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 23 of 30 Both the Detention Pond and the Collection Pond are sized and built, first and foremost, as Collection Ponds, not SRPs; they will be expected to control and treat PAF runoff and potential spills. Their function as SRPs is an important, subsidiary, benefit. Once the enabling earthworks are complete, the Collection Pond will continue to service the ongoing works of the WRS and construction of the internal access roads using PAF. Runoff directed to the Collection Pond will then be transferred to the WTP. The topsoil stockpile, magazine storage areas and other access will be serviced by SRPs designed in accordance with TR2009/02, and other minor controls such as clean and dirty water diversion and silt fences, and progressive stabilisation. Services, such as power, water (raw, potable and waste), and fibre optics must be installed from the existing Processing Plant site to the Willows Road site. The route from the Processing Plant crosses existing farmland, before progressing along State Highway 25, then turning into Willows Road to the Surface Facilities Area. Two stream crossings across the Ohinemuri River will be required. These works will be staged and progressively stabilised and will avoid works within streams. As for NRS and TSF3, before PAF material is exposed and placed, runoff will be contained within the Collection Pond and piped back to the WTP. 9.1.2. TSF3 The SRP for the main stockpile (Stockpile 2) has been sized to service the full stockpile area of 12Ha. This approach will allow a simplification of the management of the stockpile and sediment pond. The pond has been sized to provide for 4,000m3 of storage volume and will exceed the minimum design capacity recommended in TR2009/0216. While TR2009/02 recommends a maximum SRP catchment area of 5ha, in this instance the increased capacity is expected to offset the larger catchment size. It is anticipated that an average sediment retention efficiency of 95% will be achievable with this chemically treated SRP. Stockpile 1 will be managed through a separate SRP that will slightly exceed the recommended SRP catchment area (5.1ha proposed). The separation of that stockpile is necessary as it will be receiving different material. Once the paleo gully is excavated and the shear key and access road bund is formed, the permanent Collection Ponds will be formed. At that stage, runoff from the main gully stripping and initial filling with NAF will collect within the lower end of the valley and then be pumped to the stormwater pond for settlement before decanting or pumping from the site to the Ruahorehore Stream. Under that scenario, the management or sediment-laden runoff should be as good or better than that from a TR2009/02 device. 9.1.3. NRS The establishment of the NRS, including stream relocations, stockpile management and main works will be managed with TR2009/02 compliant ESCs. The NRS establishment earthworks will utilise three existing Collection Ponds where any collected water will report to the WTP. Once the new Collection Pond is constructed the existing Collection Ponds will be decommissioned and all water from the NRS will report to the new Collection Pond. The permanent uphill clean water diversion requires the diversion of an existing stream to a new alignment to provide for the full extent of the NRS. A draft methodology has been provided in the SSESCP which will be finalised prior to the commencement of earthworks within this area and provided to WRC for certification. 16 3% criteria i.e. 300m3 of storage for each hectare of contributing catchment.
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