The Council is replacing the remaining shallow wells that supply water to Christchurch’s northwest with deep wells to reduce the small risk of contamination from those shallow wells.
The northwest zone has a D grading under criteria set out in the Drinking Water Standards for New Zealand(external link). This is because of the shallow wells, which have a small risk of contamination from surface influences.
In 2012, the Council began a programme to replace the shallow wells in the northwest with deeper wells. The work is being reprioritised to reduce the risk of contamination through the more shallow wells.
All 22 shallow wells on the replacement programme are turned off and most of them will be fully decommissioned and sealed by the end of June 2018.
The Council has decided not to treat water from these shallow wells with chlorine while work is done to decommission them.
Treatment with chlorine will be used in the following situations:
As well as speeding up the replacement programme, the Council will increase its testing regime for E.Coli and will check wellheads for possible vulnerability to contamination.
The Council is also cleaning and coating reservoirs with a waterproof membrane to remove the risk of direct contamination in rain events.
The additional cost of fast-tracking of the northwest shallow wells replacement programme is expected to be about $480,000. This will be paid for by bringing forward spending from future budgets and deferring other less critical projects.