Excess levels of chlorine pumped into Dingle reservoir

People living in Dingle in County Kerry were left with a bad taste in their drinking water in January after council staff mistakenly pumped excessive levels of chlorine into the town’s reservoir.

An audit by the Environmental Protection Agency found that up to five times the level of chlorine recommended by the World Health Organisation was poured into Dingle’s drinking water supplies on Jan 12 to address concerns they were inadequately disinfected due to low chlorine levels in the water.

The EPA said an alarm alerted council staff to low chlorine levels in the water leaving the treatment plant in Dingle and they poured 250 litres of sodium hypochlorite directly into the reservoir which contained 1,000m³ of water.

Sodium hypochlorite is the main ingredient in bleach and is widely used to chlorinate water in swimming pools.

“The amount dosed was far in excess of what was required,” the EPA said.

Kerry County Council estimated the actions had resulted in chlorine levels of 20-25mg/l in the drinking water in Dingle when normal levels would be 0.7-0.8 mg/l. The WHO guideline for chlorine in drinking water is 5mg/l.

The audit criticised the failure of council staff to manually test levels of chlorine in the town’s water supply after they had taken corrective action. It also criticised Kerry County Council and Irish Water over their handling of the issue including a failure to promptly notify the EPA about the incident.

“An error lead to overdosing of the disinfectant which in turn increased levels of residual chlorine in the supply between approximately 8am on Jan 12 and midday on Jan 13 when supply in the network was shut off,” the EPA said.

The Council, which operates the plant under a service level agreement with Irish Water, got 12 complaints from householders in Dingle on Jan 13 about bad taste and odour from their drinking water. The audit notes that the Council took immediate corrective action — scouring and flushing the town’s pipe network and emptying the town’s reservoir which provides drinking water to a population of 1,720. Water was cut off for about six hours before supplies were restored.

The audit found the Council had failed to notify Irish Water until 4.45pm on Jan 13, while the EPA was not made aware of the issue until the following day While Kerry County Council consulted with the HSE after it had shut down the water supply on the afternoon of Jan 13, no water restrictions were deemed necessary.

The audit recommended that Irish Water and Kerry County Council develop documented procedures for responding to alarms from the treatment plant in Dingle as well as increased monitoring of chlorine levels in the supply: “There was inadequate training and supervision of Kerry County Council staff in relation to appropriate corrective actions and treatment decisions.”

Irish Water said corrective actions are being implemented to prevent a recurrence of a similar incident including improvements in relation to induction and training of staff.