SPN7. 7th International Conference on Sewer Processes & Networks

SEWER MISCONNECTIONS IN ENGLAND AND WALES: ARE THEY

A SERIOUS PROBLEM?

J Bryan EllisUrban Pollution Research Centre,

Middlesex University, UK.

Sheffield, August 2013

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Num

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seho

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Perc

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Percentage Surface Water Sewers

Number of Households Served (Millions)

Surface Water Sewers in England and Wales

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80

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NH

3-N

(mg

l-1)

Downstream Increase in PO4 (mg l-1)

1%

5%

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20%

Average N:P ratio for sewage (DEFRA, 2008). Per-centage given is % sewage in river water

Downstream changes in NH3-N and PO4 in an urban catchment, River Colne, Oxhey, Herts.

River Classification Grade C/D

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 (??)

Procedural Flow for Misconnection Enforcement Notices

Misconnection Established by EA or WC

Ground Inspection (EA or WC pre-survey and site survey)

LA Section 59 Enforcement Notice (Notice and Recommendation of measures)

LA Takes Action

LA Takes No Action EA or LA Preliminary Visit

Pollution Problem Remains

Householder Complies (Cost split 40% to LA)

Repair Carried Out

LA Closure Visit (Site Inspection and Sign-off)

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

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2007 2008 2009 2010 2011 2012 2013 2014 2015

Hous

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Num

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ollu

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Pote

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YEAR

NUMBER OF HOUSES WITH POLLUTION POTENTIAL

HOUSES CAUSING POLLUTION AT 7% MISCONNECTION RATE

HOUSES CAUSING POLLUTION AT 2% MISCONNECTION RATE

Actual Pollution Potential of Domestic Properties in Thames Water Region

<0.01% misconnection

rate

SECTION 59 ENFORCEMENT NOTICES 2008

Company Apportioned Household Pollution

Potential(x 1000)

% Population

served

Enforcement NoticesServed

Thames 2034 24% 60

Severn Trent 1343 16% 86

Yorkshire Water

599 13% 180

Section 59 actual 326

Estimated total Section 59 requested 609

Total if all LAs fully cooperated with Section 59 869

Washing Machine

Kitchin sink

Handbasins

Dishwasher

Bath

Shower

Toilet

Bidet

Other

Domestic Misconnections by Type

Volume BOD PO4-P0

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Kitchen sinkWashing machineDishwasherWash basinShowerbath

Perc

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Domestic Misconnections by Type

Washing Machine

Sink Dishwasher Bath Shower Toilet Total Average Totals

BOD (mg l-1) 11(280-470)

5(33-

1400)

11(390-699)

7(50-173)

7(80-424)

20 62(110-350)

Phosphate (mg/l-1) 255 175 200 101 884 10060 11675

Volume (litres) 13.7(17-60)

10.0(8-14)

1.6(2-6)

25.0(16)

33.2(12-20)

28.1 121.6(68-134)

Volume assuming 2.36 persons per house (litres)

32(41.5)

24(21-31)

4(14 – 47)

59(37.8)

78(29)

90 287

Probability that appliance is misconnected

78% 96% 26% 51% 32% 22% 5%

BOD (mg l-1) 9 6 3 4 2 4 3 31

Phosphate (mg/l-1) 199 168 52 51 280 2248 384 3582

Volume (litres) 25 23 1 30 25 20 14 138

Household Appliance Misconnection Pollution Yield

2007 2008 2009 2010 2011 2012 2013 2014 2015

National Data House Potential Misconnections (No x 103)

274 294 314 335 358 378 400 423 447

Wastewater Company reported Houses Actually Causing Pollution

480 490 500 509 519 529 539 549 558

Untreated Wastewater Volume Based on National Data (litres x 106)

37.8 40.6 43.3 46.2 49.4 52.2 55.2 58.4 61.7

BOD Loading Based on National Misconnection Data (kg)

2468 2646 2826 3019 3222 3402 3600 3802 4023

BOD Loading Based on Wastewater Company Data (kg)

4.32 4.4 4.5 4.6 4.7 4.8 4.9 4.94 5.0

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

EXTRAPOLATING MISCONNECTION DATA

BOD = [(POPt/Hn) x (Ma/Hn) x La x Hn] where:BOD = B OD in kg/dayPOPt = Total Population of catchmentHn = Number of occupants per household/propertyMa = Number of each type of misconnected appliance (as

determined from site survey)Hn = Total number of households/properties in surveyLa = BOD loading for each appliance (kg/person/day)

OR

BOD = [POPt x (Ma/Hn) x Li.e estimate is independent of the number of occupants per property.

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.