Wellhead Security Improvement Programme

Scope

Seipp Construction was engaged by Christchurch City Council to provide security measures to 27 of their drinking water wells in order to meet new Drinking Water Standards.

The scope of works consisted of:

• Removing existing below ground well head pipework
• Over drilling existing well casing to nominal depth
• Extension of well head casing to above ground
• Installation of bentonite grout sanitary seal
• Demolition of existing in ground well head chamber
• Installation of new above ground headworks
• Installation of new below ground pipework and fittings to connect to existing pipework
• Installation of new power and signal ducting from wellhead to pump station
• Construction of protective concrete slab
• Installation of security cages.

Project Description

The Drinking-water Standards for New Zealand outline stringent requirements for drinking-water safety. Following revision of the Standards in March 2019, Christchurch City Council’s (CCC) water infrastructure was inspected by the Drinking-water Assessor, and several key recommendations were made.

This resulted in the Well Head Security Improvement Programme (WHSIP), with the objective to reduce risk of contamination from floodwater to 27 drinking-water wells, identified as being at risk. Works performed under WHSIP will support CCC’s ultimate goal of removing chlorination from Christchurch’s drinking-water supplies This project was to upgrade 27 of Christchurch City Councils drinking wells.

To achieve this, well casings at each well had to be extended above ground and over-drilled to depths ranging from 6m to 20m, depending on the depth of the confining layer. This was followed by the filling of annuluses with a stabilised bentonite grout mix; and valve assembly arranged horizontally over a concrete plinth. All newly installed elements were then encased in a lockable steel cage.

A proactive approach to potential challenges was part of the major success of this project. Our project management team was proactive in confronting design and constructability issues. This way we were able to minimise delays for the client whilst operating multiple sites at any one time.

During this project we also encountered significant quantities of asbestos contaminated ground. This was the result of existing landfills. The Avonhead PS site had the largest volume of in-situ Class A contaminated soil Worksafe had encountered in Christchurch so far. We worked closely with industry experts and developed a safe working procedure for dealing with the contaminated materials

Our client was extremely satisfied with the quality of our work and provided positive feedback in regards to the finished product. All programmed works were completed on time, despite the multiple variations awarded due to changes in the scope of the project, contaminated ground, and various network restraints.

Start Date: June 2019

Completion Date: February 2020

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