Te Mato Vai: PACl on Trial.
Compiled by: Andy Kirkwood, Justine Flanagan. Dec 2019.
Contact: [firstName] @ islandbooth.com.
This is a working draft. Published 12 Dec 2019. Updated 7 May 2020.
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 to coagulate and disinfect the public water supply.
The new Te Mato Vai system proposes a four step treatment process. Step 2 is (chemical) coagulation/flocculation.
[Coagulation] Removes small particles and protozoa
This is a slow mixing process. It uses a ‘coagulant’ called polyaluminium chloride (PACl) to make small bits of dirt etc. stick together and settle at the bottom of the [settlement] tank.
This step, together with filtration removes harmful protozoa (for example giardia).
-Improved water will soon flow through our new water supply system.
Cook Islands Government Release in Cook Islands News, 30 Nov 2019.
In 2014, Watercare New Zealand established a laboratory facility in Rarotonga to test raw/source water quality at the (then) 12 water intakes.
It is evident in the results that apparent and true colour increases during a rainfall event. A form of treatment to remove colour from the raw water would be required e.g. coagulation, or there needs to be the ability to divert any water that does not meet the required standard.
Cultural preference (as evidenced by technical reports, household surveys, public consultation, etc.) is for non-chemical water treatment methods. One treatment method identified by Watercare is to ‘divert any water that does not meet the required [clarity] standard’ — diversion does not require the use of coagulation chemicals.
Diversion is the option that the government of the Cook Islands people should be trialling to achieve clarity standards.
The three flow conditions that impact on water quality are described in the Watercare report as dry weather, wet weather, and after rain.
The purpose of water disinfection is to reduce the risk of illness due to the presence of pathogenic microorganisms in the water. An increase in the number of microorganisms in drinking water is often linked with high-turbidity events: wet weather/heavy rain when organic matter is washed into waterways.
Given the highly variable turbidity it is likely that there would be a significant risk of microbial pathogens present in the water supply. Upon request from GHD Ltd microbial tests were not undertaken by Watercare Laboratory Services Ltd. As a result an assessment of compliance with DWSNZ for microbial parameters (bacteria, viruses and protozoa) cannot be made…
Increased turbidity also impacts on the effectiveness of disinfection processes. This is true for chemical and physical disinfection methods (such as UV irraditation).
If UV disinfection was to be used, then at turbidity levels greater than 1 NTU, this process can be hindered through shielding of microorganisms by suspended particles. In order for disinfection treatments to be effective it would be necessary to undertake a form of solids removal such as coagulation to reduce turbidity to < 1 NTU.
UV is a non-chemical disinfection method. Installation of UV filtration systems into residential homes would ensure the safety of water ‘at the tap’; even as work continues on the replacement of the water main through the first half of 2020.
November 2019 a further report was prepared by the water engineers on the use of PACl.
All parameters including colour and turbidity are marginal as to whether the water needs to be dosed with coagulant for colour during dry weather conditions. However, due to the speed of change of flows (and resulting sediment loading) it is likely that to achieve a consistent output (without powered monitoring devices and control), coagulant will be required most (if not all) of the year. The decision to treat all of the water all of the time is to optimise water quality (the sedimentation tank will not be needed for consistent periods of dry weather and the AVG would be kept operational).
-GHD, Nov 2019
‘All parameters including colour and turbidity are marginal as to whether the water needs to be dosed with coagulant for colour during dry weather conditions… the sedimentation tank will not be needed for consistent periods of dry weather.’
-GHD, Nov 2019
As with the Watercare recommendation, GHD also note that in dry conditions coagulation chemicals are not required; the need for chemical treatment is ‘marginal’.
Although there is no mains power to the intakes, the proposed chlorine-disinfection dosing system is to be powered by rechargeable batteries. A similar strategy could be employed to power ‘monitoring devices and control’ — to stop streamwater collection when turbidity does not meet the required standard.
Along with the water in the new 1.8 and 2.2 million litre storage tanks, from the time that water-collection is stopped, the stored water in the settlement tanks and AVG sand filters is available as an alternative water source. The total stored supply provides an estimated 2-3 days of reserve water.
Engineer Ross Dillon who is overseeing training in the operation of the new Te Mato Vai systems advised that the stream water clears within 3 hours of rain at the intakes. This is the case even when the streams may still be clouded in coastal areas. Once streamwater turbidity returns to an acceptable level, collection at the intakes would automatically resume.
‘Jar’ testing of source/raw water samples can be used to assess the effectiveness of coagulation chemicals.
Q: Flocculators : Can you explain what a jar test is?
A: Jar testing is a pilot-scale test of the treatment chemicals used in a particular water plant. It simulates the coagulation/flocculation process and helps operators determine if they are using the right amount of treatment chemicals. The sample is stirred to observe the formation, development, and settlement of floc which forms when treatment chemicals react with material in the raw water and clump together.
-Flocculators. Stuart Equipment. Accessed 30 Jan 2020.
In 2014, jar tests were only carried-out at Avatiu intake; with the coagulant chemical ‘alum’ (aluminium sulfate). Jar testing of polyaluminum chloride (PACl) in wet weather conditions was recommended by Watercare but not completed at that time. Jar tests do not require PACl-dosing of the public water supply.
In order to further assess the optimum dosing range for the raw water intakes in Rarotonga it is recommended undertaking jar tests at the other intakes as well. It is also recommended that samples are taken under wet weather conditions in order to capture the ‘worst-case-scenario’ and understand to what extent coagulation will improve water quality under these conditions.
PACl jar tests have subsequently been conducted by contractors McConnell Dowell. In Nov 2019, Te Mato Vai Project Managers GHD, referring to these tests, suggested that PACl dosing would be far-lower than is required internationally.
91. Concentration of PACl dosing in the operation of the treatment plants is expected to be far lower than the equivalent water treatment plants internationally — Typical dosing rates for PACl are generally 14-24mg/L, however, the proposed dosing rate for Te Mato Vai sites are significantly lower at approximately 4-6mg/L. This reduces the likelihood that concentrations of Al will be in excess of 0.1mg/L, but does not eliminate it.
-GHD, Nov 2019
Rarotonga’s source water is considered by the water engineers to be of exceptional clarity/low turbidity. Also note that levels of dissolved aluminium (Al) in the finished water could be in excess of the regulatory maximum accepted value (MAV) for aluminium in drinking-water: < 0.1mg/L. This is due to low-turbidity water being more difficult to dose effectively; in clear water suspended particles are further apart. Unused polyaluminium chloride will continue through to the public water supply.
36. Due to the general design of the settling tanks, even relatively low levels of PACl dosing will produce ‘good’ results for a broad range of raw water turbidity conditions. This is due to the large volume of water held in the settling tanks, which create a large ‘buffering’ capacity within the tanks that can manage rapid and large change in turbidity with relatively low PACl dosing rates, without having to adjust the dosing rates to respond to a change in conditions.
The above proposes that PACl dosing is not critical to achieving ‘good’ water results; as stored water buffering will offset the (extreme) variability of flow conditions (see Watercare turbidity data, above).
There is no remote monitoring of conditions at the intakes. There is no direct communicaton, phoneline connection and cellphone coverage is not available to all intakes.
Once again the Ministry of Finance’s claim of a ‘state-of-the-art’ water treatment system, falls well short of the Mark.
13.4.3 Performance and Control …coagulation/flocculation is most reliable when raw water quality is consistent, when changes occur slowly, or when adequate automation is used to respond to changes in raw water quality.
…As raw water conditions change, optimal coagulation dose rates also change and careful control is required to prevent overdosing and underdosing.
13.7.4 Optimisation of the filtration process
Raw water that has high colour and low turbidity … can be very difficult to treat… These waters can result in elevated aluminium levels in the filtered water, and hence additional attention should be paid to monitoring filtered water aluminium.
-Guidelines for Drinking-water Quality Management for New Zealand (Updated June 2019). New Zealand Ministry of Health, 2019. (PDF) Chapter 13: Treatment processes, coagulation
Attending the Koutu Nui Vaka Puaikura water presentation in Oct 2019, water authority To Tatou Vai board member Brian Mason advised that trialling of PACl dosing was necessary to complete an Environmental Impact Assessment Process (EIA) which is required to permit development activities under the Environment Act 2003. However, proceeding with an island-wide 6-month live trial is a poor interpetation of the Precautionary Principle cited by Mason.
a live trial puts public health and stream environments directly at risk
A live trial puts public health and stream environments directly at risk. The purpose of an EIA is to protect against potential environmental degradation; it is irresponsible to ‘pollute-first-and-ask-questions-later’.
The Cook Islands National Water Policy (2016) provides further guidance regarding environmental protection.
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.
Cook Islands National Water Policy (2016)
An assessment will likely include evidence that — given the system employs standardised water engineering methods — the proposed treatment-method will ‘work’ to achieve a set water standard. However it is also necessary to evaluate the true cost of long-term chemical-use, such as fate of the wastes that are generated (water treatment residuals - WTRs). The operation of the new Te Mato Vai system proposes the discharge of WTRs into onsite storage ponds (lagoons), streams, and landfill.
There is now increasing concern on the impact to the aquatic environment (Helserman, 2009). The direct disposal of WTR to watercourses is now illegal (South Africa National Water Act No 36 of 1998)… Monitoring is required depending on the daily volume discharge, the specific municipal bylaws per region and type of permit granted whereby oil and grease and biotic index monitoring may also be required. Periodic discharges of accumulated sludge from settling tanks can possibly disrupt stable ecosystems more than a continuous low-level discharge.
Guidelines and Good Practices for Water Treatment Residues Handling, Disposal and Reuse in South Africa (2017)
The sustainability of the treatment method can be evaulated by considering the hierachy of potential waste disposal and management strategies, where preventing or minimising waste production is most favourable.
It is also necessary to consider the operation of the water treatment facilities and the proposal to store treatment residuals onsite.
The following describes a treatement system using alum, but the same applies to PACl ponds/lagoons.
Lagoons are generally operated in a cyclic sequence: fill, settle, decant. This cycle is repeated until the lagoon is full or if the decanted liquid can no longer meet [regulatory chemical] discharge limits. Solids settle to the bottom of the lagoon and liquid can be decanted from various points and levels in the lagoon after a period of hours or days. The solids are then removed for final disposal. The decanted water is often returned to the head of works. … The lagoon is filled over a long-time period (approximately a year) and then allowed to dry while another lagoon is filled. The solids never really dry unless the pond is eventually drained and the solids undergo evaporation. Contractors can also be hired to dredge the wet solids from the lagoon bottom and haul them away for dewatering and disposal. Liners made of high-density polyethylene (HDPE), leachate collection systems, and monitoring wells are common features of lagoon designs. …
A lagoon that is left to “revert to nature” will take a long time to dry out. After the supernatant, has been drained out or allowed to evaporate, the sludge at the surface forms a crust, giving the appearance that the lagoon is now filled with dry residue. The crust-covered lagoon can be compared with a frozen pond – the surface may or may not support the weight of a human or stock. Therefore, it is important to fence off the lagoon and to ensure that it remains fenced off. It may take many years before the waste dries out to the base of the lagoon. There will be a large amount of shrinkage during the drying out process.
Specific issues for Rarotonga include;
Less than 1% of Rarotonga’s water is required as drinking-water, while agricultural users represent 40% of demand.
A further environmental impact that has not been assessed (and which has been overlooked by the Cook Islands National Water Policy), is the impact of chemical residues in water that will be used for irrigation purposes.
Water that is made safe for drinking – by chemical means – may not be suitable for growing. Installing and powering filtration systems to remove residual chemicals from irrigation water may make growing commercial unviable or will result in costs being transferred to consumers.
Eleven recommendations were made by Watercare in 2014, including:
- Undertake a Sanitary Inspection of the Water Supply as part of a comprehensive Public Health Risk Management Plan in order to determine an appropriate treatment process to eliminate microbial risk.
- Undertake sampling and testing for microbial parameters in order to determine the public health risk associated with bacterial, viral and protozoan pathogens.
- Investigate appropriate disinfection treatment options to eliminate microbial risk e.g. chlorination, UV treatment.
- Undertake further jar tests using both PACl and alum at all 12 raw water intakes under wet weather conditions in order to establish the optimum dosing range to reduce turbidity.
- Consider undertaking selective abstraction and/or treatment if abstraction is to occur across all flow conditions.
- Investigate an appropriate form of treatment to reduce true colour.
- Sample the remaining five raw water intakes during wet weather conditions in order to establish a ‘worst-case-scenario’ of water quality at these intakes.…
Aside from the 2019 microbial tests of the old water supply system – the first of which was commissioned by a private company – it is not clear if the Cook Islands Government has actioned any of these recommendations. Specification and construction of the Te Mato Vai treatment system has progressed without first completing adequate investigation of the source water quality.
In December 2019 the Te Mato Vai Project Management Unit (PMU) provided reassurances to the pubic regarding the use of chemicals for water treatment.
As Te Mato Vai commissioning gets underway, we would like to highlight that the project holds all the necessary National Environment Service permits, and we have not, and will never be discharging chemically-treated water into our streams.
-Te Mato Vai (Facebook Page), Accessed 4 Dec 2019
Te Vai Ora Maori: Where does the supernatant [PACl wastewater] go?
PMU: All waste will be managed responsibly, in line with international best practise.
‘Without a permanent power supply at each site… the supernatant is proposed to be discharged to the adjacent streams.’
However the PMU’s reassurances are at odds with engineering reports by GHD detailing how the Te Mato Vai system will operate and the process of commissioning using shock-chlorination; which includes the discharge of chemically-treated water from the 1.8 and 2.2 million litre storage tanks either into the ground or streams.
Wastewater from the coagulation process – containing dissolved aluminium – will also be discharged.
Typical WTP Arrangements using PACl (outside of the Cook Islands)
63. Without a permanent power supply at each site, [pumping to the headworks] is not possible at the Te Mato Vai sites, and so the supernatant is proposed to be discharged to the adjacent streams.
-GHD. Nov 2019.
5 Monitoring and Management Practices (Environment)
62. In New Zealand and Australia, in most cases sludge supernatant (wastewater) is recycled back to the inlet of the water treatment plant…pumping the supernatant back up to the head of the works. Only the sludge becomes waste product as the supernatant is recycled…
…So, for discharges of PACl (or dissolved aluminum) to the environment (through Supernatant), there is no ‘standard’ practice. However, we have identified one example of where sludge pond supernatant is discharged back into the environment. This is at the Wairoa Water Treatment Plant (WTP) located in Frasertown…
Discharge of PACl wastewater/supernatant into the streams is not to an international standard; “there is no ‘standard’ practice’”.
The GHD report goes on to detail the 8-stage control conditions that have been set by the Hawkes Bay Regional Council in order for stream discharge to proceed at the Wairoa water treatment plant. These control conditions relate to comparing dissolved aluminium levels in the stream against regulatory values. The monitoring is not of environmental impacts that might have resulted from an increase in aluminium levels.
If WTR is discharged into a water body the solids can settle to the bottom of the water body potentially causing benthic smothering and the pollutants contained in the WTR can have negative impacts on the water body through re-suspension (USEPA, 2011). The increased turbidity of WTR can limit the growth of rooted aquatic vegetation by reducing the amount of light penetration available. The solids can also clog fish gills.
-Guidelines and Good Practices For Water Treatment Residues Handling, Disposal And Reuse in South Africa (2017)
Based on the raw water quality, engineers reports, and the upgrades to the physical filtration of source water at the intakes, the addition of turbidity monitoring and diversions systems will likely make the use of coagulation chemicals unnecessary.
Proceeding to live trial PACl which includes the discharge of wastes into an unbenchmarked environment, and without appropriate monitoring of the flow-through of chemicals into the publc water supply would be grossly-negligent. The Cook Islands Government should instead instruct the contractors to implement and trial turbidity monitoring and diversion controls.
Although not announced to the public until January 2020, the Te Mato Vai Project Management Unit has prepared an Environmental Impact Assessment Terms of Reference: Terms of Reference for PACL use EIA (Oct 2019) provides a structure and identifies the key considerations to be investigated by the appointed consultants.
The EIA report should use a level of analysis and detail that reflects the significance of the activity’s potential environmental impacts, and that allows the Cook Islands Government and interested stakeholders to clearly understand the activity’s likely environmental, social and cultural consequences.
To be included in the assessment are:
Responding to whether the trial will proceed before the TTV EIA (and before the public have an opportunity to respond):
To Tatou Vai (TTV) has commissioned the EIA. TTV is currently preparing the Environmental Impact Assessment (EIA) for the new water treatment system’s operational use of PACl. The public will have the opportunity to comment on the EIA during the consultation period. The PACl trials will provide information to inform Government and landowners’ views about longer term PACl use.
-Te Mato Vai PMU, 4 May 2020
Although the above response is openly-worded; it seems that the PMU intend to authorise the PACl trial without permit.
Feb 2020: Consulting firm Tonkin and Taylor have been appointed by To Tatou Vai to prepare the EIA submission. No ETA has been indicated for the EIA, however PACl-use trials were proposed to resume 6 Feb 2020.
February 2020 the Project Management Unit and GHD released further information regarding the 6 month PACl trial in response to questions posed by Te Vai Ora Maori.
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.
Have PACl trials started?
As at 5 February 2020, PACl trials have not yet started. We will give landowners at least 48 hours notice before beginning the trials.
Why are you trialling PACl at all 10 intakes?
1. Trialling PACl at all sites will enable us to capture information specific to each intake site;
2. Treatment, including PACl use, needs to be applied at a whole of network level to achieve its benefits — improved public water supply quality; and
3. We are able to manage and monitor the trials to mitigate any potential environmental impact.
9 Feb 2020: What happens when we commission Te Mato Vai? Te Mato Vai PMU.
Chemical coagulation is not the only method of achieving water quality standards. The WHO recommend for treatment to be based on source water quality. If the proposed chemical treatment is determined to be inappropriate or unnecessary, then a different method should be investigated.
Recording information from each site will no doubt be beneficial. Perhaps unique to Rarotonga is proposing to proceed with live operation — prior to confirming the appropriateness of a treatment method. However, collection of baseline/control source water quality data is accepted scientific method. Assessing the efficacy of the new three-stage physical filtration process; across all three flow conditions; will either confirm, or counter the stated need for chemical coagulation.
Data on the effectiveness of the physical filtration has been requested from To Tatou Vai in Dec 2019. Receipt of request has been provided, but no data at 7 May 2020.
Where ‘potential environmental impact’ is of concern, a trial should be limited and strictly controlled. The EIA requesting a permit to conduct such a trial would need to propose appropriate environmental monitoring — not just of changes in aluminium levels, but of impacts on biodiversity. The affected communities may also raise objection to being subject to the by-products of chemical experimentation.
Undertaking a concurrent, 6-month trial across 10 isolated sites when water flow conditions are highly–variable is a ‘novel’ (risk)-management strategy.
The GHD engineering description (above) introduces logistical complexity; when the disinfection wastewater is to be stored onsite until the chlorine levels have decayed; and water treated with PACl is to be tested by To Tatou Vai prior to release into the public water supply network.
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.
Working Draft. Updated: 7 May 2020.