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Water Science & Technology Vol 51 No 02 pp 147–154 © IWA Publishing 2005

Factors influencing exfiltration processes in sewers

D.J. Blackwood*, J.B. Ellis**, D.M. Revitt*** and D.J. Gilmour****

*Urban Water Technology Centre, University of Abertay Dundee, Bell Street, Dundee, DD1 1HG, UK (E-mail: d.blackwood@abertay.ac.uk; d.gilmour@abertay.ac.uk)
**Urban Pollution Research Centre, Middlesex University, Queensway, Enfield, London, EN3 4SA, UK (E-mail: m.revitt@mdx.ac.uk; b.ellis@mdx.ac.uk)
***Urban Pollution Research Centre, Middlesex University, Queensway, Enfield, London, EN3 4SA, UK (E-mail: m.revitt@mdx.ac.uk; b.ellis@mdx.ac.uk)
****Urban Water Technology Centre, University of Abertay Dundee, Bell Street, Dundee, DD1 1HG, UK (E-mail: d.blackwood@abertay.ac.uk; d.gilmour@abertay.ac.uk)


ABSTRACT
Exfiltration from sewers is widespread and emerging legislation may require water service providers to identify, and rectify, its sources in sewerage systems. This paper describes exfiltration test apparatus and a series of experiments undertaken using sewage to gain a better understanding of the influence of sewage solids and sediments on leakage rates. An overview of the results obtained is given, which demonstrates that most previous estimates of exfiltration leakage rates were too high due to a lack of appreciation of the "self-repairing" action of sewage and sewage associated solids. Exfiltration rates of 0.1% of the sewer flow or 0.001 l/s have been recorded for defects up to 6 mm wide.

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