Infiltration and inflow: Difference between revisions

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{{Short description|Groundwater entering sanitary sewers}}

'''Infiltration/Inflow and inflow''' ('''I/I''' or '''I&I''') causesis dilutionthe inprocess of [[groundwater]], or water from sources other than domestic wastewater, entering [[sanitary sewer]]s. DilutionI/I ofcauses sewagedilution 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]] definesconsiders theinfiltration termand infiltration/inflow asto 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 techreporttech 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==

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[[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=0-471-11995-4 |page=335}}</ref> Pipes may leak because of careless installation; 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 and broken sewer cleanouts are a major cause of infiltration into municipal sewer systems.<ref>{{cite report |title=Private Sewer Laterals |url=https://www3.epa.gov/region1/sso/pdfs/PrivateSewerLaterals.pdf |date=June 2014 |publisher=EPA |___location=Boston, MA |series=Water Infrastructure Outreach}}</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 |authorstitle=Metcalf & Eddy |title=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 [[sump pumpspump]]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 |url-status=dead }}</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. SecondaryIn 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> but 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.

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

High rates of infiltration/ and 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==