Water Framework Directive chemical investigation programme
by John Tidy BEng (Hons) IEng MICE MIET
skids installed electrical installation underway - Courtesy
Shirebrook STW is located approximately 5 miles north of
Mansfield town centre and caters for a population equivalent
(PE) of 12,000. As part of the AMP6 Chemical Investigations
Programme, Severn Trent Water is required to carry out a full
scale trial of a ‘proprietary’ iron dosed sand filter plant on a
works serving between 10,000 and 50,000 PE. The trial is to
assess the effectiveness of the process at removing priority
hazardous substances/hazardous substances/specific pollutants
(PHS/HS/SPs) as defined under the Water Framework Directive (WFD)
- in this case cadmium. In addition, WFD modelling has
identified there is a high probability that Shirebrook STW will
be subject to a phosphorus consent of approximately 0.2mg/l.
Severn Trent Water promoted a scheme to address this and the
requirements of the trail in March 2015 and appointed their
framework design and build contractor, NMCNomenca, to carry out
In order to satisfy the
requirements of the chemical investigation programme and meet
the new ultra-low phosphorus discharge consent, Severn Trent
Water identified a new technology which promised to fulfil these
requirements. Evergreen Engineering provided this technology and
The innovation was not
the technologies being employed but how the technologies were
integrated. The core of the solution was fundamentally a sand
filter which employed chemical dosing and specially
selected/graded sand. Working closely with Evergreen
Engineering, Design for Manufacture and Assembly (DfMA) and 3D
modelling techniques have been embraced from the outset of the
project. The challenge to the team was to modularise the entire
plant including the pipework for off-site manufacture allowing
for on-site assembly. The outcome from this challenge was the
creation of pump skids, prefabricated pipework racks,
preassembled access steelwork modules, and containerised
control, blower and dosing equipment.
The DfMA approach led to
the ability to halve the normal M&E installation time, removing
some 20 crane days, reducing working at height, enabling a high
quality and right first time assembly requiring no
redesign/rework on site.
Modular access steelwork installed - Courtesy of
completion of a trial, and collection of the required data, the
plant would normally be mothballed. Not content to accept that
any investment would be written off, the team identified a site
where there would be a need for intervention and if the trial
proved successful, no further investment would be required.
Whilst the project had
identified significant capital savings the team did not stop
there; they continued to explore further opportunities for
innovation within the design. As an example the original
location of the plant required retaining walls to be constructed
which would have involved a large muck shift being undertaken.
This was challenged and a new location was identified reducing
the muck shift by 75% and removing the need for retaining walls,
significantly reducing the project’s carbon footprint.
Filter being delivered - only just fits!
Courtesy of NMCNomenca
filters in position
Courtesy of NMCNomenca
Innovation by its very
nature requires significant levels of planning and communication
to ensure that there is a clear direction in order to realise
the innovative solution, with the added challenge of time, as
there was a requirement for a minimum period of data gathering.
The key to achieving the
challenging programme, was to ensure that all parties were fully
aware of their obligations and were committed to delivering the
project on time. All parties involved, including our key
subcontractor delivering a significant proportion of the project,
engaged early in the process. Using tools such as collaborative
planning and regular progress meetings, the project was
delivered within the programme timescales allowing STW to start
the data gathering phase on time.
Safety in design was a
key principle in the development of the project ensuring that we
meet our obligations under CDM 2015 as principal designer and
principal contractor. There are a number of examples of this;
fundamentally the approach of DfMA significantly reduced on site
By modularising the
plant, including access platforms which were transported to site
in the largest sections possible (with handrail fitted and
flooring already secured), the requirement to work at
height to construct these elements was reduced.
Further consideration was
given to the operability and ergonomics within the design of
areas such as the pipework. In these instances there were
significant controls required within the pipework design; these
controls were positioned at waist height, with instruments
placed at eye level to aid operators in their duties.
Final filter being positioned - Courtesy of NMCNomenca
Project management and
The scheme was critical
to Severn Trent Water’s AMP6 chemical investigation programme.
Therefore the scheme was required to be completed on site by the
end of June 2016. This posed a significantly challenging
programme for both the design and construction teams.
Severn Trent Water
promoted their solution and engaged with NMCNomenca at an early
stage in the project conception. This enabled both parties to
work collaboratively to progress the design in order to achieve
the requirements of the trail in a timely manner.
approach by the client, design and build contractor and supply
chain throughout the life of the project enabled the innovative
solution to be delivered within the challenging timescale.
engineering principles and judgement
practices for the delivery of this form of plant would have been
to construct the majority of the pipework, control and dosing
infrastructure in situ. This however would not have been
achievable within the time constraints, as the design period was
likely to take a significant part of the project duration as
this was the first of its kind, with all elements being bespoke.
The innovative solution identified the key aspects of the plant
that would have a major implication on any civil engineering
design. In this case the loadings from the filters were the
principal controlling factor.
installed electrical installation underway - Courtesy of
installed at ergonomic level
Whole project impact
The project has had a
positive impact on improving the water quality within the River
Meden through reducing the levels of chemicals contained within
the final effluent entering the watercourse, thus reducing
Severn Trent Water’s environmental impact. This watercourse
provides a valuable habitat for wildlife and community resources
for anglers and the like.
The level of capital
investment required by Severn Trent Water was minimised through
effective and efficient manner in which the project team
promoted the trail. As a result this has allowed Severn Trent
Water to make further investment within the business to tackle
and improve water quality and service to the wider community.
John Tidy, Contracts Manager with NMCNomenca, for providing
the above article for publication.