€3m upgrade due on Cork water treatment to avoid 'critical point of failure' for network

A €3m upgrade of the Atlantic Pond wastewater pumping station is to begin in the coming months, as Uisce Éireann documents reveal that one penstock valve is considered “a critical point of failure” for the water network in Cork city.

On January 28, there was a wastewater overflow incident at Atlantic Pond pumping station (APPS). It was caused by the mechanical failure of the penstock valve (a permanent water gate that controls the flow of water from one area to another) at the entrance to the station.

A back-up of combined sewer inflow to the pumping station, with additional loads of tidal river water, resulted in localised flooding on Monahan Rd and Centre Park Rd.

An incident report was provided by Uisce Éireann to The Echo following a Freedom of Information (FOI) request.

The report explains that Atlantic Pond serves as the main pumping station for Cork city, with 90% of all sewer network flows entering the facility.

All flow from the combined sewer/storm network enters an inlet channel just upstream of a main inlet penstock valve.

From there, flow is split in to two lines and then in to two foul sumps. Foul flow is pumped from these sumps to Ballinure header chamber for screening and grit removal.

During storm and/or tidal events, excess flow to the two foul sumps is diverted to the two ading storm sumps, and storm water is pumped to the River Lee storm outfall.

The report, circulated to staff a few days after the incident, identifies that, as of January 31, “There are numerous mechanical issues at APPS, which, in effect, restrict flow capacity.”

These included that the fine screens and wash compactors were in need of overhaul.

During peak flow, the screens would become overwhelmed within two to three hours, tripping two of the foul sumps and dropping the foul pumping rate in half.

The mechanical overflow screens from the foul sumps to the storm sumps were non-operational, thereby restricting the capability of the asset to pump storm water, as flow could not be transferred from the sumps to the storm sumps quickly enough.

The inlet works at APPS were “essentially obsolete, as the grit baskets, which were vastly undersized to deal with incoming flow, have been removed”, and there was no overflow or by upstream of APPS, meaning all flow had to enter the asset before either being pumped forward to treatment or pumped to storm overflow.

The foul sumps are 8m deep each. However, their working volume had been severely diminished by a significant build-up of rags/grit and other scurrilous material over the plant’s lifetime.

As a result, the operating volume of each foul sump was restricted to approximately 1.5m to 2m.

Due to these flow restrictions, the pump station operator had to routinely restrict network flow into APPS to protect the plant and its equipment from flooding.

GATE

The only way to achieve this was by lifting and lowering the gate of the main inlet penstock valve.

This was automatically controlled — if the level breaches a comfortable threshold, the valve would close and, when pumping conditions allow, the valve would reopen to allow flow through to the foul sumps.

Uisce Éireann noted in the report: “This whole process can repeat multiple times per day. The penstock was never intended for such use, and it has essentially now become a critical point of failure for the asset and the network as a whole.”

On Tuesday, January 28, Uisce Éireann were notified of the incident at APPS, whereby the main inlet penstock was locked in to the closed position.

The gate of the penstock valve had been lowered to protect the APPS from excess network flows, as was routine.

Upon investigation, it was determined that the threads of the brass nut attached to the top of the gate of the penstock were sheared to the point that the threaded bar controlling the movement of the valve could not be engaged.

However, the penstock itself, and all of its ancillary equipment, was located underground in an inlet works chamber.

A crew attended the site to troubleshoot, and to devise a remedial action plan.

However, their access to the chamber was restricted due to rising high tides, which caused the inlet chamber to flood as flow started to enter it through the cable ducts above the penstock.

Work was undertaken on the day of the incident, including tankering to remove floodwaters, the installation of temporary pumps, and diversion of foul flow from APPS to storm overflow.

Over the following days, additional pumps were installed, the gate was manually lifted, and mitigation measures were developed for the future.

A spokesperson told The Echo that in response to the incident, Uisce Éireann “deployed all available resources to resolve the issue and mitigate the impact”, prioritising public health, safety, and the environment.

“Uisce Éireann fully recognises the seriousness of the incident and is co-operating fully with the Environmental Protection Agency (EPA) in relation to the post-incident investigation.

“Over €4m is being invested in the Atlantic Pond pumping station,” the spokesperson said.

“€1m has been allocated to immediate remedial works to improve hydraulic resilience and reduce dependence on the main inlet penstock. This includes upgrading screens, cleaning and emptying foul sumps at the pumping station, in addition to reconditioning of follow-on waste compactors at Ballinure header chamber.

“A further €3m upgrade of the facility is set to begin in Q3, and this will include a comprehensive overhaul of all foul and storm pumps, reconfiguring of the main inlet penstock, cleaning storm sumps, remediating storm screens, and installing storm return pumping systems.”

PUBLIC CONFIDENCE

It comes as information provided to Labour councillor in the city’s South East ward, Peter Horgan, shows that the Atlantic Pond pumping station is responsible for pumping water for 184,451 people.

“It’s vital that the public has confidence in the pumping stations in our ward and certainly in the Atlantic Pond set-up, which s over 184,000 people,” said Mr Horgan.

“The investment is welcome, but must be supplemented by workers on site to ensure that the capital works operate effectively, and we minimise the potential for this type of incident to occur again.

“I fully intend to visit this vital pump station and will be maintaining pressure on all stakeholders to deliver security of service for the people who depend on this and other pump stations.”