2013/14 – Wallaville (Queensland) – Trihalomethanes

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Wallaville Water Treatment Area Queensland

The Burnett River can contain varying elevated levels of natural organics. The current configuration of the Wallaville WTP struggles to deal with the elevated levels and therefore at times the THM levels in the treated water can exceed the ADWG, health value of 250μg/L. Four (4) of eight (8) samples taken over various locations and at varying times within the Wallaville WSA exceeded the ADWG, health value. The average exceedance was around 289μg/L.

Bundaberg Regional Council Drinking Water Quality Annual Report 2013/14

Trihalomethanes Australian Guideline Level 250μg/L (0.25mg/L)

Why and how are THMs formed?
“When chlorine is added to water with organic material, such as algae, river weeds, and decaying leaves, THMs are formed. Residual chlorine molecules react with this harmless organic material to form a group of chlorinated chemical compounds, THMs. They are tasteless and odourless, but harmful and potentially toxic. The quantity of by-products formed is determined by several factors, such as the amount and type of organic material present in water, temperature, pH, chlorine dosage, contact time available for chlorine, and bromide concentration in the water. The organic matter in water mainly consists of a) humic substance, which is the organic portion of soil that remains after prolonged microbial decomposition formed by the decay of leaves, wood, and other vegetable matter; and b) fulvic acid, which is a water soluble substance of low molecular weight that is derived from humus”. US EPA