Te Vai Ora Maori: Response To Water Treatment Plants: On-Site Discharges EIA

Papua sludge pond, 23 Nov 2021.

Te Vai Ora Maori: Response To Water Treatment Plants: On-Site Discharges EIA.
Authored by: Andy Kirkwood, Justine Flanagan for Te Vai Ora Maori.

Contact: [firstName] @ islandbooth.com.

Masthead Paupa sludge pond, 23 Nov 2021. The To Tatou Vai EIA seeks permission to discharge sludge to onsite ponds, and residual, chemically-treated water from holdings tanks and the surface of the sludge ponds to the adjacent streams. The line of wire cages above the pond contain geotextile intermediate contaiment bags; later confirmed to be for the temporary holding and drying/draining of the sludge.


Submitted 22 June 2021. Webpage updated 10 Dec 2021.


This response was prepared by community lobby group Te Vai Ora Maori (TVOM), and concerns the application by water authority To Tatou Vai for an operational permit to discharge residuals from the Te Mato Vai drinking water treatment system.

This Environmental Impact Assessment (EIA) considers the potential environmental impacts of the activity of using polyaluminum chloride (PACl) as a coagulant during the operation of the water treatment plants. Specifically, the focus of this Environment Impact Assessment is on the onsite management of residual materials from the settling tank and sand filter including discharges to the adjacent streams. Off-site disposal of sludge will be covered in a separate EIA. This EIA does not consider impacts arising from disinfection of water (by chlorination or other means).
- Water Treatment Plants: Onsite Discharges EIA. Tonkin+Taylor May 2021


Objection to stream discharge

On behalf of 1433 residents of Rarotonga, Te Vai Ora Maori (TVOM) objects to the stream discharge of residuals from the Te Mato Vai water treatment system. The Rarotonga Environment Authority should refuse to permit the stream discharge of residuals due to:

  • statutory constraints;
  • uncertainty regarding the long-term impacts on freshwater ecology;
  • that alternative disposal methods have not been adequately investigated; and
  • out of respect for cultural values.

To Tatou Vai must be directed to implement improvements to operational process, or Cook Islands Investment Corporation directed to make improvement to the Te Mato Vai infrastructure to ensure that stream discharge is not required.


Te Vai Ora Maori: Response To Water Treatment Plants: On-Site Discharges EIA


Stream discharge

1. The Rarotonga Environment Authority cannot authorise unlawful activity.

Material including sludge or other by products from water treatment plants is Hazardous waste.

S.54(2)(d): …prohibits hazardous waste to be directly or indirectly deposited or discharged, or to seep, into a waterway.
-Public Health Act 2004 (emphasis added)

Supernatant is a by product of water treatment; the adjacent streams where supernatant is to be discharged are waterways. The stream discharge of residuals is unlawful.


2. Cook Islands National Water Policy 2016

The Cook Islands National Water Policy 2016 directs that infrastructure and development should avoid degrading freshwater ecology.

Precautionary Principle
Taking active measure to prevent serious or irreversible environmental damage or degradation whether the consequences are uncertain or not.

Sustainability & Environmental preservation
Strive to protect and avoid adverse interference with the natural ecology of the Cook Islands’ waters and lagoons, and ensure that usage and management of water will be conducted in a manner that will preserve and enhance this resource for generations to come.

Mitigation of the impact of Infrastructure and Development on Ecological Flows
In designing and delivering future water supplies, infrastructure, services and operations will be provided in a manner that ensures that ecological flows are maintained in natural streams and waterways to the greatest extent practicable in order to ensure the protection of freshwater and coastal ecosystems.

Stream discharge goes against these principles: the impacts of this method of operation are uncertain; discharge interferes with natural ecology; and freshwater ecological flows will be disrupted.

Safeguarding environmental values does not compromise the ability to achieve the benefits of a more reliable water supply system; or the companion Sustainable Development Goals.

As a matter of principle, alternatives to stream discharge should be investigated and implemented.


3. Stream discharge of supernatant is not ‘standard practice’.

Operating the new system using an un-researched method risks the long-term health of stream communities.

5 Monitoring and Management Practices (Environment)
62. In New Zealand and Australia, in most cases sludge supernatant is recycled back to the inlet of the water treatment plant…. Only the sludge becomes waste product as the supernatant is recycled…. So, for discharges of PACl (or dissolved aluminium) to the environment (through supernatant), there is no ‘standard’ practice.
-GHD Nov 2019 (emphasis added)

The full reference details that a single water treatment plant (WTP) practices stream discharge: the Frasertown WTP, Wairoa, New Zealand.

Postnote: The Frasertown WTP five-year resource consent for stream-discharge (Discharge permit: DP110406W) expires 31 May 2022. A Three Waters review notes:
“…ongoing environmental issues with the water quality in the Wairoa river, such as raw sewage spillages, nirates from dairying and pastoral farming. Slow responses to water quality issues has impacted on aquatic wildlife habitats, e.g. tuna.”

Stream discharge goes against standard industry practice. In the whole of New Zealand and Australia, GHD advise that Frasertown is the only drinking-water WTP that discharges PACl residuals to a natural waterway.

  • GHD — and now Tonkin+Taylor — have duplicated the Frasertown monitoring regime: measuring the aluminium levels in streamwater.
  • The Frasertown resource consent was issued under New Zealand regulatory framework and subject to the provisions of the New Zealand Resource Management Act. For example, resource consents are issued for a fixed period/subject to review and renewal.
  • The Frasertown discharge to water resource consent is location-specific. It is issued specific to a consideration of climatic conditions, temperature, river flows, biodiversity, etc.

Replicating the Frasertown aluminium monitoring regime is not sufficient precaution against long-term impact. The Frasertown monitoring regime was not established to research the impacts of stream discharge on biodiversity. To do so would require the collection of baseline data and sustained biophysical monitoring of changes to aquatic habitats, flora or fauna.

Additional steps must be taken to safeguard Rarotonga’s freshwater ecosystems, foremost being investigation and implementation of alternatives to stream discharge.


4. The Te Mato Vai Project Aquatic Ecology Baseline Report (GHD Nov 2020)

The Te Mato Vai Project Aquatic Ecology Baseline Report summarises the risk of stream discharge as: low and acceptable.

However this must be countered by the caution that there is minimal published research on Rarotonga’s stream communities; and that the long-term ecological impacts of stream discharge have not been researched.

Risk of ecological impact resulting from supernatant discharge (low-high)
reuse (low risk) -> ground discharge (med. risk) -> stream discharge (high risk)

Of the seven environmental incidents reported to TVOM [concerning the construction of the Te Mato Vai system], five coincided with the intentional or accidental discharge of commissioning residuals to the stream.

As noted in the applicable technical standard:

….[residual] water shall be drained and flushed away to a suitable outlet where no harm will result from the flow or its contents.
-Infrastructure Cook Islands Technical Standards for Water Supply in Partnership with the Institution of Professional Engineers Cook Islands, 30 May 2014

It is not only residual (chemical or physical) contents, but also the force and frequency of flow that risks harm.


5. Supernatant discharge affects stream chemistry, biology, and sediment.

To date, monitoring has been of chemistry values against regulatory trigger and guideline values: the levels of aluminium in streamwater above and below the discharge point. Samples were not collected at the settling tank mid-level drain, or the surface of the sludge ponds where chemical concentration will be highest.

Streamhealth will be impacted by changes in stream sediment: composition and distribution.

  • Biodiversity avoidance behaviours due to disruption of ecological flows may impact species distribution, migration, population size, and reproduction. Koura (freshwater prawns) are a keystone species. They eat invertebrates such as insects and worms, breakdown leaf litter, and cycle nutrients. The health of koura populations affects the health of our streams.
  • Periodic / irregular discharge can possibly disrupt stable ecosystems more than a continuous low-level discharge. (Umgeni Water 2017)
  • An increase in sediment can result in benthic smothering. Fine particles can reduce the light to streambed plant communities. (Umgeni Water 2017)
  • Aluminium has been found to bioaccumulate in the tissue of freshwater species including koura and common bully (fish). Short-term observation proposes the effect to be non-toxic, but chronic (long-term) impacts are unknown/un-researched. (Tempero 2015)

Postnote: In July 2021 a further technical report was released characterising the PACl sludge (appended to an EIA for a PACl sludge disposal site). In addition to the anticipated increase in aluminium and chloride, the laboratory analysis indentified elevated levels of total suphur - as compared to five soil samples. Sulphur can reduce pH (increase acidity), which has implications on eco-toxicity of chemical contaminants.


6. Further research is required.

To identify and evaluate the feasibility of:

  1. Changes that can be made to operational process - using the current treatment method - to prevent the need for stream discharge.
    For example, draining and clearing the settling tank over an extended period of time. This would allow supernatant removed from the settling tank to drain to ground (through the pond) before operators proceed to clear sludge. More frequent removal of of sludge for offsite disposal will also improve storage pond drainage.
  2. Modification to the Te Mato Vai infrastructure to optimise pond function.
    One such option is to enhance operation by converting the storage ponds to cyclic vegetated treatment wetlands. This will improve drainage, increase water processing, and contain contaminants. This modification would be of benefit even when operational process is changed.
    See appended concept note: Te Mato Vai Cyclic Wetland.

7. The EIA report does not sufficiently detail operational activities.

  1. How often will residuals be discharged to the stream?
    From the settling tank and from each type of pond.
  2. What is the anticipated volume of residual that will be discharged?
    The volume firstly drained to the sludge pond, and then decanted from-pond-to-stream.
    This information is necessary for evaluating the permit application; and also to determine the feasibility of alternative residual disposal methods.

Information on operational activities was requested from the Te Mato Vai Project Management Unit/GHD, but not provided prior to the filing of this submission.


8. Stream discharge is culturally-inappropriate.

In public meetings, by way of two public petitions, and through policies and legislation, the people of the Cook Islands have committed to acting as custodians of the island environment.

Rarotonga’s freshwater streams are used as a food basket, as a source for preparing natural medicines, provide materials for handcrafts, and provide family recreation. The streams sustain wetland areas and flow into the lagoon. Disruption of ecology at the level of the discharge points has the potential to impact on downstream use and enjoyment of this shared natural environment.

As noted by National Environment Service compliance manager Vavia Tangatataia:

Over and above the biophysical impacts, there is a concern around putting contaminants into water - fullstop.

It is irresponsible to rely on reassurances from offshore consultants, derived largely from desktop analysis when operation risks the majority of Rarotonga’s freshwater ecosystems; along with the cultural practices bound to these environments. More appropriate is to modify the treatment system to avoid action that is culturally inappropriate.


Due to the statutory constraints, the uncertainty regarding the long-term impacts on freshwater ecology, that alternative disposal methods have not been adequately investigated, and out of respect for cultural values, the Rarotonga Environment Authority should refuse to allow the stream discharge of residuals.


Evaluation of alternatives

The Te Mato Vai treatment system is anticipated to serve the island for the next 100 years. Alternative treatment methods must be sufficiently detailed to allow meaningful comparison.

Inherent to the EIA process is to consider likely/potential impacts before an activity takes place (T+T Jan 2020).

With the Te Mato Vai Project, evaluation of the treatment method comes after the system has already been constructed, and after nine months of [trial] operation. This may have compromised the investigation of alternative methods and processes.

Beyond direct comparison of coagulant chemicals in terms of raw water quality, relative expense, and relative waste volumes, the method of assessment lacks integrity, as determinants include:

  • whether the required infrastructure has already been constructed;
  • (only) the direct replacement of PACl by the alternative coagulant or treatment method;
  • that there is no access to power (the Watson report identifies alternative self-contained power sources);
  • minimal consideration of alternative residual disposal methods;
  • misleading conflation of coagulation with disinfection.

Direct replacement

Diversion systems could supplement (rather than replace) existing treatment steps to optimise the manual-and-fixed PACl dosing system.

The decrease in sludge production will increase the time between cleaning cycles and increase the likelihood that sludge ponds will dry naturally, meaning that that stream discharge will not be required (from the ponds).

PACl + Diversion

It is necessary to evaluate the benefit of optimising treatment with diversion systems.

  • The T+T EIA suggests that diversion systems could achieve comparable improvements in turbidity (without PACl); if the existing physical filtration steps are supplemented by physical pre-filtration (in the intake weir) and/or ‘fine’ filtration (post AVG). These options should be considered in more detail.
  • The lack of a permanent power supply is not a deterrent to implementing diversion.
    Watson detailed solar and battery-power monitoring and control. Battery-powered systems have already been installed to power the proposed chlorine disinfectant dosing equipment.
  • Full-cost analysis would factor in the savings due to reduced chemical supply and waste management. Along with minimising risk and waste, diversion systems will reduce the ongoing cost of operation.

Turbidity data from the PACl-trial suggests that diversion will have minimal impact on water collection (abstraction) rates.

Of the 1763 raw [untreated] streamwater samples collected Sept 2020-May 2021:

  • 49% meet UV-treatment turbidity standard (under 1.0NTU); and
  • 93% met the World Health Organisation turbidity standard for lower resource settings/small supplies (under 5.0NTU)
TurdibityNo. of samples
Under 1 NTU868
Between 1 and 2 NTU507
Between 2 and under 5 NTU263
5 or over NTU125

Source: GHD June 2021 (pers. comm.)

In calculating sludge volumes, Watson factored in a plant utilisation of 60% as water demand is not contant over a 24-hour period.

Overnight, water demand drops and treatment stops once the storage tanks are full. Rain events that occur during periods of already low demand will have less impact on the overall abstraction rate.

A further argument against diversion is that it would compromise supply — by not collecting all available water during periods of high rainfall.

Broadly speaking:

  • water demand falls in wet weather (less agricultural use, fewer loads of washing);
  • directly after rain, the increase in groundwater flows will rapidly recharge stored supply; and
  • household and commercial water storage tanks are recharged by rainfall, which reduces network demand.

Treatment volumes are already constrained: by sand filter throughput rates and the size of the large storage/pressure header tanks. More water flowing down the stream does not translate to more water in the tanks.

When the trunk mains from Avana and Turangi (the two major catchments) were severed in Aug 2020, the To Tatou Vai operations manager was confident that supply could be sustained by the other intakes for up to a week. Island-wide rainfall is rare, as each valley has its own microclimate. Turbidity levels peak when rain follows a period of dry weather, but then stabilises once the ‘first flush’ of surface run-off has been washed down stream. Streams clear again within three hours of rainfall.

Rather than speculation, sustained data can be used verify the feasibility of diversion to achieve required turbidity standards and meet required abstraction rates.

PACl is not a disinfectant

In isolation, PACl is not an effective or reliable method of achieving drinking-water microbial standards.

…although correlations [between turbidity and microbial content] may exist in individual drinking-water supplies, a uniform relationship has not been established.”
-World Health Organisation 2017

A reduction in turbidity is not certainty of a reduction in microbial content.

The purpose of the PACl, as a coagulant — when combined with the other treatment steps — is to improve water clarity. At best, polyaluminum chloride is a ‘chemical-filter’: as any reduction in microbial content is through the settling-out of particles.

Due to the numerous allusions in the EIA report (taking a lead from GHD’s trial summary), it is necessary to state that PACl is not a disinfectant: the chemical is not used to kill or deactivate microorganisms.

The subject of disinfection is also expressly excluded from the On-site Disposal EIA; which ‘does not consider impacts arising from disinfection of water by chlorination or other means.’ It is incongruous to make this declaration and then include in the report misleading statements that do not relate to the operational function of the PACl.

Postscript: Consulting firms GHD and T+T refer to the incidental improvement reduction in microbial levels to argue the merits of PACl. A subsequent independent cross-examination of the PACl trial report (Watson Sept 2021), highlights the failure of Te Mato Vai system to reliably achieve the target clarity (turbidity) standard in high-flow conditions. While PACl may be an effective coagulation chemical, the overall system design is flawed, and requires modification.


Appendix A: To Tatou Vai Response to Submissions to the EIA Report on Water Treatment Plants On-site Discharges

August 2021, in reply the water authority refuted the concerns raised by TVOM with the following broad points:

  1. That coagulation is part of standard water treatment processes;
  2. That ‘Only a coagulation process can make surface water consistently suitable for further treatment…’. That tanins, colour, fulvic and hulmic acids can linger for weeks; and that these can impact on the effectiveness of UV treatment.
  3. ’Coagulation is an important part of the overall treatment process, contributing to the ability to remove microbial contamination.’
  4. Generalised meterological observations; data on the storage capacity of the new holding tanks, and hydraulic head (system pressure) — as reason not to implement diversion.

The water authority further disputed GHD’s advice that stream discharge is non-standard; and argued against lobbying, policy, legislation, and public petitions providing evidence of cultural values to be considered as part of the the design and operation of the water treatment system.


To Tatou Vai Response to the EIA Report on Water Treatment Plants On-site Discharges


Appendix B: Supplementary technical data

Later 2021, additional technical documentation critical to understanding To Tatou Vai’s application was released.

These documents provide a chemical analysis of the PACl sludge (suggesting that streamwater analysis should also track levels of total sulphur); and a cross-examination of the PACl trial report.


Appendix C: Presentation to the REA

25 November 2021, the Rarotonga Environment Authority met to discuss permit applications, including the On-site Discharges EIA. TVOM requested an opportunity to present concerns and proposed alternatives.

The linked presentation (Facebook) was prepared and representative onsite, but not called upon by the REA to present.

A separate digest details a bio-engineering method of mitigating the environmental impact of operating the water treatment system.


Classification/subjects: Te Mato Vai Project, development project governance, water resource management, Rarotonga, Cook Islands, South Pacific, environmental impact assessment, EIA, Environmental Social Safeguards Framework, drinking water residuals, polyaluminum chloride, PACl, aluminium, freshwater management, water policy.


References and Further Reading

See also

PACl on Trial, PACl Trial Data, Rarotonga’s sludge crisis, Te Vai Ora Maori - Facebook Page.


Online References

References ordered by publication date.


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Updated: 10 Dec 2021.


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