Managed Aquifer Recharge Trial

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Donald Thomas
6 years ago
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1 Managed Aquifer Recharge Trial Why are we doing it? The water levels in the Makauri Aquifer are declining. The aquifer is a much needed source of water for irrigating crops - it s an estimated $20m value to our industry. If we have to reduce or stop irrigators taking water from the aquifer it will have a significant impact on local economy. The aim of the trial is to see if it s possible to use Managed Aquifer Recharge (MAR) technology to increase the water levels in the aquifer. The trial is funded by grants from Ministry for Primary Industries and the Eastland Community Trust. Much of the total cost is the initial extensive water modelling and research with expert consultants. A detailed business case would be completed for ongoing costs if the trial was successful. The trial will also provide Council with other useful information about how the groundwater interacts and provides baseflow to the rivers during dry summers, and to inform water use and quality questions for our region. How the trial would work? We re proposing to use an injection well method, which takes surplus water from another source and injects the water into the aquifer through a bore. Based on international best practice, the managed recharge would follow a Go, No Go approach. It means the trial can be stopped at any time during the process. The trial would test injecting a higher quality water into the aquifer, in small amounts at a time and monitoring any chemical and hydraulic effects in surrounding monitoring bores. The water injected would remain in a bubble around the injection bore, but the hydraulic effect should push the water level up in other areas. We can pump the water out if we find there are any negative effects. Page 1

2 Options for injection water 1. Treated water from Waingake Using drinking-water standard quality water from the treatment plant at Waingake. Residual chlorine could be removed with sunlight if needed. Council-owned infrastructure in place to pipe water to the trial location at Council s Bushmere Road Treatment Plant. There may not be enough of a surplus in winter to supply the trial, or a full programme if required. 2. Treated water from Waipaoa Using drinking-water standard quality water from the treatment plant at Bushmere Road. The infrastructure is council-owned, but operation of the treatment plant is costly. Residual chlorine could be removed with sunlight if needed. Council-owned land and infrastructure would be used at the Bushmere Treatment Plant. The river has a sufficient flow of water for the trial. 3. Filtered water through the Kaiaponi Farm system - our preferred option A private irrigation system that owners are offering to use for the trial. The system uses an infiltration gallery to remove sand, silt and bacteria from Waipaoa River water for irrigation. A cyclone filter and series of filter banks removes more solids. Sediment testing shows very low levels of sediment in the water after filtration. Additional filters could be used to remove more solids. Chlorine could be used to treat the water for bacteria and residue removed with sunlight if needed. Managed Aquifer Recharge NATURAL RECHARGE From rain and river takes years to reach aquifer SURPLUS STORED WATER SURPLUS RIVER WATER WATER TAKES From bores INJECTION WELL RECHARGE AQUIFER = GRAVEL, SAND AND WATER Page 2 Want to PO know Box 747, more? Gisborne Read 4040 our FAQs and check 0800 out 653 the 800 scientific service@gdc.govt.nz reports and information on our website.

Cost Differences Mangapoike / Bushmere $26k - $38k Kaiaponi $15k - $86k Capital costs of drilling and installation of wells and equipment are the same for all options.

3 Cost Differences Mangapoike / Bushmere $26k - $38k Kaiaponi $15k - $86k Capital costs of drilling and installation of wells and equipment are the same for all options. While there are moderate pipeline connection costs for the Mangapoike and Bushmere options, there are lower connection costs using Kaiaponi Farms system. The range of costs for Kaiaponi is dependent on if new infrastructure is required to provide additional treatment of the water. Operationally, the cost of treated water from the Bushmere plant is high, whereas there is little more than normal operating costs of Kaiaponi Farms irrigation system. Trial management, field oversight, data assessment and documentation costs are effectively the same for each option. Consultation Since the beginning of the project we ve been engaging with iwi, irrigators and affected stakeholders in the Makauri Aquifer catchment. An early cultural impact was conducted, and representatives from both Rongowhakaata and Te Aitanga a Mahaki are actively involved in the project stakeholder advisory group. Local growers, industry representatives and hydrology experts also represented on the advisory group. We re in regular contact with bore owners. A public forum was held last year and we re continuing to engage people in council and community meetings, as well as promotion and information on our website and local media. A final recommendation on how we would carry out the trial was presented to Council in April We ll lodge the three resource consents needed for the trial with Bay of Plenty Regional Council. The BOP Regional Council will determine the dates of a formal consultation period which is likely to be 30 days, followed by a formal hearings process with commissioners or referral to the Environment Court. Time frames 17 May 2016 Consent applications lodged with Bay of Plenty Regional Council (BOPRC). 19 May 2016 Report to Council to appoint hearings process and commissioners as required. June - July 2016 Notification of consents for submissions. Public consultation and information. October - November 2016 Hearings and decisions. If further consultation is required decision may be delayed. Based on submissions, Council would assess whether to pursue consents further. November February 2017 If consents are approved and Council still wants to proceed, bores constructed and pump tested. May 2017 Full injection trial begins. Page 3 Go to

Cultural value Water from the Waipaoa River is the natural recharge source for the Makauri Aquifer. Retaining the mauri and cultural values of both waterbodies is important.

4 Cultural value Water from the Waipaoa River is the natural recharge source for the Makauri Aquifer. Retaining the mauri and cultural values of both waterbodies is important. Chemical reaction Experts confirmed a very low risk of geochemical reaction. The issues Effect on water quality The aquifer already has a very poor water quality, it s not suitable for many purposes - like drinking water - because it has a high iron content. Injection water in the trial will be a higher quality water than in the aquifer. If a full MAR programme went ahead, over time the aquifer s water quality may improve. Clogging up bores Filter banks are in place at Kaiaponi Farms. Suspended solids concentrations are close to or below the detection limit of the analysis (1g/m3). Expert advice says we shouldn t need any further filtering for solids, but we can add an additional filter system if needed to meet consent conditions. During the trial, sedminent will be monitored and the injection can be stopped until levels in the river water decrease. Effects on ecology The ecosystem within the aquifer has nearly no oxygen so there is little life existing within it. Taking water from the Waipaoa River would have a very little effect on the ecology in the river as the flow and level of water in the river is still a lot more than the minimum flow needed for aquatic life to survive. Particularly in winter, the river has a large amount of water flowing out into the sea (mean flow is 30,000 litres per second the amount needed for the trial is miniscule litres per second). Adverse reactions can only occur when the right levels of chlorine are mixed with other elements found in groundwater in the right quantities and environment. These circumstances are very unlikely. If we use water treated with chlorine, we can remove residual chlorine before its injected if needed. Bacteria Testing of the Waipaoa River water after filtering through the Kaiaponi Farms system show low levels of E.coli at 1-5 cfu/100ml. Any bacteria entering the aquifer will be contained in the area (bubble) near the injection point. E.coli don t survive long in reduced geothermic environments (underground). The aquifer s water is used for irrigation not drinking water and the river water is still a higher quality than what is currently in the aquifer. We can treat the water with chlorine to disinfect it and then remove residual chlorine if needed to meet consent conditions. During the trial, bacteria levels will be monitored and tracked. Got questions? We want to know what questions or concerns you have about the project. your questions to: Mark.Joblin@gdc.govt.nz or call us on Page 4

Frequently asked questions What is the Makauri Aquifer? The Makauri Aquifer is the largest aquifer underneath the Poverty Bay Flats extending from Kaiteratahi down to Makaraka.

5 Frequently asked questions What is the Makauri Aquifer? The Makauri Aquifer is the largest aquifer underneath the Poverty Bay Flats extending from Kaiteratahi down to Makaraka. It spans both sides of the Waipaoa River but most of the aquifer is on the eastern side. The aquifer slopes from Kaiteratahi where it is relatively shallow (about 20m deep) down to the toe of the aquifer by Makaraka where it is about 80m deep. The aquifer is not an underground lake instead it is an area of gravel and sand under the flats which is saturated with water. The Makauri Aquifer sits below other aquifers on the Poverty Bay Flats. Its natural way of recharging is for water to percolate from the river and higher aquifers down through the gravel into it. This happens slowly over decades, and most of the recharge currently occurs around the Kaiteratahi area. How has the Makauri Aquifer water level declined? The aquifer has very little natural recharge from rainwater and river water, because of changes to the land such as flood control, vegetation clearance, rainfall and climate changes as well as water taken for use by farmers and growers. In the 1980s Poverty Bay had a significant boom in horticulture and water takes for irrigation of crops. Takes have remained at a constant level since then. The amount of water recharging the aquifer is less than the amount of water taken out so the overall effect is that the aquifer water level declines by up to 0.1m per year. What is a Managed Aquifer Recharge (MAR)? A Managed Aquifer Recharge (MAR) is one of the proposed solutions to managing water levels in the aquifer. MAR is a tool that has been used around the world to increase water levels in aquifers. There are also different methods of Managed Aquifer Recharge. One way is through the use of infiltration basins on the ground surface where the aquifer is close to the surface and water can be ponded to trickle down into the aquifer. Another way is through direct injection of water into a bore which goes down into the aquifer. We re proposing a trial is see whether an injection MAR will increase the level of water in the aquifer without any adverse effects. The trial would involve a staged approach using 100,000 cubic metres of water at the rate of litres per second injected into the aquifer. Page 5

Frequently asked questions Why does the Makauri Aquifer suit a recharge injection? International scientists and engineers have assessed the feasibility of a MAR in the Makauri Aquifer.

6 Frequently asked questions Why does the Makauri Aquifer suit a recharge injection? International scientists and engineers have assessed the feasibility of a MAR in the Makauri Aquifer. The Makauri Aquifer is semi confined. This means it doesn t leak so much into the sea or into other aquifers. This is due to its near impermeable soil layers of silts and clays that have been deposited by the river over time. As long as the water quality is not compromised it may be able to be used to store water without any evaporation or leakage losses. The trial will tell us if it s possible to increase the amount of water in the aquifer with minimal impact on the water quality and environment. Why not reduce water takes and let natural processes recharge the aquifer? The Makauri Aquifer supplies nearly a third of all irrigation water on the Poverty Bay Flats. Actual water takes will need to be cut by about 2/3 of current use to equal natural recharge. It s highly likely water restrictions will be introduced on water takes from the Makauri Aquifer by If irrigation water was restricted there will be significant economic impacts to the region s producers. If the trial is successful a MAR would be used in conjunction with other water management measures. We re supporting projects looking at natural infiltration from the surface into shallow aquifers. The Freshwater Plan is now in place and requires water users to improve efficiency of water use, use of surface storage and better match the amount of water needed for their crop requirement, soil type and climate. Irrigation management plans will be required and enforceable when water users renew their permits. How will Council apply for consents to do the trial? Council will apply for three resource consents to take water from another source and inject it into the aquifer. The consent applications will be applied and processed through the Bay of Plenty Regional Council to make sure the consenting process is independent, transparent and assessed fairly. Anyone will be able to make a submission to support or oppose the trial when the consents are notified. Submissions would be assessed by commissioners or the Environment Court to decide if and how the trial would proceed. How is the trial funded? Eastland Community Trust has agreed to fund $200,000 with matching funds from The Ministry of Primary Industries Irrigation Acceleration Fund of $250,000. No other funding is necessary other than Council providing the water, staff time and in-kind contributions from local irrigators. The funding covers the comprehensive modelling and research into the aquifer and source water, as well as the capital and operational costs of developing the injection well infrastructure and completing the trial. We ve been working with irrigators in the catchment on how a full MAR programme might be funded in future if the trial is successful. A detailed business case would be completed before any further support is committed by Council. Page 6

What are the cost differences of the source water options? Golder consultants have provided a decision matrix and this led to a recommendation that the Kaiaponi source be the preferred option.

Originally it was proposed to use the spill over from the Mangapoike Dams as the water source for the trial.

7 What are the cost differences of the source water options? Golder consultants have provided a decision matrix and this led to a recommendation that the Kaiaponi source be the preferred option. The main differences in costs is treating the water to an appropriate quality. How are we deciding the source of water for the trial? Originally it was proposed to use the spill over from the Mangapoike Dams as the water source for the trial. This water travels down the pipeline and joins water from the Te Arai River intake before being treated at the Waingake Water Treatment Plant. The trial could only proceed using this water if the Mangapoike Dams were overflowing. Forecasted El Nino weather conditions mean the potential to use water from Waingake is more limited than first thought. So we ve investigated using Waipaoa River water further. One option is to use water from the Bushmere Treatment Plant that is also drinking water quality - but more costly to run for the small amount of water needed in the trial. A third option is considering sourcing river water from the irrigation system used at Kaiaponi Farms Ltd. Golder International consultants were asked to provide a recommendation after investigating these options in the last six months. They ve completed a range of water testing, including when the river is high with a lot of sediment and run-off. The findings show the water quality is still very good, and well suited for the MAR trial. The recommendation is that the Kaiaponi/Waiapaoa River source should become the preferred water source. Because the Mangapoike Dams water is treated, we had the notional cost of providing the treated water for the injection well. This water has an opportunity cost of $1.21 per cubic metre and although this was not a cash cost it still needs to be considered. The maximum cost to treat the same quantity of water from the Waipaoa via the Kaiaponi infiltration chamber is assessed at $65,000 and is more likely to be around $22,000. This additional cash cost and the additional analysis costs have been taken into account and compared with the use of City supply water. Will water quality deteriorate as a result of the MAR injection? Existing water in the aquifer is a poor quality, its minerals and salts have dissolved and it s also high in iron and manganese. When the water is mixed with air or oxygen, chemical reactions can turn the iron into rust-like material that will block irrigation sprinklers and stain anything that s washed in the water. In a survey of Makauri Aquifer water users no one has used the water for drinking for the past 15 years. The main uses are for irrigation and for the provision of water for horticultural spraying. There is minor use for household gardens and very limited use for livestock. The injection trial will be using higher quality water. The small amount of injected water isn t likely to alter the overall quality, but if high volumes were injected and it did alter quality, it would more than likely improve it. Page 3 of 2

8 What are the risks and how will they be managed? The water in the aquifer has little to no oxygen. It also has minerals such as iron that if mixed with oxygen will perform chemical reactions and the character of the water can change. This will be managed very carefully. We ll inject small volumes of water in increments and gauge any changes through monitoring bores close by. The injection can be reversed and the injected water can be pumped back out if necessary. Arsenic Arsenic leaching and creation of chlorine derivatives are very unlikely to occur. There is very low natural arsenic in the rocks of the Poverty Bay Flats which makes arsenic leaching particularly unlikely. Any arsenic that might be present has to come from the rocks that the well drilling may disturb. Cuttings from the well drilling will be collected and analysed. The injection of oxygenated water from the river into the aquifer also creates chemical conditions that further reduce the likelihood of arsenic mobilisation. Dissolved Organic Carbon The groundwater is in a very low oxygen environment. When combined with the overall chemistry of the aquifer and source water, carcinogens or disinfection by-products are very unlikely, even if chlorine treated water is used. How will we know if the injection trial has worked? If the chemical reactions to the oxygen can be restricted to a small bubble within the aquifer it will be able to be managed. The smaller the bubble the better, and nature will be able to handle the changes over a short period of time. Monitoring will let us know how well we ve restricted the bubble of water. Ongoing water quality testing will be continued to ensure that the natural state is retained. The other measure of success is the hydraulic response. The water level will rise some distance away even though the injected water will not move far from the injection location. A small chemical effect and a large hydraulic effect is the aim. We ll assess the results of the trial and consider if we should proceed with a business plan and economic assessment for a full aquifer recharge programme. Clogging Clogging can also happen if fine sediment enters the aquifer. If surface water from the river is used it will need to be treated to ensure that this does not occur. Chlorine The risk of disinfection by-products from chlorine is also very low due to the natural conditions within the aquifer and the river water. The right mix of chemical precursors and environment conditions need to be present for reactions to occur. Testing for these precursors have found: 1. Organic matter quantities in the aquifer are so low that they cannot be identified in the chemical tests. 2. Nitrite levels in the aquifer are low and no other inorganic precursors such as bromides or iodides were found present. 3. Chlorine is the likely disinfection that will be used for treating injection water. If we use chlorine we can break down residual chlorine with sunlight before injection, by passing water though a transparent tank. What happens after the trial? Council has only committed to the trial to see if Managed Aquifer Recharge will work. To actually stabilise and recharge the aquifer, multiple sites and injection bores would be needed. Currently about 1 million cubic metres of water is taken out of the aquifer each year. Modelling shows that 360,000m3 per year is required to go back in to stabilise the aquifer - that could be up to five more injections bores. Even more water would need to go in on top of that to enable any expansion of irrigation. If the trial shows that MAR is a good option for the Makauri Aquifer, then an economic case would need to be made to go ahead with a full recharge. We re currently looking at how other irrigation schemes work in the rest of New Zealand. Page 8

Chapter 2: Aquifers and groundwater

Chapter 2: Aquifers and groundwater Groundwater movement through aquifers is driven by differences in groundwater levels or pressure and is controlled by how porous the material is that it passes through.