A further two pump stations have been identified where below ground wells can be isolated and unchlorinated water provided from secure above ground well heads.

The new sites are at Lake Terrace in Burwood, and Thompsons Road in Northwood.

If demand increases, or in the event of a fire, we may need to start using the below ground well heads and in that case the water would need to be chlorinated.

There is more information about this work below.

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The first tranche of works is under way with the strategy confirmed for seven pump stations. Design work is progressing and we are seeking construction tenders from potential suppliers.

The table above shows details of the pump stations, the planned work and timeframe.

We've been looking into alternatives to chlorine such as ozone and UV light treatment.

We have rejected ozone as a suitable disinfection agent because our analysis has determined it is incompatible with the chemical composition of our groundwater.

Ultra violet (UV) light is an option we are pursuing and we are assessing the costs and benefits of using UV at a number of pump stations. Preliminary design work is under way for UV disinfection at Main Pumps in the Central zone. Subject to costs and availability of equipment this is proposed for construction to begin late 2018.

Once of our areas of focus is to maximise the amount of unchlorinated water we can supply in the network. 

One of the ways we can do this is to identify any pump stations with a mix of below and above ground well heads. In some cases, we will be able to provide enough water using the above ground well heads. Once these are deemed secure and the below ground well heads are isolated, we can stop chlorination at those sites.

We have assessed 11 pump stations to determine if this can be done and found seven where we will be able to supply sufficient water, at winter demand levels, from the remaining above ground well heads. They are: Burnside, Grampian, Thompsons and Farrington in the North West; Hills and Lake Terrace in Central; and Woolston in Ferrymead.

Subject to minor remedial works being completed and the above ground well heads being signed off as secure, we intend to stop temporary chlorination at these pump stations later this year.

If demand increases over the summer or due to an emergency event (such as a fire) then the below ground well head(s) would come back into service and chlorination would resume.