Faulty probes led to thousands of litres of chemicals spilling into River Lee

Spill occurred as chemical was pumped from bulk storage into day tanks, but sonic probe failed to initiate the automatic pump shut-off, leading to tank overflowing, says report 

The Inniscarra dam in Cork. In July, about 3,400 litres of aluminium sulphate — a chemical used to purify drinking water and treat wastewater — overflowed from a day tank into the site’s drainage system, around 250m downstream of Inniscarra dam. File picture: David Keane.

Investigations were launched after faulty probes caused thousands of litres of chemicals to spill into the River Lee in Cork over the summer.

The Cork Harbour and City Public Water Supply serves more than 143,500 people. Its raw water is treated at the Inniscarra Water Treatment Plant.

In July, about 3,400 litres of aluminium sulphate — a chemical used to purify drinking water and treat wastewater — overflowed from a day tank into the site’s drainage system, around 250m downstream of Inniscarra dam.

Uisce Éireann notified the Environmental Protection Agency (EPA) and Inland Fisheries Ireland about the incident and an investigation was launched. It found the incident did not “adversely affect drinking water quality”.

The spill occurred as the chemical was pumped from bulk storage into day tanks. Operators start the pumps manually, but they should stop automatically when the chemical reaches a set level.

While Day Tank No. 4 was being filled on July 23, the sonic probe “failed to initiate the automatic pump shut-off, resulting in the tank overflowing”.

A plant operator spotted the overflow and stopped the pumps manually at 9.12pm. About 3,400 litres of aluminium sulphate were lost in 12 minutes.

Chemicals not properly managed or stored

The EPA told investigators when they visited the site that the root cause of the probe malfunction had not been established.

Uisce Éireann later found the sonic probes were out of calibration.

The audit found treatment chemicals were not properly managed or stored at the plant. It found no adverse environmental impact, with live fish observed at and downstream of the discharge point.

“Uisce Éireann advised that the length of the drainage network and flow from the Inniscarra Dam would have dispersed and diluted the spill prior to discharge to the River Lee,” the audit said.

The EPA recommended regular calibration and maintenance of all sonic probes. It also called for an independent backup, such as a high-level alarm or level switch, to prevent overflows if a probe fails.

The report also recommended examining whether spills and overflows could be diverted to a containment tank instead of the River Lee.

In a statement, Uisce Éireann said it regrets that this incident occurred and “takes its responsibility to protect public health and the environment very seriously.” 

“An immediate investigation was undertaken following the spill, and corrective actions were implemented at the site.

“These actions included a review of the equipment involved and of operational procedures associated with chemical transfers,” a spokesperson said.

“Protecting public health and safeguarding the environment are our highest priorities. We will continue to engage with the EPA and will provide all necessary updates and information as we complete the actions arising from the audit,” they added.