Milton Discoloured Water Event May 2018
In May 2018 Milton water supply was significantly affected by a 'dirty water' event. Harrison Grierson consultants were engaged to investigate the data collected and provide an explanation for the sudden outbreak.
The town water was proven to have elevated levels of iron, manganese and organic carbon. This resulted in a brown colour in the drinking water.
The retrospective assessment of the problems reveals that it was most likely two events:
- Breakdown of pH correction equipment at the treatment plant – this device injects an agent that raises the pH of the water to make it less acidic. When this happens it makes the clarifying process much less effective and this resulted in a high level of dissolved organic carbon and its associated colour to enter the water supply.
- Flushing programme – in an effort to remove the discoloured water from the water supply a vigorous programme followed where fire hydrants were opened to force the flow of water through the pipework. This is likely to have disturbed settled manganese and iron that accumulates over time within the pipe network.
Milton Dirty Water Event October 2018
During late October sporadic dirty water events occurred in Milton. The output from the treatment plant was very good in relatation to iron and manganese accumulation however, it may have been disturbed as flow rates in the pipe network increase due to warmer weather.
To minimise these events there are a number of actions that can be taken:
- Improved water treatment at the source to remove iron and manganese before it passes through the treatment process. This would require the installation of a special greensand filter that can remove these elements and prevent future build-up in the water mains. This would need to be installed between the clarifier and the membrane plant.
- Dosing the water with potassium permanganate to remove the manganese and iron.
- Continue flushing the mains to remove any remaining deposits.
Council's contractor continues to flush the water mains regularly to ensure there is no significant build-up of sediment.
If Milton residents are still having issues with their water, then please make sure you lodge a service request through Council by ringing 0800 801 350.
The Clutha District is now in Stage 1 Summer Mode water restrictions. Watering is allowed from 8pm to 8am with systems not to be left unattended or on overnight.