2013/20 – Lake Monduran (Queensland) – Trihalomethanes

2013/19: Lake Monduran –  Queensland – Trihalomethanes

Lake Monduran can contain varying elevated levels of natural organics. The current configuration of the Lake Monduran 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. Three (3) of four (4) samples taken at Lake Monduran WSA throughout the year exceeded the ADWG, health value. The average exceedance was around 326μg/L

Bundaberg Regional Council Drinking Water Quality Annual Report 2013/14

Lake Monduran WSA:  In the 2014/15 water year four (4) samples were taken for THM analysis. One (1) of these samples exceeded the ADWG health value. The average THM value was around 233μg/L.

Bundaberg Regional Council Drinking Water Quality Annual Report 2014/15

A total of Sixteen (16) samples were taken for THM analysis over the year within the Gregory River WSA. Nine (9) of these exceeded the ADWG, health value. The average exceedance was around 290μg/L.

Bundaberg Regional Council Drinking Water Quality Annual Report 2015/16

A total of four (4) samples were taken for THM analysis throughout the year. Two (2) of these slightly exceeded the ADWG health value. Both samples returned a result of 255μg/L

Bundaberg Regional Council Drinking Water Quality Annual Report 2016/17

A total of eighteen (18) tests were undertaken for THM analysis over the year within the Gregory River WSA. Eight (8) of these exceeded the ADWG, health value. The average of these exceedances was around 300ug/L

Bundaberg Regional Council Drinking Water Quality Annual Report 2017/18

Lake Monduran (Fred Haigh Dam) can also contain elevated levels of natural organics. The existing configuration of the Lake Monduran WTP can have difficulty in treating elevated levels of these organics and therefore, at times, the THM levels in the treated water can exceed the ADWG Health limit of 250ug/L. A total of four (4) samples were taken for THM analysis throughout the year. Three (3) of these tests exceeded the ADWG Health limit. The average of these exceedances was 297ug/L.

Bundaberg Regional Council Drinking Water Quality Annual Report 2018/19

Lake Monduran (Fred Haigh Dam) can also contain elevated levels of natural organics. The existing configuration of the Lake Monduran WTP can have difficulty in treating elevated levels of these organics and therefore, at times, the THM levels in the treated water can exceed the ADWG Health limit of 250μg/L. A total of four (4) samples were taken for THM analysis throughout the year. Two (2) of these tests exceeded the ADWG Health limit. The average of these exceedances was 310μg/L.

Bundaberg Regional Council Drinking Water Quality Annual Report 2019/20

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