2015 – Moledinar (Queensland) – Trihalomethanes, Fluoride

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11/2/15 – Molendinar (Queensland) – Trihalomethanes

Southern Regional Pipeline (SRP) – Molendinar (Total trihalomethane 0.29 mg/L, 11/02/2015). The affected water was from Mt Crosby WTP and had received break point chlorination at the Chambers Flat WQMF. This process combined with relatively long detention times in the SRP resulted in total THM formation above the ADWG limit. Seqwater reviewed the delivery of this water to the remainder of the SRP and the distribution system reservoirs and undertook further testing. The affected water was found to have been sufficiently diluted by blending with water supplied from the Gold Coast’s WTPs so that water supplied to the community was below the ADWG limit.

SEQWater Annual Drinking Water Quality Plan 2014/15

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

2015 – Moledinar (Queensland) – Fluoride

Molendinar WTP Fluoride (Operational monitoring indicating Fluoride 1.5 – 1.7 mg/L for approximately 45 minutes on outlet mains). 26/06/2015. A minor operational overdose occurred during flow meter interlock testing of the fluoridation system before the interlocks on the online fluoride analysers shut down the system. The Fluoridation system was shut down and the treated water was tested by a series of grab samples. This confirmed that no affected water had left site and the on-site storages were not affected due to their large capacity and the short duration of the exceedance. Further sampling and testing in the distribution system confirmed that fluoride concentrations were not affected by the incident.

“Fluoride occurs naturally in seawater (1.4 mg/L), soil (up to 300 parts per million) and air (from volcanic gases and industrial pollution). Naturally occurring fluoride concentrations in drinking water depend on the type of soil and rock through which the water drains. Generally, concentrations in surface water are relatively low (<0.1–0.5 mg/L), while water from deeper wells may have quite high concentrations (1–10 mg/L) if the rock formations are fluoride-rich.” 2011 ADWG.