The Future Of Wellhead Protection

Wells are our gateway to underground drinking-water reserves which serve many communities around New Zealand. Contamination of the Havelock North supply in August 2016 not only highlighted the importance of source protection and good management, but also the need for good quality infrastructure and in particular the protection of well heads. The Havelock North Drinking Water Inquiry Stage 2 report recommended new installations of below ground well heads be prohibited, abolishing the secure bore water status, and mandating universal treatment. Exemptions from treatment are likely to require evidence of high quality infrastructure being in place and demonstration of sound risk management practices.

The water supply for Christchurch is groundwater taken from 139 wells across the city, pumped directly into the reticulation via 53 pump stations. Late in 2017, Christchurch City Council (CCC) requested experts undertake routine well head inspections of 25 well heads to confirm that the well heads remained secure, and would not allow contaminants to enter the water supply. Previous inspections had found that the wells were secure, however these inspections found none of those well heads were adequately protected which resulted in the Drinking Water Assessor revoking the provisionally secure groundwater status on 22 December 2017. The difference is because of stricter interpretation of the DWSNZ applied by the experts following the Inquiry. As a result, CCC made a decision to temporarily chlorinate the water supply while the well heads are remediated to the required standard.

Whilst new above ground well head installations in Christchurch are of a very high quality and represent best practice in New Zealand, many of the older below ground well heads were installed prior to the DWSNZ requirements for well head protection.

CCC are now proactively planning a remediation programme for the well heads to bring them into line with current standards so that secure groundwater status can be regained and temporary treatment can cease. Beca supported CCC to evaluate two main options for well head remedial works:

Remediation of the existing below ground well heads

Raising all below ground well heads above ground

CCC were faced with the difficult decision of which option to select: remediating to meet the current standard, or spending more to meet what might become the future standard. Raising all well heads above ground and replacing shallow aquifer wells appears to provide the best chance of seeking an exemption from mandatory treatment should this be imposed by the government, alongside other reticulation management measures. This option was selected as the preferred solution.

Cost estimates for the two remediation options were required to adequately compare the options. Due to the number of below-ground drinking water well heads owned by CCC, it was not practical to prepare and cost individual designs for each bore in the timeframe available. Instead, costs for the common remediation activities were estimated and applied to each well as required.

This paper shows real-world examples of well heads and discusses the practical realities of remediating well heads to meet the requirements that are likely to emerge from the Havelock North Drinking Water Inquiry.