United States
Environmental Protection
Agency
Office of Water
(WH-595)
830/F-92/001
May 1992
Small Wastewater Systems
Alternative Systems
For Small Communities
And Rural Areas
-------
PAGE NOT
AVAILABLE
DIGITALLY
-------
COMMON ONSITE SYSTEMS
Septic Tank & Gravel
Absorption Trench
This is the most common system used on level land with adequate soil
depth above the water table. Heavy solids in the liquid settle and greases
float to the top of the tank. Bacteria break down some solids. The liquid
flows from the tank through a closed pipe into perforated pipe and into
gravel-filled trenches where it seeps into the soil. Bacteria and oxygen
purify the liquid as it slowly moves through the soil. Inspection ports permit
checking liquid depth. Regular pumping of the tank reduces the solids
discharged into the trenches and extends the life of the system. Using two
compartment septic tanks and resting the trenches (#4) are also recom-
mended to extend trench life.
Septic Tank &
Leaching Chambers
Open bottom concrete chambers or arched plastic chambers create an
underground cavern that stores effluent. The effluent floods the soil
surface prior to seeping vertically through the bottom of the chamber.
Leaching Chambers
Septic Tank With
Serial Distribution
Starting with the highest, each trench fills completely, then overflows
through one drop box to the next. The effluent floods all soil sur-
faces. The drop box enables inspection of the system and control of
discharge into each trench. Capping the pipe outlets in the upper trench
forces resting. Serial distribution automatically loads upper trenches and
minimizes the loading on lower trenches. Used on gently to steeply
sloped sites.
Absorption Field
on Slope
Drop Box
Working
Trenches
\ Trench
Septic Tank With
Alternating Trenches
One set of trenches rests while the other treats the liquid from the septic
tank. This design extends system life and provides a backup should one
field clog. For system repairs, a new field and valve box may be added to
the old system. The new field works while the old field rests and renews.
Switch the fields annually in the summer.
Valve Box
Working Trenches
Septic Tank
Resting Trenches
Pressure Dosed
Distribution
A pump or siphon doses a pressure distribution manifold that disperses the
effluent evenly to each trench. Dosing prolongs system life by flooding a
larger area and by forcing the exchange of air in the soil. Dosed systems
are more common for larger flows. The pressure manifold can include
valves or plugs that permit more control over trench loading or trench
resting. Annual inspection is suggested.
Shallow Trench
Low-Pressure Pipe Distribution
Small diameter pipe, located at a more shallow depth than a conventional
system, receives pumped effluent. Effluent moves under pressure through
small holes in the pipe and soaks the entire trench network area. Even
dosing of more open and aerobic soil horizons improves treatment. Used
in areas with high groundwater or shallow soils (because it places the
treatment higher in the soil profile) or on steep slopes that require hand
excavation. Professional maintenance is needed to flush the lines
annually.
Small Diameter
Pressure Distribution
Septic Tank
Cleanout
-------
iPTIONS FOR DIFFICULT SIT
Pretreatment &
Soil Absorption
Pretreatment addresses the need to treat higher strength waste (such as from restaurants) and can help repair biologically overloaded systems where no
additional absorption area is available. Aerobic treatment systems and filters can be used for this purpose. For aerobic treatment (called "package plants"),
wastewater and air mix in a tank. Bacteria grow in the tank and break down the waste. For filters, septic tank effluent passes over porous media that trap the
solids. Bacteria that grow in the media break down the waste. Professional maintenance by certified operators and a lot of energy are required for aerobic
systems.
(A) Aerobic Treatment System
OR
(B) Sand Filter
Septic Tank &
Mound System
Pumps dose effluent (#6) into a gravel bed or trenches on top of a bed of
sand. Sandy soil carefully placed above the plowed ground surface treats
the effluent before it moves into the natural soil. The system extends
onsite system use in areas with high groundwater, high bedrock, or tighter
clay soils. Regular inspection of the pumps and controls and flushing of the
distribution network are needed.
Vegetation
Pressure Distribution Top Soil Absorption Field
Cross-Section
Diagram
Evaporation &
Absorption Bed
Effluent from a septic tank or aerobic tank flows into gravel trenches or
chambers in a mound of sandy soil. Less permeable soil placed at the
surface of the mound helps shed rain from the system. Trees that grow
around the system and plants on top of the system pull liquid from the
sand and transpire the water into the air. Some effluent may seep into the
soil. This system requires a climate where evaporation consistently
exceeds rainfall.
Rocky or Tight Soil or High Groundwater
Septic Tank, Sand Filters,
Disinfection & Discharge
Open or buried beds of sand may receive single or repeated applications
of effluent. Effluent passes through the media and drains from the gravel
and pipe network below the filter. Effluent may be discharged to the
environment directly or into a soil absorption or land treatment system
(#16). Disinfection often precedes discharge into a stream or land
irrigation. Certain types of filters can significantly reduce nitrogen and may
be used in areas where soil absorption is not possible. Requires inspec-
tion and periodic maintenance. Surface discharge requires management.
Constructed
Wetlands
Effluent from a series of septic tanks passes through a bed of rocks
planted with reeds. Liquid evaporates and drains into a soil absorption
system or discharges. Used for additional treatment or where soils are not
suitable for absorption. Discharge usually requires disinfection.
Vegetation
(Optional)
Disinfection
(Optional)
& Discharge
Septic
Tanks
Recirculation Tank
-------
OPTIONS FOR SPECIAL SITUATIONS
Holding
Tank
Sewage flows from low-flush toilets and water-saving fixtures into a large
watertight storage tank. The alarm in the tank signals the owner to have
the sewage hauled away. Only recreational housing utilizes holding tanks
because of the high hauling cost. Public management is frequently
required. Contracting for hauling helps to reduce costs.
Lagoon
A series of septic tanks or other pretreatment systems (#7, #10, #11)
discharge into a lagoon. Sunlight and long storage limes support the
natural breakdown of the waste and die off of harmful organisms. Effluent
evaporates, slowly seeps into the soil, or receives further treatment
through land application (#16). Onsite lagoons require large lots and may
be fenced.
Visible
Alarm
Watertight Tank
Evaporation
From
Home
Infiltration
Waterless or Ultra Low-Flush
Toilet System
Composting Toilets: No water
Serve commercial and single family units. Well-designed units produce a
dry mixture that should be managed by professionals. Reduces discharge
of nutrients into water resources. Electric vent, fan, and heating element
common. Proper care is essential.
Incinerating: No water
Electricity, gas, or oil burns solids and evaporates the liquid, which is
vented to the roof. Small amounts of ash are removed weekly. Proper care
is essential. Limited to less frequent use sites, such as recreational cabins.
Water Conservation Toilets: Low water
Low-flush toilets use 1.6 gallons or less per flush. They generally cost
slightly more than conventional units, but pay for themselves by lowering
the water bill. They perform well. Many work as well as 4 gallons per flush
models.
Recycling Water: Low water
Treated wastewater or graywater recycles to flush toilets. Treatment
systems use electricity and require professional maintenance.
Dual
Systems
Two systems treat the waste. Composting toilets or low-flush (1.6 gallons
or less) toilets coupled with a holding tank (#14, #12) exclude nutrient rich
toilet wastes (blackwater) from the wastewater disposal system. All other
household wastewater (graywater) must be treated in an approved septic
tank and absorption system, which is usually smaller.
(A) Blackwater (Toilet Wastes)
(B) Graywater
(Other Household Wastewater)
To Septic Tank or Other
Approved Treatment
& Disposal
Land
1 Application
Effluent from a septic tank is further treated (#7, #10, #11, #13) and stored. Timed
sprinklers apply the effluent at night or below the soil surface to plants and trees in
a large treatment area. Protects high groundwater in more permeable soils as
plants take up nutrients and water. Disinfection and fencing may be required for
individual home use. More common in warm climates, but not widely permitted by
health authorities.
(A) Slow-Rate Land Treatment
(B) Overland Flow
Constructed Wetland
or Other Pretreatment
& Storage
Collect Effluent
for Reuse or
Discharge
Treated effluent from a lagoon (#13) or wetland (#11) is sprayed
on the surface of a gentle, grass covered slope. Effluent flows
over the clay soil through the grass and collects at the base
where it is disinfected before being discharged. Best for tight
soils where absorption systems are not possible. A professional
operator usually cares for the grass and disinfection system.
-------
COLLECTION OPTIONS FOR OFFSITE TREATMENT
Small Diameter
Gravity Sewers
Liquid from a septic tank flows under low pressure in 3-inch or larger
collection pipes. Houses below the pipe must use small pumps (septic
tank effluent pumps such as #19A and #20). Houses higher than the
pipes may drain by gravity. Larger developments favor treatment by a
discharging technology such as #10, #11, #13, or #16. Common in rural
areas where the community treatment site is generally downhill. Central
management is required.
Soil Absorption Field or Other
Treatment & Disposal
Vacuum
" Sewers
A vacuum station maintains a vacuum in the collection lines. When the
sewage from one or several homes fills the storage pit, a valve opens, and
the sewage and air rush into the collection line toward the vacuum station.
Pumps in the vacuum station transfer the sewage to a treatment system.
Power is required only at the vacuum station. Most economical where
many homes are served or in areas with high excavation costs and lift
stations. Requires a professional operator.
Sewage
from Dwelling
li
Central Vacuum
Pump
Septic
Tank
Central Collector Pipe
Pressure Sewers: Grinder Pump (GP) or
Septic Tank Effluent Pump (STEP)
Sewage is first pretreated in a septic tank or grinder pump and then a pump forces the liquid through small diameter lines to a conventional gravity sewer or to a
neighborhood treatment plant such as #10, #11, #13, or #16. The community usually owns and operates shared pumping units. Plastic lines located near the
surface ease installation and reduce cost. Best for low-density or slow-growth areas or where conventional sewers are costly. Central management is required.
(A) Septic Tank Effluent Pumping System
(B) Grinder Pump System
Separate or Integrated
Septic & Pumping Tank
To Effluent Sewer
To Pressure Sewer
Storage
Tank
Alternative Effluent
Collection
System
Liquid from most onsite septic tanks flows by gravity in small diameter effluent lines
(#17) to a small neighborhood pump station on public property. A few homes below the
sewer may also use small effluent pumps. The neighborhood lift station stores the
liquid then pumps it into a higher pressure sewer going to a treatment system. This
design can cut costs in flat terrain or where one pump unit can easily serve a number
of homes. Central management is required.
Pump
Station
Low-
Pressure]
Sewer
Pumping
Station with
Effluent Pump
-------
Lower Water &
Sewer Rates
Rates skyrocket when a few people have
to pay for a large sewer system. Small
natural systems are generally much
simpler to operate and maintain and make
use of the inherent capacity of the land.
Save Energy,
Water & Materials
Most small systems rely on the soil,
Save Prime Farmland &
Prevent Urban Sprawl
Large regional sewage systems in rural
natural biological processes, and recharge areas encourage growth and loss of open
of groundwater as well as use much less space.
energy and mechanical equipment.
U.S. EPA's Small Community Outreach & Education (SCORE) Program
If your small community needs to build or upgrade its wastewater system, one of the small systems this foldout describes may be for
you. This foldout is one of several publications, available through the SCORE program, that provides useful information on financial
management and appropriate technology for small communities. EPA's SCORE program can direct you to organizations that can
give you additional information or technical assistance. Check with your EPA Regional Office SCORE coordinator or the National
Small Flows Clearinghouse.
Total System Management Makes It Possible
The figure for Skiville and Lake Pristine shows a variety of technologies serving different land uses and environments, all served by
one wastewater management entity. More restrictive environments require a variety of advanced systems that need careful siting,
design, and construction as well as more oversight of operation and maintenance. Total system management provides the expertise
and oversight to insure this careful siting and design. Total system management also certifies that the system is properly built. During
construction some systems installed in fragile environments require frequent inspection by trained professionals. Having a manage-
ment agency also assures the community that the systems will be cared for. Many communities choose operating permits to guaran-
tee maintenance by professionals, while other communities own onsite systems and assume the responsibility for system inspection
and maintenance. Finally, the management agency educates the citizens on the value of their systems and how to protect their
investment and the environment.
Through total system management, small communities can maintain their rural character while having the freedom to develop natural
systems that harmonize with the environment. Communities may also choose less expensive alternative sewers with cluster treatment
systems that reduce collection cost, the most expensive component of wastewater systems. For small communities and rural areas, a
variety of professionally managed natural systems are usually less expensive, simpler to operate, require less energy, and can be
more reliable than a conventional mechanical treatment system.
Other Small Community Systems Information Available From:
National Small Flows Clearinghouse
West Virginia University, PO Box 6064, Morgantown, WV 26506
800-624-8301
Or Your EPA Regional SCORE Coordinators:
1. Boston
(CT, ME, MA, NH, Rl, VT)
JFK Federal Bldg.
1 Congress St.
Boston, MA 02203
(617)565-3492
2. New York
(NJ, NY, PR, VI)
26 Federal Plaza
New York, NY 10278
(212)264-8969
3. Philadelphia
(DE, MD, PA, VA, WV, DC)
841 Chestnut Bldg.
Philadelphia, PA 19107
(215)597-6526
4. Atlanta
(AL, GA, FL, MS, NC, SC, TN, KY)
345 Courtland St., NE
Atlanta, GA 30365
(404) 347-3633
5. Chicago
(IL, IN, OH, Ml, MN, Wl)
77 W. Jackson
Chicago, IL 60604
(312)886-0246
6. Dallas
(AZ, LA, OK, TX, NM)
1445 Ross Ave.
11th Floor, Suite 1200
Dallas, TX 75202
(214)655-7130
7. Kansas City
(IA, KS, MO, NE)
726 Minnesota Ave.
Kansas City, KS 66101
(913)551-7217
8. Denver
(CO, UT, WY, MT, ND, SD)
999 18th St., Suite 500
Denver, CO 80202-2405
(303)294-1169
Center for Environmental Research Information
26 West Martin Luther King Drive, Cincinnati, OH 45268
(513)569-7562
9. San Francisco
(AR, CA, Guam, HI, NV, American Samoa)
75 Hawthorne St.
San Francisco, CA 94105
(415)744-1935
10. Seattle
(AK, ID, OR, WA)
1200-6th Ave.
Seattle, WA 98101
(206) 553-8575
Engineers, Regulators, and Consultants: For
detailed technical information, get EPA's Onsite
Wastewater Treatment and Disposal Systems
Design Manual, Septage Treatment and Disposal
Handbook, Alternative Sewer Systems Design
Manual and others from the Center for
Environmental Research Information, 26 W.
Martin Luther King Dr., Cincinnati, OH 45268,
(513)569-7562.
This publication is not meant to be a comprehensive guide to alternative systems. It tries to acquaint the layperson with some representative systems used in
the United States. EPA does not endorse, approve, or disapprove any system here. Not all systems shown are approved by all jurisdictions.
------- |