6.1.1 Incident Description
On 29 August 2019, whilst investigating a taste and odour enquiry at two properties on Rainbow Drive, Mudgeeraba, samples were collected from internal plumbing, property water meters and nearby hydrants. Analysis results showed that BTEX compounds were detected from the samples collected on the properties as well as the water meters, these compounds were not detected in the nearby hydrants. Benzene was detected at a concentration of 0.0016 mg/L which is above the ADWG health guideline value of <0.001 mg/L. It was noted during the investigation that a vehicle was parked over the area where the water service lines enter the properties with evidence of oil or fuel spillage on the gutter and the road.

Corrective and Preventive Actions
Immediately upon notification of the ADWG exceedance the incident management procedures were activated. Customers at both properties were notified immediately and informed to avoid using the water until the issue was rectified. They were supplied with bottled water during this time until repairs were completed. Civil Maintenance crews attended the site and excavated and removed all of the soil around the affected area. The polyethylene service connections from the water main were replaced with copper to prevent further contamination, as were the impacted water meters. Additional sampling was undertaken over the following weeks to confirm that the issue had been resolved.

The investigation concluded that the likely cause of the issue was a fuel or oil spillage from a vehicle parked on the nature strip over the area where the service connections were. To prevent this happening again in the future the customers were informed that they should park their vehicles in the driveway and were also given information regarding the risks of fuel spillage around the property. (Gold Coast Water Drinking Water Quality Management Plan Annual Report 2018/19)

Based on health considerations the concentration of benzene in drinking water should not
exceed 0.001 mg/L.

GENERAL DESCRIPTION
Benzene is a clear, colourless-to-yellow liquid and highly flammable aromatic hydrocarbon. It is presentin petroleum products such as motor fuels and solvents, and motor vehicle emissions constitute the mainsource of benzene in the environment. Benzene occurs naturally in crude oil and coal and is an additive and a by-product of oil-refining processes. It constitutes approximately 1-2% of unleaded gasoline by volume (US DHHS, 2011). Tobacco smoke is another significant source of exposure (WHO, 2010). It also occurs in natural gas and emissions from volcanoes and forest fires.

Human exposure to benzene occurs primarily through inhalation (WHO, 2010). When released to surface waters, benzene rapidly volatilises to the air (WHO, 2010). Benzene is not persistent in surface water or soil and either volatilises to air or is degraded by bacteria under aerobic conditions (WHO, 2010). For water contamination, benzene is therefore of most concern in groundwater. Benzene can also occur in foods and drinks as a product of the reaction between benzoate and ascorbic acid, and has been found in soft drinks in the UK at concentrations as high as 0.028 mg/L (FSA, 2006).

Benzene is also used widely as an industrial solvent by the chemical and pharmaceutical industries in theproduction of styrene/ethylbenzene, cumene/phenol and cyclohexane. The use of benzene as a solvent has been greatly reduced in recent years. Unlike other petroleum hydrocarbons such as ethylbenzene, toluene and xylene the odour threshold for
benzene is relatively high at 10 mg/L (WHO, 2003). ADWG 2011