The SRPs will be sized in respect to their contributing catchment area and slope steepness. - Where slopes are less than 10% and less than 200m in length, the SRP will be constructed with a minimum volume of 2% of the contributing catchment. - Where slopes are greater than 10% and/or more than 200m in length, the SRP will be constructed with a minimum volume of 3% of the contributing catchment. An additional 10% of this volume is to be used as a forebay. The SRPs will be located to allow access for removing sediment from the pond. The details of the Collection Pond and Detention Pond have been described in Sections 2.1 and 2.2 above. They provide significant excess capacity beyond that required by TR2009/01. Any pumping of sediment laden water required throughout the duration of the earthworks will be to a SRP forebay or to the Detention Pond for treatment prior to being discharged from the site. 3.4. Decanting Earth Bunds Decanting earth bunds (DEBs) may be used to capture runoff from earthwork areas of up to approximately 0.3ha (or as otherwise stated). Decanting earth bunds will be sized in accordance with TR2009/02 in respect to their contributing catchment area and slope steepness. - Where slopes are less than 10% and less than 200m in length, the DEB will be constructed with a minimum volume of 2% of the contributing catchment. - Where slopes are greater than 10% and/or more than 200m in length, the DEB will be constructed with a minimum volume of 3% of the contributing catchment. The total storage volume of a DEB will be split into 50% live storage and 50% dead storage. 3.5. Chemical Treatment The Chemical Treatment Management Plan (CTMP) provided as Appendix A of the Erosion and Sediment Control Assessment Report provides the methodology for determining the effectiveness and dose rates for chemical treatment to enhance the sediment retention efficiency of sediment retention ponds, decanting earth bunds and other water impoundment devices that will be used throughout the project. It is intended that all SRPs will be chemically treated if necessary and monitored in accordance with the CTMP While the Collection Pond and Detention Pond service their respective areas during the enabling earthworks (Non Acid Forming soils) chemical treatment will likely be employed. Once the Surface Facilities earthworks are complete the area will be stabilised, and chemical treatment removed for the Detention Pond. Once the mining operations commence PAF water will report to the Collection Pond and pumped to the Water Treatment Plant. 3.6. Silt Fences and Super Silt Fences Silt fences or Super Silt Fences may be used to capture runoff from small areas that cannot actively drain to a SRP, DEB, Collection or Detention Pond. Super silt fences will be installed below the footprint of all SRPs, Collection Pond and Detention Pond to capture any runoff during the construction phase of these devices. Once the device is constructed then the super silt fence will either be returned up either side of the emergency spillway or removed. 3.7. Stabilisation Progressive stabilisation will be undertaken throughout the earthwork operations. Both temporary and permanent stabilisation measures will be employed on site. Common stabilisation measures include spreading of aggregate, grassing (with a full cover of grass), applying mulch and the use of geotextiles.
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