File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. EXECUTIVE SUMMARY Engineering Geology Limited (EGL) was engaged by Oceana Gold (New Zealand) Limited (OGNZL) to assess the ground settlement effects from dewatering due to mining and access tunnel development for the Waihi North Project. Assessment of ground settlement is based on both review of past settlement trends and theoretical calculations (where relevant). The large number of settlement observations at Waihi, spanning some 32 years, provides a reliable database for estimating likely future settlements associated with further dewatering. Overall ground settlement effects are assessed to not cause damage to any structures if mitigations and recommendations are followed. The assessed ground settlement effects are summarised below, followed by the mitigations and recommendations. Assessment of ground settlement effects • The settlement effects for the Waihi North Project are summarised below: o Settlements can be expected around Gladstone Open Pit (GOP) (Figure 3) from dewatering of the younger volcanics and andesite near the pit in the order of 120 to 200mm (see Section 6.1.1). These settlement effects are on land near to Gladstone Open Pit owned by OGNZL. o South of the Ohinemuri River (Figure 3) additional settlements from the mining of GOP are assessed to be in the order of 10 to 50mm with low additional tilts (See 6.1.1) and therefore the residential dwellings in this area will not be damaged. Settlement monitoring is required in this area to confirm settlement effects are as expected. o The proposed Martha Underground (MUG) Decline (Figure 3) is expected to cause additional localised depressurisation of the andesite and additional settlements in the order of 10 to 50mm locally above the decline (See Section 6.1.2). There are no structures above the decline at risk. The proposed decline potentially intersects historic workings and the interface of the andesite with the younger volcanics. Drawdown of groundwater in the younger volcanics and historic workings present a risk, if not mitigated, of more notable settlement and tilt which could potentially extend to Moore Street, Boyd Road and Barry Road (Figure 3) where there are residential dwellings. Residential dwellings in Moore Street, Boyd Road and Barry Road that are not owned by the company are at least 190 m distance (in plan) from the proposed MUG Decline. Historic workings on record at the potential level of intersection only extend 90 m (i.e. part of the way) towards the dwellings in Barry Road. OGNZL owns the properties between the proposed MUG Decline and the non-company owned residential dwellings. There are mitigation options available that OGNZL will implement in response to evidence of groundwater drawdown or settlement of the younger volcanics as part of a specific Trigger Action
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