United States
Environmental Protection
Agency
Office of Wastewater
Management
(4201)
EPA 832-K-96-001
Summer 1996
Sanitary Sewer Overflows
What are they,
and how do we reduce them?
What Are Sanitary Sewer Overflows?
sanitary sewer overflow can spill raw sewage
J* into basements or out of manholes and onto city
%"*>^*V *
**- ^streets, playgrounds and into streams, before it
can reach a treatment facility.
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EPA has found that Sanitary Sewer Overflows
(SSOs) caused by poor sewer collection system man-
agement pose a substantial health and environmental
challenge in some parts of our nation. The response to
this challenge varies considerably from state to state.
Many municipalities have asked for national consisten-
cy in the way permits are considered for wastewater
discharges, including SSOs, and in enforcement of the
law prohibiting unpermitted discharges.
Sewage gushes from a manhole.
(Photo courtesy of ADS/Environmental Services, Inc.)
In response, EPA has convened representatives of
states, municipalities, health agencies, and environ-
mental advocacy groups to advise the Agency on how
best to meet this challenge. This SSO Federal Advisory
Subcommittee examines the need for national consisten-
cy in permitting and enforcement, effective sewer oper-
ation and maintenance principles, public notification
for SSOs with potential health or environmental dan-
gers, and other public policy issues.
EPA carefully considers the Subcommittee's recom-
mendations for regulatory and nonregulatory actions to
reduce SSOs nationally.
, - <:.-,
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[ Sanitary Sewer Overflows
sewer systems comes from service lines. The chart
below shows major types of problems that cause SSOs
most frequently.
A deteriorating sewer system. When sewers are
not properly installed or maintained, widespread
problems that can be expensive to fix develop
over time. Some municipalities have found severe
problems, necessitating billion-dollar correction
programs. Often, communities have had to curtail
new development until problems are corrected or
system capacity is increased.
Estimated Occurence of Sanitary Sewer Overflows by Cause
Insufficient System
Capacity
Pipo
Broaks
Based on a sample
o( six communities.
Tbo cause 5 erf SSOs can
wuysignKcantiyhom
community to community.
Pipe
Blockages
What Health Risks Do SSOs Present? 1
.;..;. ...:,..;:...,,.;;-;Ji
ecause SSOs contain raw sewage they can carry
. bacteria, viruses, protozoa (parasitic organisms),
'helminths (intestinal worms), andbioaerosols
(inhalable molds and fungi). The diseases they may
cause are shown in the table on the next page and
range in severity from mild gastroenteritis (causing
stomach cramps and diarrhea) to life-threatening ail-
ments such as cholera, dysentery, infectious hepatitis,
and severe gastroenteritis.
People can be exposed through:
Sewage in drinking water sources.
Direct contact in areas of high public access such
as basements, lawns or streets, or to waters used
for recreation. At least one study has estimated a
direct relationship between gastrointestinal illness
contracted while swimming and bacteria levels in
the water.1
Shellfish harvested from areas contaminated by
raw sewage. One study indicates that an average
of nearly 700 cases of illness per year were report-
ed in the 1980s from eating shellfish contaminat-
ed by sewage and other sources. The number of
unreported cases is estimated to be 20 times that.2
Some cases of disease contracted through inhala-
tion and skin absorption have also been documented.3
% 4: - What Other Damage Can SSOs Do?
I SOs also damage property and the environment.
iWhen basements flood, the damaged area must
thoroughly cleaned and disinfected to reduce
the risk of disease. Cleanup can be expensive for
homeowners, and municipalities. Rugs, curtains,
flooring, wallboard panels, and upholstered furniture
usually must be replaced.
A key concern with SSOs which enter rivers,
lakes, streams, oceans, or brackish waters is their
effect on water quality. When bodies of water cannot
be used for drinking water, fishing, or recreation soci-
ety experiences an economic loss. Tourism and water-
front home values may fall. Fishing and shellfish har-
vesting may be restricted or halted. SSOs can also
close beaches. One 1994 study claims that SSOs
closed beaches across the nation that year for more
than 300 days.4
Sewage in streets exposes adults and children to pathogens. (Photo
courtesy of U.S. EPA.)
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What are they, and how do we reduce them? ;
/How Big Is the Problem?
,» * o - > <- > -
f"*£ ~^he total number of SSOs that occur nationwide
$ each year is not known. In some areas, they might
JA* not be reported or are underreported to EPA and
state environmental agencies. Two surveys, however,
help to define the size of the problem:
In a 1994 survey of 79 members of the Association of
Metropolitan Sewerage Agencies, 65 percent of
respondents reported wet weather SSOs.5 They
reported that between 15 and 35 percent of their
sewers were filled above capacity and/or over-
flowed during wet weather. However, municipal
respondents with SSOs had only limited informa-
tion about them. Only 60 percent had estimated the
annual number. Half of those had estimated the
amount of sewage discharged, and 17 percent had
determined what pollutants were in their overflows.
A1981 survey conducted by the National Urban
Institute indicated an average of 827 backups and
143 breaks per 1,000 miles of sewer pipe* per year.
Breaks occurred most often in the young, growing
cities of the South and West. The report authors sug-
gested that cities with the most collection system
problems were doing the least to correct themeven
cleaning pipes at a very low rate.
*About 1,000 miles of sewer pipe are needed to serve 250,000
people.
Pathogens In'Raw Sewage6
> Organisms Diseases and Symptoms
Bacteria
Vlryses
E»wfezo«t
£hotera, satmoneiiosis (food poisoning),
- ^typhoid fever, taePiary dysentery, gas-
° - troenteritis (including diarrhea and
abdominal pair)}" ^ ° ,/
Hepatitis, meningitis/ pneumonia, fever, .
'^.dommoiijiolds.Jfjaratysis, encephalitis,
'rgastro'eoterltiSrdiarrhea, respiratory
> ° jnfections, °-, *;
/ Gastrxiertbritisr acute enteritis, gtardiasis
':, {ihctudfeg diaVrhea, abdominal cramps,
^'"%f weight loss)^ dysentery^ toxoplasrho-
"i "'
"- Helminths Digestive and nutritional disturbances;
" * "S X- abdominal pain/vomitteg, restlessness,,
-^' v cpughirtg, chest pain/Jever, abdominal "-
\ ^,- %J ;v? c'pa% diarrhea, anemia; weight loss, fever
Itv^ r
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[ Sanitary Seuxr Overflows
How Can SSOs Be Reduced or Eliminated ?
What Costs Are Involved?
* /*" any avoidable SSOs are caused by inadequate
I \ /1 or negligent operation or maintenance, inade-
J» T JLquate system capacity, and improper system
design and construction. These SSOs can be reduced
or eliminated by:
Sewer system cleaning and maintenance.
Reducing infiltration and inflow through system
rehabilitation and repairing broken or leaking ser-
vice lines.
Enlarging or upgrading sewer, pump station, or
sewage treatment plant capacity and/or reliability.
Constructing wet weather storage and treatment
facilities to treat excess flows.
Communities also should address SSOs during
sewer system master planning and facilities planning,
or while extending the sewer system into previously
unsewered areas.
A few SSOs may be unavoidable. Unavoidable
SSOs include those occurring from unpreventable van-
dalism, some types of blockages, extreme rainstorms,
and acts of nature such as earthquakes or floods.
:L|MKII|SS
anitary sewer collection systems are a valuable
I part of the nation's infrastructure. EPA estimates
that our nation's sewers are worth a total of
more than $1 trillion. The collection system of a single
large municipality is an asset worth billions of dollars,
and that of a smaller city could cost many millions to
replace. Sewer rehabilitation to reduce or eliminate
SSOs can be expensive, but the cost must be weighed
against the value of the collection system asset and the
added costs if this asset is allowed to further deterio-
rate. Ongoing maintenance and rehabilitation adds
value to the original investment by maintaining the
system's capacity and extending its life.
The costs of rehabilitation and other measures to
correct SSOs can vary widely by community size and
sewer system type. Those being equal, however, costs
will be highest and ratepayers will pay more in com-
munities that have not put regular preventive mainte-
nance or asset protection programs in place.
Assistance is available through the Clean Water
State Revolving Fund for capital projects to control
SSOs. State Revolving Funds in each state and Puerto
""' -.o can help arrange low-interest loans. For the name
your State Revolving Fund contact please call the
A. Office of Water Resource Center, (202) 260-7786.
Roadside overflows can cause erosion and roadbed maintenance prob-
lems, in addition to health hazards and nuisance odors. (Photo cour-
tesy of U.S. EPA.)
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What are they, and how do we reduce them? \
Identifying SSO Problems and Finding Solutions
Cabool, Missouri7
' In 1990 the sewer system for this city of 5,000 exceeded
its capacity, causing overflows .and backups at severaljoca-
tions. BreakVin drinking water mains lowered the water
pressure, allowing contamination from nearby SSOs to enter
' the drinking-water-system. ,
Researchers l!nked;these overflows with a pathogenic
strain of Escherichia coli which Rilled 4 people, hospital- -
ized 32 and caused diarrhea and .other problems in- ,
243 people. , - , "
Ocoee, Florida8
Sewage overflows'from November 1988,to April 1989 '
periodically flooded a "mobile home park during heavy rains
and caused occasional outbreaks'of. disease.- _' " /
- Thirty nine cases of hepatitis A-were identified among -
residents, ^addition, four infected food handlers, living in
'the park were linked.to 100 cases of-hepatitis A in Ft;
Laltderdale where they worked. Hepatitis A is a chronic
liver disease that can lead. to,permanent health injury and
shorten life expectancy. Using a special health analysis ,',
scale, health damages were measured at up to 20 years'
lost life expectancy. Diarrhea and .other symptoms contin1 "
ued for 2 years, > '.""' - - - '"
Washington Suburban Sanitary
Commission, Maryland9
From .1990 to'1994,the number, of SSO-related" base-
ment backups ranged from 484 to ,659 per year, for a total
of 2,960. Basement cleanups costan average of $700 ,f
each, including removal and disposal of sewage; removal
and cleaning or disposal of carpet, wallpaper.-waliboard,',
insulation, and other materials; disinfection;,and drying, ' -
Overflows at sewage pumping stations and treatment..
plants occurred from 11 to 50 times per year. >
, The costs of upgrades to reduce the level of overflows
in the system (which serves 1.4-million people and handles
180 million gallons of wastewater a day) include:
Upgrades at pumping stations and sewage treatment
plants: $38 million
Collection system improvements: $22 million
Sewer reconstruction: $6 million (annual) , -
'Maintenance program: $10 million (annual)
These upgrades cost-system users about $50 per
household per yean - , ,
Lynn, Massachusetts1
. -SSOs caused street flooding, basement flooding, and '
sewer house connection backups in low-lying locations.
Some homeowners had to install sump pumps to reduce
basement flooding, >,.,' '
Some of the SSQ-prdblems were attributed to badly
cracked pipes, blocked; damaged manholes, leaky pipe
joints, and large debris in some sewer sections.
'. The city has undertaken sewer-separation and rehabilita-
tion projects that have reduced the number and the fre-
quency of SSOs at a cost of $2.6 million. - Additional work -
will further reduce'overflows: Costs are estimated.at about
$10 per household per year. '
Louisville/Jefferson County, KY11
From 1989 to 1994,165 overflows were reportedjn 80
different locations, 70 percent caused by wet weather infil-
tration and inflow.
-The county began corrective actions to reduce the num-
ber and frequency of SSOs through sewer rehabilitation
and preventive maintenance. Further work was planned to
remove private infiltration and inflow.source connections
. such as sump pumps, foundation drains, and other con-
nections. Future SSO reduction projects were investigated.,
The long- term budget plan for corrective actions
totaled $14.6 million. This program costs each household
about $40 per year.
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Sanitary Sewer Overflows
JOWM
Oean water... a better environment
Office of Wastewater Management
For more information about EPA's work to help reduce
sanitary sewer overflows please write to:
SSO Program Manager
U.S. EPA Office of Wastewater Management
401MSt,S.W.(4201)
Washington, D.C 20460
For publications about U.S. EPA Office of Wastewater
Management programs and policies please consult these
sources:
Office of Water Resource Center
RC 4100-2615 OWM
401M. Street, SW
Washington, DC 20460
(202) 260-7786
FAX: (202) 260-0386
(U.S. EPA Office of Water publications including
information about storm water and combined sewer
overflows. Also available is a list of commonly-used
technical references for managing sanitary sewer
overflows.)
Center for Environmental Research Information (CERI)
26 West Martin Luther King
Cincinnati, OH 45268
(513) 569-7562
FAX: (513) 569-7566
(Technical information about all U.S. EPA regulatory
programs.)
Education Resource Information Center
Clearinghouse for Science, Mathematics and
Environmental Education (ERIC/CSMEE)
1929 Kenny Road
Columbus, OH 43210-1080
(800) 276-0462 or (614) 292-6717
FAX: (614) 292-0263
(Comprehensive information about environmental
education. Charge applies.)
U. S. Dept of Commerce
National Technical Information (NTIS)
5285 Port Royal Road
Springfield, VA 22161
(800) 553-6847 (rush orders) or (703) 487-4650
FAX: (703) 321-8547
(Many U.S. government agency publications. Charge
applies.)
National Small Flows Clearinghouse
West Virginia University
PO Box 6064
Morgantown, WV 26506-6064
(800) 624-8301
FAX: (304) 293-3161
(Small communities technical assistance and information.
Charge applies.)
Also see the U.S. EPA Office of Water Internet Home Page
at http:\\www.epa.gov\OW
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SSOs can reach streams, lakes, rivers, and other water ladies, impairing water quality and increasing health risks from recreational activities such
as swimming. (Photo courtesy of U.S. EPA.)
1 Santa Monica Bay Restoration Project, 1996, An
Epidemiological Study of Possible Adverse Health Effects of
Swimming in Santa Monica Bay. May.
2 Rippey, 1994, Infectious diseases associated with mol-
luscan shellfish consumption. Clinical Microbiology
Reviews October, pp. 419-425.
3 Berry et al., 1994, Suggested guidelines for remedia-
tion of damage from sewage backflow into buildings.
Journal of Environmental Health October; Roberts, 1981,
Hypersensitivity to lung disease presumptively due to
Cephalosporium in homes contaminated by sewage
flooding or by humidifier water. Journal of Allergy and
Clinical Immunology 68(2):128-132; Robinson, 1994,
Warning of public health hazard: Rio Grande River
and the City of Rio Bravo Water System settling pond
contain water that is hazardous for human contact.
Memo from City of Laredo Health Department,
Laredo, XX.
4 National Resources Defense Council, 1995, Testing the
Waters lfNewYork,NY.
5 AMSA, 1994, Separate Sanitary Sewer Overflows: What
Do We Currently Know? Association of Metropolitan
Sewerage Agencies, Washington, DC, September.
6 U.S. EPA, 1992, Technical Support Document for
Reduction of Pathogens and Vector Attraction in Sewage
Sludge. Office of Water, Office of Science and
Technology. EPA/822/R-93-021.
7 Geldreich et al., 1992, Searching for a water supply
connection in the Cabool, Missouri, outbreak of
Escherichia coli 0157:H7. Water Resources
26(8):1127-1137; Swerdlow et al., 1992, A waterborne
outbreak in Missouri of Escherichia coli 0157:H7 associ-
ated with bloody diarrhea and death. Annals of
Internal Medicine 117(10):812-819.
8V6nstille et al., 1993, Hepatitis A epidemics from utility
sewage in Ocoee, Florida. Archives of Environmental
Health 48(2):120-124.
'Washington Suburban Sanitary Commission, MD,
1995, Separate Sanitary Sewer Overflows: Report to the
U.S. Environmental Protection Agency.
10Lynn, MA, 1988 and 1989, Combined Sewer Overflow
Facilities Plan.
"Fort Worth, TX, 1995, Sanitary Sewer Main 161 and 221
Drainage Areas Inflow/Infiltration Evaluation Study.
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