B-2 – Area 2 - Assessment of Environmental Effects 81 Actual or Potential Effect Recommended Mitigation / Management Recommended Monitoring / Future Action Additional Measures Proposed by OGNZL Trigger levels for pH, conductivity and water levels to provide an early warning indicator of potential changes of groundwater quality as a result of the activities associated with the WRS; and A contingency plan in the event a trigger level is breached over two consecutive readings, and which is sufficient to assess the source of the change, and to determine what, if any, mitigation measures are needed. Groundwater Groundwater dewatering at Willows Access Tunnel resulting in minor reduction of flows to Mataura Stream and depletion of water resources which may affect users of water. Monitoring of shallow groundwater is recommended using the existing network of wells to ensure sustained lowering of groundwater levels does not occur and that there is no potential for long term stream loss. If dewatering activities adversely affect existing stock, domestic or other water supplies, OGNZL will be required to provide an alternative supply within 12 hours. See Dewatering and Ground Settlement section. See Dewatering and Ground Settlement section. None. Discharge of contaminated groundwater into the environment during construction of Willows Access Tunnel. All groundwater collected in the tunnel will be sent to the WTP for treatment. None. None. Effects on groundwater quality See geochemistry section above See geochemistry section above
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