Beenhams Heath WTW (2021)
South East Water’s Beenhams Heath WTW serves the surrounding area of Maidenhead and Bracknell. Raw water is pumped via submersible borehole pumps from two off-site locations at Hurley and Waltham. The Hurley flows are directed through a membrane filter before passing through the GACs and combining with the Waltham flows via a collecting tower and water is then super chlorinated through a mixer into the above ground contact tank. Water is then mixed in with the third off-site supply from Malders Lane Reservoir in the above ground balancing tank before being de-chlorinated with sodium bisulphite and pumped into the distribution network via the high lift pumps.
The main drivers for the project were:
- Health and Safety observations from site that had highlighted spalling concrete from various sections of the main treatment works building.
- Ageing water quality monitoring/chemical dosing equipment on site aiding to the security of supply.
- Upgrading the visibility of site equipment onto the South East Water prism telemetry network to enable trends.
The project was delivered under the Engineering and Construction Contract (NEC3 form of contract), which was drafted, issued for pricing, then awarded to Enisca Browne in 2020 for the design and construction of this scheme as principal contractor and principal designer. South East Water and Enisca Browne are co-located at the Morley Road depot office. In this collaborative working environment, the South East Water and Enisca Browne team has successfully managed and delivered the Minor and Intermediate programme of works in AMP6. During the design phase it was necessary to identify potential cost and/or time saving opportunities by value engineering/innovation.
Early engagement was fundamental to the framework delivery model. On receipt of the Beenhams Heath project brief, the South East Water/Enisca Browne teams discussed and reviewed the scope of work and set about developing high level options. Key considerations at this stage were:
- Environmental constraints due to occupation of Bats within the existing building.
- Scope and construction methods to environmental, timescale and budget constraints
- Maintaining constant water supply from the WTW to the network, keeping outages to a minimum.
The South East Water/Enisca Browne team early engagement provided the opportunity to understand the key project drivers and use them to guide the scope development. This allowed cost saving measures and efficiencies to be captured at concept stage. The project brief was:
- To repair the failing concrete internally and external of the main pump house and protect from further corrosion.
- Demolish the upper section of the old coal bunkers and two lower sections used to house the redundant boiler and storage room.
- Refit out the dosing room with new upgraded CTC controller and WQ monitors.
- Upgrade several additional legacy monitors on the site and introduce a new turbidity monitor pre contact.
- Refurbish the sewage filter with the inclusion of a new Mcerts flow meter
- Integrate the site systems for better visibility and trends site wide to telemetry.
- Main Contractor & designer: Enisca Browne
- Concrete repairs: BSF Consulting Engineers
- Technical documentation: 3rd Light Media
- Systems integration: Profitec
- Sewage filter refurbishment: Mechanica
- Chemical delivery area: CJ Thorne
- Ducting & kiosk plinths: South Coast Contractors
- Panel build: Motrol
- Demolition/concrete repairs: High Five Construction
Prior to demolition works, Enisca Browne worked with South East Water’s Environmental Team to obtain all necessary environmental permits and assents as the demolition area was a roost for several species of bats. Alongside the environmental permissions the demolition licence was applied for with the local council obtained in good time to meet the programme constraints. Once these were in place letters were sent to neighbouring properties. Following H&S approvals, a scaffold was constructed around the demolition area including erection of scaffold protection and sheets to protect live plant and equipment from the demolition activities.
The structure was the broken up and removed starting with the external wooden cladding under the ecologist’s supervision to ensure compliance with the environmental permit. Following this the structure was broken from the roof down by hand in manageable sections and removed from site. Once down to the first-floor level specialist asbestos contractors were brought in to remove the original boiler and flue. Once removed the demolition of the lower two room could continue down to ground level.
The remaining area was protected against the outdoor environment and painted to blend with the rest of the building. All throughout the process numerous live and remaining services were encountered and with good collaboration with the South East Water teams we were able to minimise site disruption when diverting the services.
There was a need to repair a great number of areas of the main building inside and out due to the poor degrading condition of the exposed concrete areas. Working from the consultant’s condition report, Enisca Browne worked with the selected subcontractor to identify all the affected areas, break out all the dead concrete, re-measure and record the total size/cost of the defect. This was compiled on a report which was discussed weekly with the South East Water delivery team to ensure any additions to the scope were captured contractually.
Once agreed the areas were treated, filled, and painted to prevent against further corrosion and defects. A total of 389 total repairs were undertaken and all exposed concrete surfaces were treated and painted internal and external of the main works building.
Water quality monitors
There are nine existing monitors throughout the site which were aging and in need of replacement (six chlorine monitors and three turbidity monitors) and the installation of a new combined pre-contact turbidity monitor. The chlorine monitors sample the site for pre-contact, post-contact, balancing tank, final, 14” final final & 20” final final.
The turbidity samples the site for micro filter inlet, micro filter outlet, GAC outlet, and combined pre-contact. A staged programme for replacement was detailed out involving contractor and client teams to ensure minimal disruptions to the site outputs.
The replacement turbidity monitors were able to be installed in a different location to the existing, this meant that we could have both monitors (old and new) running simultaneously for a time giving assurance to the site production teams of the accuracy of the new system before finally switching over.
The Chlorine monitors had to be replaced due to space constraints in the dosing room. The new monitors were soak tested off site using neutralised water to ready them for replacement, this meant the changeover time on site could be greatly reduced. We undertook the replacement of the chlorine monitors in pairs spread over a couple of weeks to ensure the new systems were back operational and reliable each time. During each replacement we took the opportunity to upgrade the sample lines to include new pumps, and flow switches.
Enisca Browne’s panel manufacturer partners Motrol were engaged to build a South East Water compliant emergency shutdown panel (ESD) for both final turbidity and chlorine, and chemical treatment controller (CTC).
There were three existing ESD panels on site at various points in the process, these were combined into one final ESD which will hard-wire shutdown the high lift pumps should the need arise. We were able to install the new system alongside the old system to allow for minimal disruption in the changeover and testing.
The existing site CTC was outdated and in need of being brought up to South East Water’s most recent specifications. There were four available dosing control systems to integrate within the new panel but during talks held with the South East Water engineering and production teams it was decided to simplify the control operation and reduce to two control loops as the site no longer had the requirement for four.
The chemical treatment controller, like the chlorine monitors, had to be replaced in situ due to space constraints in the dosing room. Due to the complexity of the changeover this was undertaken over a 2-day shutdown period to ensure the control functionality could be fully tested before being put back online.
Within the initial brief was the requirement for a new sewage filter refurbishment filter system to be installed but upon taking a weeks’ worth of discharge samples and having them analysed against the discharge permit requirement, the existing filter system was found to be well within the permit parameters. Enisca Browne then held discussions with the South East Water engineering team to advise that a refurbishment of the existing system would meet a key project driver (value engineering/innovation).
The existing system was removed in between operations and taken off site by the sub-contractor for refurbishment before being re-installed and finished off with a netting over the filter to prevent future vegetation build-up.
Enisca Browne’s systems integration partner Profitec were engaged to aid with project scope and design, there we various existing plant to be added to the site PLC network as well as telemetry visibility along with the new installations. The existing systems integration comprised of three separate PLCs of three manufacturers, Profitec had to investigate the code obtained from a site download of each, compare with the copy of the FDS’s on file, they then had to run a check on each to ascertain how many spare inputs and outputs where available for use.
Profitec were able to prepare and submit for acceptance the new FDS for each existing PLC for the integrations as well as identifying the correct places in the network to install the equipment signals. These FDS were reviewed by South East Water who could then create the new telemetry list for the site.
The commissioning of the new PLC programmes and HMI changes was carried out across several planned partial site shutdowns to thoroughly test all of the new system and telemetry.
The addition of a chemical delivery catchment area was requested mid-contract. Enisca Browne and South East Water conducted a site meeting to discuss the scope of the delivery area, then Enisca Browne provided an outline design for South East Water’s review that adhered to South East Water Genius Specification.
Once agreed, Enisca Browne liaised with the site production teams to ensure that access and deliveries to the working area were scheduled to not coincide with the timing of the works. Signage was displayed to redirect site staff on an alternate pedestrian route whilst the works was undertaken.
The civils contractor then attended site to mark out the area as per the agreed design and strip ready for shuttering and concrete pour, the area was designed to minimise concrete pours and having to seal gaps between slabs. Also designed, was an interlocking valve arrangement to isolate the collection area from the drainage whilst the chemical delivery is in progress, capturing any spillage to be contained until disposal.
With the Covid-19 pandemic still fresh, additional safety measures were adopted to set the site up for the works and ongoing employee safety:
- Designating all project staff (including the supply chain) as key workers.
- Providing additional PPE, following social distancing requirements.
- Providing additional welfare facilities.
- Plan in work activities to best minimise site attendance each day.
- Liaise site activities with South East Water to ensure no conflict with their site operational commitments.
Key to the project success during this ongoing period was the physical separation between South East Water engineering team, the production team and Enisca Browne teams with all meetings being conducted via video conferencing and site inspection undertaken via remote video.
Through collaborative working between the South East Water, Enisca Browne and stakeholders, the scheme was delivered on time, within project budget with minimal disruptions to the site’s outputs. The value engineering benefit to South East Water for the south east waterage filter refurbishment was in the main a CAPEX saving.