Upload
oliver-mills
View
213
Download
0
Tags:
Embed Size (px)
Citation preview
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
0
1
2
3
4
5
6
0
5
10
15
20
25
30
35
Num
ber o
f Hou
seho
lds S
erve
d (M
illio
ns)
Perc
enta
ge Su
rfac
e W
ater
Sew
ers
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
1
2
3
4
5
6
7
8
9
10D
owns
trea
m In
crea
se in
NH
3-N
(mg
l-1)
Downstream Increase in PO4 (mg l-1)
1%
5%
10%
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
0
100
200
300
400
500
600
6800
7000
7200
7400
7600
7800
8000
8200
2007 2008 2009 2010 2011 2012 2013 2014 2015
Hous
es C
ausi
ng P
ollu
tion
Num
ber o
f Hou
ses w
ith P
ollu
tion
Pote
ntial
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
5
10
15
20
25
30
35
40
45
50
Kitchen sinkWashing machineDishwasherWash basinShowerbath
Perc
enta
ge C
ontr
ibuti
on (%
)
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.