EGL Ref: 9049 23 June 2022 Page v File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. MUG Decline development mitigations and recommendations • The MUG Decline could potentially dewater the shallow younger volcanics (ignimbrites and tuffs) and cause settlement effects in Moore Street, Boyd Road and Barry Road. EGL recommends that OGNZL mitigate this risk through: o Detailed assessment of the MUG Decline alignment. ▪ Avoidance of the younger volcanics may be possible through refinement of the decline alignment and level, so to stay completely within the andesite. ▪ Avoidance of historic workings may be possible. o Specific geotechnical and groundwater investigations to assist in determining the ground conditions and groundwater profile between the decline and closest properties. Such investigations can be undertaken on OGNZL property. o Monitoring of groundwater levels and ground surface settlement to detect possible effects. o Development of Trigger Action and Response Plans (TARPS) that set triggers and specific actions including mitigation measures if trigger levels are exceeded. o Mitigation of groundwater inflows into the decline (as required) during construction with grouting methods. o Mitigation of shallow groundwater drawdown by re-injection of captured groundwater back into the ground. Wharekirauponga Access Tunnel decline development mitigations and recommendations • The Wharekirauponga Access Tunnel decline from the WUG portal to Barry Road could potentially dewater the shallow younger volcanics (ignimbrites and tuffs) and cause settlement effects at Boyd Road and eastern end of Barry Road. EGL recommends that OGNZL mitigate this risk through: o Detailed assessment of the decline tunnel alignment to confirm options and risks. ▪ Avoidance of the younger volcanics may be possible through refinement of decline alignment and level, so to stay completely within the andesite.
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