2014/15 – Glenmore Water Treatment Plant – Trihalomethanes – Rockhampton
THM concentrations exceeding the health guideline value of 250 µg/L were measured in two (2) reticulation sample points and a supply reservoir on 19 March 2015. All follow-up samples from these sites had THM levels less than 250 µg/L however, slight exceedances were detected on 3 other reticulation sample sites on 31 March and 8 April. These elevated levels of THMs were due to chlorine predosing at the GWTP which was undertaken to treat high levels of manganese and associated organic carbon following the Tropical Cyclone Marcia event.
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
2014/15 – Glenmore Water Treatment Plant – Manganese – Rockhampton
A Manganese concentration of 0.8 mg/L was measured in the drinking water from the Glenmore Water Treatment Plant (GWTP) on 11 March 2015. A follow-up sample collected from the GWTP on the same day also exceeded the health guideline value of 0.5 mg/L. Fifteen (15) of the more than 250 samples collected from Rockhampton water supply scheme from 12 to 31 March were also non-compliant for manganese. The exceedances for manganese was due to the very low dissolved oxygen levels (<2 mg/L), high organic carbon load, and greater amounts of dissolved, organically complexed manganese ions in the source water flushed out from Alligator Creek following the Tropical Cyclone Marcia event.
Manganese: ADWG Guidelines 0.5mg/L. ADWG Aesthetic Guideline 0.1mg/L
Manganese is found in the natural environment. Manganese in drinking water above 0.1mg/L can give water an unpleasant taste and stain plumbing fixtures