Before Greater Wellington Regional Council Under the Resource
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Before Greater Wellington Regional Council Under the Resource Management Act 1991 In the matter of the Proposed Natural Resources Plan for the Wellington Region And In the matter of Submissions (S135) and Further Submissions (FS25) by Wellington Water Limited EVIDENCE OF ASLAN MICHAEL PERWICK 25 May 2018 M J Slyfield Barrister Stout Street Chambers Wellington Telephone: (04) 915 9277 Facsimile: (04) 472 9029 PO Box: 117, Wellington 6140 Email: [email protected] 1. My full name is Aslan Michael Perwick. Qualifications and Experience 2. I am a senior hydrogeologist and Groundwater Services Leader employed by Pattle Delamore Partners Ltd (PDP) - specialists in water resources management and environmental engineering. 3. I hold the degrees of Bachelor of Science (Geology) from the University of Auckland, New Zealand., and Master of Science (Hydrogeology) from the University of Birmingham, United Kingdom. I am a member of the International Association of Hydrogeologists (IAH), New Zealand Hydrological Society (NZHS), and Australasian Tunnelling Society (ATS). 4. I have 10 years’ experience as an environmental practitioner, specialising in groundwater management. I have practiced in both New Zealand and Australia where I have completed numerous groundwater assessments for both abstraction and contaminant management purposes; including source protection zone assessments in alluvial settings. Code of Conduct 5. I confirm that I have read the Code of Conduct for expert witnesses in the Environment Court Practice Note 2014 and that I have complied with it when preparing this evidence. Other than when I state that I am relying on the advice of another person, this evidence is within my area of expertise. I have not omitted to consider material facts known to me that might alter or detract from the opinions that I express. Scope of my evidence 6. In May 2018, PDP was commissioned by Wellington Water Ltd to undertake a review of all current information and recommendations relevant to the identification of a groundwater protection zone (GPZ) in the Lower Hutt Valley. 2 7. PDP’s work and all of the information taken into account is set out in a Technical Memorandum dated 25 May 2018, which is attached to this statement of evidence. 8. I have reviewed the work completed by my PDP colleagues, including background works which have been incorporated into the current advice provided for WWL. I have undertaken my own independent assessment of this work and agree with the assessment approach and conclusions made; as they are presented in the 25 May 2018 memorandum. 9. The assumptions and limitations that apply to my evidence not only reflect but focus on those that have been highlighted in the technical reports that support the proposed GPZ. The information presented by GWRC and its associated technical advisors contains inherent assumptions and limitations, which are largely based around aspects where knowledge gaps due to data paucity exist. The relevant documents do clearly identify these, and provide recommendations for further works to address the identified knowledge gaps. However, it is my opinion that until further works are completed to address the situation, a more precautionary approach to defining the GPZ should be adopted. Summary 10. My colleagues at PDP have undertaken a review of available information and technical recommendations regarding the proposed GPZ in the Lower Hutt Valley. After conducting my own review, I agree with the findings of this review and the recommendations made. 11. The majority of reviewed information has been prepared by Greater Wellington Regional Council and their associated technical advisors. A list of the information/reports that have been reviewed is provided in the attached memorandum. 12. The key technical concerns I have with the proposed southern limit of the proposed GPZ (as presented in the s42A report), are summarised as; 3 (a) uncertainty regarding the degree of natural hydraulic confinement that exists between the Waiwhetu Aquifer and potential contaminant sources at ground surface south of the proposed GPZ. This is primarily due to knowledge gaps associated with the paucity of geological data; to confirm the presence and properties of the aquitard in certain areas outside the proposed GPZ, such as the Woburn, Waiwhetu, Moera, and Epuni suburbs. (b) uncertainty regarding the ‘piercing’ of on any natural confinement due to the drilling of boreholes, and / or installation of deep engineering structures such as building foundations / piles, within the area outside (south) of the proposed GPZ. There are >100 known boreholes which are likely to have been drilled into or through the aquitard within the area outside the proposed GPZ. These man-made structures may have artificially created preferential flow pathways for contaminant migration from the surface and/or shallow groundwater to the Waiwhetu Aquifer i.e. a connection(s) to ‘short-circuit’ through the aquitard. (c) the influence of groundwater abstraction from boreholes within Waiwhetu Aquifer in the area outside (south) of the proposed GPZ, and how abstraction activity may influence groundwater flow and contaminant migration characteristics i.e. the potential to draw contaminated shallow water into Waiwhetu Aquifer, and then into an abstraction bore(s). (d) the approach to incorporating the above outlined assumptions, limitations, and uncertainties, into the application of defining an appropriate GPZ. 13. I would note that there is evidence that at least one of risks above has materialised in the recent past when enterococci was detected in one of the Gear Island bores when WWL were using that field for supplementary supply. 14. Overall it is my opinion that, on balance of all of the above listed technical elements, a more precautionary approach to resource management decisions and associated protections should be 4 adopted for the Waiwhetu Aquifer. This should involve extending the proposed GPZ to encompass the entirety of the Lower Hutt Valley floor southwards all the way to the Wellington Harbour shoreline. Residual risks from gaps in current level of knowledge are considered too high to exclude this area from the protection zone. Aslan Perwick 25 May 2018 5 .