Investigations

This section contains summaries of reports on drinking water
quality incidents and investigations.

Report on drinking water quality incident at:
Camphill Water Treatment Works in July 2007

Scottish Water Executive Summary

On Wednesday 4th July 2007, a quantity of mineral was oil mistakenly put into hydraulically operated equipment used to drive the valves on the rapid gravity filters at Camphill WTW.

This followed a burst which occurred on the high pressure side of the hydraulic power pack. This burst was remote from the filters. The burst caused the system to lose pressure and without manual intervention would consequently have closed all the filter valves stopping production of water at the site. Seventy five litres of mineral oil was put into the hydraulic oil reservoir which has a total volume of three hundred litres.

The plant operator intervened by manually closing the valves on the pressurised system thus keeping filter inlet and outlet valves open, maintaining production of water.

Between Wednesday 4th and Friday 6th July 2007 a quantity (75 litres) of mineral oil (Scot West ISO 32) was mistakenly used to top up the system, food grade type (HTG 32) is normally used.

A leaking seal (seep) on the pressurised cylinder of the filter No.1 wash water outlet valve may have led to a very small (if any) quantity of mineral oil coming into contact with the clarified water within the filter. This was a known seepage which normally did not affect water quality due to the oil being food grade.

On Monday 9th July 2007 a second burst occurred on the pressurised side of the power pack. This again caused the system to lose pressure and again the operator intervened by closing down the valves on the system to maintain production of water.

It was then discovered that the oil previously used to top up the power pack was not of food grade type. This led immediately to the realisation that the seepage on the valve on Filter No.1 meant there was the potential for a very small quantity of mineral oil to have seeped into the clarified water, and the operator immediately isolated the filter and escalated the issue to his line manager.

Samples were taken from the works and from distribution on the 9th and 10th July 2007. These showed hydrocarbon levels at below the measurement threshold of 10ug/l. The customer contact system was searched and no complaints of taste or odour had been received from the supply area.

The oil reservoir was emptied and re-filled with food grade oil on Tuesday 10th July 2007 and a methodical purging/flushing and refill of the complete pipework system will be carried out by 17th August 2007.

The seeping valve was removed, refurbished and re-fitted by 23rd July 2007. Filter No. 1 was washed down and backwashed twice, with wash water removed from site. Samples were then taken on 23rd July 2007, and the filter was returned to service on 26th July 2007 after the samples showed clear and a final backwash.

DWQR Assessment on the incident

The incident report highlights several issues that Scottish Water should have addressed prior to the chain of events that led to this incident. The seeping seal on the cylinder of filter No 1 Wash Water Valve had been known about for some considerable period of time prior to the event, certainly it was known about from June 2006 when the seals had been replaced in an attempt to stop "the historic seepage [leak]" associated with this equipment. The failure to implement a more effective intervention after the June 2006 replacement of the seals suggests a systemic failure of the management of the maintenance of the plant. Given that Scottish Water in the Incident Report states that the actions to refurbish filter No 1 wash water actuator cylinder to resolve the leak were completed on 23 July 2007 - only 14 days after the incident being discovered - suggests that effective and timely actions could have been taken at any time prior to the 7 July (when the events that led to the incident occurred). The DWQR views this failure to take effective action prior to the incident as a very serious matter and it will be raised directly with Scottish Water's Director of Assets.

The Incident Report suggests that the cause of the Incident arose as a result of a conversation between the senior treatment operative and a fitter about the suitability of replacement hydraulic oil - whether a certain type of oil was food grade or not. DWQR reject that any suggestion that this was the case; had appropriate written procedures been in place staff would not have been in a position of trying to remember the correct type of oil to be used. Clear and effective stock control and labelling of equipment together with clear procedures laid down in the works manual for the replacement of hydraulic fluids should have been provided by Scottish Water to ensure their staff were adequately trained and supported to undertake such activities. DWQR will ensure that the failure in Scottish Water's procedures with regard to stock control and replacement of hydraulic fluids is addressed across all water treatment works as a matter of urgency. DWQR does not consider the proposed "tool box talk" on food grade oil or the distribution of learning points to all regional managers, team leaders, treatment operators and E/M craftsmen is an adequate response to this incident.