Download xt150224 annex to de Mauley letter

ANNEX 1
Assessment of substantive points raised in Lord Berkeley’s letter of 19
January 2015 to Lord de Mauley.
Summary
There are concerns regarding the statements made by Lord Berkeley in his letter of
13 January 2015. These statements are based on the report dated 10 December
2014 by Professor Chris Binnie entitled “Thames Tideway: Review of Tideway spills
and their environmental impact.” This report concludes that the Thames Tideway
Tunnel is not needed to meet environmental and legal objectives, and that the
Thames Tideway can be regarded as satisfactory under the terms of the Urban
Waste Water Treatment Directive (UWWTD).
Careful reading of this report and the appendices that underpin the conclusions it
makes, shows that a great number of these conclusions are based on either a
misunderstanding of the data sets used, inappropriate assessment methodology, or
unsupported assumptions. This means that the conclusions are being based on
unsound science, and are incorrect.
The Environment Agency (EA) has been in dialogue with Professor Binnie over the
last three years on this and a range of other issues relating to the need for the
Thames Tideway Tunnel, and has expressed concern to him on a number of
occasions in recent months about the technical work incorporated into the supporting
arguments of the conclusions in his 10 December report. These conclusions, when
read in the abstract, may appear reasonable at first glance. However, when the
body of supporting work is assessed in detail, the overall conclusion that the Thames
Tideway currently complies with the UWWTD and the environmental standards set
for the Tideway, is not supported.
The main concerns relate to:
 an inappropriate analysis of dissolved oxygen using the Automatic Quality
Monitoring Station (AQMS) data which masks low DO levels;
 the analysis of combined sewer dry weather flow and its associated impacts;
 a misunderstanding of the different requirements for discharges from
Combined Sewer Overflows (CSOs) and Sewage Treatment Works (STW);
 a misunderstanding of probability modelling;
 no solution for the remaining west London CSO discharges (following
completion of the Lee Tunnel and upgrades to the five main London STWs);
and
 the role of booms, bubblers and skimmers (in-river solutions).
These concerns are set out in detail below.
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1. Dissolved oxygen (DO) standards compliance assessment
Summary:
1) With respect to industry standard Urban Pollution Management (UPM)
procedure, the Thames Tideway Strategic Study (TTSS) approach to
DO compliance assessment conforms to UK industry norms. The
methodology in Professor Binnie’s report does not.
2) The methodology used in Professor Binnie’s report for the analysis of
DO compliance is not sound. It masks the critical low DO periods that
impact on aquatic ecology.
3) There are fundamental issues in the DO compliance assessment
approach used in Professor Binnie’s report. The methodology
suggests there are no failures; EA review of the same data shows how
Professor Binnie’s approach fails to identify frequent and regular noncompliance over the same period.
1.1 Aspects with respect to industry standard UPM approach
Professor Binnie’s method is not appropriate for assessing the number of breaches
of each of the four thresholds established for the Thames Tideway DO standard, as
it does not check compliance as defined by the standard. It also masks the range in
DO of any given tide.
Lord Berkeley states in his letter of 19 January that: "In any case the Chiswick and
Cadogan AQMSs have already met the relevant standards for the last 5 years, much
longer than the one year used initially at Mogden." (page 3, paragraph 5). The
evidence does not support this statement, and this highlights a significant error in
Professor Binnie’s analysis and conclusions.
Professor Binnie claims that when using his methodology to assess the AQMS DO
dataset provided by the EA, he demonstrates that there has not been a failure of the
DO standard during the 2007 – 2014 period. The EA has reviewed the dataset in
light of that claim, and its analysis indicates that this is not the case. The resulting
discrepancy between the two analyses is entirely due to a fundamental error in
Professor Binnie’s analysis and associated methodology.
The EA repeatedly asked Professor Binnie to clarify the objective of his DO analysis,
but did not receive a response. Had the EA understood that the objective was to
assess compliance with the DO standards, it would have advised Professor Binnie of
the appropriate methodology to use to ensure compatibility with the UPM industry
standard.
By setting appropriate standards to protect aquatic life, the impact of intermittent
discharges can be assessed and solutions designed for an environmentally
acceptable discharge. The DO standards relevant to the tideway are exactly that:
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design standards. This represents an adaptation of the UK industry standard UPM
methodology, insofar as they are standards specific to the Thames Tideway.
It is important to note that design standards are not primarily intended to test the
performance of a scheme, once complete, especially where long return periods
apply as they do in the Tideway. However, the DO monitoring data does present the
possibility of testing performance, and it is an interesting approach.
The Thames Tideway Strategic Study aimed to provide standards which ensure the
long-term survival of fish and other biological life. Fish are useful indicators of the
quality and health of the water environment. A 2012 review by a panel of experts
found the Tideway standards for fish are a good surrogate for wider ecology in the
Tideway as a whole. Intermittent standards for water quality in the UK are based on
the following parameters:
(a) return period (probability) of an event;
(b) the duration of the event; and
(c) the magnitude of the pollution impact on the environment.
This UPM procedure is more commonly applied to flowing freshwaters and
incorporates intermittent standards appropriate for freshwaters, but the sensitive
ecology they aim to protect are also present in the Thames Tideway. Bespoke
intermittent standards were developed for the tidal Thames, during the TTSS (20002005), to be used to design solutions to London’s CSO problem. These standards
are still appropriate as design standards today, as confirmed by a review of experts
in 2012. The duration element of the Thames Tideway intermittent standards is
defined in terms of consecutive tides, and a distance element equivalent to
approximately one tidal zone1 is also incorporated into the standards to reduce the
risk of misreporting compliance due to erroneous data.
The Thames Tideway intermittent standards are made up of four thresholds with
different return periods and durations, in line with the principle that the more acute
concentrations should be encountered more rarely, and for shorter periods of time.
A failure occurs if any one (or more) of the four standards are exceeded. That is
because each of the thresholds is designed to protect different aspects of the
ecology, ranging from subtle and less severe (sub-lethal) impacts of long periods
below a DO level of 4 mg/l (which are “allowed” relatively frequently) to the acute and
severe effect of DO concentrations below 1.5 mg/l, which should happen very rarely
indeed.
For the record, the four thresholds are defined as below:
Standard
(no.)
1
DO
(mg/l)
4
Return
(years)
1
1
Duration
(tides)
29
A tidal zone is a unit of water in the Thames Tideway that is used by the Environment Agency to
manage water quality.
3
2
3
4
3
2
1.5
3
5
10
3
1
1
They apply to any continuous stretch of river 3 km or more in length. Duration
means that the DO concentration must not fall below the limit for more than the
stated number of tides. A tide is a single ebb or flood.
Standard 1 was selected to ensure protection against the chronic effects of reduced
oxygen, such as growth depression and behavioural impacts linked to fish trying to
avoid affected areas. Standards 2 and 3 are both designed to limit the scale and
frequency of fish kills. Standard 4 is aimed at preventing mass fish mortality across
several life stages.
The 3km length aspect is not considered in Professor Binnie’s analysis. It is
assessed by performing half tide correction (HTC) on the measurements collected by
the AQMS network over the course of a tide.
The HTC procedure is designed to convert the location at which a water sample is
taken to the location along the estuary that the water sampled would have been
under half tide conditions. The definition of half-tide, for any location in an estuary, is
the point in time when the volume of water upstream of the location is at its mean
value (given that the volume upstream reduces over an ebb tide, and increases
during a flood).
This allows the results to be plotted along the length of the estuary at locations which
correspond to the half tide position of any measurement. The resulting plots can be
used to see if any portion of the estuary exceeding 3km in length is below a
threshold during that particular tide.
1.2 Design standards versus reality
In order to compare CSO spill frequency and volume for a number of proposed
solutions, the TTSS and subsequent Thames Water projects used a typical year.
The selection of the typical year was based on rainfall records from 10 sites across
London and Beckton STW and Crossness STW flows. The actual year that was
assessed as most typical in the period 1970 - 2003 was the 1980 water year
(October 1979 to September 1980).
Professor Binnie’s reports appear to assume that a "typical year" is simply defined as
a year with broadly "normal" rainfall, and that CSO spill frequency in any year
exempting floods or droughts should be directly comparable. That is not the case.
The compliance testing procedure used by Thames Water to assess the
performance of proposed engineering solutions to the Tideway CSO problem against
the design standards used a 41-year rainfall series, and not the typical year. Any
formal compliance procedure to assess the actual performance of the Thames
Tideway Improvements Programme (i.e. the Lee and Thames Tideway Tunnels
together with the upgrades of the 5 STWs) against the Thames tideway intermittent
standards will need to use an appropriately long data period, to ensure compliance
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with all four DO standards can be reliably assessed. Professor Binnie, as Chair of
the Thames Tideway Strategic Study, is aware that this was the agreed approach for
assessment. The EA would expect these principles to be applied to any current
assessment.
1.3 Technique and methodology
The EA has reviewed the same datasets that it provided to Professor Binnie, and
has reached very different conclusions. This is related to the methodology he has
used, which masks critical DO periods. As an example to illustrate the differences,
consider the recent six-year 2009-2015 period where there is good optical DO data
from the Cadogan AQMS.
The Cadogan AQMS data shows 3 clear dips below the 3mg/l threshold in 2011,
despite Professor Binnie’s report Appendix A claiming that “from 2009 onwards
Cadogan AQMS shows no breaches or failures over the following 5 year period”
(page 34).
AQMS are fixed to a structure in the river. The tide washes past the monitor, which
takes a sample every 15 minutes. That means that the entire tidal excursion passes
the monitor over the course of the tide, giving good representation of most of the
river across the AQMS network as a whole. An AQMS will “see” the full 13km+ tidal
excursion over the course of a tide, so averaging the data across that time period will
mask the lowest observed levels of DO, and any statistics will not be representative
of the worst-affected 3km river segment. It is these low levels of DO that will have
an impact on the ecology of the river, and must be recognised in any analysis of the
data.
An exceedance of a DO standard is defined as more than a continuous 3 km stretch
below a concentration threshold for more than a certain number of tides. The
standard is only failed if an exceedance occurs more frequently than defined by the
return period of the standard. So for example, standard 4 is failed if the river falls
below 1.5 mg/l for longer than 1 tide, more frequently than once every 10 years. A
failure of any of the 4 standards constitutes non-compliance.
In the Cadogan AQMS data being considered here there are six clear exceedances
of Standard 2 (3 mg/l) and five of Standard 3 (2 mg/l). Given the acceptable return
period of these thresholds are 3 and 5 years respectively, this demonstrates that the
Tideway has not met the standard even in the short section of river monitored by the
Cadogan AQMS. Professor Binnie’s method, which ignores these events by
averaging the DO measurements across a tide, is entirely inappropriate.
The error is related to the fact that Professor Binnie’ methodology seemingly ignores
the tidal excursion of the receiving water, and the ecology the standards are
designed to protect.
Because DO concentrations in the Tideway typically vary a great deal along its
length, Professor Binnie’s methodology smoothes out the DO sags and therefore
misses the true depth of the sag; precisely the part that will have maximum impact
on aquatic ecology.
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1.4 Preferred way and what this means for results and conclusions
To illustrate why Professor Binnie’s method, although speedy, returns misleading
results consider the event of the 27 August 2011: here Professor Binnie states that
the minimum DO encountered was 1.47 mg/l, but that as the 1-tide average using his
methodology works out as 2.1 – 2.5 mg/l, that’s “OK” (report page 33, Appendix A,
Section: “Period before 2014”).
Looking at the DO values across the upper tideway for four consecutive tides in the
table below, the longitudinal variation is evident and shows a range between 2 and 8
mg/l. It is clear that for all four tides more than 3km of river is below the Standard 2
concentration threshold. Standard 2 is intended to protect the wider ecology and
against fish mortality, and this incident is expected to have had a significant impact
on both.
Looking at Cadogan alone in the chart below, over a flood – ebb sequence, the
AQMS sees a range of 2-5mg/l. 3-4km of river is below the threshold.
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That this continues for longer than the duration “allowed” by standard 2 is evident
when five consecutive tides are plotted together (this is easier to see when more
AQMS are plotted simultaneously, but here Cadogan is shown in isolation in the
chart below for the purposes of illustration:
While this is easy to see on the half-tide corrected plots above, it’s also clear from
the simple time-series plot below (the distance element is not clear from this type of
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plot, but the above two plots do show it). The specific issue is with standards 2 and
3:
Standard 2, as over 3km of river is under 3mg/l for 8 consecutive tides, and anything
over 3 tides every 3 years is unacceptable for the ecology in the river.
Standard 3, as over 3km of river is under 2mg/l for 3 consecutive tides, and anything
over 1 tide every 5 years is unacceptable.
Standard 4 is not actually breached, as less than 3km of river was below 1.5mg/l for
more than 1 tide.
Standard 1 is not considered here, as the impact did not last longer than the allowed
29 tides.
The above graph clearly shows that following this one release of storm sewage in
August 2011, several of the DO standards are failed simultaneously; which means
that the overall DO objective is failed. A breach of any one of the four standards
means that the Tideway has failed the objective to maintain sufficient DO for the
ecology to avoid unacceptable polluting effects. By contrast, Professor Binnie’s
average DO readings are shown in the graph above as a solid black line.
When a simplistic tide-by-tide statistical analysis is applied, the averages are clearly
significantly higher than the minimums, as one would expect:
8
Tide
28/8 0040 0707 ebb
28/8 0707 1309 flood
28/8 1309 1948 ebb
28/8 1948 0129 flood
29/8 0129 0808 ebb
27/8 0606 1219 flood
27/8 1219 1848 ebb
27/8 1848 0040 flood
Minimum
DOO
1.9
1.84
2.63
2.57
2.54
1.32
2.43
1.47
Average
DOO
3.58
2.74
3.61
3.09
3.54
2.89
3.86
2.84
This is why Professor Binnie erroneously concludes that this period does not fail
standard 2 – his averaging methodology does not account for the variation observed
in the data. It is essential to recognise that the point of the standard is to protect the
environment. Any analysis of the DO data must be appropriate to the way the
standards are defined, by capturing the periods of low DO impacting on the aquatic
ecology.
2. Combined sewer Dry Weather Flow (DWF) and headroom
Summary:
1) Sensitivity analysis testing of Professor Binnie’s proposals demonstrates that the
additional headroom provided by reducing sewer dry weather flows would not
have a significant effect on reducing CSO spill frequency and volume.
2) Professor Binnie’s interpretation of the figures in the Water Resource
Management Plan (WRMP) is inconsistent with national water industry resource
planning approaches. His use of baseline figures for water going into supply fails
to account for uncertainty, a requirement of the water industry.
2.1 Sensitivity of sewer network spill frequency to DWF
In Appendix C of Professor Binnie’s report supporting evidence there is an
assumption that a reduction in dry weather flow would have a significant effect on
CSO performance.
Sensitivity testing the effect of a reduction in water use was carried out by the TTT
project. DWF reduction had only a marginal effect on spill frequency. The extreme
scenario tested considered hypothetical assumptions leading to a 26% reduction in
the dry weather sewage flow of the sewer network, in order to consider how sensitive
the system was to changes in this parameter.
As an example of just one of the CSOs, even after making the adjustments to baseflows that Professor Binnie proposes, leading to the removal of 26% of the dry
weather flow from the model, it still predicts over 50 spills in the typical year from
Hammersmith Pumping Station alone. Therefore, the additional headroom provided
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by removing some of the dry weather flow is insufficient to accommodate the rainfallderived storm sewage component.
2.2 TWUL WRMP data assumptions
The figures quoted in Professor Binnie’s report from the WRMP regarding baseline
water into supply are correct. However, this is the baseline figure for water going
into supply, and does not account for any uncertainty. Ofwat, EA and water
companies use uncertainty values in the planning process to ensure that future
demand can be met. This is an integral part of the water supply planning process.
Professor Binnie’s work does not cater for any uncertainty in future supply with the
figures he has used. Similarly, he has not accounted for these issues (including not
meeting demand reductions and climate change) in other parts of his work (which he
freely admits). It is unwise to plan without taking these uncertainties into account,
and the regulatory process ensures that the EA does that. These uncertainties
include uncertainty associated with the uptake levels of demand management
measures that Professor Binnie relies upon to maintain a low base-flow in the
sewers.
The figures used in Appendix C of Professor Binnie’s report misleadingly assume
that there is no increase in water supply, and this method is not used by the
regulatory bodies to plan for the future. All water resource planning for London
shows that there will need to be a significant increase in the amount of water
available for supply, with new potable supply sources planned to be delivered in
future water resource management plans for the London Resource Zone.
3. Urban Waste Water Treatment Directive (UWWTD) compliance
Summary:
1) Professor Binnie’s report fails to recognise the different requirements for STWs
and CSOs imposed by the UWWTD.
2) The report misrepresents the reasons why the EA considers that Mogden STW is
compliant following its recent upgrade work.
3) The “do nothing more” approach with respect to Central London CSOs is not
compliant with the UWWTD; Professor Binnie’s assessment does not provide a
solution to this issue.
3.1 Different requirements for CSOs and STWs
There is a lack of clarity in the report about the difference in the way that the
UWWTD considers STWs and CSOs. Member States are required to limit pollution
from storm water overflows. To that end there is a requirement for an adequate
system to collect and transfer all waste water under normal climatic conditions to
treatment. Professor Binnie’s report assumes that the current performance of the
Mogden STW is directly comparable to the performance of the Tideway CSOs. He
incorrectly concludes that spills from the CSOs have little environmental impact on
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the Tideway, failing to recognise that discharges from CSOs have a higher pollutant
load by volume than equivalent discharges from STW storm tanks. This
demonstrates a fundamental misunderstanding of the different requirements for the
management of STW and CSO spills. STWs are required by the UWWTD to provide
secondary treatment of waste water before discharges. Storm sewage at Mogden
STW is screened and settled before discharge; CSO discharges are not, and are
more polluting as a result. Given the continuing CSO spill levels that will occur even
after the Lee Tunnel is operational and London STW upgrades have been
completed, action therefore must be taken to reduce those.
Professor Binnie does not apply these differences to the analysis in his report, and
this leads to a gap of assessment for Central London CSO compliance. The Central
London CSOs will still frequently discharge into the Tideway even after the five
London STW improvements and the Lee Tunnel are in operation, and so pollution
from these discharges has not been limited as required by the Directive.
3.2 Mogden STW compliance
Professor Binnie has misunderstood why the EA considers the Mogden STW is
compliant, and suggests that this is solely because it has not caused a major
pollution event in the Tideway. He cites his interpretation of the water quality data as
evidence for this position. The EA has explained its assessment of the Mogden
STW to Professor Binnie on numerous occasions.
The EA is working with TWUL to ascertain the reasons for the Mogden STW storm
tank spills that have happened since the works upgrade was completed in 2013.
The driver for this is ascertaining compliance with their discharge permit for the
STW, and concern among local people about the STW’s performance. It is not
about the environmental impact of these spills on the Tideway.
Discharges from STW storm tanks have a less polluting load than the equivalent
volume of discharge from a CSO. This is because the storm sewage from the storm
tank receives some treatment before discharge, in the form of screening and
settlement. For this reason, it is inappropriate to assume that CSOs discharging at
the same frequency as STW storm tank discharges are satisfactory, just because the
STW storm tank discharges may be regarded as satisfactory. Instead, regard needs
to be given to the environmental impact of each individual CSO to determine whether
it is satisfactory or not. CSOs are different to STW storm tank discharges as they do
not have settlement or screening.
3.3 “Do nothing more” does not support compliance
In his report, Professor Binnie also assumes that his approach to discharge analysis
of the remaining CSOs in central London is relevant and legal. However, this is
erroneous, as his analysis fails to identify the breaches of the DO standards resulting
from the discharges. In addition, the discharges from the remaining very large CSOs
and their associated effects are completely disregarded. The correct compliance
assessment confirms that the river is failing to meet the DO standards, and therefore
doing nothing about the remaining central London CSOs is not an option.
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4. Probability models
The EA disagrees with the statistical assumptions founded on probability in
Professor Binnie’s report. The report suggests that data from the upper estuary
(Chiswick & Cadogan AQMS) since April 2013, when the Mogden STW
improvements were completed, can be used to demonstrate that future performance
will be satisfactory. There is no statistical basis to support this assumption.
UK Water Industry planning uses historic datasets to predict the likelihood of future
events occurring, but this does not guarantee that any given event will occur in any
given year or to an exact frequency. An analogy of this approach would be the
delivery of flood risk management infrastructure: these are not deemed to have been
inappropriately planned if a 1-in-30 year event or a 1-in-100 year storm does not
manifest itself in the first 10 years of operation.
Professor Binnie’s approach is to assume that as there has not been a failure of the
1.5 mg/l standard in the two summers since the Mogden STW improvements were
completed, the risk of this occurring has disappeared. The EA finds no basis to
support this conclusion.
5. Central London CSOs are not dealt with by the “do nothing more” option
In the report, Professor Binnie uses his assessment of STW and sewer DWF to
suggest that the Tideway is compliant with UWWTD requirements. However, the
report does not specifically provide an analysis or solution for the 34 most polluting
London CSOs, which continue to discharge into the Tidal Thames.
There are no planned upgrades or improvements to these CSOs through any other
process than the Thames Tideway Tunnel. Applying the proposals set out in
Professor Binnie’s report (i.e. “do nothing more”) leaves these CSOs to continue
frequently discharging and polluting the river to the same extent as currently,
meaning that they would continue to be categorised as unsatisfactory by the EA.
The “do nothing more” approach, therefore, does not comply with the UWWTD.
6. Booms, bubblers and skimmers
Summary:
1) These measures do not address the mix of pollutants in CSO spills, such as
those derived from road runoff, and submerged litter.
2) Booms, bubblers and skimmers are in-river measures, and therefore cannot
be a permanent solution in compliance with UWWTD requirements.
6.1 Pollutants in CSO discharges
Lord Berkeley’s letter of 19 January 2015 states that “…the water spilling from the
overflows is basically storm water with a foul water component, thus it is not just
sewage as you imply but diluted sewage” (page 2, paragraph 4).
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Arguably, all sewage is water with waste added to it. Using booms, bubblers and
skimmers as alternatives to capturing the remaining CSO spills after the Tideway
improvements, does not deal with the environmental risk posed by the mix of
pollutants they contain. Road runoff in isolation also has the potential to cause
pollution.
Storm sewage is raw sewage mixed with rainwater. Despite the sewage element
being diluted, it still contains levels of bacteria far in excess of World Health
Organisation recommended limits to protect human health, and it contains
pathogens that are harmful to humans if ingested. Storm sewage is also a source of
sewage-derived litter and sewage solids that pollute the river and its foreshore,
leaving unsightly and harmful deposits in places used for recreation. It contains
organic matter that exerts an oxygen demand on the river, causing DO levels to drop
rapidly, causing unacceptable damage to the environment and aquatic ecology.
Lord Berkeley’s letter also states that “I cannot find where he proposes bubblers in
his report and believe you are mistaken on this” (page 2, paragraph 6). In fact, from
a full reading of his report, and supporting work in Appendix F, it is clear that
Professor Binnie relies upon bubblers and other measures for the solutions he
proposes, and his further work is based upon this.
To cope with aesthetics issues, Professor Binnie proposes booms and skimmers for
surface litter collection. These are currently already used on the Tideway to collect
wind-blown and other litter. There is recent published evidence2 to suggest that
there is a significant submerged litter quantity in the Thames Tideway, comprised of
sanitary components and plastics. This litter has been shown to travel within the
water column, and not on the surface, and therefore would not be collected by
surface booms and skimmers.
6.2 These measures are interim measures
Skimmers and bubblers are already in use on the Thames Tideway, but can only
ever be interim measures to mitigate the worst effects of CSO pollution in the
immediate short-term. While they undoubtedly have environmental benefits, they
are inappropriate as a permanent solution as they do not prevent CSO spills entering
the river in the first place, and thus do not meet the UWWTD requirements in that
regard. They cannot therefore be considered as an alternative to the Tideway
Tunnel as proposed in Appendix F of Professor Binnie’s report.
Booms are an in-river solution unless somehow incorporated into the waste water
collecting system required by the UWWTD. There are significant practical
challenges to using booms to screen very large discharges with significant solid
component in a very visible public area, with tidal dynamics, and health risks
associated with sewage detritus.
2
“Plastic in the Thames: A river runs through it”, Marine Pollution Bulletin 78 (2014) 196-200
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7. Other issues
7.1 The use of Meteorological data
Professor Binnie’s report makes incorrect assumptions regarding the use of
meteorological data. In the Compliance Test Procedure used by the EA, actual
rainfall data covering a 41-year period has been used to derive the event series in
the procedure. This matter has formed part of wider discussions between Professor
Binnie and the EA prior to the publication of his report.
Appendix C, on which so much of Professor Binnie’s report conclusions are based,
does not use an appropriate rainfall analysis. His stated assumption on rainfall
variability is that the 41 years of rainfall data “will not be that reliable” (report page
42, Appendix C, paragraph 5). This assumption is unfounded and the report
contains no evidence to support it. Additionally, Professor Binnie’s report fails to
clarify what might constitute a better estimate of rainfall than a combination of gauge
and radar data as used in the Compliance Test Procedure.
7.2 Underlying foundations for Professor Binnie’s report conclusions
Appendix C, on which so much of Professor Binnie’s report conclusions have been
based, is flawed in the stated assumption on rainfall variability when it states that 41
years of rainfall data “will not be that reliable” (page 42, last line). As noted above,
this assumption is unfounded with no supporting evidence.
Professor Binnie’s assumptions on future sewer flows are not consistent with the
water industry national planning process; this undermines his report Appendix C.
Professor Binnie’s assessment in the report Appendix A, regarding the assessment
of AQMS data in relation to meeting DO requirements, has been shown above to be
inappropriate.
Professor Binnie’s report conclusions rely heavily on the work in these Appendices.
In the light of the above assessments the EA therefore has to regard the conclusions
as based on flawed science.
7.3 Specific points in Lord Berkeley’s letter of 19 January of relevance to the
Environment Agency
"I understand there are few records of when CSOs spill and pumping station
discharges are assessed on the basis of hours pumped. Thus the spill frequency
data is not robust." (letter page 2, paragraph 1)
Pump records are not available for most of the gravity CSOs, and only for the large
pumping stations. These pumping stations represent the largest discharges in terms
of volume, and the three in the western reaches of the Tideway (Hammersmith, Lots
Road, and Western) alone account for over 50 spills and 5 million cubic metres in the
base-case scenario, after the Lee Tunnel is completed. The verification monitoring
referred to was intended to verify the model assumptions for the remaining gravity
CSOs and the actual spill frequencies in any given year is not comparable to the
typical year, as described above.
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"For other CSOs the spill frequency model is based on constant per capita water
consumption…" (letter page 2, paragraph 2)
As described above, the model sensitivity tests indicate that the meteorological data
(most importantly rainfall) is the primary factor affecting spill frequency, not the dry
weather flow composed of infiltration, domestic and trade sewage.
"First the water spilling from the overflows is basically storm water with a foul water
component, thus it is not just sewage as you imply but diluted sewage." (letter page
2, paragraph 4)
Storm sewage does have a large component of rainwater, but the CSOs are at the
end of a large combined drainage catchment which means it is mixed with the dry
weather flow - the wastewater spilling from the CSOs cannot be described as
inoffensive, and as described above contains excessive levels of harmful bacteria
and other pathogens.
"As the objective of the UWWTD is “to protect the environment from the adverse
effects of waste water discharges”, the rejection of bubblers and skimmers, actually
litter collectors, which have already been in use for many years, seems illogical."
(letter page 2, paragraph 5)
This statement may be the result of a misunderstanding in Professor Binnie’s report,
where he states that "The UWWTD requirement is to collect and treat and that is
what the litter collectors allow to happen." (report page 21, paragraph 1). The
assumption that the Directive allows for collection/treatment of sewage derived litter
after this has left the collection system is incorrect: the Directive requires treatment
plants to perform sufficiently under all normal local climatic conditions, and for CSOs
and STW storm tanks to only discharge in situations such as unusually heavy
rainfall. The strategy of in-river treatment was dismissed by the TTSS Solutions
working group as it "really cannot be considered a true strategy or an appropriate
solution in that once in the river the polluting effects can only be ameliorated[...]"
(Solutions Working Group Vol.1, 2005). The TTSS was Chaired by Professor Binnie,
and he should be well aware of this requirement.
"You state that “they do not provide a good representation of all discharge and tide
circumstances”. However, the Environment Agency in its notes of the meeting on
25th September stated “We have explained that the WQ monitoring is a better
indicator of how often each DO standard is breached.”" (letter page 2, last
paragraph)
The context is lost here - the original reference was that WQ monitoring data was a
better indicator than the record of fish kills, which the EA maintains is correct.
"Above you state that the 3 sites provide “reasonable coverage of the Tideway” [...]
and the 9 locations were selected by the Environment Agency." (letter page 3,
paragraph 1)
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The monitoring network and its coverage are determined by the objective - to
manage water quality incidents from an operational perspective. The primary
objective is not to assess compliance.
"However, whilst this will have a significant effect, these changes will occur slowly
and further measures such as SuDs, BGI, Real Time Control etc are very likely to be
able to be implemented in time to cope with such changes..." (letter page 3,
paragraph 8)
The EA’s Rapid Evidence Assessment of October 2013 shows that there is no
evidence that SUDS and associated measures can be implemented to the degree
required within an appropriate timescale, so the basis for this assertion is not clear.
"For the one tide condition, Prof Binnie took the minimum average of 24 consecutive
every 15 minutes readings to get the worst period, irrespective of whether this was
part of different tides or not." (letter page 3, last paragraph)
It is unclear what the "minimum average" means, but the fact that Professor Binnie
did not consider which tide the data pertained to further illustrates the point made
above that his analysis was not framed within the context of the DO standards.
"Whilst meteorological data has been discussed previously, we are not aware that
the current report relies on any such analysis of meteorological data." (letter page 4,
paragraph 7)
Professor Binnie’s report does consider rainfall data, in the appendices.
"This would indicate that, for the 5 year period 2010 to 2014 relevant to the Chiswick
and Cadogan assessment, the summers were both wet and dry and typical." (letter
page 5, paragraph 2)
This does not mean that this period is comparable to the typical year, defined by the
TTSS as the 1980 water year.
"Whist (sic) Professor Binnie believes that the modelling system are (sic) probably
the best available at the time, the problem is with the quality and reliability of the
input data. As his report identifies in Appendix C these issues include:
- Rainfall spatial variation particularly of the critical summer thunderstorms
- Few reliable sewer flow gauges in the complex sewer system
- Lack of discharge measurements at most CSOs
- Use of wrong data on future sewer flows
- Limited data on quality of spilled flows
- Variability of Tideway water quality.
- Variability of tidal data.
- Variability of tributary flow and water quality." (letter page 5, paragraph 8)
It is important to note that the EA does not agree with any aspect of this assessment
of the modelling approach, except that it was the best available at the time of TTSS.
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"The importance of any model is not so much whether it has been peer reviewed but
whether its output actually reflects actual conditions that occur" (letter page 6,
paragraph 2)
As the EA has sought to explain above (and in previous meetings with professor
Binnie), the purpose of the water quality model was to design an appropriate solution
and predict its effectiveness in the long term.
"Thus the water quality model does not reflect the relevant conditions." (letter page
6, paragraph 5)
To re-iterate, the water quality model was intended to predict long-term performance
as required by the DO standards.
"This the water quality model has failed to reflect either initial conditions or conditions
after the upgrades sufficiently. Thus it is not so much Professor Binnie’s report that
challenges the water quality model, it is its failure to reflect actual conditions as
found by other analysis." (letter page 6, paragraph 7)
The EA’s view, for the reasons outlined above, is that Professor Binnie’s analysis is
not fit for purpose. The water quality model was used to ensure any proposed
solution was neither inadequate nor gold plated in the sense that it was
overprotective and therefore unnecessarily expensive.
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