2006/17 – Gunbalunya (Northern Territory) – E.coli, Turbidity, Iron, pH

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Gunbalunya – E.coli

2006/07: The susceptibility of Gunbalanya’s source waters to microbiological contamination is relatively high due to the shallow depth of the bores, seasonal recharge of the groundwater, the accessibility of the weir to animals and the monsoon activity that regularly floods the borefield. Heavy monsoonal rains led to flooding in Gunbalanya in late February 2007, which inundated sewage pump stations and the borefield. Consequently a Boil Water Alert was issued although analysis of the water samples did not detect E. coli. Gunbalanya currently has a sodium hypochlorite system in place and additional UV disinfection is proposed as part of the Strategy for Safe Water in 2007-08.

2009/10: 99% Gunbalunya E.coli performance over year

2015/16: Gunbalunya E.coli 1 detection, 99% compliance

“E.coli

Thermotolerant coliforms are a sub-group of coliforms that are able to grow at 44.5 ± 0.2°C. E. coli is the most common thermotolerant coliform present in faeces and is regarded as the most specific indicator of recent faecal contamination because generally it is not capable of growth in the environment. In contrast, some other thermotolerant coliforms (including strains of Klebsiella, Citrobacter and Enterobacter) are able to grow in the environment and their presence is not necessarily related to faecal contamination. While tests for thermotolerant coliforms can be simpler than for E. coli, E. coli is considered a superior indicator for detecting faecal contamination…” ADWG

Gunbalunya (Northern Territory) – Turbidity

2015/16: Gunbalunya Turbidity 6.1NTU

Chlorine-resistant pathogen reduction: Where filtration alone is used as the water treatment
process to address identified risks from Cryptosporidium and Giardia, it is essential
that filtration is optimised and consequently the target for the turbidity of water leaving
individual filters should be less than 0.2 NTU, and should not exceed 0.5 NTU at any time
Disinfection: A turbidity of less than 1 NTU is desirable at the time of disinfection with
chlorine unless a higher value can be validated in a specific context.

Aesthetic: Based on aesthetic considerations, the turbidity should not exceed 5 NTU at the
consumer’s tap.

Gunbalunya (Northern Territory) Iron

2007/08: Gunbalunya Iron 0.8mg/L

2015/16: Gunbalunya Iron 0.4mg/L

Based on aesthetic considerations (precipitation of iron from solution and taste),
the concentration of iron in drinking water should not exceed 0.3 mg/L.
No health-based guideline value has been set for iron.

Iron has a taste threshold of about 0.3 mg/L in water, and becomes objectionable above 3 mg/L. High iron concentrations give water an undesirable rust-brown appearance and can cause staining of laundry and plumbing fittings, fouling of ion-exchange softeners, and blockages in irrigation systems. Growths of iron bacteria, which concentrate iron, may cause taste and odour problems and lead to pipe restrictions, blockages and corrosion. ADWG 2011

Gunbalunya (Northern Territory) – pH (acidic)

2007/08: Gunbalunya pH 5.9

2008/09: Gunbalunya pH 6

2009/10: Gunbalunya pH 5.9

2010/11: Gunbalunya pH 5.9

2013/14: Gunbalunya pH 5.8

2015/16: Gunbalunya pH 5.6

2016/17: Gunbalunya pH 5.7

Based on the need to reduce corrosion and encrustation in pipes and fittings, the pH of
drinking water should be between 6.5 and 8.5.

New concrete tanks and cement-mortar lined pipes can significantly increase pH and
a value up to 9.2 may be tolerated, provided monitoring indicates no deterioration in
microbiological quality.

pH is a measure of the hydrogen ion concentration of water. It is measured on a logarithmic scale from 0 to 14. A pH of 7 is neutral, greater than 7 is alkaline, and less than 7 is acidic.

One of the major objectives in controlling pH is to minimise corrosion and encrustation in pipes and fittings. Corrosion can be reduced by the formation of a protective layer of calcium carbonate on the inside of the pipe or fitting, and the formation of this layer is affected by pH, temperature, the availability of calcium (hardness) and carbon dioxide. If the water is too alkaline (above pH 8.5), the rapid deposition and build-up of calcium carbonate that can result may eventually block the pipe.