Water bores and casings

By John Pfahlert, CEO, Water New Zealand 

THE HAVELOCK NORTH water inquiry highlighted widespread systemic failure in our drinking water system. Water suppliers should now be aware that so called “secure” bore water status is not so secure, and that there need to be changes to how we abstract and use groundwater.

What’s been less publicised following the release of the report has been the findings around the construction and maintenance of bores and casings. The inquiry identified a number of problems with current practice and has recommended a comprehensive review of NZS4411 – the environmental standard for drilling of soil and rock.

This coincides with separate discussions involving Water New Zealand and the New Zealand Drillers Federation.

These two organisations are currently considering working in collaboration to develop a new guidance document on the operation, maintenance and testing practices for the different types of bores including irrigation, monitoring and drinking water bores.

We are optimistic that this could address the issues the inquiry raised without the need for a total review of NZS4411.

The inquiry said that the investigations, “highlighted a number of deficiencies in the current regime and practices that have national implications”.

It said these included the design and supervision of the construction of new bores and associated headworks (including the use of below-ground level bore heads), inspection and maintenance practices, determining expected services lives, and the adequacy of controls on safely decommissioning and securing redundant bores.

The report said that there is currently no single point of reference or code or required technical specifications for any of the activities associated with bores, casings and headworks and that this is a weakness in the system. Bore head requirements sit in a number of places including:

• NZS4411
• Drinking water guidelines
• Regional plans under the RMA
• Resource and building consents
• Policies and standards of individual water suppliers.

This of course gives rise to variation and inconsistency and leads to a lack of clarity and certainty for those responsible for bores and casings.

Many submissions to the inquiry concurred that the current bore and casing regime is fragmented and unsatisfactory.

The report said that there is a particular need to critically assess the flood risk for below-ground bore heads.  These carry additional risk and with changing rainfall patterns and consequent flooding risk, the risk of contamination through these bore heads may be increasing.

A number of submissions suggested that more regular inspection and reporting is required and that the current five year period in the DWSNZ for bore head security reports is too long.

Those at the inquiry also heard that during a recent Australian review of the concept of secure groundwater, the engineers’ biggest concern was their inability to detect the failure of bores, casings and surface structures.  The inquiry heard examples of extensive inspections that had failed to detect faults.

This means that even with the best codes of practice and construction techniques, inspection and maintenance programmes cannot guarantee security under all circumstances.

This led the Inquiry to conclude that a comprehensive review of NZS4411 should be carried out and that it should cover the design, construction, as-built records, supervision, maintenance, refurbishment, renewal and decommissioning of all bores that draw water from any groundwater source intended for drinking or those that penetrate the aquitard protecting any drinking water groundwater source.

It also recommended that no new below-ground bores be permitted. For all existing bores with below-ground headworks, the inquiry said that drinking water assessors should ensure that special attention is given to this risk in future Water Safety Plans (WSPs) and appropriate mitigation measures be implemented, including treatment and raising them where practicable.

To this extent no industry-recognised competent drillers have been constructing below-ground bore heads since the Havelock North contamination event occurred.

The inquiry recognised that there are thousands of existing bores that will not meet modern best practice.  It said that for water supply bores, all future WSPs should assess the risks associated with the existing facilities and how these are best avoided or mitigated.

For other bores which penetrate an aquitard, any risks would need to be managed through their resource or building consents.

It has asked that the government invite the Controller and Auditor-General to monitor and report to Parliament on the implementation of all the recommendations and initiatives set out in the stage 2 of the report during over the next five years.

So, some food for thought for contractors involved in this line of work. Staff at Water New Zealand are happy to talk to contractors about the ongoing implications of these processes.

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This article was first published in Contractor‘s April issue.