2016: Bamaga Primary School (Queensland) – Trihalomethanes
Primary School: THM result of 253 μg/L recorded 1/4/16. Operational THM monitoring has been undertaken at site utilising HACH THM plus method (10132). Whilst accurate for screening and formation potential testing, this method is not suitable for regulatory reporting. The field THM method has been undertaken as part of an initial risk assessment for disinfection by-products as this had previously been uncharacterised as part of a system assessment. It is recommended operational testing be transferred to a NATA accredited laboratory compliant to ISO17025. Regulatory reporting to DEWS should be considered for approved APHA procedures outlined in section 6232 A, B, C and D of the standard methods manual. Although a result >250μg/L has been noted a non-standard method has been applied in this case outside of contractual monitoring requirements with DILGP. Trend control analysis of the FY 2015 / 16 results indicatmonthly monitoring of THMs performed by a NATA accredited contract laboratory should be programmed for FY 2016 /17.
Drinking Water Quality Management Plan (DWQMP) Annual report – NPA Water Supply System FY 2015 / 2016
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