Sanitary sewer overflow: Difference between revisions

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{{Short description|Discharge of untreated sewage}}

: ''Not to be confused with [[Combined sewer#Combined sewer overflows (CSOs)|combined sewer overflow (CSO)]]''

{{distinguish|Combined sewer overflow}}
[[File:Sewer overflow RI EPA.jpg|thumb|right|A [[sanitary manhole|manhole]] cover unable to contain a sanitary sewer overflow]]

'''Sanitary sewer overflow''' ('''SSO''') is a condition in which untreated [[sewage]] is discharged from a [[sanitary sewer]] into the environment prior to reaching [[sewage treatment]] facilities. When caused by rainfall it is also known as '''wet weather overflow'''. ItCauses isof primarilysanitary meaningfulsewer inoverflows include: Blockage of sewer lines, [[developedinfiltration/Inflow]] countriesof excessive [[stormwater]] into sewer lines during heavy [[rainfall]], whichmalfunction haveof extensive[[pumping treatmentstation]] facilities.lifts Frequentor causeselectrical [[power failure]], broken sewer lines. Prevention of SSOsuch spillsoverflow include:events involves regular maintenance and timely upgrades of infrastructure.

SSOs can cause [[gastrointestinal illness]]es ([[waterborne diseases]]), beach closures and restrictions on fish and [[shellfish]] consumption.

'''Sanitary sewer overflow''' ('''SSO''') is a condition in which untreated [[sewage]] is discharged from a [[sanitary sewer]] into the environment prior to reaching [[sewage treatment]] facilities. When caused by rainfall it is also known as '''wet weather overflow'''. It is primarily meaningful in [[developed countries]], which have extensive treatment facilities. Frequent causes of SSO spills include:

== United States ==

* [[Infiltration/Inflow]] of excessive [[stormwater]] into [[sanitary sewer|sewer]] lines during heavy [[rainfall]]

The [[U.S. Environmental Protection Agency]] (EPA) estimates that at least 23,000 to 75,000 SSO events occur in the United States each year.<ref>{{cite web |url=https://www.epa.gov/npdes/sanitary-sewer-overflows-ssos |title=Sanitary Sewer Overflows |author=<!--Staff writer(s); no by-line.--> |date=2015-11-16 |access-date=2023-02-17 |website=National Pollutant Discharge Elimination System |publisher=U.S. Environmental Protection Agency (EPA) |___location=Washington, D.C.}}</ref> EPA estimated that upgrading every municipal treatment and collection system to reduce the frequency of overflow events to no more than once every five years would cost about $88 billion as of 2004.<ref name="EPA-RTC">{{cite report |date=August 2004 |title=Report to Congress: Impacts and Control of CSOs and SSOs |url=https://www.epa.gov/npdes/2004-npdes-cso-report-congress |access-date=2023-02-17 |publisher=EPA |id=EPA-833-R-04-001}}</ref> This cost would be in addition to approximately $10 billion already invested. Although the volume of untreated sewage discharged to the environment is less than 0.01 percent of all treated sewage in the United States, the total volume amounts to several billion gallons per annum and accounts for thousands of cases of gastrointestinal illness each year.<ref name="EPA-RTC" />{{rp|Ch. 6}}

* Rupture or blockage of [[sanitary sewer|sewerage]] lines

* Malfunction of [[pumping station]] lifts or electrical [[power failure]]

== Worldwide perspective ==

In many countries there are obligations to measure and report SSO occurrence using real-time [[telemetry]] to warn the public, bathers and shellfishery operators.

Developed European countries and Japan have similar or somewhat larger percentages of SSO events compared to the U.S.{{citation needed|date=June 2015}}

ItIn is[[developing difficult to visualize the issue of SSO in perspectivecountries]], since underdeveloped countries discharge most ofwastewater theis sewagestill theynot createtreated aswhen effluentdischarged into the environment. Even a highly industrialized developing country such as theThe [[People's Republic of China]] dischargesdischarged about 55 percent of all sewage without treatment of any type, as of 2001.<ref>"[[World Bank]] Supports China's Wastewater Treatment", ''The People’s Daily'', November 30, 2001, Beijing</ref> In a relatively developed [[Middle East]]ern country such as [[Iran]], the majority of [[Tehran]]'s population has totally untreated sewage injected to the city’scity's groundwater.<ref>Massoud Tajrishy and Ahmad Abrishamchi, "Integrated Approach to Water and Wastewater Management for [[Tehran]], [[Iran]]", [[Water Conservation]], Reuse, and Recycling: Proceedings of the Iranian-American Workshop, National Academies Press (2005)</ref> In [[Venezuela]], a below-average country in [[South America]] with respect to wastewater treatment, 97 percent of the country’scountry's [[sewage]] is discharged rawuntreated into the environment.<ref>Appropriate Technology for Sewage Pollution Control in the Wider [[Caribbean]] Region, Caribbean Environment Programme Technical Report #40 1998</ref> Most of [[sub-Saharan Africa]] is without wastewater treatment, contributing to the excessive [[infant]] death rates in that region.

The concept of SSO containment valves has been pioneered in the UK and they are installed to mitigate dry spills, by correlating rainfall data with SSO spill activity.

In many countries there are obligations to measure and report SSO occurrence using real-time [[telemetry]] to warn the public, bathers and shellfishery operators.{{citation needed|date=June 2016}}

==Magnitude of the problem==

EPA estimates that about 40,000 SSO events occur in the [[United States]] each year.<ref>U.S. Environmental Protection Agency (EPA). Washington, DC. [http://cfpub.epa.gov/npdes/home.cfm?program_id=4 "Sanitary Sewer Overflows and Peak Flows"], Updated February 2012.</ref> The Agency estimated that upgrading every municipal treatment and collection system to reduce the frequency of overflow events to no more than once every five years would cost about 88 billion dollars as of 2004.<ref name="EPA-RTC">

EPA. [http://cfpub.epa.gov/npdes/cso/cpolicy_report2004.cfm "Report to Congress: Impacts and Control of CSOs and SSOs"], Executive Summary. August 2004. Document No. EPA-833-R-04-001.</ref> This cost would be in addition to approximately ten billion dollars already invested. Although the volume of untreated sewage discharged to the environment is less than 0.01% of all treated sewage in the United States, the total volume amounts to several billion U.S. gallons per annum and accounts for thousands of cases of gastrointestinal illness each year.<ref name="EPA-RTC" />{{rp|Ch. 6}} Advanced European countries and Japan have similar or somewhat larger percentages of SSO events.<ref>{{cite web|url=http://septiczone.com/global-sso-events |title=A Worldwide View Of Sanitary Sewer Overflow |accessdate=19 July 2009}}</ref>{{Failed verification|date=June 2015}}

== Causes ==
===Engineering aspects===

[[Image:Aparissewer.jpg|thumb|230px|Sanitary sewer line in [[Paris]] more than two meters in diameter.]]

Sewers that were built in the early stages of urbanization were usually built before [[sewage treatment]] was practicedimplemented.<ref>''See'' [[History of water supply and sanitation]].</ref> Early sewers were simple drainage systems to remove [[surface runoff]] with any waste material it might contain. These drainage systems became [[combined sewers]] when sewage from kitchens, baths, and toilets was added; and the discharge became offensive. Early sewage treatment plants were built to treat the offensive sewage during dry weather; but it was infeasible to treat the larger volume of mixed sewage and precipitation runoff from combined sewers during wet weather. Some Sanitarycities sewersbuilt weresanitary builtsewers to keep sewage from being mixed with surface runoff so the sewage could be efficiently treated during both wet and dry weather.<ref>{{cite book |last=Okun |first=Daniel A. |authorlink = |title =Sewage Treatment Plant Design |publisher =[[American Society of Civil Engineers]] and Water Pollution Control Federation |volumedate =1959 |editionpage =6 |date}}</ref> (About 860 communities in the U.S. continue to use combined sewers.<ref>{{cite web |url=1959https://www.epa.gov/npdes/combined-sewer-overflow-frequent-questions |___locationtitle=Combined Sewer Overflow Frequent Questions |author=<!--Staff writer(s); no by-line.--> |pagedate=2017-12-20 |access-date=6 |isbnwebsite=National Pollutant Discharge Elimination System |publisher=EPA}}</ref>)

===Blockages===

Sewers were built before sewage treatment was practiced. Early sewers were drainage systems to remove surface runoff with any waste material it might contain. These drainage systems became [[combined sewers]] when sewage from kitchens, baths, and toilets was added; and the discharge became offensive. Early sewage treatment plants were built to treat the offensive sewage during dry weather; but it was infeasible to treat the larger volume of mixed sewage and precipitation runoff from combined sewers during wet weather. Sanitary sewers were built to keep sewage from being mixed with surface runoff so the sewage could be efficiently treated during both wet and dry weather.<ref>{{cite book |last=Okun |first=Daniel A. |authorlink = |title =Sewage Treatment Plant Design |publisher =[[American Society of Civil Engineers]] and Water Pollution Control Federation |volume = |edition = |date =1959 |___location = |page =6 |isbn =}}</ref>

Decentralized failures in dry weather mainly occur from collection sewer line blockages, which can arise from a [[debris]] clog or tree root intrusion into the line itself. Approximately half of SSOs in the United States are caused by blockage.<ref name="EPA-RTC"/>{{rp|p. 4–26}} [[Brown grease|Grease]] is the blocking agent in approximately half of U.S. SSOs attributed to blockage, and solid debris is the blocking agent for another 25 percent. [[Root]]s are a contributing factor in approximately one-quarter of United States SSOs attributed to blockage. Grease deposits are caused by cooking fats liquified with hot water for discharge to sanitary sewers. These fats congeal as solid deposits in the cooler sewer. Solid debris includes soiled clothing, [[diaper]]s, and [[sanitary napkin]]s flushed down the toilet rather than being put in a waste bin.<ref name="EPA-RTC"/>{{rp|p. 4–28}}

Many U.S. municipalities require restaurants and food processing businesses to use [[grease interceptor]]s and regulate the disposal of fats, oil and grease in the sewer system.<ref>For example, the [[Washington Suburban Sanitary Commission]] (WSSC) in Maryland, U.S.: {{cite web |title=Fats, Oils, & Grease |url=https://www.wsscwater.com/fog |website=Special Wastewater Discharge Requirements |date=2023-12-29 |publisher=WSSC |___location=Laurel, MD}}</ref>

==Infiltration/inflow==

Decentralized failures in dry weather mainly occur from collection sewer line blockages, which can arise from a [[debris]] clog, line rupture or tree root intrusion into the line itself. One of the main problems of a decentralized line failure is the difficulty of defining the ___location of overflow, since a typical urban system contains thousands of miles of collection pipagepipes, and the central treatment plant has no way of communicating with all the lines, unless expensive monitoring equipment has been installed. Companies in the UK have widely deployed bulk dielectric transducers[[transducer]]s suspended in the sewers to detect high levels and to report the events back over fixed wireless data networks. In certain locations it has been said that this practice has permitted the reduction of pollution events by up to 60% percent.{{citation needed|date=June 2016}}

By far the most common cause of Sanitary Sewer Overflow are heavy [[rainfall]] events, which can cause massive inflow of [[stormwater]] into sanitary sewers through damage, improper connections, or flooding buildings and lift stations in low-lying areas of the collection system. The combined flow of sewage and stormwater exceeds the capacity of the sanitary sewer system and sewage is released into homes, businesses and streets. This circumstance is most prevalent in older cities whose subsurface infrastructure is quite old; [[Paris]], [[London]], [[Stockholm]],<ref>Monica Spendilow, ''Impeller Magazine'', ITT Flygt AB, SE-174 87 Sundbyberg, Sweden (2004)</ref> [[New York]], [[Washington, DC]], and [[Oakland, California]]<ref>''Environmental Impact Statement for the [[East Bay Municipal Utility District]] Wet Weather Overflow Project'', Earth Metrics Incorporated, prepared for the U.S. EPA and East Bay Municipal Utility District, Oakland, Ca. (1985)</ref> are typical examples of such locations. Inflow into the sanitary lines can be caused by tree root rupture of subsurface lines or by mechanical fracture due to age and overpressure from trucks and buildings above.

Dry weather blockage is less likely within combined sewers,; because combined sewers aredesigned sofor the additional volume of surface runoff are much larger than sanitary sewers. Combined sewerssewer storm water regulators may be vulnerable to blockage at the storm waterby regulatordebris, but dischargesoverflow from such blockage typically enterenters the diversion [[outfall]] to avoid flooding private or public property.

Historically, one of the biggest causes of SSO operation is the overloading of the sewer during storms and there has been a call to reduce the amount of water entering sewers by introducing SuDS.

===Infiltration/inflow===

==Malfunction==

ByApproximately farone-quarter theof mostUnited commonStates causeSSOs ofoccur Sanitary Sewer Overflow areduring heavy [[rainfall]] events, which can cause massive inflow of [[stormwater]] into sanitary sewers through damage, improper connections, or flooding buildings and [[lift stationsstation]]s in low-lying areas of the collection system. The combined flow of sewage and stormwater exceeds the capacity of the sanitary sewer system and sewage is released into homes, businesses and streets.<ref name="EPA-RTC"/>{{rp|p. 4–26}} This circumstance is most prevalent in older cities whose subsurface infrastructure is quite old; [[Paris]], [[London]], [[Stockholm]],<ref>Monica Spendilow, ''Impeller Magazine'', ITT Flygt AB, SE-174 87 Sundbyberg, Sweden (2004)</ref> [[New York City]], [[Washington, DC]], and [[Oakland, California]]<ref>''Environmental Impact Statement for the [[East Bay Municipal Utility District]] Wet Weather Overflow Project'', Earth Metrics Incorporated, prepared for the U.S. EPA and East Bay Municipal Utility District, Oakland, Ca. (1985)</ref> are typical examples of such locations. Inflow into the sanitary lines can be caused by tree root rupture of subsurface lines or by mechanical fracture due to age and overpressure from trucks and buildings above.

===Malfunctions===

Another mode of system failure can include [[power outage]]s, which may disable [[lift station]] pumps and cause sewage overflow from the lift station wet well. Lift station mechanical or power failure causes approximately ten percent of United States SSOs. This type of discharge is uncommon from combined sewers, because the combined volume of sewage and storm water discourages use of lift stations. Broken sewer lines are responsible for approximately ten percent of U.S. SSOs.<ref name="EPA-RTC"/>{{rp|p. 4–27}}

Power failure, [[human error]], or mechanical failure may cause similar discharge of untreated or partially treated sewage from a sewage treatment plant; but this is typically regarded as a sewage treatment plant malfunction rather than a sanitary sewer overflow. Sewage treatment plants may be designed to capture overflow from malfunctioning units and discharge it to alternative treatment facilities. Flooding of private or public property is typically avoided by discharging the overflow to an outfall designed for discharge of treated sewage.<ref name="EPA-RTC"/>{{rp|p. ES–3}}

==Human health and ecological consequences==

==Blockage==

[[Image:Overflowepa.gif|thumb|230px|left|Decentralized wet weather overflow event]]

Human health impacts include significant numbers of [[gastrointestinal illness]] illness each year, although death from one overflow event is uncommon. Additional human impacts include [[beach]] closures, [[human swimming|swimming]] restrictions and prohibition of the consumption of certain aquatic animals (particularly certain [[mollusc]]s) after overflow events. Ecological consequences include [[fish kill]]s, harm to [[plankton]] and other aquatic microflora and microfauna. Turbidity increase and dissolved oxygen decrease in receiving waters can lead to accentuated effects beyond the obvious [[pathogen]]ic induced damage to aquatic [[ecosystem]]s. It is possible that higher life forms such as [[marine mammal]]s can be affected since certain seals and [[sea lion]]s are known to experience peaks in pathogenic harm.<ref>Johnson, S. P., Jang, S., Gulland, F.M.D., Miller, M., Casper, D., Lawrence, J., Herrera, J., [http://www.jwildlifedis.org/cgi/reprint/39/1/136.pdf "Characterization and clinical manifestations of Arcanobacterium phocae infections in marine mammals stranded along the central California coast"], ''Journal of Wildlife Diseases'', 39:136-144 (2003).</ref>

Decentralized failures in dry weather mainly occur from collection sewer line blockages, which can arise from a [[debris]] clog, line rupture or tree root intrusion into the line itself. One of the main problems of a decentralized line failure is the difficulty of defining the ___location of overflow, since a typical urban system contains thousands of miles of collection pipage, and the central treatment plant has no way of communicating with all the lines, unless expensive monitoring equipment has been installed. Companies in the UK have widely deployed bulk dielectric transducers suspended in the sewers to detect high levels and to report the events back over fixed wireless data networks. In certain locations it has been said that this practice has permitted the reduction of pollution events by up to 60%.

==Mitigation techniques==

Dry weather blockage is less likely within combined sewers, because combined sewers are so much larger than sanitary sewers. Combined sewers may be vulnerable to blockage at the storm water regulator, but discharges from such blockage typically enter the diversion outfall to avoid flooding private or public property.

{{Further|Combined sewer#Mitigation of CSOs}}

The concept of SSO containment valves has been pioneered in the UK and they are installed to mitigate dry spills, by correlating rainfall data with SSO spill activity.{{citation needed|date=June 2016}}

==History==

==Human health and ecological consequences==

[[Image:Wonga wetlands sewage plant.jpg|thumb|250px|left|[[Sewage treatment plant]] used to create the Wonga Wetlands, [[Australia]]]]

[[Image:Overflowepa.gif|thumb|230px|left|Decentralized wet weather overflow event]]

Since medieval times rulers have been aware of the impact of raw sewage improperly discharged to the environment. Before treatment systems existed in 16th century [[England]], [[Henry VIII of England|King Henry VIII]] decreed that sewage troughs should be kept flowing so that they would not stagnate in [[London]] prior to reaching the [[River Thames]] ([[London sewer system]]).{{citation needed|date=June 2016}}

In the 19th century, sewage treatment plants were first developed and installed in the U.S. and parts of Europe, and the concept of SSO was identified. SSOs were not recognized as a widespread environmental problem until the rise of environmental awareness in the 1960s. Around that time government agencies in the U.S. began identifying locations and frequencies of SSOs in a systematic way. Local governments heard complaints of citizens, and beach closure protocols were systematised to reduce risks to public health.

Human health impacts include significant numbers of [[gastrointestinal]] illness each year, although death from one overflow event is uncommon. Additional human impacts include [[beach]] closures, [[human swimming|swimming]] restrictions and prohibition of the consumption of certain aquatic animals (particularly certain [[mollusc]]s) after overflow events. Ecological consequences include [[fish kill]]s, harm to [[plankton]] and other aquatic microflora and microfauna. Turbidity increase and dissolved oxygen decrease in receiving waters can lead to accentuated effects beyond the obvious [[pathogen]]ic induced damage to aquatic [[ecosystem]]s. It is possible that higher life forms such as [[marine mammal]]s can be affected since certain seals and [[sea lion]]s are known to experience peaks in pathogenic harm.<ref>Johnson, S. P., Jang, S., Gulland, F.M.D., Miller, M., Casper, D., Lawrence, J., Herrera, J., [http://www.jwildlifedis.org/cgi/reprint/39/1/136.pdf "Characterization and clinical manifestations of Arcanobacterium phocae infections in marine mammals stranded along the central California coast"], ''Journal of Wildlife Diseases'', 39:136-144 (2003).</ref>

After passage of the [[Clean Water Act]] in 1972, the U.S. spent billions of dollars on upgrades to sewage treatment plants, with some associated repairs and improvements to the associated collection systems, where the overflows occur. EPA continues to provide funding for low-interest loans to communities for addressing SSO problems, through the [[Clean Water State Revolving Fund]].<ref>{{cite web |url=https://www.epa.gov/npdes/sanitary-sewer-overflow-sso-frequent-questions |title=Sanitary Sewer Overflow (SSO) Frequent Questions |author=<!--Staff writer(s); no by-line.--> |date=2015-11-16 |access-date= |publisher=EPA}}</ref>

==Worldwide perspective==

[[Image:Indiasewerman.jpg|thumb|289px|Man unclogging sewer overflow, [[Chennai]], [[India]]]]

It is difficult to visualize the issue of SSO in perspective, since underdeveloped countries discharge most of the sewage they create as effluent into the environment. Even a highly industrialized developing country such as the [[People's Republic of China]] discharges about 55 percent of all sewage without treatment of any type.<ref>"[[World Bank]] Supports China's Wastewater Treatment", ''The People’s Daily'', November 30, 2001, Beijing</ref> In a relatively developed [[Middle East]]ern country such as [[Iran]], the majority of [[Tehran]]'s population has totally untreated sewage injected to the city’s groundwater.<ref>Massoud Tajrishy and Ahmad Abrishamchi, "Integrated Approach to Water and Wastewater Management for [[Tehran]], [[Iran]]", [[Water Conservation]], Reuse, and Recycling: Proceedings of the Iranian-American Workshop, National Academies Press (2005)</ref> In [[Venezuela]], a below-average country in [[South America]] with respect to wastewater treatment, 97 percent of the country’s [[sewage]] is discharged raw into the environment.<ref>Appropriate Technology for Sewage Pollution Control in the Wider [[Caribbean]] Region, Caribbean Environment Programme Technical Report #40 1998</ref> Most of [[sub-Saharan Africa]] is without wastewater treatment, contributing to the excessive [[infant]] death rates in that region.

In the 1990s [[Japan]], the [[UK]] and a number of other European countries began earnest investigation of some of their countries’ overflow issues.{{citation needed|date=June 2016}}

While developed countries such as the United States, [[Canada]], most [[Western Europe]]an states, [[Australia]] and [[Japan]] are considered to be struggling with a public health problem of SSO prevention, the [[underdeveloped countries]] of the world discharge approximately 20,000 times the amount of raw sewage into the environment as those advanced countries collectively, approximately (the equivalent of) 100 trillion U.S. gallons (380&nbsp;km³) of untreated sewage per year. This dichotomy of expenditure and [[public health]] benefit is arguably the greatest disparity between developed and underdeveloped nations as of the year 2006.{{citation needed|date=June 2010}}

==History==

[[Image:Wonga wetlands sewage plant.jpg|thumb|250px|left|[[Sewage treatment plant]] used to create the Wonga Wetlands, [[Australia]]]]

Since medieval times rulers have been aware of the impact of raw sewage improperly discharged to the environment. Before treatment systems existed in 16th century [[England]], [[Henry VIII of England|King Henry VIII]] decreed that sewage troughs should be kept flowing so that they would not stagnate in [[London]] prior to reaching the [[River Thames]] ([[London sewer system]]). It was not until the 19th century when America and parts of Europe developed wastewater treatment, that the concept of SSO materialized; however, communities were merely happy to have wastewater treatment systems, and did not complain greatly about overflows until the dawning of 20th century environmental awareness in the 1960s. At that time the [[USA]] began recognizing locations and frequencies of SSOs in a systematic way. Local governments heard complaints of citizens, beach closure protocols were systematised and the U.S. [[United States Environmental Protection Agency|Environmental Protection Agency]] (EPA) began detailed engineering analyses for major cities across the country. After passage of the U.S. [[Clean Water Act]] in 1972, the 1980s saw spending of billions of dollars on system upgrading (although most funds during this period were spent on upgrades to [[secondary treatment]] rather than addressing SSO problems). In the 1990s [[Japan]], the [[UK]] and a number of other European countries began earnest investigation of some of their countries’ overflow issues.

==See also==

* [[Fatberg]] (sewer blockage)

* [[Combined sewer]]

* [[Sanitary sewer]]

* [[Water pollution]]

== References==

{{Reflist|2}}

==External links==

*[https://www.epa.gov/npdes/sanitary-sewer-overflow-sso-additional-resources Technical reports and additional SSO resources] - EPA

*[http://cfpub.epa.gov/npdes/home.cfm?program_id=4 EPA - Sanitary Sewer Overflows Program]

*[http://www.swrcb.ca.gov/sso/docs/factsheet_wqo20060003.pdf California State Water Quality Control Board SSO Guidance]

{{Sewerage}}

*[http://aslo.org/phd/dialog/199709-1.html Seine River sewage discharge scenario]

[[Category:Public healthSanitation]]

[[Category:Sewerage]]

[[Category:Water pollution]]