PACl Trial Data

Ngatoe Water Treatment Facility, Rarotonga.

PACl Trial Data.
Compiled by: Andy Kirkwood, Justine Flanagan. Nov 2020.

Contact: [firstName] @

Masthead Ngatoe water treatment facility.


This is a working draft. Published 10 Nov 2020. Updated 27 Mar 2023.


As part of the Te Mato Vai Project - Stage 2, the Government of the Cook Islands has constructed water treatment facilities. These include chemical-treatment systems that use polyaluminium chloride (PACl) to remove fine particles from streamwater.

The use of PACl will generate hazardous waste. The method of operation risks impacts on biodiversity due to the routine, or accidential, discharge of chemical wastewater, and then the long-term stockpiling of sludge.

Treatment facilities have been constructed in ten locations, on the majority of Rarotonga’s main freshwater streams. Waste will be discharged at elevated locations, and the streams are used to irrigate food crops, run through residential areas, and sustain wetland ecosystems before being discharged to the lagoon.

The Cook Islands Government claims to have consulted extensively with intake landowners, but project managers GHD have failed to complete the required regulatory process to obtain a Project Permit for the trial.

As the PACl trials commence (Sept 2020), there is no plan in place for the disposal of sludge, which has been estimated at 4,000 cubic meters per year (Expert Report, Mar 2020), This equates to a 20-foot shipping container of sludge, per intake, each month. Although methods of sludge reuse have been researched internationally, all require investment in infrastructure to dewater, dry, and store the material. In New Zealand, sludge disposal is typically to landfill.

  • Wastewater discharge points are within 4km of the lagoon.
  • The stream discharge of water treatment waste is prohibited in New Zealand, Australia, and the Cook Islands.
  • The existing solid waste site in Arorangi is over-full, and sludge must be contained and groundwater quality monitored due to the risk of leaching. Any plan for a long-term disposal site would require a (separate) Project Permit, dependent on completing an environmental impact assessment including public consultation.

Material including sludge or other by products from water treatment plants is Hazardous waste.
Public Health Act 2004

The relevant legislation, policies, and standards relevant to the Te Mato Vai Project were identified in the EIA report prepared for the Stage 2 Construction Permit.

The release of water treatment waste to waterways is prohibited under the Cook Islands Public Health Act 2004. Material including sludge or other by products from water treatment plants is Hazardous waste. Section 54(2)(d) prohibits hazardous waste to be directly or indirectly deposited or discharged, or to seep, into a waterway.

Te Mato Vai systems have been constructed to discharge water treatment by-products to the stream (see aerial view of Ngatoe below). Although sludge is intended to be moved off-site, surface flooding may result in wash-out of the storage ponds. This occured after heavy rain in Aug 2020 — prior to the operational use of chemicals.

Ngatoe waterworks showing discharge points.

Above Ngatoe waterworks showing the five stream discharge points Treatment flow is right-to-left.



Ngatoe Intake - Take a Look. View on Facebook.

GHD has described the first six-months of operation as a trial. Landowners were led to believe that no chemically-treated water would leave facilities, and that waste would be contained within the onsite holding tanks and waste storage ponds. However the data and accompanying notes released from Ngatoe (28 Sept-11 Oct 2020) show that the new system is Operational (on-line).

If acceptable results are achieved for the off-line trial the results are forwarded to TTV for their “confirmation to proceed” to discharge the treated water to the Network system…

The next stage is called the on-line trial. Once the on-line PACL trial is started it will continue at each intake for the whole period of the overall trial which could be as long as six months depending on achieving a good level of data which will be used to operate the plants in the future.
-MFEM, Oct 2020

The Ngatoe results show that trial data was collected for three days, Sept 28-30 2020. Approval was then obtained from To Tatou Vai and water released to the ‘Network system’ — the public water supply. The Te Mato Vai system was on-line from 1 Oct 2020. For the remaining five-plus months, chemicals will be used in a live environment.

How will you monitor the impact of PACl use on the streams?
During the trials, we’ll do a mix of tests within the water treatment plant and in the streams. This includes testing for dissolved aluminium in water. These tests will be at regular intervals, and each time we need to adjust the amount of PACL we’re using.
9 Feb 2020: What happens when we commission Te Mato Vai? Te Mato Vai PMU.

Assuming the data provided from Ngatoe is representative, it is unlikely that a ‘good level of data will be achieved’. Among many ommissions is the initial dose of PACl, whether dosing was continuous; and if dosing was at a constant rate over the trial period.

The lack of data prevents independent interpretation, and also exhibits a bias to proving chemical treatment. No baseline data has been collected on the effectiveness of non-chemical operation, and the new system introduces three forms of physical treatment: a coarse screen, three hour settling tank, and sand filtration.

Ngatoe PACl trial data.

Above Ngatoe PACl trial data: 28 Sept-11 Oct 2020

Further reports were released in Dec 2020. Avana and Turangi are two intakes on the island (although natural flows are now less relevant as water production is limited by sand-filter through-put).

Avana PACl Trial Data, Nov 2020 Turangi PACl Trial Data, Nov 2020

Turbidity Standards

The data tables provide a desciption of how intake performance will be assessed. For turbidity, treatment is considered successful if:

The turbidity after the AVG should be lower than the raw stream turbidity.
-PACl Trial Results Memo 1 - Avana. GHD.

This seems a reasonable metric, however there are formal standards applicable to the monitoring of water clarity. TTV require water to the delivery point to be under 2.0 NTU, where a lower NTU value means clearer water.

At Ngatoe, the untreated streamwater met To Tatou Vai’s draft service delivery turbidity standard in 25/27 samples. For Avana 26/27 samples and Turangi 39/46 were under 2.0NTU. When untreated streamwater already meets the turbidity standard, then the PACl serves no purpose.

Whether improvements in turbidity should be attributed to the PACl is also debateable. Turbidity is also improved by physical processes: coarse screening, settling time, and sand filtration. The trial method only samples water at the stream and after the sand filter, the contribution of each of the physical steps to improved clarity cannot be isolated.

Clearer water is also more difficult to coagulate. Clumps can only form when particles are in close proximity. In clear water the particles are more widely distributed.

To Tatou Vai clarity service level: optimal clarity under 1.0 NTU; maximum level 2.0 NTU.

Above:To Tatou Vai Clarity service levels Source: To Tatou Vai: Code of Practice for Design and Construction of Water Supply Infrastructure. Aug 2019. To Tatou Vai Ltd.

Interim standards for Cook Islands drinking water were proposed in 2019.

  • Turbidity / water clarity: < 2.0 NTU (Customer Level of Service). To Tatou Vai: Code of Practice for Design and Construction of Water Supply Infrastructure. Aug 2019.
  • E. coli: 0 / Most probable number (MPN) less than 1 / < 1 MPN. World Health Organisation.
  • Dissolved Aluminium: < 0.1mg/L (Guideline Value). Draft Cook Islands Drinking Water Standards. May 2019.
    Above represents aesthetic/taste impacts.
  • Australian and New Zealand Environment and Conservation Council (ANZECC) aluminium in freshwater and marine water trigger value is 0.055mg/L.

A genuine trial

Stakeholders including environmental protection organisations also have an interest in the viability of (solely) physical treatment processes. The Te Vai Ora Maori lobby group provided to landowners an assessment of the trial - critical of the method; the sample points; the (lack of) environmental monitoring; the test regime; and the data collected.

Ngatoe Water Sample Points

Above: Ngatoe Treatment Process Showing Approximate Water Sampling Points
(A) Stream; (B) Mid-level Drain Proposed; (C) Post Settling Tank; (D) Post AVG - Finished Water.
Te Vai Ora Maori propose that all water quality parameters be tested at all four sample points. In the Ngatoe data, turbidity readings are only taken at the Stream (A) and Post AVG (D).

The review also recommends A/B comparison: a concurrent trial with and without PACl. A/B trials can be conducted at facilities where there are dual treatment paths with separate settling chambers and sand filters for each path.

Edited data table identifying water sample point location along treatment

Above: Edited data table indicating water sample point location along treatment path
The sample locations biases chemical treatment as the efficacy of the physical treatment steps cannot be constrasted.

  • Chemical sludge began to accumulate in the settling tank 28 Sept 2020.
  • The AVG sand filters automatically self-clean (backwash) to onsite storage ponds. Ponds are located alongside the streams and have been observed to overflow in storm conditions (e.g. Takuvaine Aug 2020).
  • Chemically treated water was fed into the unified, island-wide public water network from 1 Oct 2020.
  • Environmental risks are not solely due to chemical use; physical processes such as the force of the discharge can disrupt ecosystem functions - erode streambanks, stir-up sediment, etc.
  • No EIA process has been completed for managing water treatment residuals (sludge and wastewater). Sludge accumulating the the settling tank will impact treatment efficacy. Maintenance cycles are impacted by climatic conditions: more rain means more sludge, and more frequent clearing. The setting tank may need to be cleared every 33 days (Expert Report, Mar 2020).
  • Trials at all ten new water treatment facilities are being conducted concurrently; without a Project Permit; without assessment of environmental impacts; and without any plan in place for the disposal of hazardous waste.

Sludge cannot be contained in the settling tanks without compromising drinking-water quality, and ponds are not large enough to contain six-months of waste. The timing of the trial also coincides with Rarotonga’s wet season increasing the risk of accidental wash-out.

The risks associated with use of PACl arise from operating the system. Treated water is fed into the public supply network and waste is generated. When the trial is trial-operation; then an EIA is required, and informed public consent is required.


Monitoring environmental impact

The environmental monitoring proposed by GHD as part of the trial-operation is to record:

  • dissolved aluminium levels;
  • pH;
  • and turbidity (water clarity).

The above are all streamwater chemistry parameters. Genuine environmental monitoring would include also record water flows, climatic conditions (e.g. rainfall, storm events), and survey streamhealth indicator species/population size.

Additional chemistry parameters effect the ecotoxicity of dissolved alumininium: dissolved organic carbon and total hardness (levels of calcium carbonate).

Dissolved oxygen content is also a useful indicator of overall stream health (monitoring oxygen levels is also proposed when discharging of wastewater de-chlorinated using sodium thiosulphate).

Following the release of the proposed monitoring regime; discussion with landowners; and subsequent meeting with the Te Mato Vai Project Management Unit; Te Vai Ora Maori delivered a formal request to the Avarua office.

The request included: “recording of baseline values against which to track change… to enable independent interpretation and evaluation of the PACl dosing system”.

PACl Trial Regime Request, Te Vai Ora Maori, 7 Dec 2020

Cook Islands Biodiversity Database: Freshwater Species.

Freshwater Species Search Result, Cook Islands Biodiversity Database. The above result include estuarine species, but not insects that may also depend on freshwater ecosystems such as dragonflies and damselflies.


Expert Report - March 2020

In February 2020 an independent water engineer was appointed by the Ministry of Justice to answer landowner questions about the Te Mato Vai treatment system. The report was completed March 2020, and identified environmental risks associated with the use of an aluminium-based coagulant (polyaluminium chloride):
  1. Spillages while transporting the chemical to the plants and handling it while on each site.
  2. Leaks from chemical tanks and chemical pipework.
  3. Overflows from the settling tank.
  4. Discharges to the stream from the scour pond and/or backwash ponds.
  5. Flood flows from the stream, and/or runoff from the pond’s catchment, overflowing into the pond and causing sludge sediment to flow into the stream.
  6. Recovering and disposing of the sludge from the ponds.

-Te Mato Vai - Stage 2 - Expert Independent Report, Mar 2020

Point 3 - Overflows from the settling tank is not directly detailed in the report:

This risk has been reported on separately - refer letter to Judge (sic) Keane dated 9 March.

The Expert offered no firm conclusion regarding the suitability of PACl, but recommended landowners be provided with the ecological report study.

“… the residual aluminium could be in the range of 0.05 to 5 mg/L (as Al)”. If the aluminium in the discharge was greater than the lower end of this range, and stream was in low or zero flow, then this is concerning. There are also the potential adverse effects in the mixing zone to be considered…
Given the number of unknowns in the above, and I suspect the rather unique freshwater ecology of the streams of Rarotonga, I think the recent ecological report study (referred to in Mr. Free’s letter to me dated 4 March) should be circulated to the parties.

Untangling the above, the Expert is advising that:

  • Rarotonga’s streams can run dry. If wastewater is discharged in drought conditions (‘low or zero flow’), then the potential impact of contaminants will be greater.
  • The dissolved aluminium levels will be dependent on the amount of water in the stream. Aluminium at a concentration over 0.055 mg/L has the potential of impact on biodiversity (referred to as a trigger value). The highest values recorded at Ngatoe (1 Oct) were 0.172 and 0.133mg/L; trending an increase just prior to the sand filter being shut off.
  • There will also be physical impacts along the stream where wastewater is discharged (‘mixing zone’). Bank and streambed erosion and an increase in the amount of sediment in the water.

Not mentioned by the Expert is that species such as koura (prawns) burrow into the stream bed in drought conditions. Discharge may coagulate streamwater to form a seal on the streambed, resulting in benthic smothering. The Te Mato Vai Stage 2 EIA Report also identifies that discharge should avoid spawning cycles (for koura, this is the three days either side of the full moon).


PACl trial results: April 2021

From early April 2021, the Te Mato Vai PMU presented the findings from the six-month PACl trial to intake Landowners. An agenda was provided in the invitation to Landowners:

  1. The history of the project and the need for PACl.
  2. What is PACl and what it aims to do.
  3. The water quality results from the trial.
  4. The environmental impacts of PACl.
  5. Information on PACl sludge and what we found.
  6. Our recommendations and next steps.

-PACl Trial Results Presentation, 31 Mar 2021. Te Mato Vai PMU (pers. comm.)

  • The PMU are to recommend to the Cook Islands Government that dosing continues.
  • The proposed dose is 15-20mg/L in dry conditions; and 20-35mg/L in wet weather conditions.
  • A site for long-term disposal of sludge is yet to be confirmed.

PACl Project Permit Timeline

  • Te Mato Vai PACI Trial Report GHD March 2021
    This verion of the report does not include the data (appendices) referred to by Waton.
  • Te Mato Vai PACI Trial Results Summary GHD April 2021
  • May 2021: An EIA was submitted to the National Environment Service seeking permission for onsite discharges.
  • June 2021: TVOM submit a response to the EIA: this includes augmenting the operation of the infrastructure to avoid the need for stream discharge.
  • Sept 2021: Watson completes an independent quality assurance review of the GHD PACl Trial Report.
    NB: The Beca QA report was not available for public consideration, nor referred to by the onsite discharges EIA.
  • May 2021: TTV begin tranfer of sludge from the Turangi ponds to the Papua treatment facility.
  • Nov 2021: Onsite Discharges Permit authorised by the Rarotonga Environment Authority (REA).
  • Nov 2021: Out-of-pond storage of sludge (in geotextile bags); and cutting of sludge drying platform observed at Papua.
  • July-Aug 2022: TVOM observe unauthorised operations at Turangi and Avana.
  • Nov 2022: Turangi and Avana observations presented to National Environment Service.
  • Nov 2022: Onsite Discharges permit extended by the REA.
  • Feb 2023: Consultants prepare REA Breifing Paper.
  • Feb 2023: Onsite Discharges permit extended by the REA.

Classification/subjects: Te Mato Vai, To Tatou Vai, coagulation, flocculation, water treatment residuals, polyaluminum chloride, PAC, PACL, water standards, water quality, Rarotonga, Cook Islands, South Pacific, environmental impact assessment, EIA.


References and Further Reading

See also




  • 30 Nov 2019: Govt turns on filtered water to homes. Anneka Brown, Cook Islands News.
    After last minute talks with land-owners went right down to the wire yesterday, the Government has instructed contractor McConnell Dowell to begin turning on the taps.
    Most land-owners of the 10 water intakes have agreed to a six-month trial of poly-aluminium chloride, a coagulant that cleans the water of smaller particles and harmful protozoa, like those that cause Giardia.
  • 3 Dec 2019: Turn-on is a turn-off. Anneka Brown, Cook Islands News.
    Furious Matavera resident Renall Vogel joined anti-chemical group Te Vai Ora Maori yesterday to protest government turning on the taps of the new filtered water intakes.… The Matavera water plant and pipes will, however, be flushed with chlorine to disinfect the new infrastructure, before it is washed out and the new water supply is switched on.…The water engineers will also begin a six-month trial of poly-aluminium chloride…
  • 4 Jan 2020: The water debate continues. Te Ipukarea Society in Cook Islands News
    Flocculation is a process of settling out particulate matter, for example dirt, from the water. Given that PACl is a chemical that produces a potentially toxic sludge as a byproduct of the flocculation process, this trial needed to be properly assessed for environmental impacts before it was approved.
    Another purpose of an EIA is to look at alternatives that may have a lesser negative impact. Therefore, from an environmental perspective, the logical thing to do to reduce dirt getting into the water is to first trial alternatives which provide a lower level of risk to our freshwater ecology.
  • 15 Jan 2020: To Tatou Vai makes progress with Environmental Impact Assessment. Media Release.
    The EIA will advise as to potential effects of the by-products – sludge and discharge water from the coagulation, flocculation and sedimentation as part of the designed water treatment process for the Te Mato Vai project.
  • 24 Jan 2020: Something in the water. Moana Makapelu Lee, Cook Islands News.
    Ecologists have this week begun an ecological survey of the streams flowing through Te Mato Vai’s water intakes. The study includes a wide spanning survey of the aquatic habitat and wildlife populations as well as the stream conditions. Information gathered will contribute to the Environmental Impact Assessment report commissioned by Rarotonga’s water supplier, To Tatou Vai… Leading the study are aquatic ecologists Dr Natalie Clark and Lauren Pratt, who are employed by GHD New Zealand, which is engaged by the Cook Islands Government to deliver and manage Rarotonga’s new water facilities.
  • 31 Jan 2020: Cook Islands water system EIA ‘too narrow’ Te Ipukarea Society / Radio New Zealand News.
    “After talking to the consultants [Tonkin and Taylor] this EIA is only looking at the use of polyaluminium chloride…it’s not looking at chlorination and they may as well do the whole thing all at once…The EIA is not really looking at alternatives, it’s merely looking at the impacts of the PACl and how these may be reduced or mitigated on the assumption that PACl will be used.”
    -Kelvin Passfield
  • 9 Feb 2020: What happens when we commission Te Mato Vai? Release, Te Mato Vai PMU.
  • 18 Feb 2020: Why only collecting stream water when the water is running ‘clear’ is not an option Release, Te Mato Vai PMU.
    There are good reasons why turbidity detection and diversion systems are not a viable alternative to PACl. The option to bypass the intake during wet weather events is impractical and detrimental for three reasons:
    1. PACl dosing is still required for treating ‘clear’ water flows.
    2. Collecting water when the streams are in high flow (generally during heavy rain) will help prevent public water supply shortages.
    3. An effective bypass system would most likely need a permanent power supply at each intake site.
  • 19 Feb 2020: Chemical water trial is ‘lawful’. Losirene Lacanivalu, Cook Islands News.
    [To Tatou Vai CEO] Manning said the initial work was lawful. “This has been agreed with landowners through a consultative process, noting however that there is some opposition to the use of water treatment chemicals, but that doesn’t necessarily make it unlawful.”
  • 21 April 2020: How does polyaluminium chloride (PACl) work. Te Mato Vai PMU.
    We need to use PACl in Rarotonga because stream water contains high levels of contaminants — everything from bird poo to leaves and soil. This is true for water taken from streams, rivers or lakes around the world, not just in Rarotonga. Even stream water that looks clear still contains harmful protozoa and bacteria too small for people to see.
  • 2 May 2020: Andy Kirkwood: Sludge! Letters in Cook Islands News.
    A March 2020 expert review estimates the scale of the issue. The use of polyaluminum chloride (PACl) – a chemical that helps to remove dirt during rain – will generate 4,000 cubic metres of chemical sludge each year.
  • 23 May 2020: Andy Kirkwood: Water treatment: Don’ be hasty Letters in Cook Islands News.
    The Government intends to proceed with a separate six-month PACl trial, despite not having a permit to do so. The Government claims the trial is necessary to inform the environmental impact assessment. This claim is not supported by the GHD technical documentation, the Court-expert assessment, or the opinion of the consultancy firm preparing the To Tatou Vai environmental impact assessment submission. The Government’s claim a trial is necessary – is a fiction.
  • 25 Jun 2020: Turning on the taps Katrina Tanirau, Cook Islands News.
    Authorities acknowledge they need to be as transparent as the water they plan to pipe into people’s homes in Rarotonga.…
    Storm damage to the main water storage pond meant it had to be reconstructed, and that delayed the project.
  • 20 July 2020: Complaint filed against Govt . Rashneel Kumar, Cook Islands News.
    Deputy Prime Minister Mark Brown said the Government haven’t commenced dosing the public water supply with the coagulant poly aluminium chloride. Brown said they will follow due process by notifying the landowners before any dosing is to proceed. “At this point in time, this is a matter before the court.”
    TVOM: “We’ve repeatedly asked our government for information - what are the risks, are all the intakes affected, and have all the faults now been fixed? A permit is required, and the people have a right to be consulted.”
  • 22 July 2020: Andy Kirkwood: Te Vai Ora Maori- says no permit is an offence. Cook Islands News.
    Te Vai Ora Maori now calls for the Minister release the expert finding on the settlement tank overflow fault, and details of the “storm damage” that was sustained by the main water storage pond in June.
    Both the settlement tank and storage pond are part of the PACl dosing system. Similar faults may affect all 10 of the Te Mato Vai waterworks, and risk impacts on the health and safety of residents living downstream.
  • 20 Aug 2020: Water treatment: ‘No one is above the law’ . Rashneel Kumar, Cook Islands News.
    …a body corporate is liable for a fine of $100,000, Flanagan said. There is also provision for a further fine of $10,000 for each day the offence continues, she added.
    “There are 10 intakes – that’s 10 offences. We are seeking expert advice on whether the respondent should be the Cook Islands government, GHD, McConnell Dowell – or all three. No one is above the law, not even government. We have prepared a legal brief; and invite anyone interested to get in touch.”
  • 24 Aug 2020: Activists claim Cook Islands Govt set to illegally use chemicals in water. RNZ.
    The Cook Islands News reported the group alleged last month, in a complaint to the National Environment Service, that the government was dosing the water supply with a chemical coagulant without a proper permit.
    The group said its complaint is not about the science of water treatment, but about the “regulatory process”.
    Earlier this month To Tatou Vai, the authority being set up to run the scheme, wrote to landowners saying it was about to start a six month trial using the coagulant.
  • 5 Sept 2020: Water dosing ‘trials’ starts . Katrina Tanirau, Cook Islands News.
    The government says poly aluminium chloride trials for the next six months will allow for making better-informed decisions about the future of Rarotonga’s public water supply, but opponents say proceeding with the trial is irresponsible.
  • 5 Sept 2020: Te Mato Vai water system one step closer to delivering safe and reliable drinking water. Cook Islands government, Cook Islands News.
    “As I have already confirmed, permits are in place for the construction and commissioning of the Te Mato Vai Stage Two project. The Cook Islands Government has committed to managing the PACl trials in a way that protects the health of our community and environment and provided all reassurances necessary that the use of chemicals during the commission will not cause significant environmental harm or breach any requirements of the Environment Act 2003.”
    -Nga Puna, Director National Environment Service
  • 8 Sept 2020: Water issue. Justine Flanagan in Cook Islands News.
    Statements attributed to the director of NES (National Environment Service) are deliberately evasive. He confirms that Te Mato Vai have a permit for “construction and commissioning”. He does not state that the permit covers the use of PACl.
  • 29 Sept 2020: A step closer to ‘cleaner drinking water’. Cook Islands News.
    The first dosing of poly aluminium chloride (PACI) to the settling tank took place at the Ngatoe water intake yesterday.
    Following “extensive consultation”, PACI dosing was witnessed by the National Environmental Service, landowners and Aronga Mana prior to the milestone being marked by government officials and other dignitaries.
  • 29 Sept 2020: Andy Kirkwood: The many hats of GHD. Cook Islands News.
    In effect, a New Zealand company is both proposing; and then self-approving the use of a chemical that industry guidelines do not recommend. Without environmental monitoring, damage to Rarotonga’s stream ecosystems will go undetected. The reality of chemical-use is that it generates chemical waste. The reality of water technicians, is that they’re not freshwater ecologists.
  • 24 Oct 2020: Chemical trials could be unlawful: Lobby group. Cook Islands News.
    Use of polyaluminium chloride (PACl) is ‘not a trial but a test’ according to Te Vai Ora Maori, but Prime Minister Mark Brown says it’s simply another attempt by the water lobby group to stall progress.
  • 7 Nov 2020: Andy Kirkwood: Water project points to need for enforcement of environment laws. Cook Islands News.
    When executive government flaunts existing regulations; NES and the Ombudsman are uanble to execute their duties; and public petitions are routinely derailed, we don’t need new laws. We need law enforcement.
  • 11 Nov 2020 Everything you need to know about PACl. Te Mato Vai PMU.
    We will be following industry practice and guidelines to ensure PACl is used safely and effectively.
    Is sludge safe? Well documented water treatment process science tells us that the PACl sludge is in many respects like a soil, and can be reused or disposed of in a number of ways without damaging the environment. However, like any waste product, PACl sludge must be managed responsibly.
    How much sludge will the Te Mato Vai system produce? We can’t accurately predict how much sludge the Te Mato Vai system will produce because it will depend on weather, its effect on stream flows, and the unique conditions of each intake site. For example, heavy rainfall that disturbs the soil and carries more sediment into the stream will result in more PACl needed to remove the contaminants in the water and more sludge produced. This is one of the reasons for the PACl trials — the trials will help us understand how much PACl to use at each site, how much sludge will be produced and the sludge consistency.
  • 26 Nov 2020 LETTER: What are the effects of water treatment on Rarotonga’s streams? / Nutrient — more or less? Cook Islands News.
    Freshwater streams are not used as drains for water treatment residuals in New Zealand - or in Australia. There is no scientific research on the long-term effects of PACl waste on stream life.
  • 26 Nov 2020 LETTER: Landowner concerns with water treatment.. Cook Islands News.
    There are no aluminium tests, the filter is off, and people are drinking chemical water. How is this a trial?
  • 27 Nov 2020 MPs attend intake tour. Cook Islands News.
    Nine out of 10 intakes are undergoing trials where a chemical called polyaluminium chloride, or PACl, is added to the settlement chambers to remove small dirt particles and other contaminants found in water, such as bird droppings. Napa said the answers provided by officials during the tour didn’t adequately explain how PACl sludge and the by-product from sand filtration will be disposed in an environmentally responsible manner. “This is a major inland development that will affect our water supply, our streams that flow out to sea. Why didn’t this government first obtain an EIA? Everyone seems to be avoiding that question and ducking for cover.”
  • 28 Nov 2020 Time to turn on the tap, but it’s not that simple. Cook Islands News. Rarotonga’s geography, ecology, and weather are posing unique challenges. “It’s very different here. Water gets dirty very fast, but it cleans up fast.” Developing water treatment systems is never an easy process, says Free, and getting to this stage has been a lengthy process. “They always are, but this one, probably a little longer than most. There’re 10 plants. I’ve never worked on 10 plants at the same time.”
  • 4 / 22 Dec 2020 Te Mato Vai Aquatic Ecology Report Released. GHD.
    Earlier this year a field study on the 10 streams where water intakes have been upgraded was conducted. … Alongside the field study a report that described the existing aquatic ecological values of the 10 intake and discharge sites was produced. As part of this study, we assessed the potential impacts of the water treatment plant operations…
  • 8 Dec 2020 Government’s ecological report challenged. Cook Islands News. A desktop review relies on published reports. The consultants did not conduct any fieldwork on the sensitivity of Rarotonga’s freshwater ecosystems to pollution.
  • 22 Dec 2020 PACl trial update. GHD.
    Trial results so far have been positive, with the water treatment plant performing as expected and delivering a significant increase in water quality overall.
  • 26 April 2021 Rarotonga water treatment waste ‘no gift to growers’. Cook Islands News.
    NKA: “…if [an organic] grower is found to be using sludge, their organic certification will be revoked.”
    GHD: “Aluminium is not toxic to plants when the soil pH is near neutral or mildly acidic (the pH values are above pH 6). Most Rarotonga soils are above pH 6, and the silts and clays have very high natural buffering capacity meaning that their pH doesn’t change much when something more acidic is added. In fact, the PACl sludge we have tested is not acidic so it won’t make the soil more acidic.”
    Ministry of Agriculture: “the sludge will also contain aluminium (Al) and chloride (Cl) and possibly other elements such as heavy metals which can negatively impact plants and crops.…elevated levels of Al and Cl can have adverse effects on the growth of certain tree species and many vegetable crops such as tomatoes, lettuce, and melons.”
  • 26 April 2021 The potential for PACl sludge use. Te Mato Vai PMU.
    Initially PACl sludge was being considered for fill or capping material. At their request, and with the support of the Government, the PMU conducted preliminary tests to understand the composition of the PACl sludge and whether it would be suitable for reuse on the land.

News Archive: 2011–

Working Draft. Updated: 27 Mar 2023.


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