Infiltration and inflow: Difference between revisions

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{{Short description|Groundwater entering sanitary sewers}}

'''Infiltration/Inflow''' is water from unexpected sources flowing within [[sanitary sewer]]s. Although inflow is technically different from infiltration, it may be difficult to determine which is causing dilution problems in inaccessible sewers. The [[United States Environmental Protection Agency]] defines the term infiltration/inflow as combined contributions from both.<ref>[http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=e59aece1945f2c220e3474257ee2a251&rgn=div5&view=text&node=40:1.0.1.2.32&idno=40#40:1.0.1.2.32.4.142.4 40CFR35.905] Accessed 2010-12-29</ref>

'''Infiltration and inflow''' ('''I/I''' or '''I&I''') is the process of [[groundwater]], or water from sources other than domestic wastewater, entering [[sanitary sewer]]s. I/I causes dilution in sanitary sewers, which decreases the efficiency of treatment, and may cause sewage volumes to exceed design capacity. Although inflow is technically different from infiltration, it may be difficult to determine which is causing dilution problems in inaccessible sewers. The [[United States Environmental Protection Agency]] considers infiltration and inflow to be combined contributions from both.<ref name="EPA definition">U.S. Environmental Protection Agency (EPA), Washington, D.C. ''Code of Federal Regulations.'' "Part 35—State and Local Assistance."

* "Definitions; Excessive inflitation/inflow." 40 CFR 35.2005 (b)(16). {{USCFR|40|35|2005}}

* "Grants for Construction of Treatment Works; Infiltration/Inflow." {{USCFR|40|35|2120}}</ref><ref>{{cite tech report |date=June 2014 |title=Guide for Estimating Infiltration and Inflow |institution=U.S. EPA New England |url=https://www3.epa.gov/region1/sso/pdfs/Guide4EstimatingInfiltrationInflow.pdf |access-date=8 May 2023}}</ref>

==Background==

Early [[combined sewer]]s used [[surface runoff]] to dilute waste from [[toilet]]s and carry it away from urban areas into natural waterways. [[Sewage treatment]] can remove some [[pollutant]]s from toilet waste, but treatment becomesof inefficientdiluted whenflow thefrom wastecombined issewers dilutedproduces inlarger combinedvolumes sewers.of treated sewage with similar pollutant concentrations. Modern sanitary sewers are designed to transport domestic and industrial [[wastewater]] directly to treatment facilities without dilution.<ref name="steel">{{cite book |last1=Steel, |first1=E.W. and |last2=McGhee, |first2=Terence J. ''|title=Water Supply and Sewerage'' (|date=1979) |publisher=McGraw-Hill ISBN |isbn=0-07-060929-2 p.|page=318}}</ref>

==Infiltration==

[[Groundwater]] entering sanitary sewers through defective pipe joints and broken pipes is called ''infiltration''.<ref name="king">{{cite book |last=King, |first=James J. ''|title=The Environmental Dictionary'' (|date=1995) |publisher=John Wiley & Sons ISBN |isbn=0-471-11995-4 p.|page=335}}</ref> Pipes may leak because of careless installation; or they may also be damaged after installation by differential ground movement, heavy vehicle traffic on roadways above the sewer, careless construction practices in nearby trenches, or degradation of the sewer pipe materials. In general, volume of leakage will increase over time. Damaged Infiltrationand willbroken occursewer wherecleanouts localare groundwatera elevationmajor iscause higherof thaninfiltration theinto municipal sewer pipesystems.<ref>{{cite report In|title=Private areasSewer ofLaterals low groundwater, sewage may exfiltrate into groundwater from a leaking sewer|url=https://www3.epa.<refgov/region1/sso/pdfs/PrivateSewerLaterals.pdf name|date="eddy">MetcalfJune &2014 Eddy|publisher=EPA ''Wastewater|___location=Boston, Engineering''MA (1972)|series=Water McGraw-HillInfrastructure pp.39-44Outreach}}</ref>

Infiltration will occur where local groundwater elevation is higher than the sewer pipe. Gravel bedding materials in sewer pipe trenches act as a [[French drain]]. Groundwater flows parallel to the sewer until it reaches the area of damaged pipe. In areas of low groundwater, sewage may exfiltrate into groundwater from a leaking sewer.<ref name="eddy">{{cite book |title=Metcalf & Eddy Wastewater Engineering |date=1972 |publisher=McGraw-Hill |___location=New York |pages=39–44}}</ref>

==Inflow==

[[File:Manhole and sandbagging outside Cricketers Cottage - geograph.org.uk - 3874272.jpg|thumb|[[Sanitary manhole]] inflow due to a flood<ref>{{cite book |title=Hambledon Infiltration Reduction Plan |date=June 2016 |publisher=Southern Water |pages=6–7 |url=https://www.southernwater.co.uk/media/default/PDFs/hambledon-IRP.pdf |access-date=25 February 2024}}</ref>]]

Water entering sanitary sewers from inappropriate connections is called ''inflow''.<ref name="king"/> Typical sources include roof drains, cellar drains, and yard drains where urban features prevent surface runoff, and storm drains are not conveniently accessible or identifiable. Sources of inflow can sometimes be identified by [[smoke testing]]. Smoke is blown into the sewer during dry weather while observers watch for smoke emerging from yards, cellars, or roof gutters.<ref name="hammer">Hammer, Mark J. ''Water and Waste-Water Technology'' (1975) John Wiley & Sons ISBN 0-471-34726-4 pp.303-304&441-442</ref>

Water entering sanitary sewers from inappropriate connections is called ''inflow''.<ref name="king"/> Typical sources include [[sump pump]]s, roof drains, cellar drains, and yard drains where urban features prevent surface runoff, and storm drains are not conveniently accessible or identifiable. Inflow tends to peak during precipitation events, and causes greater flow variation than infiltration. Peak flows caused by inflow may generate a [[foul flush]] of accumulated [[biofilm]] and sanitary solids scoured from the dry weather [[wetted perimeter]] of oversized sewers during peak flow [[turbulence]].<ref>{{cite web |url=http://netlab.cs.ucla.edu/rrr/wiki-internal/files/sediment%20control.pdf |title=Sewer-Sediment Control: Overview of an EPA Wet-Weather Flow Research Program |last1=Fan |first1=Chi-Yuan |last2=Field |first2=Richard |last3=Lai |first3=Fu-hsiung |publisher=EPA and University of California, Los Angeles |access-date=12 March 2016 |archive-url=https://web.archive.org/web/20160313121934/http://netlab.cs.ucla.edu/rrr/wiki-internal/files/sediment%20control.pdf |archive-date=13 March 2016 }}</ref> Sources of inflow can sometimes be identified by [[smoke testing (mechanical)|smoke testing]]. Smoke is blown into the sewer during dry weather while observers watch for smoke emerging from yards, cellars, or roof gutters.<ref name="hammer">{{cite book |last=Hammer |first=Mark J. |title=Water and Waste-Water Technology |date=1975 |publisher=John Wiley & Sons |isbn=0-471-34726-4 |pages=303-304, 441-442}}</ref>

==Significance==

Dilution of sewage directly increases costs of pumping and [[Water chlorination|chlorination]], ozonation, or [[ultraviolet disinfection]]. Physical treatment structures including screens and pumps must be enlarged to handle the peak flow. Primary clarifiers must also be enlarged to treat average flows, although [[primary treatment]] of peak flows may be accomplished in [[detention basin]]s. Biological [[secondary treatment]] is effective only while the concentration of soluble and colloidal pollutants (typically measured as [[biochemical oxygen demand]] or BOD) remains high enough to sustain a population of microorganisms digesting those pollutants. In U.S. federal regulations, secondary treatment is expected to remove 85 percent of soluble and colloidal organic pollutants from sewage containing 200&nbsp;mg/L BOD.<ref>EPA. "Part 133—Secondary Treatment Regulation." {{uscfr|40|133}}</ref> BOD removal by conventional biological secondary treatment becomes less effective with dilution and practically ceases as BOD concentrations entering the treatment facility are diluted below about 20&nbsp;mg/L. Unremoved organics are potentially converted to [[disinfection by-products]] by chemical disinfection prior to discharge.

Dilution of sewage increases costs of pumping, requires increased volumes of treatment chemicals, and generally decreases the efficiency of treatment (increases the mass of pollutants discharged) by producing larger volumes of treated sewage with similar pollutant concentrations. High rates of infiltration/inflow may make the sanitary sewer incapable of carrying sewage from the design service area. Sewage may back up into the lowest homes during wet weather, or street manholes may overflow.<ref name="hammer"/>

[[File:Sewer overflow RI EPA.jpg|thumb|right|Excessive infiltration and inflow may cause sanitary sewer overflows during wet weather.]]

DilutionHigh of sewage increases costsrates of pumping, requires increased volumes of treatment chemicals,infiltration and generally decreases the efficiency of treatment (increases the mass of pollutants discharged) by producing larger volumes of treated sewage with similar pollutant concentrations. High rates of infiltration/inflow may make the sanitary sewer incapable of carrying sewage from the design service area. Sewage may back up into the lowest homes during wet weather, or street manholes may overflow.<ref name="hammer"/>

==Correction==

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==References==

{{reflistReflist}}

{{Sewerage}}

{{Wastewater}}

{{DEFAULTSORT:Infiltration Inflow}}

[[Category:Sewerage]]

[[Category:Water pollution]]