Hathershaw Fields CSO & Bardsley WwPS (2023)
Both Hathershaw Fields CSO and Bardsley CSO are located within the borough of Oldham, Greater Manchester and line the River Medlock, which flows into the River Irwell, approximately 10 miles west of the sites in Manchester City Centre. Hathershaw Fields is located in a college playing field within a predominantly residential part of the borough, whilst the Bardsley CSO is located off a busy main road in a largely industrial area, but located close to some residential properties and the Manchester and Ashton Canal.
In 2019, United Utilities undertook the Medlock Quality Programme, a comprehensive investment which included the installation of below-ground detention tanks at existing sites to provide increased storage capacity and reduce spills into the River Medlock and adjacent CSO and pumping station, to comply with the Water Framework Directive (WFD) to improve water quality in the River Medlock.
The programme was successfully completed, however there was a requirement to further reduce the amount of sewer litter by screening discharges from both overflows. This would be achieved by the installation new powered aesthetic screens within Hathershaw CSO and Bardsley PS to screen stormwater and retain solids such as wet wipes and cotton buds, reducing unscreened spills into the River Medlock and improving water quality during periods of heavy rainfall.
There were a number of constraints at each site: both had to remain operational 24 hours a day and 7 days a week, and due to the location of each site within close proximity of residential properties, it was important to ensure that there was no detrimental impact in terms of noise and vibrations.
United Utilities network modelling team had defined a notional solution as a starting point for this project. The Costain MSP team were then initially engaged to undertake some advanced investigation work, define the full project scope and advise on constructability, enabling residual risks to be quantified and managed via a lump sum design and build main award contract.
During the main implementation contract, Costain worked with United Utilities, the lead design and build contractor, VJ Donegan Civil Engineering Ltd, and their appointed consultants to undertake the detailed civil, mechanical, electrical, ICA design, supply, install, commission and handover of the operational asset, updating DSEAR, Health & Safety file records for safe future operation and maintenance.
VJ Donegan Civil Engineering Ltd undertook the detailed civil design via their lead consultant Wood Group. The civil design was relatively complex in that it was necessary to modify pre-existing infrastructure to accommodate the new screens, on small site footprints. Assessments were made on the existing ground conditions and water levels as one of the main concerns was an increase in buoyancy of the Hathershaw structure resulting from the creation of a larger internal void to accommodate the screens and maintenance access.
VJ Donegan Civil Engineering Ltd worked with their civil designer to prepare the design for solution model and integrate with the network baseline model provided by client. This was an iterative process requiring liaison with the UU modelling team and additional surveys to provide confidence in the verified solution model. During the build phase, a discrepancy was found between the network model parameters and existing sewer network, however the team worked collaboratively to engineer a solution within the constraints of the existing infrastructure, to ensure the screens performed as required by the terms of the discharge permit.
The introduction of new MEICA equipment required the DSEAR documentation to be re-assessed and updated to ensure compliance to the latest requirements.
The installation of powered screens and associated motor control centre (MCC) kiosk at Hathershaw Fields were considered permitted development and did not require planning permission. However, as there was a requirement to establish a temporary access road off an existing highway in order to access the working area, planning permission was required. A detailed planning application package was prepared by consultants WSP and submitted to Oldham Metropolitan Council, the Local Authority within which the site is located. The planning application was approved by Oldham Council in December 2021.
The site at Hathershaw was established in April 2022, starting with the installation of the temporary access road into the site and establishment of the compound and welfare.
In the first instance it was necessary to expose the existing CSO chamber and the raise the level of the concrete roof. This was achieved by sheet pile excavation works and by cutting sections of concrete from the CSO roof.
Before work could take place in the CSO chamber it was necessary to set up a system of over pumping from one chamber to the other. A safety monitoring system was later installed which included an alarm which would sound at times of heavy rain, acting as an early warning system for the team working within the chambers to ensure they could carry out work safely.
Following the installation of the new powered screens and several tests it was necessary to modify the existing chamber adjacent to the CSO. In order to undertake this work successfully, sheet piling was installed prior to the modifications. This work was completed within 6-weeks, ensuring that the newly installed powered screens were correctly sized. Water Engineering Services Ltd was the mechanical and electrical sub-contractor responsible for the screen installation. Following completion of this work the temporary ramp was removed and the site reinstated.
The site at Bardsley was also established in April 2022 and before work in the CSO could commence it was necessary to install temporary over pumping to ensure work could be carried out safely.
The CSO required an in-depth survey to confirm that the finalised design was correct and so therefore following this survey there was a period of time whilst no work was carried out on the site.
Main construction work at the CSO took place between August and September 2022, which included the cutting and removal of the existing reinforced concrete (RC) cover slab, modifications to the existing RC weir walls, installation of new powered screens, installation of associated instruments and cabling, installation of new control panels, dry and wet commissioning of the new system and finally the installation of a new RC cover slab and reinstatement of the site.
The Hathershaw Fields site is located in a quiet suburban residential neighbourhood with several residents overlooking the site. As extensive work had already taken place on site in 2019 to install a new detention tank as part of the original scheme, it was important to ensure that residents were engaged with regularly and made aware of any potential disturbances that could be caused throughout the construction process.
Letters were distributed regularly to residents keeping them abreast of all activities on site at programme milestones. This was often undertaken by the team in person to give residents to opportunity to speak with the team should they have any issues or questions.
As a smaller more compact site, Bardsley PS has fewer neighbouring residents but several adjacent landowners who share access with United Utilities. Site meetings were held on site at project milestones to explain upcoming work and answer question. During the main constriction programme weekly emails were issued to the landowners updating them on progress.
The project was completed on time, allowing United Utilities to meet key Regulatory Dates set by the Environment Agency for both sites, in turn improving water quality in the River Medlock - a key aspiration of United Utilities.
The ambitious programme was achieved by working together, with a close team consisting of United Utilities, Costain and VJ Donegan Civil Engineering Ltd, holding regular collaborative planning meetings to successfully manage the programme. Good relations were maintained throughout the works, with positive comments received from residents in relation to the conduct of the team on site and a WOW award nomination was received.