OceanaGold Waihi North Project Vibration Performance Assessment Page 11 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 (3) Overpressure (PMax) 120dBL (4) Peak Amplitude (VMax) 5.0 mm/second (5) Time of Day 0700-1800 (6) Days Monday to Saturday (excluding public holidays) Section 8.3.2.4 of the District Plan states the following in relation to the 95-percentile: (7) For resource consents, transient ground vibration is typically set in terms of a 95 percentile, and may include a maximum limit. The percentile limit will generally be applied to the design for each and every blast so that induced disturbances will not exceed the 95 percentile limit on more than 5 percent of occasions (and will never exceed the maximum limit where set). The 95 percentile limit has little meaning for the activities that are permitted under the transient ground vibration limits set in this standard as the derivation of the relationship between explosive charge, distance and ground response required to undertake such a design can only be achieved through a series of trial blasts. Accordingly it is the VMax level as referred to and defined in this standard that is the performance standard for transient ground vibration. 6.2. Airblast Overpressure Overpressure from blasting refers to the momentary levels of pressure above atmospheric pressure. It is measured irrespective of frequency with no weighting, and on this basis, is distinguished from noise criteria, which are weighted to account for human noise response. Blasting is not assessed against a value with respect to its audibility. In terms of personal injury, in a United States Bureau of Mines (USBM) document4, reference is made to the likelihood of injury and hearing damage from impulsive noise. The document refers to a threshold of ear drum rupture and inner ear damage of 178 to 185dBL. Although these levels are high, the same reference further states that no ear protection is required for peak levels below 140dBL, regardless of the number of events per day or the duration of these events. Perhaps more appropriate is the reference to work completed by the Committee on Hearing, Bioacoustics and Biomechanics in Washington discussing tolerance for humans. Their work, also referenced in the same USBM document, identified an allowable level with respect to personal impact of 139dBL for blasting type activities. Little research has been completed on the issue of the subjective response of people to blast overpressure. The challenge arises because a significant portion of the energy contained in the overpressure response is outside of the usual hearing frequency range, is of short duration and affects relatively few people for anything other than short periods of time. The most observed effect of elevated overpressure levels is the associated rattling that it may cause to some parts of a dwelling, such as ill-fitting windows, loose timber panelling and so on. In this manner, the effect is often confused with that of elevated vibration. At low levels of overpressure like those generated by well controlled blasting, the effect is not detrimental to persons, is incapable of damaging any property, and furthermore, unlikely to cause rattling and other side effects mistaken for increased vibration levels. Compliance with an overpressure level of 128 dBL has previously been a condition of blasting for the Martha 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. 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. 4 Siskind, D.E., Stachura, V.J., and Stagg, M.S., 1980. “Structure Response and Damage Produced by Airblast from Surface Mining”, United States Bureau of Mines, Report of Investigations No 8485.
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