Chemically Treated Drinking-Water: Environmental Impacts, Rarotonga, Cook Islands.
Compiled by: Andy Kirkwood, Justine Flanagan, 2019.
Contact: [firstName] @ islandbooth.com.
This is a working draft. Updated 8 Dec 2020
The Te Mato Vai Project to update Rarotonga’s intakes and water main includes implementation of a 4-stage treatment process. Chemicals have been proposed for Stage 2: Coagulation/Flocculation to remove fine particles; and Stage 4: Water Disinfection to kill or inactivate micro-organisms.
Polyaluminum chloride (PACl) has been proposed to improve water clarity (turbidity). When added to the source water, the chemical causes smaller particles to clump together; these clumps then fall to the bottom of a settlement tank or are removed by subsequent filtration methods.
Disinfection requires that water is clear. Particles in clouded water can prevent the disinfection from deactivating potentially harmful micro-organisms. Clear water improves the effectiveness of disinfection: whether the disinfection method is chemical (e.g. chlorine solution); or physical (e.g. UV irradiation).
Adding a coagulation chemical is one method of treating water to improve clarity. There are alternative physical (non-chemical) treatment methods that can also be used to improve clarity, such as not collecting water in high-turbidity conditions (diversion); centrifugal separation; passing water over a electrical plate; or use of fine filtration.
Although the Cook Islands Government has continued to issue the statment that ‘No decision has been made on disinfection’; chlorine solution storage and dosing equipment was ordered in 2018 and installed by contractors at each of the ten intakes from early 2019; prior to the community presentation and discussion of disinfection options in May 2019.
The chlorination chemical preferred by government is calcium hypochlorite.
The Cook Islands National Water Policy (2016)“[brings] together government policies for water resources management, infrastructure, water supply, drinking-water safety planning and sanitation.”
This document makes a number of references to water management and environmental considerations that apply to the Te Mato Vai Project and the operations of the new water authority To Tatou Vai.
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.
Cook Islands National Water Policy (2016)
Groundworks and construction in areas of specific concern are subject to regulation in the Cook Islands under the Cook Islands Environment Act 2003; areas of concern include sloping lands and sites in close proximity to waterways/streams. The new Te Mato Vai water treatment plants are located in such areas.
Before construction can commence, the applicant may be required to complete a report detailing possible environmental impacts of the project and the measures and monitoring that will be taken to minimise such impacts. The resulting Environment Impact Assessment (EIA) report must be made available for public consultation to allow for formal community and stakeholder response.
An EIA for the Te Mato Vai Stage 2 construction was produced in August 2015. The only mentions of chemical use are indirect, and relate to the operation of the system (not the construction of the system).
3.1.2 Water Treatment Upgrade (schematic), Te Mato Vai Detailed Design for Stage 2, Draft Environmental Impact Assessment Report. GHD, August 2015
Accompanying caption: Figure 3 - Indicative flow diagram to illustrate how the proposed gravity operated water supply and treated system works.
With the project now nearing completion, it can now be seen that ommitting detail from the EIA report has prevented the public from raising concerns about the treatment method (prior to the commencement of the construction project), and is a likely violation of the intended consultation and approval process.
The construction EIA report stressed that the constractors should take steps to prevent the accidental discharge of wastes: excess soil, vegetation, sanitary waste, and machinery fluids. The report also proposed conditions for activities that had the potential for (unintended) impact on the stream.
Contractors are expected to prepare an Erosion and Sediment Control Plan as part of the [Construction Management Plan] for approval by NES [to] assist in minimizing the anticipated effects of these activities. Activities that have the potential to impact on stream conditions must avoided during the full moon days (three days before and after the full moon), the spawning times for koura or Macrobrachium.
-Te Mato Vai Stage 2 Construction EIA Report. GHD, 2015.
An Expert Review, commissioned by the Cook Islands Ministry of Justice, confirms that the Stage 2 Permit, does not cover the operational use of chemicals. The proposed PACl trial is the operational use of chemicals.
There will be an aluminium residual in the supernatant discharged from the ponds to the streams. The EIA for TMV Stage 2 was prepared in the very early stages of design (2014) and, although a schematic of the treatment process mentions that “Flocculating agent may be injected (if required) to aid removal of finer particles”, the assessment ignores the potential impacts of using flocculant chemicals on the environment. The Mott MacDonald Detailed Design Report does not cover any environmental impacts.…
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.
Other non-aluminium coagulants could be considered as this would eliminate the risks from aluminium to the freshwater ecology.…
-Te Mato Vai - Stage 2 - Expert Independent Review. Ministry of Justice. March 2020.
Concerns have been raised as to the pipes and construction of the distribution system with estimates of 17km of the new water main requiring replacement (Cook Islands News, Dec 2018). These concerns were confirmed in Oct 2019 with a contracting company taking up a tender to repair the faulty sections of the main. The repair works have been referred to euphemistically by government as a Stage 1 Upgrade; Remedial, or Resilience works.
Above: Pipes leaking into the Turangi stream, approx 100m from the water treatment plant. June 6 2019.
Network failure will result in chemically-treated water contaminating waterways as pipework often follows the stream route out of the valleys.
Freshwater aquatic life is highly sensitive to chemicals, with acute toxicity to chlorine at very low dosage.
Active chlorine is toxic to fish from levels as low as 4 parts chlorine to 100,000,000 parts water. In periods of low waterflow/drought, leakage from the water main may be the only water in the streambed (below the intake point).
Active chlorine is very toxic to fish. Its toxicity largely depends on water temperature: for example, an active chlorine concentration of 3.5 mg per litre has a sublethal effect on carp at a water temperature of 3–7°C but when exposed to the same concentration at a temperature of 15–20°C they die in 1 to 2 hours. In general, a prolonged exposure to active chlorine concentrations of 0.04 to 0.2 mg per litre is considered to be toxic to the majority of fish species.
(PDF) Water Quality and Fish Health, United Nations FA0 (1997)
The WHO standard for residual chlorine disinfection is 0.2-5 mg/L. At this level water ‘from the tap’ will be toxic to the majority of fish species. Leakage nearer the intakes will be more toxic due to the higher levels of active chlorine.
WHO recommends that the concentration of active chlorine in water entering the network to be at least 0.5mg/L and no greater than 5mg/L. (The concentration of chlorine in pool water is 2-4ppm).
Prior to the new Te Mato Vai system being made ‘live’ the network pipes and plant (including storage tanks) are required to be disinfected, using a ‘shock’- or super-chlorinated solution. This is to remove any construction waste and disinfect surfaces that might pose a health-hazard to the public.
When instructed to do so by the Engineer, the Contractor shall disinfect the pipeline by chlorination either in sections or as a whole. The Contractor shall provide a suitable chlorine dose pump and chlorine which is capable of accurately injecting the required concentration of chlorine solution at steady rate into the pipeline.
The Contractor shall introduce at least 20ppm of chlorine or such greater quantity of chlorine as will produce a residual of at least 1ppm of free chlorine at any point along the pipeline being sterilised 2 hours after the section of pipeline has been filled with water.
If after 24 hours, the residual chlorine is 1ppm or greater, then disinfection shall be deemed to be complete and the chlorinated water shall be drained and flushed away to a suitable outlet where no harm will result from the flow or its contents. Dispose of disinfected wastewater to meet relevant Regulation and ICI Requirements.…
-Infrastructure Cook Islands Technical Standards for Water Supply in Partnership with the Institution of Professional Engineers Cook Islands, 30 May 2014
Specific chlorine dosage values from standard-to-standard, but in New Zealand can reach starting levels of up to 100mg/L (prior to neutralisation). Even when reduced to the recommended disposal dosage of 1ppm, this is still 25 × the level at which the chemical is toxic to freshwater aquatic life.
Along with the connecting pipework, commissioning includes the sterilisation of the new 1.8–2.3 million litre water storage tanks (some intakes have two such tanks). Given the remote inland locations (lacking a suitable outlet for disposal); logistics of removing the wastewater, sterilisation water will be discharged either into the ground or into the intake valley streams.
The coagulant chemical polyaluminum chloride (PACl) is proposed to remove sediment and fine particles from source water.
Aluminium in the aquatic environment can have a major impact on aquatic life. Acid precipitation [acid rain] has been implicated in the loss of fish populations from acid sensitive waters through the mobilisation of aluminium… The short-term changes in aluminium concentrations caused by these events can have severe effects on aquatic biota.
Canadian Water Quality Guidelines for the Protection of Aquatic Life: Aluminium. Candian Council of Ministers for the Environment, 2003 (Withdrawn).
In the Cook Islands, infrastructure projecs in areas of specific (environmental) concern are required to complete an environmental impact assessment process. This includes public consultation processes. Despite initially claiming that the necessary regulatory processes had been completed, in January 2020 a release was issued through the Te Mato Vai Facebook Page (later attributed to the new water authority - To Tatou Vai), that a stream survey was to be undertaken as part of an EIA into the operational use of PACl. The stream survey was conducted over a 1-2 week period in January 2020 by government consultants GHD (pers. comm. To Tatou Vai).
Although better-late-than-never, a two-week spot sample may be insufficient given that operation of the new system proposes to decant dissolved aluminium wastewater into the freshwater streams (also noting the companion risk of unintended overflow of the sludge storage ponds).
Conditions of pH, total hardness and dissolved organic carbon (DOC) may vary within a waterbody throughout the year, thereby affecting the bioavailability of aluminum over time. To ensure the criteria will be protective during the times when aluminum is most bioavailable (and most toxic), the EPA recommends that the state or authorized tribe collect, if possible, 24 months of monthly sampling data for the three input parameters. This approach will help to account for both intra- and inter-annual variability of the input parameters.
Implementing the 2018 Recommended Aquatic Life Water Quality Criteria for Aluminum. United States Environmental Protection Agency (EPA).
Dissolved aluminium bonds with phosphorous and can be used to remove excess amount of this nutrient from freshwater systems, chiefly lakes that are negative affected by excess fertiliser run-off.
The practise of dosing with alum (aluminiuim sulphate), has led to renewed interest in the long-term impacts of aluminium on freshwater ecosystems.
Aluminium is a common element in the Earth’s crust and under neutral pH conditions forms a white, non-toxic solid susbstance. However, under acidic (low) or basic (high) pH, aluminium dissolves and becomes toxic to aquatic animals. Fish are the most susceptible group to aluminiuim toxicity effects, with first clogging of the gills and then disruption of their ability to regulate water content in the body occuring as pH decreases.
-Ecotoxicological Review of Alum Applications to the Rotorua Lakes
When determining a dosage for freshwater lakes, consideration must be given to the ability of the water body to resist/offset any change to pH, the ‘buffering’ capability.
In addition, eutrophic systems often experience photosynthetic driven alkaline pH shifts, resulting in Al solubilisation and the formation of the toxic Al species Al(OH)4-.
A eutrophic system is one where excessive plant growth occurs due to increased availablity of sunlight, carbon dioxide or nutrient fertilisers. High levels of nutrient have previously been recorded in Rarotonga where streams discharge to the lagoon, and algal bloom has been observed both in the streams and lagoon.
A difference between streams and lakes regarding toxicity, is that the settling of aluminium floc to the lake floor can isolate it from transitory changes in pH. In Rarotonga, where streams can run-dry, the periodic heavy rainfall can remobilise silt, and would likewise resurface any aluminium floc that might form in the streambed when aluminium wastewater is discharged from the water treatment facilities.
Current research suggests that the risks of AI bioaccumulation are relatively low. … Increased tissue concentrations of AI have been reported in koura (Paranephrops plonifrons) and common bully (Gobiomorphus cotidianus) in the Utuhina Stream but no toxicological effects have been observed. …It should be noted that chronic effects of AI exposure are not as well studied and a cautious approach is recommended.
Sediment Accumulation of Aluminium Deposition and Potential Release
There is a notable absence in the published literature of the long-term fate and effects of anthropogenic AI in sediments. Despite alum first being used for lake restoration in Europe from 1968 (lake Umgsjon) … no applied or theoretical research has been published examining the effects of high AI deposition over sustained time periods (i.e. >10 years). This includes both the ultimate fate of aluminium in sediments and effects on biota.
Also see: PACl on Trial.
Without surveying the valley streams and waterways prior to chemical use it will be difficult to track or attribute impacts.
Bodies of freshwater in the Cook Islands are extremely limited, with no large lakes or rivers, only wetlands, streams and a few small freshwater lakes present. Freshwater biodiversity is therefore extremely limited. The Cook Islands National Biodiversity Strategy and Action Plan (NBSAP) lists only nine native and four introduced fish species, two native and three introduced gastropods, and six native and one introduced crustacean.
Cook Islands 4th National Report to the Convention on Biological Diversity (2011), National Environment Service.
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.
Potential impacts on plants and insect life should also be further researched.
As a regional and regulatory reference-point, the New Zealand policy statement on the management of freshwater ecosystems may help to identify impact areas requiring monitoring:
In a healthy freshwater ecosystem ecological processes are maintained, there is a range and diversity of indigenous flora and fauna, and there is resilience to change.
Matters to take into account for a healthy freshwater ecosystem include the management of adverse effects on flora and fauna of contaminants, changes in freshwater chemistry, excessive nutrients, algal blooms, high sediment levels, high temperatures, low oxygen, invasive species, and changes in flow regime. Other matters to take into account include the essential habitat needs of flora and fauna and the connections between water bodies.
New Zealand: National Policy Statement for Freshwater Management 2014 (amended 2017)
Impacts of water treatment chemicals on the lagoon, reef and ocean require research specific to Rarotonga. International research indicates linkages between freshwater quality, chemical pollution, and reef health.
“Citing climate change as the exclusive cause of coral reef demise worldwide misses the critical point that water quality plays a role, too. While there is little that communities living near coral reefs can do to stop global warming, there is a lot they can do to reduce nitrogen runoff… the fight to preserve coral reefs requires local, not just global, action.”
15 July 2019: Thirty years of unique data reveal what’s really killing coral reefs. Science Daily. Accessed 29 July 2019.
Consideration of liability for environmental damage involves analysis of whether the Government has a “power of control” over the work of contractors such that the Government is vicariously liable:
The test [to prove vicarious liability] involves:
- a right to direct the subcontractor in circumstances where the right is capable of exercise and is, or is likely to be effective; and
- actual control of a course of action taken by the independent subcontractor; ie, control over the way in which the tasks are to be performed or how they are to be carried out.
Liability for Environmental Incidents – Are You in Control?. Andrew Petersen and Irene Wales, Findlaw Australia. Accessed 28 July 2019.
In other words, it is critical whether the Government controls how work is carried out by the consultancy or contracting firm.
The Cook Islands Government announced commissioning in a double-page spread appearing in the Cook Islands News, 30 November 2019.
The Cook Islands Government has instructed the Te Mato Vai Stage 2 contractor McConnell Dowell to begin commissioning the new intake water supply systems. Currently the public water supply is still connected to the old intake infrastructure.
Improved water will soon flow through new water supply system. Cook Islands Government Release in Cook Islands News, 30 Nov 2019.
If the wording seems awkward, it’s likely as result of the vicarious liability issue outlined above; to make clear that the contractor has been directly instructed by government to proceed (and is carrying out works to the specification of the national water supply standards). It is now the government that assumes all responsibility for environmental damage that might occur as a result of the shock-chlorination.
According to the To Tatou Vai Public Notice appearing in the same paper:
Matavera Intake Shut Down
The contractor is undertaking commissioning works for Matavera intake and may require a shut down on the following days
Monday 2 December, 8am to 1PM…
Community group Te Vai Ora Maori protested the commissioning the morning the work was scheduled to commence.
The following Wednesday a further notice was published; and the same week letters were delivered to Landowners to notify that the Takuvaine WTP was to be commissioned Fri 13 Dec.
Landowners visiting the plant on Monday 16 Dec saw operations staff in personal protection equipment dosing the settlement tank with chlorine solution.
The Landowners had previously been advised that chlorinated water was to be held in the settlement tank for 24 hours and then drained through the treatment plant network to the lower water storage tank, where it would remain for 3-6 weeks to allow the chlorine to disappate / be reduced to non-toxic levels. Instead it appears that chemical water was partially or entirely discharged into the Takuvaine stream.
Above: Takuvaine Stream Die-off / Shock-cholorination Commissioning Video. Filmed 17 Dec 2019.
Emptying the Settlement Tank (enlargement added) from ‘Information to support approval to commission Te Mato Vai Stage 2’.
GHD, Nov 2019.
The diagram suggests that operator inattention to the process of disinfecting the settlement tanks could result in chemically-treated water overflowing to the stream.
1. Raw water from the intake (stream) is piped to the Inlet Mixing Chamber.
2. (When operational) the PACl line feeds a solution of polyaluminum chloride into the Mixing Chamber.
3. When the Settling Tank is full; the Overflow returns water from the Mixing Chamber back to Stream (dosing of PACl will also stop when the tank is full).
Chemicals have been proposed for the ongoing treatment of Rarotonga’s water supply for the purpose of coagulation and disinfection.
Estimated value of coagulation and disinfection chemical contract: $350-500k / year.
See also: Chemicals and Pathogens.
All reports are PDFs.
Working Draft. Updated: 8 Dec 2020.