Investigations

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

Report on drinking water quality incident at:
Fort William Water Treatment Works in September 2006

Scottish Water Executive Summary

The Fort William Camisky water treatment works is situated near to the River Lochy, between Fort William and the village of Spean Bridge. The works can operate at flow of between 4.3 and 12 ML/D and supplies a population of approximately 11,530.

The works comprises of 7 boreholes with wellhead pumping stations, flow control, cascade aeration, disinfection (chloramination), orthophosphate dosing and pH correction.

On the afternoon of Friday 15th September 2006 an E&M team leader was asked if he could take a look at a chemical dosing mixer motor. The operator reported that the mixer had been making an abnormal noise and had been switched off earlier that day. It was immediately obvious to the E&M team leader that oil from the mixer gear box had leaked and had run down the shaft to the paddle and into the treated water held in the final contact tank. The oil around the mixer motor and shaft was cleaned up and the works clear water tank (CWT) was visually inspected. The operator observed a very slight oily sheen on the surface of the water, so the decision was made to increase the flow through the works and flushed the surface of the water to waste through the overflow of the CWT. Samples were taken from the CWT outlet (water going to supply) and the surface of the water of the tank (where it was felt that concentrations of lubricant would be highest). Analysis for hydrocarbons and lithium was carried out once the lubricant was confirmed as Mobilux EP023, a Lithium Hydroxystearate grease.

The samples taken on the 15th did not indicate that the water entering into supply was contaminated with oil. Further samples were taken on Saturday 16th and Monday 18th September again from the Camisky CWT outlet and surface water and service reservoirs in the zone. None of these samples showed evidence of gear box oil contamination. The bearing in the mixer gear box had collapsed which caused damage and distortion to the gear box and shaft and resulted in the loss of integrity of the seals, allowing lubricant to leak down the mixer shaft into the treated water. The date and time the seals failed is unknown, therefore it has not been possible to ascertain for how long the lubricant had been leaking prior to discovery.

The gearbox was supplied from the manufacturer with mineral oil as standard. The contractor had indicated to the SWS project manager that it had been changed for food grade vegetable oil during commissioning. On inspection of the motor it appeared that the paint on the bolts had not been broken, this indicated that it was unlikely that an oil change had been carried out since the unit had left the factory. There was also the distinctive smell of mineral oil from the lubricant in the gear box.

If a work order had been raised by the treatment operator, with the E&M team, as soon as the mixer started making an abnormal noise and appropriate action taken following a risk assessment, it would have been possible to prevent the extensive damage to the gear box and shaft that allowed the seals to pass oil.

Actions are being taken to:

• ensure operators are briefed on the importance of immediate reporting of faulty assets;
• ensure the Customer Operations Team Leaders are briefed on the importance of prioritising work orders based on risk;
• ensure that the Camisky works has been assessed for all risk based maintenance (RBM);
• review the situation at all new water treatment works to ensure that appropriate measures are in place to prevent contamination from lubricants for use within pumps, motors gear boxes used above water process streams.

DWQR Assessment on the incident

The DWQR's assessment of this incident is that it was due to a failure of a bearing in a chemical dosing mixer motor which did not have food grade oil in it. The failure of the bearing caused a failure of a seal which, in turn, caused the oil within the motor to escape and contaminate the clear water tank below it. The situation was exacerbated by the fact that the oil was not of food grade quality as it should have been. In general DWQR is content with the actions being taken by Scottish Water as a result of this incident. However, DWQR has asked Scottish Water to review the situation at all water treatment works and not just new ones to ensure that appropriate measures are in place to prevent contamination from lubricants in mechanical equipment above water treatment processes.