12552081 2 2. Recommendations 2.1 Monitoring Locations Currently, OceanaGold continuously monitor flow (via pressure level transducers) at five locations within the Wharekirauponga catchment (WKP1, WKP2, WKP3, T-Steam East and T-Stream West). The continuous data is supplemented with manual gauging events approximately once every quarter at the same locations. Additional manual gauging events have periodically been undertaken at tributary locations, the most extensive of which occurred in December 2020 and May 2021 as reported in WSP (2021a)1 and WSP (2021b)2. It is recommended that continuous monitoring continue at the currently monitored locations (WKP1, WKP2, WKP3, T-Steam East and T-Stream West) and that calibration occurs at least 4 times a year by manual gauging events (the later targeting low flow events). Additional manual gauging events during low flow periods will significantly increase the resolution of the baseline data set. OceanaGold may therefore wish to increase the frequency of these manual gauging events pre-mining. Together with concurrent continuous flow data, the robustness of the statistical flow model (refer Section 2.2) will be strengthened by an increased number of manual gauging events. In addition, five additional locations (Identified as #A - #E) on Figure 1 are recommended to be included within the continuous and manual surface water monitoring network (subject to the suitability of these locations for both access and continuous flow monitoring being confirmed). In addition, manual gauging measurements of both the Hot Spring and Adams Stream should be incorporated into the regular gauging events. Together with the existing baseline dataset, collated data from all 10 continuous sites (5 existing, 5 proposed) should enable a detailed understanding of the catchment hydrology, provide a robust baseline going into the mining phase (assuming data is collected for at least a few years prior to mining) and provide a monitoring network to assess effects (if any) of surface water depletion during mining. These locations have been selected based on one or more of the following criteria: – Current known flow records are considered suitable for continuous flow measurements (many of the measured flows in WSP (2021a)1 and WSP (2021b)2 are considered too small to measure reliably via continuous methods). – Locations are considered suitable for the installation of continuous monitoring hardware. Due to the steep bouldery nature of the catchment streams, reliable and consistent monitoring locations are limited and it is GHDs understanding that suitable locations are absent and/or severely restricted in locations further up catchment from those surveyed during the site walkover. – Sites are considered accessible for manual measurements and maintenance. Locations further in the catchment headwaters (than indicated on Figure 1) are considered unsuitable due to challenging access in steep relatively untracked terrain. – Locations are down hydraulic gradient of identified groundwater seepage points and during low flows are likely to be significantly influenced by groundwater flow. – Locations are adjacent to the GWS recommended piezometer locations to enable direct comparisons in water level / flow changes and enable potential combined telemetered functionality. – Locations are immediately down hydraulic gradient steeper head water catchment areas which should enable a greater understanding of rainfall / flow response at the head of the catchment. – Locations cover the major tributaries above the proposed underground mine draining in to the Wharekirauponga catchment. It is recommended that new locations and existing locations are installed with vented water level loggers which will increase the accuracy of measurements (due to localised barometric effects) and eliminate the need for post barometric data correction. Alternative measurement methodologies such as the installation of a weir or flume will increase the accuracy of measurements significantly; however it is GHDs understanding that installation of such devices are not preferred due to their relative impact on the stream 1 WSP, 2021a. OGL – Wharekirauponga Radon sampling/gauging progamme: 14-16 December 2020 2 WSP, 2021b. OGL – Wharekirauponga Radon sampling/gauging progamme: 4-5 May 2021
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