Erosion and Sediment Control Assessment Report Rev. 0 This is an uncontrolled copy if photocopied or printed from the Intranet. Copyright © 2016, SouthernSkies Environmental Ltd. All rights reserved. Page 17 of 30 1. Erosion control will be given emphasis at all sites to minimise the risk of sediment discharge. This will be achieved with structural (physical measures) and nonstructural (methodologies and construction staging) erosion control measures. 2. Sediment control will be to treat sediment-laden runoff from all exposed earthworks areas. 3. The existing WTP capacity must be prioritised for the treatment of PAF runoff, tunnel inflows, and production activities. Consequently, sediment-laden runoff (including dewatering) arising from NAF material will be discharged via sediment control devices directly to the receiving environment so that treatment via the WTP is limited to PAF. 4. All runoff from PAF material will be directed to the existing WTP. During the initial construction phases, the new Collection Ponds can be utilised as sediment retention ponds for NAF runoff, with treated runoff being discharged directly off site. Once PAF is to be placed, the Collection Ponds will be diverted to the WTP. 5. Earthworks and construction water management measures will be confirmed in the final SSESCPs which will allow for flexibility and practicality of approach to ESC and allow the ability to adapt appropriately to specific site conditions. 6. Progressive and rapid stabilisation, both temporary and permanent, of disturbed areas using mulch, aggregate and geotextiles will be on-going during the earthworks phase. Temporary stabilisation will apply particularly with respect to stockpiles, ground improvement locations where topsoil is removed, concentrated flow paths and batter establishment. Stabilisation is designed for both erosion control and dust minimisation. 7. Stream works and works in the vicinity of streams will be undertaken in a manner that recognises the higher risk of this activity from a sediment generation and discharge perspective, and the sensitivity of the receiving environments. Works within active stream channels will be undertaken in a “dry” environment by working off-line or diverting upstream flows. 8. Comprehensive site monitoring and management will allow for continuous improvement in response to monitoring outcomes on an ongoing basis. Monitoring will include visual inspection of the construction water management devices and the downstream environment. 6.3. Design of Erosion and Sediment Control Devices 6.3.1. Erosion Control - Construction Staging and Sequencing The extent of exposed soil and length of time an area is exposed directly influences the sediment yield from a particular area. Earthworks and construction activities will be staged and sequenced in order to minimise open areas at any given time to the greatest extent practicable. Open earthworks areas will be progressively stabilised to reduce the potential for erosion to occur. 6.3.2. Erosion Control - Clean Water Control Clean water diversions (CWDs) are diversion channels or bunds which divert clean water runoff away from the earthwork areas. Permanent and temporary CWDs will be used on the Project to prevent runoff from the undisturbed catchment above the works from entering the construction area to ensure the works are sufficiently protected from flows from the natural catchment outside of the work area.
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