EGL Ref: 9018 22 June 2022 Page 15 WAI-985-000-REP-LC-0006_Rev0.docx This report shall only be read in its entirety. neutralising capacity, and rehabilitation capping to restrict long term infiltration of oxygen and water. This is the same strategy used and shown to be effective in the construction of the existing TSFs. Seepage collected by the leachate drains above the liner is pumped to the Water Treatment Plant. Groundwater seepage from the subsurface drains beneath the liner is directed to sumps and pumped to the Water Treatment Plant. A series of detection and compliance groundwater monitoring wells check the performance of the facility so long-term closure conditions can be estimated. Surface water runoff from the operational stockpile is captured in lined perimeter drains and is directed to the proposed NRS Collection Pond, which will be sized to manage runoff from a 1 in 10 year 72 hour storm event without discharging. The water is pumped back to the Water Treatment Plant or Processing Plant before being discharged to the Ohinemuri River or reused for the Processing Plant operation. Stockpiles for rehabilitation material (topsoil and stripped surficial soils) are required. 184,500 m3 capacity for stockpiling of rehabilitation material is shown in Drawing 0715. The volumes assume 3H:1V slopes and any undercut required will be managed in stockpile. The northern rehabilitation stockpiles are positioned along Golden Valley Road, which leaves room for future expansion of the NRS for future projects as required. These stockpiles will require erosion and sediment control in the form of sediment fences, bund and silt retention ponds (SRPs). Conceptual positions of the SRPs required outside of the NRS footprint are shown in Drawing 0715. Access to the stockpiles adjacent to Golden Valley Road will be via a single lane access track which will be formed by widening the farm tracks and upgrading the culverts across the stream as required. The Northern Rock Stack requires: • Uphill diversion drain to collect run-on clean water and divert it around the site to the Ohinemuri River. This diversion drain will also divert the stream (TB1). This drain also collects the existing Northern Uphill Diversion drain flow from behind Storage 2. • Subsurface subsoil drains installed in the foundation up the existing gully features to intercept groundwater for construction of the lining and long-term control of seepage. • Subsurface toe drain installed at the base of the slope. This will be combined with a 30 to 50 m wide shear key to rock around the toe of the embankment. The toe drain and shear key will assist long term stability and favourable performance in earthquakes and assist interception of any seepage of groundwater from beneath the facility. It will also intercept any seepage of leachate through the liner. • A Zone A base earth liner, 0.75 m thick, over the full extent of the foundation. • Leachate drainage installed on top of the Zone A liner at the toe of the slopes and in the low points of the liner. • NAF perimeter embankment with a lined perimeter surface drain, and access road. The perimeter drain will be lined with a HDPE liner as is done for Storage 1A. • Lined NRS Collection Pond to collect run off water from PAF rock areas, with pumps to return the run off to the Water Treatment Plant and Processing Plant. • Perimeter “ring” system of sumps and pipes to collect groundwater seepage and leachate from the associated subsurface drains, which are pumped back to the Water Treatment and Processing Plant. • Placement of PAF material with lime addition to improve acid neutralising capacity of the placed material.
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