2016/22 – Midge Point (Queensland) – E.coli, Trihalomethanes, Manganese, Iron, Turbidity

2016/21- Midge Point – (Queensland) – E.coli

2016 February: Midge Point (Qld) 1 MPN/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.

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

15 Jan 2021: “E. coli was detected in a sample collected from the Midge Point Park reticulation sample point as part of the routine drinking water verification monitoring program. It is believed that the most likely cause of the E. coli was related to a decline in residual chlorine levels across the network, allowing for the water to be contaminated at the sample point. In response to the E. coli detection Council commenced a flushing program for the Midge Point water supply scheme to flush out low chlorine residual waters. Investigation into the incident highlighted the issue with the configuration of the Midge Point water supply scheme in  that Midge Point Reservoir at the rechlorination facility was serviced off a single offtake main from the trunk, meaning that when the reservoir was filled from the Kelsey Creek Pump Station, the Midge Point township was supplied with water from the Kelsey Creek Trunk Main. The water from the trunk main does not have a chlorine residual. Council undertook network configuration improvements to ensure all water supplied to the Midge Point township had adequate chlorine residual by undergoing rechlorination at the rechlorination facility. This network configuration improvement involved the installation of a return pipeline from the Kelsey Creek Trunk Main to Midge Point Reservoir to prevent water bypassing the Midge Point rechlorination system when the Kelsey Creek Pump Station operates. The return pipeline was connected August 17, 2021″

“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

Jan – April 2022: Midge Point (Queensland) – Trihalomethanes

Routine monitoring results from Midge Point Park, Midge Point SES and Midge Point Balance Tank, returned Total Trihalomethanes (THM) results above the ADWG health guideline values. In response to iron and manganese issues at Midge Point Water Supply Scheme, chlorine dose rates had been increased prior to the THM exceedance. This may have contributed to the increased THMs. Ongoing THM exceedances occurred between 14 January 2022 and 6 April 2022. Investigations found the exceedances were related to an increase in the Total Organic Carbon (TOC) levels of the raw water supplied through the Crystal Brook Bores. The water supplier confirmed the water source body had been impacted by an aquatic weed outbreak. Minor adjustments were made to the chlorine operating limits to minimise the level of THM’s generated. More frequent water quality monitoring was implemented between January and April 2022, and network operators continued regularly monitoring of chlorine levels.

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”. Source: https://water.epa.gov/drink/contaminant

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.

April 6 2021: A non-routine sample collected from the Proserpine Airport sample point returned a manganese result of 0.67 mg/L, breaching the 0.5 mg/L ADWG health guideline value. Investigation into this incident, including increased frequency of sampling within the Midge Point water supply scheme revealed iron and manganese issues for the scheme. These issues were deemed likely caused by or exacerbated by the following:
• Current treatment processes at the Midge Point TF are not providing for adequate iron and manganese removal (i.e. the current TF is not handling the increased concentrations of iron and manganese in the source water).
• Increased residence time in the network results in iron and manganese biofilms forming which slough off during high demand / water quality changes.
• Higher manganese and iron concentrations are delivered to Midge Point water supply scheme when water is supplied direct from the trunk main.
Council identified the following three key areas for Midge Point water supply scheme improvement:
1. Scheme operations – Chlorine dosing rate changes and scheme scouring. Dose rate changes and scouring programs had been implemented at the time of reporting.
2. Treatment performance – Treatment changes (e.g. packed tower aeration system or equivalent installation). Treatment changes were being finalised at the time of reporting.
3. Network configuration – Midge Point Reservoir return pipeline installation to prevent water bypassing the Midge Point rechlorination system when the Kelsey Creek Pump Station operates. Network configuration improvements were complete at the time of reporting with the recently installed return pipeline connected August 17, 2021.

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.