People and the environment can be harmed if a home's onsite wastewater treatment system does not work properly after a flood or power outage. This publication explains the steps to take after such an event to get the system back into service. 4 pp., 1 figur

Alexander, Rachel

Lesikar, Bruce J.

Mechell, Justin

Texas A&M University

1) Source
Well
2) Collection 
and storage
3) Pretreatment
Groundwater
4) Final treatment and dispersal
Onsite wastewater treatment systems
Responding to power outages 
and floods
L-5475
9-08
Figure 1:  Components of an onsite wastewater treatment system.
Electrical power outages and floods can affect a home’s onsite wastewater treatment system. Onsite wastewater treatment systems remove organic matter, solids and living organisms (viruses, bacteria, and protozoa from 
wastewater. If a wastewater treatment system stops working properly, it can result 
in harm to people and the environ-
ment.
The appropriate response to a 
disaster depends upon the type of di-
saster and the type of treatment unit 
at your home. To properly respond, 
homeowners need to know the com-
ponents of their on-site wastewater 
treatment systems as well as the steps 
to take after a power outage or flood. 
Components
Onsite wastewater treatment 
systems can be divided into four com-
ponents: 1) wastewater source or use, 
2) wastewater collection and storage, 
3) pretreatment, and 4) final treat-
ment and dispersal. 
The wastewater source or use is 
the home or a business that the waste-
water treatment system is serving. 
The wastewater collection sys-
tem is generally the plumbing that 
conveys the wastewater from the 
source to the pretreatment compo-
nent. Most collection components are 
constructed of piping with an access 
port placed on a slope to allow gravity 
to move the waste and water to the 
pretreatment component. 
However, some collection com-
ponents have a pump tank and pump 
placed in the plumbing network to 
collect wastewater from the source 
and then pump the wastewater to the 
pretreatment components. 
Bruce Lesikar, Courtney O’Neill and David Smith
Professor and Extension Agricultural Engineer, Extension Assistant and Extension Assistant 
The Texas A&M System 
The pretreatment component 
varies with site conditions and the 
type of final treatment and dispersal 
component installed. Pretreatment 
components include septic tanks, 
aerobic treatment units, media filters, 
constructed wetlands, and/or disin-
fection units.
The pretreatment component 
removes contaminants from the 
wastewater to obtain an effluent (out-
flow) that can be accepted and treated 
by the final treatment and dispersal 
component. 
The final treatment and dispersal 
component completes the treatment 
process and disperses the effluent 
into the receiving environment. Final 
treatment and dispersal components 
include media-filled trenches, gravel-
less trench technology, low-pressure 
pipe drain fields, drip distribution 
fields, and spray distribution fields. 
For more information on these 
technologies, visit the Onsite Waste-
water Treatment & Reuse Web site at 
http://ossf.tamu.edu.
Electrical outages
The most common cause for an 
interruption of service for an onsite 
wastewater treatment system is an 
electrical outage. The appropriate 
response depends on the type of 
pretreatment and final treatment and 
dispersal components of your onsite 
wastewater treatment system. 
A gravity collection system 
feeding into a septic tank and gravity 
distribution soil absorption area will 
continue to operate properly, and you 
will be able to continue using your 
system. 
However, if your system contains 
electrical components, the wastewater 
will collect in the system during the 
electrical outage, and it will have to 
be treated and dispersed after electri-
cal service resumes. 
Onsite wastewater treatment 
components that use electricity 
include:
Aerobic treatment units ✔
Sand filters ✔
Recirculating media filters ✔
Flow equalization tanks ✔
Low pressure distribution ✔
Subsurface drip distribution ✔
Spray distribution ✔
These components usually have a 
reserve or alarm capacity that allows 
some water usage during electrical 
power outages or when the compo-
nents break. However, that reserve is 
small. 
For example: In Texas, an onsite 
wastewater treatment system serving 
a three-bedroom house is required 
to be able to treat at least 240 gallons 
of wastewater a day. State regulations 
stipulate that a system requiring elec-
tricity must have minimum reserve 
capacity of one-third the amount 
of wastewater that the system was 
designed to treat in a day. Thus, an 
onsite wastewater treatment system 
for a three-bedroom residence must 
have a reserve capacity of 80 gallons. 
In a typical shower, 2.5 gallons 
are used per minute, so one 10-min-
ute shower would send 25 gallons 
to the wastewater treatment system. 
Toilets use from 1.6 to 2.5 gallons per 
flush. A reserve capacity of 80 gallons 
would allow very little emergency 
water usage per day.
If your system has electrically 
operated components and the power 
goes out:
Limit your water usage to es- ✔
sentials such as toilet flushing 
and hand washing. Minimize 
or eliminate laundry, bathing, 
showering, and dishwashing.
Stop all water use if the electri- ✔
cal outage is extended or the 
plumbing begins to drain slowly. 
Slow-draining plumbing may 
indicate that the reserve capacity 
is exceeded and the system is full. 
Once power is restored:
Limit laundry and dishwashing  ✔
if your system has an advanced 
pretreatment component and the 
power outage is less than 1 day. If 
the power outage is longer than 
a day, discontinue these activi-
ties for a day, and limit shower 
time and bathwater volume for 
at least 1 day. This period allows 
the microorganisms that treat 
the wastewater to begin work-
ing again and properly treat the 
wastewater. 
Allow the system to continue  ✔
to operate normally until the 
water level drops to the normal 
operating level in the system. A 
time-dosed system may take 24 
hours to have all the stored water 
distributed and the high-water 
alarm deactivated.
System components that require  ✔
electricity are usually equipped 
with a high-water alarm. When 
the power is restored, this alarm 
may sound, depending on your 
water usage during the power 
outage. You can silence the alarm 
if it has a silence switch option. 
Contact your service provider if 
the alarm remains activated for 
more than 24 hours. 
If your final treatment and  ✔
dispersal component has an on-
demand pumping system (that is, 
if it is a low-pressure or subsur-
face drip distribution system), 
you may need to manually con-
trol the length of time that the 
treated wastewater is delivered to 
the dispersal field immediately 
after the outage, to prevent flood-
ing of the field. Otherwise, the 
first dose after the power is re-
stored can overload your system, 
and untreated wastewater could 
flow onto your lawn. 
If  ✔ the power outage lasted less 
than a day and you minimized 
water usage during the out-
age, your system will probably 
recover by itself. However, if the 
power was out for more than a 
day, check your system design 
information to find out the usual 
dosage and rest times. After the 
power outage, allow the pump 
to operate for its usual dosage 
time, then turn the power off by 
flipping the breaker. Wait for the 
specified rest period, then allow 
another dosage for the usual 
amount of time. Continue this 
pattern until the pump turns off 
by itself after its normal dosage 
time. 
An  ✔ alternative is to ask your 
service provider for instructions 
on how your system should be 
brought back into operation after 
a power outage.
If your system’s final treatment  ✔
and dispersal component is a 
spray distribution system, and 
the power outage was longer than 
1 day, the effluent being distrib-
uted on the ground surface may 
not be treated to its normal ex-
pected quality. You should make 
sure the disinfection treatment 
component is working correctly, 
and limit activity in the distribu-
tion area while the ground and 
grass are moist after the treated 
wastewater is sprayed there. 
Flooding
In a flood, an onsite wastewater 
treatment system may become inun-
dated with surface water. The extent 
of the flooding’s effect on the system 
will be related to the amount of water 
flooding over the system and the 
length of time the system is flooded. 
During a flood: 
Discontinue electrical power to  ✔
the system by turning the power 
off at the main circuit panel.
Stop water usage going into the  ✔
system because it may not receive 
much treatment.
To prevent water from backing  ✔
up through the system and into 
the home, plug any floor drains 
in the home connected to the 
wastewater treatment system. 
After a flood:
Do not use the system until the  ✔
floodwater has receded from all 
components of the system. 
Inspect the system for any signs  ✔
of damage to its surface, such as 
damaged lids or inspection ports, 
or exposed components because 
soil has washed away. 
If the system components are  ✔
filled with floodwater, call a ser-
vice provider to check the system 
for sediment or other debris. 
Some water may be removed 
from the pretreatment compo-
nents to reduce the water level 
to the normal operating level. 
Do not pump the tanks empty 
or below their normal operat-
ing level because the ground 
will usually be saturated after 
flooding. Empty tanks are buoy-
ant and will tend to float out of 
the ground. This upward force 
can make the tanks shift, which 
could damage the piping or even 
cause the tanks to float to the 
ground surface.
If your final treatment and dis- ✔
persal component is a trench sys-
tem and it has inspection ports, 
the service provider may be able 
to pump water from the trenches 
to help the soil dry and aerate. 
If the onsite wastewater treat- ✔
ment system has components 
requiring electrical power, the 
ability to restart the system 
depends on the flood elevation. 
If the floodwater covered only 
the tanks and the components in 
the tanks, the system may be able 
to be restarted without further 
evaluation of the components. If 
the floodwater covered the com-
ponents located on the ground 
surface (such as air pumps or 
panels), have the system in-
spected by a service provider to 
determine the condition of the 
components before using the 
system and restarting electrical 
service.
If your system’s final treatment  ✔
and dispersal component is a 
spray distribution system, the 
effluent being distributed on 
the ground surface may not be 
treated to its normal expected 
quality. The microbes (microor-
ganisms) providing the treatment 
need a day or two to recover and 
provide proper treatment. Make 
sure the disinfection treatment 
component is working correctly, 
and limit activity in the distri-
bution area while the ground 
and grass are moist after a spray 
distribution event.
Summary
Electrical power outages and 
floods can affect your wastewater 
system. During and after these events, 
wastewater treatment can be limited 
and can pose health concerns and 
hazards if not managed appropriately. 
Know the components of your 
onsite wastewater treatment system 
and the proper response after a flood 
or power outage. 
This publication was funded by the Rio Grande Basin Initiative administered by the Texas Water Resources Institute of 
the Texas AgriLife Extension Service, with funds provided through a grant from the Cooperative  
State Research, Education, and Extension Service, U.S. Department of Agriculture, under Agreement  
No. 2005-45049-03209.
The Onsite Wastewater Treatment Systems series of publications is a result of collaborative efforts of various agencies, 
organizations and funding sources. We would like to acknowledge the following collaborators:
Texas State Soil and Water Conservation Board USEPA 319(h) Program
Texas On-Site Wastewater Treatment Research Council Texas AgriLife Extension Service
Texas Commission on Environmental Quality Texas AgriLife Research
Consortium of Institutes for Decentralized Wastewater Treatment USDA Natural Resources Conservation Service
Educational programs of the Texas AgriLife Extension Service are open to all people without regard to race, color, sex, disability, 
religion, age, or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as 
amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Edward G. Smith, Director, Texas 
AgriLife Extension Service, The Texas A&M University System. 
10M, Revision
Produced by AgriLife Communications, The Texas A&M System
Extension publications can be found on the Web at: http://AgriLifeBookstore.org.
Visit Texas AgriLife Extension Service at http://AgriLifeExtension.tamu.edu.
All publications in the On-Site Wastewater Treatment Systems series can be downloaded from the World Wide Web at:  
http://AgriLifeExtension.tamu.edu.


English

Onsite Wastewater Treatment Systems: Responding to Power Outages and Floods

Texas A&amp;M Repository

1) SourceWell2) Collection and storage3) PretreatmentGroundwater4) Final treatment and dispersalOnsite wastewater treatment systemsResponding to power outages and floodsL-54759-08Figure 1:  Components of an onsite wastewater treatment system.Electrical power outages and floods can affect a home’s onsite wastewater treatment system. Onsite wastewater treatment systems remove organic matter, solids and living organisms (viruses, bacteria, and protozoa from wastewater. If a wastewater treatment system stops working properly, it can result in harm to people and the environ-ment.The appropriate response to a disaster depends upon the type of di-saster and the type of treatment unit at your home. To properly respond, homeowners need to know the com-ponents of their on-site wastewater treatment systems as well as the steps to take after a power outage or flood. ComponentsOnsite wastewater treatment systems can be divided into four com-ponents: 1) wastewater source or use, 2) wastewater collection and storage, 3) pretreatment, and 4) final treat-ment and dispersal. The wastewater source or use is the home or a business that the waste-water treatment system is serving. The wastewater collection sys-tem is generally the plumbing that conveys the wastewater from the source to the pretreatment compo-nent. Most collection components are constructed of piping with an access port placed on a slope to allow gravity to move the waste and water to the pretreatment component. However, some collection com-ponents have a pump tank and pump placed in the plumbing network to collect wastewater from the source and then pump the wastewater to the pretreatment components. Bruce Lesikar, Courtney O’Neill and David SmithProfessor and Extension Agricultural Engineer, Extension Assistant and Extension Assistant The Texas A&M System The pretreatment component varies with site conditions and the type of final treatment and dispersal component installed. Pretreatment components include septic tanks, aerobic treatment units, media filters, constructed wetlands, and/or disin-fection units.The pretreatment component removes contaminants from the wastewater to obtain an effluent (out-flow) that can be accepted and treated by the final treatment and dispersal component. The final treatment and dispersal component completes the treatment process and disperses the effluent into the receiving environment. Final treatment and dispersal components include media-filled trenches, gravel-less trench technology, low-pressure pipe drain fields, drip distribution fields, and spray distribution fields. For more information on these technologies, visit the Onsite Waste-water Treatment & Reuse Web site at http://ossf.tamu.edu.Electrical outagesThe most common cause for an interruption of service for an onsite wastewater treatment system is an electrical outage. The appropriate response depends on the type of pretreatment and final treatment and dispersal components of your onsite wastewater treatment system. A gravity collection system feeding into a septic tank and gravity distribution soil absorption area will continue to operate properly, and you will be able to continue using your system. However, if your system contains electrical components, the wastewater will collect in the system during the electrical outage, and it will have to be treated and dispersed after electri-cal service resumes. Onsite wastewater treatment components that use electricity include:Aerobic treatment units ✔Sand filters ✔Recirculating media filters ✔Flow equalization tanks ✔Low pressure distribution ✔Subsurface drip distribution ✔Spray distribution ✔These components usually have a reserve or alarm capacity that allows some water usage during electrical power outages or when the compo-nents break. However, that reserve is small. For example: In Texas, an onsite wastewater treatment system serving a three-bedroom house is required to be able to treat at least 240 gallons of wastewater a day. State regulations stipulate that a system requiring elec-tricity must have minimum reserve capacity of one-third the amount of wastewater that the system was designed to treat in a day. Thus, an onsite wastewater treatment system for a three-bedroom residence must have a reserve capacity of 80 gallons. In a typical shower, 2.5 gallons are used per minute, so one 10-min-ute shower would send 25 gallons to the wastewater treatment system. Toilets use from 1.6 to 2.5 gallons per flush. A reserve capacity of 80 gallons would allow very little emergency water usage per day.If your system has electrically operated components and the power goes out:Limit your water usage to es- ✔sentials such as toilet flushing and hand washing. Minimize or eliminate laundry, bathing, showering, and dishwashing.Stop all water use if the electri- ✔cal outage is extended or the plumbing begins to drain slowly. Slow-draining plumbing may indicate that the reserve capacity is exceeded and the system is full. Once power is restored:Limit laundry and dishwashing  ✔if your system has an advanced pretreatment component and the power outage is less than 1 day. If the power outage is longer than a day, discontinue these activi-ties for a day, and limit shower time and bathwater volume for at least 1 day. This period allows the microorganisms that treat the wastewater to begin work-ing again and properly treat the wastewater. Allow the system to continue  ✔to operate normally until the water level drops to the normal operating level in the system. A time-dosed system may take 24 hours to have all the stored water distributed and the high-water alarm deactivated.System components that require  ✔electricity are usually equipped with a high-water alarm. When the power is restored, this alarm may sound, depending on your water usage during the power outage. You can silence the alarm if it has a silence switch option. Contact your service provider if the alarm remains activated for more than 24 hours. If your final treatment and  ✔dispersal component has an on-demand pumping system (that is, if it is a low-pressure or subsur-face drip distribution system), you may need to manually con-trol the length of time that the treated wastewater is delivered to the dispersal field immediately after the outage, to prevent flood-ing of the field. Otherwise, the first dose after the power is re-stored can overload your system, and untreated wastewater could flow onto your lawn. If  ✔ the power outage lasted less than a day and you minimized water usage during the out-age, your system will probably recover by itself. However, if the power was out for more than a day, check your system design information to find out the usual dosage and rest times. After the power outage, allow the pump to operate for its usual dosage time, then turn the power off by flipping the breaker. Wait for the specified rest period, then allow another dosage for the usual amount of time. Continue this pattern until the pump turns off by itself after its normal dosage time. An  ✔ alternative is to ask your service provider for instructions on how your system should be brought back into operation after a power outage.If your system’s final treatment  ✔and dispersal component is a spray distribution system, and the power outage was longer than 1 day, the effluent being distrib-uted on the ground surface may not be treated to its normal ex-pected quality. You should make sure the disinfection treatment component is working correctly, and limit activity in the distribu-tion area while the ground and grass are moist after the treated wastewater is sprayed there. FloodingIn a flood, an onsite wastewater treatment system may become inun-dated with surface water. The extent of the flooding’s effect on the system will be related to the amount of water flooding over the system and the length of time the system is flooded. During a flood: Discontinue electrical power to  ✔the system by turning the power off at the main circuit panel.Stop water usage going into the  ✔system because it may not receive much treatment.To prevent water from backing  ✔up through the system and into the home, plug any floor drains in the home connected to the wastewater treatment system. After a flood:Do not use the system until the  ✔floodwater has receded from all components of the system. Inspect the system for any signs  ✔of damage to its surface, such as damaged lids or inspection ports, or exposed components because soil has washed away. If the system components are  ✔filled with floodwater, call a ser-vice provider to check the system for sediment or other debris. Some water may be removed from the pretreatment compo-nents to reduce the water level to the normal operating level. Do not pump the tanks empty or below their normal operat-ing level because the ground will usually be saturated after flooding. Empty tanks are buoy-ant and will tend to float out of the ground. This upward force can make the tanks shift, which could damage the piping or even cause the tanks to float to the ground surface.If your final treatment and dis- ✔persal component is a trench sys-tem and it has inspection ports, the service provider may be able to pump water from the trenches to help the soil dry and aerate. If the onsite wastewater treat- ✔ment system has components requiring electrical power, the ability to restart the system depends on the flood elevation. If the floodwater covered only the tanks and the components in the tanks, the system may be able to be restarted without further evaluation of the components. If the floodwater covered the com-ponents located on the ground surface (such as air pumps or panels), have the system in-spected by a service provider to determine the condition of the components before using the system and restarting electrical service.If your system’s final treatment  ✔and dispersal component is a spray distribution system, the effluent being distributed on the ground surface may not be treated to its normal expected quality. The microbes (microor-ganisms) providing the treatment need a day or two to recover and provide proper treatment. Make sure the disinfection treatment component is working correctly, and limit activity in the distri-bution area while the ground and grass are moist after a spray distribution event.SummaryElectrical power outages and floods can affect your wastewater system. During and after these events, wastewater treatment can be limited and can pose health concerns and hazards if not managed appropriately. Know the components of your onsite wastewater treatment system and the proper response after a flood or power outage. This publication was funded by the Rio Grande Basin Initiative administered by the Texas Water Resources Institute of the Texas AgriLife Extension Service, with funds provided through a grant from the Cooperative  State Research, Education, and Extension Service, U.S. Department of Agriculture, under Agreement  No. 2005-45049-03209.The Onsite Wastewater Treatment Systems series of publications is a result of collaborative efforts of various agencies, organizations and funding sources. We would like to acknowledge the following collaborators:Texas State Soil and Water Conservation Board USEPA 319(h) ProgramTexas On-Site Wastewater Treatment Research Council Texas AgriLife Extension ServiceTexas Commission on Environmental Quality Texas AgriLife ResearchConsortium of Institutes for Decentralized Wastewater Treatment USDA Natural Resources Conservation ServiceEducational programs of the Texas AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin.Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Edward G. Smith, Director, Texas AgriLife Extension Service, The Texas A&M University System. 10M, RevisionProduced by AgriLife Communications, The Texas A&M SystemExtension publications can be found on the Web at: http://AgriLifeBookstore.org.Visit Texas AgriLife Extension Service at http://AgriLifeExtension.tamu.edu.All publications in the On-Site Wastewater Treatment Systems series can be downloaded from the World Wide Web at:  http://AgriLifeExtension.tamu.edu.

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Onsite Wastewater Treatment Systems: Responding to Power Outages and Floods

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Onsite Wastewater Treatment Systems: Responding to Power Outages and Floods

Abstract

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Full text

Available Versions

Texas A&M University

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Texas A&M Repository