Gregory River Water Treatment Area (Childers/Woodgate) Queensland

Throughout the year, the Gregory River can contain varying elevated levels of natural organics. The current configuration of the Gregory River 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 250ug/L. Eleven (11) of sixteen (16) samples taken over various locations and at varying times within the Gregory River WSA exceeded the ADWG, health value. The average exceedance was around 294ug/L.

Bundaberg Regional Council Drinking Water Quality Annual Report 2013/14

Gregory River WSA: … A total of sixteen (16) samples were taken for THM analysis over the year within the Gregory River WSA. Five (5) of these exceeded the ADWG, health value. The average exceedance was around 343μg/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 290g/L

Bundaberg Regional Council Drinking Water Quality Annual Report 2015/16

Gregory River WSA: … A total of Sixteen (16) samples were taken 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 290μg/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

Throughout the year, the Gregory River can contain varying elevated levels of dissolved natural organics. The current configuration of the Gregory River WTP struggles to deal with these and therefore at times the THM levels in the treated water can exceed the ADWG Health limit of 250ug/L. A total of sixteen (16) tests were undertaken for THM analysis over the year within the Gregory River WSA. Ten (10) of these tests exceeded the ADWG Health limit. The average of these exceedances was 311ug/L.

Bundaberg Regional Council Drinking Water Quality Annual Report 2017/18

Throughout the year, the Gregory River can contain varying elevated levels of dissolved natural organics. The current configuration of the Gregory River WTP struggles to deal with these and therefore at times the THM levels in the treated water can exceed the ADWG Health limit of 250μg/L. A total of sixteen (16) tests were undertaken for THM analysis over the year within the Gregory River WSA. Ten (10) of these tests exceeded the ADWG Health limit. The average of these exceedances was 354μg/L.

Corrective and Preventative Actions
Council is acutely aware of this situation and in conjunction with QH and QWSR, Council diligently carries out quarterly THM analysis with results going to the QWSR. The filtered water is also analysed at a monthly frequency for Total Organic Carbon (TOC) as a surrogate for THM precursors. As indicated, Gregory River water can contain high levels of dissolved organics that are difficult to remove with the current treatment process. BRC has considered various treatment and transfer strategies and has determined that the preferred strategy is to continue sourcing water from the Gregory River at the weir and to build a new treatment plant at the exiting site. In view of the process and hydraulic limitations of the existing plant and the plant’s age, BRC has commenced construction of a new WTP adjacent to the existing plant with construction due for completion in October 2020. The plant will be online early 2021.

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