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Water woes put council in a big hole

CDC chief executive Geoff Hamilton and infrastructure, services, and regulatory manager Dave Gittings inspect two wastewater ponds. PHOTOS/EMILY IRELAND

Contractor removed after years of delays and a bill to fix the damaged pond lining running into the millions of dollars.

Rips, punctures, and scratches – extensive damage has been discovered at Carterton District Council’s $12.7 million dollar wastewater ponds.

Now, the council has taken possession of the site and has removed the main contractor after repeated delays and the discovery of the damage to the lining of its three new ponds.

It will cost an unbudgeted $1.3-$1.9m to fix and complete the project, the council says.

In 2018, Central Hawke’s Bay Earthmovers [CHBE] was contracted to undertake upgrades to the Wastewater Treatment Pond Upgrade Project, part of which included earthworks and lining three new ponds.

The work had an expected completion date of May 30, 2019.

But to date the project had been delayed by a mudfish relocation task, the discovery of a high level of unsuitable ground material, the need for additional drainage work, bad weather, ephemeral channel relocation, and covid-19 lockdowns.

CHBE claimed additional time extensions last year to enable them to complete major works.

This was also done in an attempt to “prevent additional costs being passed on to ratepayers”, council chief executive Geoff Hamilton said.

But project delays continued into 2021, and the council’s project management team discovered the new pond liners had been damaged by the contractor.

One hundred and twenty-two notices were issued to CHBE throughout the earthworks contract, with the latter of these to fix the damage and alter work practices to avoid further damage.

Proposed remediation plans were considered insufficient, and the contractor was removed from the site on September 9, 2021.

“Upon taking possession of the site in September, the council discovered significantly more damage to the pond liners than was first anticipated,” Hamilton said.

“Some of the concerns were in regard to the anchor trenches – an important structural element of the ponds – and had subsequently been covered over with fill by the contractor.

“Damage to the liner consisted of rips, tears, and scratches of varying depths in the new liner, as well as damage to gas vents.

“Damage to the liner at the top of the ponds is more of a risk, due to the additional effect of sunlight and ultra-violet light accelerating degradation of the liner material.”

Carterton District Council would need to repair the damage before the ponds were filled to ensure the integrity of the liner and minimise any potential negative environmental impacts or breaches of resource consent conditions.

“The expected cost of repairs and completing the project ranges from $1.3-$1.9m,” Hamilton said.

“This will be loan-funded, with the interest resulting in an approximate rate increase of up to 0.3 per cent in the 2022-2023 financial year, and subsequent years.

“Council will seek to claim the cost of the repairs from the contractor, CHBE.”

The contract with CHBE allowed for the council to complete the contract and seek reimbursement for additional costs within the agreed scope of works.

The council intended to follow this process to recover the cost of liner remediation and completing the contract works.

The legal costs to enforce this could not be recovered and were expected to be from $150k to $300k.

For the council to still be within its consent requirements the ponds must begin filling with partially treated wastewater by April 2022. This meant the damage must be assessed and repaired as soon as possible.

The real driver was the end of the council’s discharge consent in January 2023 which was when the project must be completed.

The reservoirs had been repaired to a level that would provide functional ponds and remediation recommendations could be completed by the engineering experts.

The council was set to meet on December 15 to approve additional budget for remediation and completion of the project.

Carterton Mayor Greg Lang said he was “hugely disappointed, personally and on behalf our community, that we have found ourselves in this situation”.

“I fully support Carterton District Council’s actions ensuring stage 2 is completed on time and to a high quality.

“We are still on target for an outstanding wastewater facility which will have a 35-year consent and will be completed at relatively low cost compared to other facilities constructed across New Zealand.”

The Carterton District Council meeting will be open to the public and livestreamed, with the full report available in the agenda at www.carterton.infocouncil.biz.

CHBE was approached for comment but requested more time for a formal substantiated response to the council’s claims, due to this being a legal matter.

On the sidelines

Carterton District Council’s wastewater ponds were designed to a high standard, and high-grade conductive lining with a thickness of 1.5mm was used.

Damage to the lining.

The lining has a 70-year life expectancy, but an engineering report has found that because of the damage, the ponds would not meet the life expectancy in the current condition and may not meet the 35-year requirements of the resource consent if there are significant leaks.

Scratches in all three ponds have undergone a high-level visual mapping and recording by Tonkin and Taylor.

A manual, slow, but more detailed survey and recoding is in process using a digital optical micrometer.

A range of representative samples of damaged liner have been sent to an Australian laboratory who are a leading independent geomembrane testing facility.

The test results and report on the impact of the damage are not expected to be completed before February 2022.

Repairs will likely require additional conductive geomembrane liner to be ordered and imported, which has a lead time of about four months.

Meanwhile, the tears, rips and major scratches have been patched which will provide Carterton District Council with functional reservoirs that can receive treated wastewater.

Having functional reservoirs allows for the finalisation of the construction works and provides time for the engineering and geomembrane experts to develop a repair strategy that is technically and contractually sound and promotes the longevity of the ponds.

Remedial repairs can be undertaken on a single pond at a time and these are not time-bound by consenting requirements.

Timeline of the project


Carterton District Council began a process of upgrading its Wastewater Treatment Ponds.


Council obtained a 35-year resource consent from Greater Wellington Regional Council.


Council issued a contract to build to Central Hawke’s Bay Earthmovers [CHBE] with an expected completion date of May 30, 2019.



Council met CHBE to set a final completion date and gain assurances that construction would be completed by that time. During that meeting, CHBE stated that the reservoirs would be completed by September 20, 2020.


The completion date was not met, and a notice of default was issued to CHBE by the council’s engineer to contract, Tonkin and Taylor. The default notice was issued through a Notice to Contractor [NTC] that claimed CHBE was persistently, flagrantly, or wilfully neglecting to carry out its obligations under the contract.

This claim was rejected by CHBE and they stated that they were committed to resolving the issues.

The council’s governance group considered CHBE’s position at the time and weighed up the costs to complete for the outstanding works against the lower contractual rates CHBE had submitted.

A decision was made to continue with CHBE because the work would be done at a lower cost to ratepayers.

Throughout the construction of the reservoirs Tonkin and Taylor have held the position of Engineer to the Contract and provided project management resource. The council’s project management officer submitted daily updates and records three days a week and Tonkin and Taylor were physically on site two days a week.



Tonkin and Taylor observed issues with CHBE’s actions regarding the geomembrane liner. A Notice to Contractor directed CHBE not to drive equipment directly on the liner surface and provided guidance on what could be done to access areas of the reservoirs. CHBE was directed to repair the damage.


A Notice to Contractor identified damage to the western crest of reservoir 3 and instructed CHBE to repair it.

Despite multiple reminders issued through the Notice to Contractor system, quality issues were not being addressed, the council said.

The primary concerns centred around the construction and backfilling of the anchor trench holding the liner in place at the top of the embankments and damage to the geomembrane liner.

CHBE were given 10 working days to provide a remedial action plan.

This was considered by both Carterton District Council and its Engineer to the Contract – Tonkin and Taylor.

Both the council and its engineer concluded the proposed remediation plan was inadequate to resolve the faults and the council resumed possession of site on August 31.


Once the council had resumed control of the site, a local contractor was arranged to oversee the clean-up of the site and completion of the lining installation.

Careful cleaning of the excessive soil overspill on, and in the reservoir was undertaken using handheld soft brooms and plastic shovels.

This found a greater extent of lining damage than was initially thought.


As at the end of November, the project is more than 80 per cent complete. After liner remediation, the majority of the work left to complete focused on the pipe and pump work.

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