CASE STUDY – BROMATE CONTAMINATION OF GROUNDWATER AND IMPACT ON THAMES WATER … Bishop.pdf ·...
Transcript of CASE STUDY – BROMATE CONTAMINATION OF GROUNDWATER AND IMPACT ON THAMES WATER … Bishop.pdf ·...
CASE STUDY – BROMATE CONTAMINATION OF GROUNDWATER AND IMPACT ON THAMES WATER OPERATIONS
2
Background
New drinking water standard for bromate (2003) = 10 ug/l.
Bromate contamination of Hertfordshire Chalk discovered mid-2000
Groundwater pollution plume of some 20 km length from Sandridge to Middle Lee valley
Contamination impacts two Three Valleys PWS boreholes and several Thames Water boreholes (the Northern New River (NNR) wells)
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Plume
10 kmKeyRed>500 ug/lOrange50 - 500 ug/lYellow10 - 50 ug/l
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Bromate at NNR wells
Bromate Levels in the NNR Wells
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
1-M
ay-0
11-
Jul-0
11-
Sep
-01
1-N
ov-0
11-
Jan-
021-
Mar
-02
1-M
ay-0
21-
Jul-0
21-
Sep
-02
1-N
ov-0
21-
Jan-
031-
Mar
-03
1-M
ay-0
31-
Jul-0
31-
Sep
-03
1-N
ov-0
31-
Jan-
041-
Mar
-04
1-M
ay-0
41-
Jul-0
41-
Sep
-04
1-N
ov-0
41-
Jan-
051-
Mar
-05
1-M
ay-0
51-
Jul-0
51-
Sep
-05
1-N
ov-0
51-
Jan-
061-
Mar
-06
DATE
CHADWELL SPRING
BROADM EAD BOREHOLERAW WATER
AM WELL END WELL RAWWATER
AM WELL HILL WELL RAWWATER
AM WELL M ARSH WELLRAW WATER
RYE COM M ON WELLRAW WATER
M IDDLEFIELD RD WELLRAW WATER
HODDESDON WELL RAWWATER
BROXBOURNE WELLRAW WATER
TURNFORD WELL RAWWATER
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Bromate at Hoddesdon
Bromate Levels in the NNR Wells
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
1-M
ay-0
11-
Jul-0
11-
Sep
-01
1-N
ov-0
11-
Jan-
021-
Mar
-02
1-M
ay-0
21-
Jul-0
21-
Sep
-02
1-N
ov-0
21-
Jan-
031-
Mar
-03
1-M
ay-0
31-
Jul-0
31-
Sep
-03
1-N
ov-0
31-
Jan-
041-
Mar
-04
1-M
ay-0
41-
Jul-0
41-
Sep
-04
1-N
ov-0
41-
Jan-
051-
Mar
-05
1-M
ay-0
51-
Jul-0
51-
Sep
-05
1-N
ov-0
51-
Jan-
061-
Mar
-06
DATE
HODDESDON WELL RAWWATER
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Lee Valley system
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Recharge to New River from Groundwater Source
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Operational impacts
TW takes a Deployable Output (DO) hit at Hornsey if unable to use NNR wells – bromate contamination likely to be highest in drought years
DO impact on Hornsey = DO impact for London
Impacts on operational flexibility for Hornsey –Hornsey currently relies on well water dilution to overcome problems with river water source (turbidity, algal blooms, etc)
Hornsey serves a discrete area not easily served by other Works – risks of disruption to supply
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Management to date
TW has a crude spreadsheet mass balance model for the NNR/New River system
Assumes a % growth factor year-on-year for NNR well bromate concentrations and suggests which wells can be operated each month
Situation reassessed continuously and modifications to suggested operating profile made
North London Artificial Recharge Scheme (NLARS) boreholes used to dilute bromate concentrations in 2003
No bromate exceedences at Hornsey to date
10
AMP4 (and beyond?)
AMP4 solution treatment at Hornsey
2 phases – pre-treatment (to allow more use of river water) by December 2006 and bromate treatment by December 2008 (RO formal basis of AMP4 submission)
Potential impacts of bromate on wider Lee Valley system via Northern Transfer Tunnel and bromate in River Lee – AMP5?
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Wider Impacts
12
Understanding (or misunderstanding?) the plume
Atkins commissioned to refine predictions for NNR wells
Short timescale, but did develop flow and contaminant transport models (Modflow/MT3DMS)
Significant problems modelling plume between Hatfield area and NNR (last 10 km of plume) –indicates bromate flow in discrete fractures
“scoping” calculations and modelling did provide some further insight (to be advanced with UCL)
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Contaminated Land Regulations
EPA 1990 Part IIA – Contaminated Land Regulations
Focussed on source of contamination – contaminated land
Local Authority proceedings started in 2000
Special Site status declared in 2002 and passed to EA
Remediation Notice served in 2005
Appropriate Persons (2) have appealed
Remediation timescale ?
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Conclusions/what can we learn?
Largest groundwater pollution plume in UK (?)
Major impact on water resources – drinking water quality, operational flexibility, DO
Thames Water (and Three Valleys Water) have already spent substantial sums on investigation and much more will be spent
We still don’t know how the problem may develop in the future and the wider impacts
The Regulations have proved a slow vehicle for delivering a solution which benefits the Water Industry
Just like the CWC vs ECL case, the issue of “foreseeability” arises