OceanaGold Waihi North Project Vibration Performance Assessment Page iii of 41 Project Number: HP2006-2 Heilig & Partners Save Date: 21/06/2022 5:55:00 PM ABN 56 082 976 714 File Name: WAI-985-000-REP-LC-0018_Rev 0 For the WUG, a vibration limit at any location on the surface above the mine of 95% no greater than 15mm/s is proposed. Because of the relatively isolated location of WUG, it is proposed to extend blasting outside of the normally permissible underground blast window (from 7am to 8pm, Monday to Saturday). The more lenient blast limits recognise the distance between the blast area and the nearest properties being sufficient to attenuate vibration levels to low undetectable values. The proposed vibration magnitude is set to reduce the impact on Archey’s frog. Blasting windows for the GOP cannot be synchronised with the underground blast windows at the other Waihi underground operations. The blasting windows for the underground operations will continue to be constrained by shift changes and breaks. The morning underground blast window will not allow enough time to prepare for the open pit blasts. The evening underground blast window is scheduled after the proposed open pit blasting window. The midday underground blast window is unlikely to be amenable to synchronised blasting. It is proposed that the blast windows for the GOP be specified in the Vibration Management Plan. It is recommended that the Vibration Management Plan is the appropriate document to detail specifics on the blast windows, which complies with current practices. A similar condition to this applies for the other Waihi open pit blasting activities. The duration of the open pit blast activities is not currently restricted by conditions. It has been shown that the geology of the Waihi area affects the number of blastholes that can be initiated within a pattern, necessitating that a delay is introduced between successive blasts to control vibration levels. It is proposed that the duration of the open pit blasting is not restricted by conditions to allow these practices to continue. Compliance with an overpressure level of 128 dBL has previously been a condition of blasting for the open pit. Given the low levels of overpressure that have been recorded and the demonstrated compliance with the limit, regular monitoring for compliance has not been routinely undertaken but rather assessed in the uncommon instance of overpressure related complaints, or where infrequent blasts that could generate elevated overpressure levels are planned, such as pre-split blasting. Rather than routine monitoring of overpressure, it is proposed that the overpressure levels from blasting are representatively assessed a minimum of once per quarter, during periods when blasting occurs, or more frequently if complaints that could be linked with elevated overpressure levels are reported. It is proposed that the maximum limit of overpressure is aligned with section 8.3.2.3 2(b) of the Hauraki District Plan which shows 120 dBL as the maximum limit from blasting The vibration monitoring locations for GOP blasting will utilise, where possible, the existing Favona vibration monitoring system with key locations at Boyd Road, and Moore and Clarke Streets. A monitoring network has been suggested in this report. The vibration results from each of the monitoring locations will continue to be displayed shortly after each blast on OceanaGold’s web page. The same approach has been successfully implemented for existing operations. Monitoring the level of vibration at WUG is complicated by access requirements through the heavily vegetated terrain above the orebodies. The proposed method for monitoring the vibration from the WUG blasting activities will include measuring vibration at selected locations within the underground mine and adjusting the level to reflect the value that would have been measured at the surface. These values will be compared to the permissible criterion. It is proposed to use the same monitoring equipment and assessment software that have been successfully used for previous blast monitoring at the various Waihi orebodies, including the predictive modules used for the AEP calculations. The likely scale of blasting, and the associated effects, for WUG and the GOP have been based upon an analysis of the recorded vibration levels monitored over the previous mining history. These data have been analysed to establish relationships between vibration level, distance and explosive quantity for each of the projects. The outcomes of the assessment have been presented as a series of vibration contours. These contours represent the likely level of vibration at some time throughout the reported period and not the level that would be recorded day to day from each and every blast. In broad terms, the impact of WNP includes: The mining of the GOP changes the existing vibration environment for only a small, isolated area at the eastern end of Moore and Clarke Streets and Boyd Road. The location of the GOP virtually eliminates any combined effects from the existing underground blasting. The envelope of impact for the GOP is estimated as around 50 properties with most of these subjected to only low and marginally perceptible
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