B-2 – Area 2 - Assessment of Environmental Effects 64 these conditions, and will ensure the construction, operation and closure of these shafts are geotechnically sound. Magazine A magazine for storage of explosives is proposed at a site on relatively flat ground located up an existing farm access road. The site was investigated, and the ground conditions indicate that suitable founding strata are present for supporting lightweight structures such as the magazine. Willows Rock Stack and Water Management Infrastructure The proposed WRS is located in a relatively steep gully to the north of the Willows SFA. WSP (2022a) considers it appropriate to construct the WRS in this location, using bottom up construction techniques to ensure stability. This involves stripping of topsoil and weaker materials within the footprint, placing material in compacted layers, and establishing drainage control from a flat bench surface as each layer is placed. In terms of potential natural hazard risk, if significant seismic activity were to occur during the design life of the structure WSP (2022a) predicts that the resulting effects would be limited to minor deformation and cracking, which could be easily remediated. This is because the tunnel spoil material has inherently high internal strength, and the foundation material will not be susceptible to liquification or significant strength loss once the surficial soils are removed from the toe area. WSP (2022a) recommends weekly monitoring to check for any deformation of the WRS during construction and upon completion is undertaken. This monitoring would comprise visual inspections to check for movement in the natural ground at the toe, and any movement evident in the WRS. The Willows Collection Pond and the WRS Toe Seepage Pond are not considered to be ‘large dams’, however both will be designed and constructed applying the general considerations and principles of best practice dam engineering. Accordingly, the embankments will be designed to impound the reservoirs without excessive seepage, have adequate stability and to incorporate a suitable spillway to control outflows if the capacity of the impoundment is exceeded during a large inflow event. Culvert and drains will also be appropriately located, constructed and sized to manage peak flows. Site Surface Infrastructure The geotechnical investigations indicate that the site is underlain by silts and clays interpreted to be volcanic ash or colluvium, gravelly alluvium and underlying highly weathered, very weak tuff. The thickness of these various layers varies across the site. With appropriate consideration to the stability of the cut slopes and fill platforms, the site
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