Telscombe Lower Portobello PS & Screening Works (2021)

Lower Portobello PS & Screening Works - Courtesy of CMDP

The original treatment works was built in the 1970s in an area carved out of the cliff face. It comprised a screening plant for grit and fat removal, before flows are pumped via a hand-dug long sea outfall 2.5km out to sea. This outfall replaced the original Victorian short sea outfall built in 1874, although the latter was retained for emergency overflows. The condition of the redundant treatment building was poor, having suffered from the environmental effects of its coastal location and corrosive effects of hydrogen sulphide (H2S), saline influent and saline wash water spray. Sections of the building roof were being held up by scaffold and the entire basement mezzanine slab was propped by a series of MP30 propping, meaning it could not be loaded with any plant.

Project background

CMDP is a non-incorporated joint venture between Costain and MWH Treatment and is a principal delivery partner for Southern Water’s AMP7 capital investment programme, delivering a range of schemes to maintain and improve water supply and wastewater treatment in East Sussex and Kent, whilst protecting the environment.

The collaborative CMDP/Southern Water team has delivered a complex and innovative wastewater treatment solution at Lower Portobello Pumping Station, taking account of difficult Health and Safety conditions on a very tight footprint.

The works comprised a new sewerage storm overflow pumping station and screening facility at an existing coastal site in between Brighton and Peacehaven WwTWs, catering for a large part of Brighton’s storm overflows.

In order to prevent spills to the environment, the new works had to be built without interrupting existing storm flows in excess of 3000l/s, and infiltration and tidal ingress of around 600l/s from the Victorian Brighton and Hove sewerage system. To achieve this, a temporary pumping station was set up inside the basement of the old redundant treatment building while the new works took place.

Demolition of existing works – Courtesy of CMDP

Project scope

he original concept for the project was to convert part of the treatment plant into a wet well pumping station, and repair the building, and install a bespoke 3000l/s screenings facility within it. However, the delivery team’s constructability review and risk assessment identified significant short and long term safety risks for this proposal, including:

• A suspended floor slab which could not be loaded.
• Corroded support beams with crash protection.
• Plant and steelwork including handrails and floors badly corroded.
• H2S Issues.
• Confined space working.
• Incoming HV at risk of water damage.
• High levels of bird guano.
• Basement areas prone to flooding.
• Incoming flows into proposed wet well from ingress.
• Surcharging of tidal outfall into the building.
• Maintenance in an unsafe environment.

2 (No.) duty/duty band screens with the capacity of treating 3000l/s – Courtesy of CMDP

As an alternative, the collaborative project team proposed abandoning and demolishing the building and providing a new external above-ground plant instead, achieved through a phasing of temporary works allowing the building to be demolished prior to the new works construction. Not only did this simplify and safeguard the construction phase, but it also reduced project costs, with the demolition estimated to be at least three times more expensive if carried out afterwards.

The new solution required a considerable amount of enabling works, such as temporary over pumping, capable of pumping 600l/s; demolition of an existing building; and the complex removal of an old, large penstock and the concrete plugging of a 10m deep 3m diameter pipe in a tidal chamber.

Digital technologies

A combination of digital technologies such as BIM 360 FIELD, and GLUE enhanced communication, as well as problem-solving efficiency on site were used. This formula enabled effective collaboration with the numerous subcontractors involved and close liaison with the client. The 3D model was expanded upon by the demolition contractor to develop the demolition sequence, which had to be robust due to the close proximity to the public beach and the temporary pumping station.

MCC which controls the variable speed drive pumps, screens, screenings plant – Courtesy of CMDP

Lower Portobello PS & Screening Works: Supply chain

• Project delivery: CMDP
  • MWH Treatment
  • Costain
• Main works design support: Stantec UK
• Temporary works design: Ward & Burke
• Civil/mechanical/demolition: Ward & Burke
• Electrical: Econotech Ltd
• MCC: MCS control systems
• Supporting steelwork & GRP platforms: Pipe Systems
• Screenings handling plant/inlet works: M and N Electrical and Mechanical Services
• Pump supplier: Xylem Water Solutions
• Standby generator: P&I Generators
• Access ladders, stairs, platforms, handrail, chamber covers & hatches: Step on Safety Ltd

Construction

Once the building had been demolished, the new pumping station could be built offline due to the flow being diverted by the temporary pumping station.

The new pumping station is innovative in the way that it makes use of part of the existing inlet/basement structure. It makes it possible to get the most out of the existing asset and vastly reduce the extent of the construction works at the same time.

Amidst this complex operation and the unforgiving coastal weather conditions, the delivery team adopted more stringent PPE standards, rapidly implemented a DfMA solution for the screening plant, and expertly managed the complications associated with a physically constrained site.

The new inlet works and screenings plant, MCC and standby generator. The photo also shows the basement walls of the old building. The above ground concrete walls and roof were crushed on site and used as fill material, reducing the scheme’s carbon footprint – Courtesy of CMDP

Outcome

The outcome of the project is a vastly improved operational working environment with respect to Health & Safety, eradication of a rapidly degenerating unsafe building asset, and fast and efficient construction through maximised use of DfMA strategies. It represents a leading example of collaborative working between client and contractor.