The current water treatment processes at the Westport Water Treatment Plant (WTP) comply with the current Drinking Water Standards for Chemical composition, and the treatment of bacteria, however it does not comply for the treatment of Protozoa.
Protozoa is a waterborne bug that is so small it cannot be seen by the naked eye, and it is difficult to remove by filtering. It can remain dormant in the water supply, but if ingested through drinking water, will quickly multiply and thrive in the warm conditions of the gut, causing moderate to severe sickness which can last for several months.
The introduction of Ultra Violet (U.V.) treatment will sterilise Protozoa bugs, so they cannot reproduce and will pass harmlessly through the gut.
The turbidity metre will detect changes in the raw water turbidity and the Water Treatment Plant will automatically alter the chemical dosing regime to adequately treat the changing water conditions.
The construction of the Flocculation tank will allow longer retention time for the formation of larger Floc particles. These are more easily filtered out.
The backwash tank will retain sufficient water for regular programmed backwashing of the water filters.
Installation of the U.V. facility allows the sterilisation of protozoa which as previously mentioned was untreated and harmful if ingested through drinking water.
Increased capacity to store treated water will provide greater Plant efficiency and limit the effect of plant outages, such as equipment malfunctions, and power failure by having more treated water available.
What all these terms mean:
- Turbidity – Water particles (low=clear water and high= dirt/muddy water)
- Coagulant – Chemical additive to combine water particles together, this makes filtration easier
- Flocculation tanks – Where particles combine together to form larger particles
- Filters – Removes Flocculation particles
- U.V. (ultra violet light) – Sterilises bugs and other nasties that are in the water
- Chlorine – Kills all bugs in water except for Protozoa
- PH correction – To remove acidity in water (reduce pipe corrosion)
What has been considered?
Opus International Ltd consultants were engaged to complete a peer review of the strategic study that was carried out at an earlier stage by Connell Wagner, conduct an operational review of the current Westport plant, and assess any alternative options Council could consider.
Throughout all of the research conducted two areas were considered worth pursuing, to continue with the existing system or to go to the Buller River.
From this report there were three options:
Option 1 – Upgrade the current supply costing $11 million
Option 2 – Go to the Buller River with a Gravity system costing $15 million
Option 3 – Go to the Buller River with a pump system costing $13 million
The gravity system in the Buller River proposed to pump water from an infiltration gallery next to the river to an elevated reservoir above Te Kuha which would then be gravity fed to the reticulation.
The proposed pump system in the Buller River would pump water from the Nine Mile area above the tidal mark, this water would be pumped to a new Water Treatment Plant which would be located around the Holcim packing plant on Nine Mile Road then be pumped to the reticulation.
Council decided to upgrade the current supply as the capital expenditure was identified along with the average running cost over a 25 year period.
In 2012 Council completed it’s Long Term Plan which details plans for the next ten year period, to be reviewed in three years time. In this document there is a detailed plan of when work would be carried out on the Westport Water Supply upgrade.
After the 2012 Long Term Plan was approved, Buller District Council received a subsidy from the Ministry of Health of $1,474,250 to go towards the upgrade, making the Westport Water Supply meet the NZ Drinking Water Standards.
Council has had to re-plan when this work will be carried out as the subsidy is only available during a certain time period, so all items that are being subsidised need to be completed while the funding is available. the revised programme is now as follows:
Planning and design
Raw water quality management
Flocculation tanks and foundation
Filters refurbishment and seismic upgrade
Provision of treated water storage for backwash filters
Filter to waste system
Upgrade buildings, monitoring and control
U.V. disinfection and control
Bypass raw water ponds
New treated water reservoirs
Total cost for year:$5,604,200
Replace trunk main
Raw water ponds clean out
Total cost for year: $4,237,000
To be considered at a later date: Lining of the raw water ponds and piping tunnels 1, 2 & 3.