2016/21 – Midge Point (Queensland) – E.coli, Manganese, Iron, Turbidity

2016 – Midge Point – (Queensland) – E.coli

2016 February: Midge Point (Qld) 1 MPN/100mL

2020/21: Midge Point (Qld) 5MPN/100mL

Various samples were collected throughout the Midge Point water mains during an air scour conducted from 4-10 February 2016. The air scour was conducted in response to the high
levels of manganese detected in the Midge Point reticulation system (see non-compliance above).

E.coli was detected in some of the water samples collected during the air scour. These results were not surprising considering that the chlorinator at the Midge Point Reservoir was offline during the majority of the air scour.

Further review of this non-compliance has revealed that the mains were in fact isolated during the air scour and therefore the water was not being supplied to the public and did not pose
a threat to public health. As such this non-compliance should not have been reported to the regulator and these results have not been included as part of the rolling 12 month annual E.coli
value calculated in accordance with the Public Health Regulation 2005.

The Midge Point Reservoir chlorinator was turned on towards the end of the air scour and water samples were taken to confirm compliance with ADWG health values before the mains
were reconnected and water supplied to the public.

“Coliforms are Gram-negative, non-spore-forming, rod-shaped bacteria that are capable of aerobic and facultative anaerobic growth in the presence of bile salts or other surface active agents with similar growth-inhibiting properties. They are found in large numbers in the faeces of humans and other warm-blooded animals, but many species also occur in the environment.

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 2011

Midge Point (Queensland) – Manganese

29/12/15 – 6/1/16: 1.468 – 3.377 mg/L

Two complaint samples collected from within the Midge Point reticulation system (at 45 Nielsen Parade and Jackson St Caravan Park) on 29 December 2016 exceeded the ADWG health value for manganese.

Investigation into these non-compliances revealed that the raw supply to the Midge Point water supply scheme has high dissolved iron and manganese. Chlorine gas dosing at the Kelsey Creek Balance Tank (KCBT) oxidises some of the iron and manganese in the source water and minimises growth of iron/manganese associated micro-organisms in the vicinity.

The high manganese concentrations recorded at the complaint sample locations were believed to have been a result of a fault in the pre-chlorination unit at the KCBT in December 2015. It is
believed that the fault allowed for oxidation of manganese further downstream at the Midge Point Reservoir. The pre-chlorinator was fixed as soon as the fault was recognised.

City Water Technology was engaged by council in early 2016 to evaluate the manganese removal process at KCBT and disinfection process at both KCBT and Midge Point Reservoir.
The network was flushed with fresh water in January 2016 and an air scour conducted in February 2016 to remove any traces of manganese.

Manganese: ADWG Guidelines 0.5mg/L. ADWG Aesthetic Guideline 0.1mg/L
Manganese is found in the natural environment. Manganese in drinking water above 0.1mg/L can give water an unpleasant taste and stain plumbing fixtures and laundry.

Midge Point (Qld) – Iron

2020/21: Midge Point (Qld) – Iron 0.3754mg/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

Midge Point (Queensland) Turbidity

2016/17: Midge Point (Queensland) – Turbidity 68 NTU (max), 9.1 NTU (av.)

2016/17: Midge Point Park (Queensland) – Turbidity 62.2 NTU (max), 3.95 NTU (av.)

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.