2007/11 + 2017: Avoca (Victoria) – Trihalomethanes, NDMA, Total Dissolved Solids, Hardness, Cyanide

Avoca (Victoria)

14 March 2017 Avoca Clear Water Storage Outlet (Entry point to Avoca system) NDMA – 0.41 μg/L (410ng/L) (Highest NDMA level detected in Australia!)

3/4/17 Avoca NDMA 183ng/L

13/4/17 Avoca NDMA 182ng/L

“Avoca reticulation Informed DHHS. Reviewed past history of NDMA trends. Conducted further extensive sampling of treated water concentrations and tested for NDMA in the raw water supply. Commenced a comprehensive investigation into potential formation pathways which included sampling throughout the treatment train and investigations into current water treatment chemicals and disinfection conditions. Conducted a laboratory bench trial on the potential change in NDMA concentration with a change in disinfection method. Changed the final disinfection mode to free chlorination to mitigate formation. Routine NDMA test frequency increased on an ongoing basis to more closely monitor for any fluctuations.”

2017/18: Avoca NDMA 63ng/L (highest level)

“Based on health considerations, the concentration of NDMA in drinking water should not
exceed 0.0001 mg/L (100 ng/L). Action to reduce NDMA is encouraged, but must not compromise disinfection, as non disinfected water poses significantly greater risk than NDMA.

NDMA is used as an industrial solvent, an anti-oxidant, a rubber accelerator, and in the preparation of polymers, where it may be used as an initiator or a plasticiser. The compound has been used in the production of rocket fuel, as a biocide for nematodes, and an intermediate for 1,1-dimethylhydrazine to inhibit nitrification of soils.

NDMA is formed under mildly acidic conditions by the reaction of natural and synthetic secondary, tertiary or quaternary amines with nitrate and nitrite. Precursor amines include alkylamines, dimethylamine (DMA), tetramethylthiuram disulfide (thiram) and polyelectrolytes used in water and wastewater treatment. NDMA is also produced as a by-product of chloramination of drinking water (due to the presence of dimethylamine in source waters subject to wastewater discharges or the oxidation of natural organic matter by chlorine in the presence of ammonia) and to a lesser extent by chlorination. NDMA formation can be facilitated in soils by biochemical pathways in micro-organisms, and this compound is resistant to microbial degradation under both aerobic and anaerobic conditions. Ozonation of drinking water contaminated with the fungicide tolyfluamide can also lead to the formation of NDMA…

There are no data in the public domain or peer reviewed literature on NDMA in Australian drinking water distribution systems and water treatment plants. Anecdotal evidence suggests a bi-modal distribution, with several water authorities indicating that NDMA is present at levels at or near the limit of determination of 1 to 2 ng/L, whereas preliminary sampling and analysis by other authorities indicates levels in the range of 60-90 ng/L. A recent report from South Australia has indicated that NDMA may originate from rubber components of newly commissioned drinking water pipelines, regardless of the disinfectant used. This
may account at least partly for the divergent results reported by different water suppliers…” ADWG 2011

Avoca (Victoria) – Trihalomethanes

2007/8 Avoca THM’s 0.822mg/L (822ug/L)

Trihalomethanes Australian Guideline Level 250μg/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”. Source: https://water.epa.gov/drink/contaminants/index.cfm

Avoca – Victoria – Total Dissolved Solids

2008/9: Avoca (Victoria) – Total Dissolved Solids 1800 mg/L (Maximum Level)

2009/10: Avoca (Victoria) – Total Dissolved Solids 1700 mg/L (Maximum Level)

2010/11: Avoca (Victoria) – Total Dissolved Solids 1400 mg/L (Maximum Level) 880mg/L (mean)


“No specific health guideline value is provided for total dissolved solids (TDS), as there are no
health effects directly attributable to TDS. However for good palatability total dissolved solids
in drinking water should not exceed 600 mg/L.

Total dissolved solids (TDS) consist of inorganic salts and small amounts of organic matter that are dissolved in water. Clay particles, colloidal iron and manganese oxides and silica, fine enough to pass through a 0.45 micron filter membrane can also contribute to total dissolved solids.

Total dissolved solids comprise: sodium, potassium, calcium, magnesium, chloride, sulfate, bicarbonate, carbonate, silica, organic matter, fluoride, iron, manganese, nitrate, nitrite and phosphates…” Australian Drinking Water Guidelines 2011

Avoca – Victoria – Hardness

2008/09: Avoca (Victoria) – 930mg/L

2009/10: Avoca (Victoria) – 900mg/L

2010/11: Avoca (Victoria) – 840mg/L

2012/13 Avoca Hardness 210mg/L


“To minimise undesirable build‑up of scale in hot water systems, total hardness (as calcium
carbonate) in drinking water should not exceed 200 mg/L.

Hard water requires more soap than soft water to obtain a lather. It can also cause scale to form on hot water pipes and fittings. Hardness is caused primarily by the presence of calcium and magnesium ions, although other cations such as strontium, iron, manganese and barium can also contribute.”

Australian Drinking Water Guidelines 2011

Avoca – Victoria – Cyanide

2008/9: Avoca (Victoria) 0.006mg/L (highest level) (7.5% of Australian Guideline)

Based on health considerations, the concentration of cyanide in drinking water should not
exceed 0.08 mg/L.
Cyanide can be present in drinking water through the contamination of source water, or through the natural decomposition of some plants that synthesise cyanoglycosides. Some microorganisms, such as the cyanobacterium Anacystis nidulans and the bacterium Chromobacterium violaceum, produce free cyanide. In uncontaminated water sources, free cyanide concentrations are usually less than 0.01 mg/L. Sodium cyanide is used in the extraction of gold and silver from low-grade ores. It is also used in the electroplating, steel and chemical industries. Some foods can contain quite high concentrations of cyanide. Green almonds and improperly treated cassava are of particular concern.

In major Australian reticulated supplies cyanide concentrations range up to 0.05 mg/L, with typical concentrations usually less than 0.02 mg/L.

There are no published reports on methods for the removal of cyanide from drinking water. Chlorine gas or hypochlorite will react with cyanide to form cyanate. Ozone is also an effective oxidant.

Cyanide is highly toxic. It is rapidly absorbed by the gastrointestinal tract and metabolised to thiocyanate. In humans, long-term consumption of improperly prepared cassava in the tropics has been linked with effects on the thyroid gland and particularly the nervous system. Cyanide may deplete vitamin B12 and result in a deficiency that can cause goitre and cretinism. People most at risk are those with a nutritionally inadequate diet…. ADWG 2011