The Exploratory Works will include management systems to minimise disturbance to water resources by avoiding discharge to or extraction from the Yarrangobilly River, and by on-site controls for sediment and erosion, water re-use and for safe storage of chemical compounds. The works will have minimal influence on flood water behaviour and infrastructure will, as far as possible, be above the flood plain.

An assessment has been prepared to determine the impacts of Exploratory Works on surface water and groundwater. Surface waters within the project area include Yarrangobilly River, Wallaces Creek and Talbingo Reservoir. The impacts on aquifers, groundwater and flood behaviour were also considered. Separate assessments have also been prepared to determine the impacts of dredging and construction of barge access infrastructure and subaqueous placement of excavated material in Talbingo Reservoir.

Key elements of Exploratory Works such as tunnelling, dredging, excavation and rock emplacement will impact surface and groundwater systems. The potential issues include fine sediment in runoff, accidental spills, disturbance of reservoir bed sediments, seepage at rock emplacement sites and changes to flow regimes from new infrastructure such as bridges. These impacts will, however, be minimised through a number of design and control measures.

Erosion and sediment controls will be an important management measure to prevent sediment laden and process water from being uncontrollably released to the environment. A water treatment plant will be built at the portal construction pad and a wastewater (sewage) treatment plant built at the accommodation camp, to ensure water quality objectives for discharge water to Talbingo Reservoir are met. To minimise water taken from Talbingo Reservoir, water captured while tunnelling can be reused as water for construction works.

Talbingo Reservoir near Middle Bay.

Sites where excavated materials are placed on land (ie rock emplacement areas) will be designed to be physically and chemically stable landforms. Monitoring of surface and groundwater will be designed to detect potential changes in water quality resulting from these areas.

The initial phase of subaqueous placement in Talbingo Reservoir has been designed to minimise impacts by selecting suitable placement locations, methods, and environmental controls. Adverse impacts at the reservoir bed are considered to be low and localised provided these measures are put in place. The strategy for managing and monitoring subaqueous placement will be confirmed in consultation with Environment Protection Authority (EPA) before starting subaqueous placement activities.

There will be some localised drawdown of groundwater due to tunnelling but this will not adversely impact local ecosystems or vegetation potentially dependent on groundwater.

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