OceanaGold Waihi North Project Vibration Performance Assessment Page 15 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 The percentile calculation is based upon all recorded vibration data that exceeds the pre-set threshold level set in the Vibration Management Plan. Given the separation distance between the GOP and the existing underground operations, there is no requirement for the blasting to be synchronised. Aside from being difficult to link the firing electronically, a delay in firing in one mine would delay the firing in another, and in the case of the underground could result in missing a production blast window entirely and delaying that shot to the following day. The duration of a blasting event for the open pit blast activities is not currently limited by conditions. It has been shown that the geology in some sections of the Waihi area affects the number of blastholes that can be initiated within a pattern in order to maintain vibration levels at less than 5mm/s, commonly 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 conditioned. The vibration monitoring locations for the GOP will utilise where possible the existing Favona vibration monitoring network and if required, the possible relocation of monitors from the existing Correnso project to alternative locations to provide a more representative network across the Waihi area. It is proposed that blasting results from each of the monitoring locations are displayed on the OceanaGold’s web page. The data will be automatically pre-assessed to nominally display only blast related events. It is also proposed that the overpressure levels from blasting be aligned with the 120 dBL in accordance Section 8.3.2.3 2(b) of the Hauraki District Plan showing as the maximum limit from blasting rather than the existing 128dBL limit applicable to other open pit blasting within Waihi. Overpressure is to be representatively assessed at a minimum of once per quarter. Where no open pit blasting is undertaken in the quarter, there is no requirement for overpressure monitoring. 8.2. Willows and Plant Access Tunnels Blasting to construct the access tunnels from the processing plant to the northern extent of the Willows Road farm, and from the Willows portal to the same point, could potentially generate detectable vibration at some residences. Where potentially detectable, such effects would occur for short periods as development approached then moved away from a receiver. Once the tunnels are constructed, there would be no further blast-related effects. Due to the potential for blast vibration to be detectable, control of vibration magnitude and timing during construction of the tunnels is considered appropriate. However, the currently applied vibration assessment requiring the complex tasks of calculating, maintaining and reporting both the 95th percentile and “average” levels of vibration for each monitoring location is considered unnecessarily complex, and perhaps impractical for developing these section lengths, while not adding a meaningful level of amenity protection. In recognition of the difference between the transitory effects that may be associated with construction of these tunnels and those associated with the ongoing underground mining within Waihi, a modified and simplified set of conditions is proposed, being: The level of vibration for all blasts events must be monitored at non-company owned residences, and the peak level of vibration at any location must comply at the 95th percentile with 5mm/s between the hours of 7am to 8pm, Monday to Saturday, excluding public holidays. The 95-percentile with 1 mm/s will apply for all blast events at all other times. The percentile calculation is based upon all recorded vibration data that exceeds the pre-set threshold level set in the Vibration Management Plan. The duration of the underground development blast events shall be limited to no more than 12 seconds. The vibration monitoring locations for the southern section of the plant access tunnel will utilise the existing Favona and Correnso vibration monitoring network where possible. However, much of the blasting will be remote from the existing monitors. Therefore, for most of the access tunnel lengths it is
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