overload the
drain field. Surface and ground water that enters the septic or pump tank
can easily fail a system even though household water use is well within
the design capacity of the system. |
| Don't dispose of water from hot tubs into the
septic tank. Large volumes of water and
residual chlorine can be extremely harmful to your septic system. Check
with local jurisdictions for proper disposal of water from hot tubs.
|
| Keep a detailed record of all maintenance
activities. |
| Be aware of the location of all septic system
components. A septic system as-built is the
best source of this information. Know where the septic tank, pump tank,
drain field and reserve areas are located. Protect these areas from
impacts of any driveway, out building, patio, deck, swimming pool, sports
court or landscaping projects. |
| Don’t plant trees and shrubs over septic tanks
or drain fields. The water-seeking roots of
these plants can damage your home septic system. Grass or shallow-rooted
plants tend to be the best cover for septic systems. |
How will I know when to pump the tank?
| The frequency with which you will need to pump depends on three
variables: the size of your tank, the number of people in the household
contributing to the volume of your wastewater, and the volume of solids in
your wastewater. If you are unsure about when to have the tank pumped,
observe the yearly rate of solids accumulation in the septic tank. The
solids should be pumped out of the septic tank by a licensed septic
contractor. Most county health departments recommend that the accumulated
solids in the bottom of the septic tank be pumped out every three to five
years although if the tank is large and the household is small a tank can
function longer without requiring pumping (see Table 1).
|
Table 1. Estimated Septic Tank Pumping
Frequencies in Years:
|
Tank size* |
Household Size (number of people) |
| (Gals) |
|
|
|
|
|
|
| 500 |
5.8 |
2.6 |
1.3 |
1.0 |
0.7 |
0.4 |
| 750 |
9.1 |
4.2 |
2.6 |
1.8 |
1.3 |
1.0 |
| 900 |
11.0 |
5.2 |
3.3 |
2.3 |
1.7 |
1.3 |
| 1000 |
12.4 |
5.9 |
3.7 |
2.6 |
2.0 |
1.3 |
| 1250 |
15.6 |
7.5 |
4.8 |
3.4 |
2.6 |
2.0 |
| 1500 |
18.9 |
9.1 |
5.9 |
4.2 |
3.3 |
2.6 |
| 1750 |
22.1 |
10.7 |
6.9 |
5.0 |
3.9 |
3.1 |
| 2000 |
25.4 |
12.4 |
8.0 |
5.9 |
4.5 |
3.7 |
| 2250 |
28.6 |
14.0 |
9.1 |
6.7 |
5.2 |
4.2 |
| 2500 |
31.9 |
15.6 |
10.2 |
7.5 |
5.9 |
4.8 |
| For example, when waste backs up in your backyard, the system has
obviously failed. If significant amounts of biological or nutrient
contaminants reach your well or surface waters, the system is also
failing, even though it may appear to be working just fine. |
| Most septic systems are designed to have a lifetime of 20 to 30 years,
under the best conditions. However, many septic systems will fail before
this time. Eventually, the soil around the absorption field becomes
clogged with organic material, making the system unusable.
|
| Many other factors can cause the system to fail well before the end of
its “design” lifetime. Pipes blocked by roots, soils saturated by storm
water, crushed tile, improper location, poor original design or poor
installation can all lead to major problems.
|
| But by far the most common reason for early failure is improper
maintenance by homeowners. When a system is poorly maintained and not
pumped out on a regular basis, sludge (solid material) builds up inside
the septic tank, then flows into the absorption field, clogging it beyond
repair. |
How to know if your system is failing:
These symptoms tell you that you have a serious problem:
| Sewage backup in your drains or toilets. This is often a black liquid
with a disagreeable odor. |
| Slow flushing of your toilets. Many of the drains in your house will
drain much slower than usual, despite the use of plungers or drain
cleaning products. |
| Surface flow of wastewater. Sometimes you will notice liquid seeping
along the surface of the ground near your septic system. It may or may not
have an odor associated with it. |
| Lush green grass over the absorption field, even during dry weather.
Often, this indicates that an excessive amount of liquid from your system
is moving up through the soil, instead of downward, as it should. While
some upward movement of liquid from the absorption field is good, too much
could indicate major problems. |
| The presence of nitrates or bacteria in your drinking water well. This
indicates that liquid from the system may be flowing into the well through
the ground or over the surface. Water tests available from your local
health department will indicate if you have this problem. |
| Buildup of aquatic weeds or algae in lakes or ponds adjacent to your
home. This may indicate that nutrient-rich septic system waste is leaching
into the surface water. This may lead to both inconvenience and possible
health problems. |
| Unpleasant odors around your house. Often, an improperly vented
plumbing system or a failing septic system causes a buildup of
disagreeable odors around the house. |
| A number of products are marketed with the pledge that they can keep
septic systems operating smoothly, correct system upsets, or do away with
the need to pump the tank periodically. Chemical additives are strong acids
or alkalis, or organic solvents. Biological additives are cultures of
harmless bacteria, plus waste-digesting enzymes. These sometimes contain
yeast cultures.
|
| Although some manufacturers of additives have test data showing how their
products perform, there has been almost no independent testing of these
products in full-sized septic systems. The information that exists does not
show improved long-term performance in systems where additives have been
used. If a system is not being misused by the homeowner, these products are
unlikely to pose a benefit. The amount of material added with each dose of
product is very small compared to the biological material already present
and working in the tank.
|
| Occasionally a system suffers an upset, when the septic tank bacteria are
harmed or destroyed. This can happen if the home is vacant for a long period
and the tank receives no fresh wastewater, or if strong cleaning agents are
flushed down the drain. After a few days of normal use, the biological
system in the tank will re-establish itself. In this situation the
biological additives may help speed the recovery of the septic tank.
|
| Every septic tank needs to be pumped periodically, because all wastewater
contains inert matter that cannot be degraded in the tank. No additive can
do away with this need.
|
Could an additive harm my system?
| The biological additives are unlikely to be harmful. The chemical
additives could definitely harm your system. These products have the
potential to sterilize your system temporarily. The resulting passage of
raw sewage into the drain field will hasten its failure. The acid and
alkali products can corrode the plumbing and the tank. The organic
solvents pass through the system unchanged. They can then infiltrate into
the groundwater, creating a chemical plume that endangers nearby wells.
|
Septic System Safety Warnings for Home Owners and Home
Buyers:
Septic system concerns for a building owner start with safety. Here are some
red flags:
| Signs of collapse-possible fatal hazards: include depressions or "soil
subsidence" anywhere on or around the property. Any suspect area should be
roped-off and absolutely no one should walk over or even close to such a
spot until it has been investigated by a professional. |
| Old or abandoned systems: such as site-built cesspools or drywells
were often made with a thin steel or wood cover which with age can
collapse. If the history of the site or visual observation suggests that
there are or were old systems at the property, professional investigation
is warranted. Improper "abandonment" (failing to fill-in a pit) can lead
to sudden collapses. Signs that there may be old systems at a property
might come from anecdotal evidence (ask a neighbor, ask the local septic
installing or service companies), or visual evidence such as seeing
abandoned waste pipes at basement or crawl space walls or floors. Don't
assume that an old house which is now connected to the public sewer didn't
previously have an on-site waste disposal system. |
| Septic service by untrained workers: such as aerating, agitating, or
pumping out an old site-built cesspool, can lead to sudden system
collapse. Prevent access over or near any such systems. |
| Unsanitary conditions such as discharge of sewage effluent to the yard
surface, to a nearby well or stream, or previous septic backups into a
building deserve professional attention. Indoors special cleaning may be
needed to remove bacteria or other pathogens. |
| Septic testing by inexpert "inspectors" who may not follow an adequate
procedure increases the risk of a costly surprise. |
| Uninformed home owners & home buyers may not notice a danger or
malfunction. Home owners & home buyers should review the safety warnings
listed above. The information here is general in nature. Since conditions
and requirements vary widely at individual sites, always obtain
qualified expert advice pertaining to the specific system about which you
have questions, |
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