The ERP (Excavated Rock Placement) assessments were prepared in accordance with the Secretary’s Environmental Assessment Requirements (SEARs) for Snowy 2.0 Main Works. The New South Wales (NSW) Department of Planning, Industry and Environment (DPIE) invited relevant government agencies to advise on matters to be addressed in the EIS in order to properly inform the SEARs. 

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The primary objectives brought about by the SEARs of the ERP assessment were to:

•  Assess the impacts of the project on the quantity and quality of the region’s surface and ground water resources, including Yarrangobilly River, Wallaces Creek, and the Tantangara and Talbingo Reservoirs

• Develop a strategy to manage the emplacement of excavated rock in the Tantangara and Talbingo Reservoirs and enhance any new landforms created

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The project's contractors recommended 2 possible plans for the placement of excavated rocks: 

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The Contractor's primary proposed placement design in Talbingo Reservoir is termed ‘Ravine Bay Placement’

 

Placement of excavated rock in Talbingo involves pushing excavated rock from the shoreline at Ravine Bay into the reservoir by conventional earth-moving plant, such as dumping trucks and excavators, and installing a rock armour layer formed by larger sized excavated rock (>200mm) along the top edge of the emplacement slope batter. With a final volume of 2.86 million cubic meters of rock. 

 

The alternative plan would cut down the amount of rock going into the Talbingo Reservoir by half: 

In the alternative “Hybrid” excavated rock placement methodology only Drill and Blast (D&B) excavated rock is placed in Talbingo Reservoir (Ravine Bay), with land placement being used for all Tunnel Boring Machine (TBM) material. This design is termed ‘Hybrid Placement’.

 

In this scenario, it is assumed that 1.4 Million cubed meters (bank) of excavated rock would be placed in the reservoir using the Ravine Bay Placement method that was presented in the above Section. The placement time period is assumed to be 27 months at an average placement rate of 1750 m3/day. The resultant placement footprint would be reduced from that defined by the Ravine Bay Placement plan. 

 

In order to assess the impacts of ERP methodologies, CSIRO undertook a series of assignments to provide information for environmental risk assessment associated with the handling of excavated rock materials from the proposed works. CSIRO worked with EMM to develop conceptual models and agreed to undertake an initial series of assignments: 

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• Laboratory-based investigations to assess the settling performance of crushed samples from the geological formations that would be encountered during excavation 

• Development of hydrodynamic and sediment models of both reservoirs  to investigate and assess the key hydrodynamic and sediment transport processes (e.g. freshwater flow, thermal stratification, and sedimentary processes) in the study area

• The assessment of the impact of the placement of excavated rock is based on a three-year simulation of suspended sediment behaviour which includes two years of placement and a year to simulate the return of the reservoir to near background suspended sediment levels. 

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