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SPN7. 7 th International Conference on Sewer Processes & Networks

SPN7. 7 th International Conference on Sewer Processes & Networks. SEWER MISCONNECTIONS IN ENGLAND AND WALES: ARE THEY A SERIOUS PROBLEM? J Bryan Ellis Urban Pollution Research Centre, Middlesex University, UK. Sheffield, August 2013. Surface Water Sewers in England and Wales.

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SPN7. 7 th International Conference on Sewer Processes & Networks

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  1. SPN7. 7th International Conference on Sewer Processes & Networks SEWER MISCONNECTIONS IN ENGLAND AND WALES: ARE THEY A SERIOUS PROBLEM? J Bryan Ellis Urban Pollution Research Centre, Middlesex University, UK. Sheffield, August 2013

  2. Surface Water Sewers in England and Wales

  3. Downstream changes in NH3-N and PO4 in an urban catchment, River Colne, Oxhey, Herts. River Classification Grade C/D

  4. MISCONNECTION SOURCES • household/commercial premise misconnections (greywater and blackwater) • connection of industrial/commercial floor drains to surface water drainage system • abuse of surface water drainage system e.g illegal disposal of solvents, paints etc; vehicle jet-washing; wash-down of cafe/restaurant frontages/courtyards etc; illegal dumping • failing septic tanks. • dual/shared manhole chamber overflows—cross-connection rather than misconnection (??)

  5. Procedural Flow for Misconnection Enforcement Notices

  6. MISCONNECTION DATA AND TRENDS • NATIONAL DATA • - CES (1999); >1M; ~29% of all connections) • Defra (2007); 1.35M (~7M properties; £235M/year; >7% misconnection rate) • Defra (2009); 300,000 – 500,000 (3% - 5% misconnection rate) • UKWIR (2013); 130,000 – 140,000 (<1% misconnection rate; £190M) • REGIONAL DATA • Thames Water (2010); 1.2M or 3% - 5%. (Based on 1 :10/20 misconnection rate; £78 - £104M reconnection cost + survey + enforcement notice) • SITE SURVEY DATA • - Moston Brook, Manchester (2013); 1.5km2 ; 1700 population; ~24% misconnections) • Brent, N London (2008); 30km2 ; 236,464 population; >7% misconnection rate; £10.4M

  7. Actual Pollution Potential of Domestic Properties in Thames Water Region <0.01% misconnection rate

  8. SECTION 59 ENFORCEMENT NOTICES 2008

  9. Domestic Misconnections by Type

  10. Domestic Misconnections by Type

  11. Household Appliance Misconnection Pollution Yield

  12. Estimated Misconnection Wastewater Volumes and Pollution Loads Entering Thames Region Surface Waters

  13. EXTRAPOLATING MISCONNECTION DATA BOD = [(POPt/Hn) x (Ma/Hn) x La x Hn] where: BOD = B OD in kg/day POPt = Total Population of catchment Hn = Number of occupants per household/property Ma = Number of each type of misconnected appliance (as determined from site survey) Hn = Total number of households/properties in survey La = BOD loading for each appliance (kg/person/day) OR BOD = [POPt x (Ma/Hn) x L i.e estimate is independent of the number of occupants per property.

  14. CONCLUSIONS • Site surveys required to give accurate estimation of misconnection numbers and severity of impact. National estimations deflate likely potential scale and costs of the misconnection problem. • Misconnection rates likely to vary between average minimum of 1% to mean of 3% and average maximum of 7%. Hotspots greater than 12% - 24% can occur with observable receiving water impacts where SWOs discharge in groups or in series along an urban reach as demonstrated by N:P ratios. Need for robust and tested catchment scale extrapolation techniques to adequately quantify WFD receiving water risks. • Source tracking and compliance procedures need to be more stringent and without need to resort to third party engagement. • Need for twin-track approach with misconnection remediation (“clean-up”) in conjunction with long term “preventative” community-based programmes/campaigns of both public and professional trade knowledge and awareness. • Surface water misconnections likely to be a continued issue for urban drainage and urban receiving water quality in the UK into the foreseeable future.

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