EGL Ref: 9215 23 June 2022 Page 34 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx. 4.9.2. Porewater Pressures Monitoring of piezometric pressures over the life of the project indicates a rise is measured in Zone B as tailings are emplaced. Over time as the depth of tailings increases and the tailings consolidate the piezometric levels stabilise and reduce. In the downstream shoulders of Storage 1A and Storage 2 the piezometric levels are generally very low. This is due to the rockfill nature of much of the fill. Some higher piezometric levels were measured in weathered rock (soil like) material in one area of Storage 2 in its early stages. This was because of the high-water content and low permeability of the fill. The higher piezometric levels dissipated as the fill consolidated and drained. 4.9.3. Environmental monitoring Extensive environmental monitoring is undertaken. This includes sampling and testing of water quality in the TSF, Collection and silts ponds, subsurface seepage drains, and groundwater monitoring wells. Flows in subsurface seepage drains are measured. Water levels in monitoring wells are also measured. Conditions of the resource consents require regular review and interpretation of environmental monitoring and reporting to the Waikato Regional Council. The results are reviewed by the PRP. 4.9.4. Deformation monitoring Benchmarks have been established on the embankment to enable measurement of embankment deformations (horizontal and vertical) on both Storage 2 and Storage 1A. The last survey of the deformation markers was undertaken by OGNZL in July 2021. The results have been provided in terms of plots of both horizontal components and the vertical component of movement versus time. Since monitoring of the benchmarks began in 1996 for Storage 2, horizontal measurements up to 53 mm and vertical settlements up to 140 mm have been recorded on Storage 2. Storage 1A has had up to 40 mm horizontal movement and vertical settlements up to approximately 105 mm. Largest deformations are generally on benchmarks at high elevations which are underlain by greater depth of fill. Measured movements also include a component of creep in the ripped and lightly compacted outer plant growth zone (Zone H). The maximum settlement measured is 140 mm on Storage 2. The total settlement up to July 2021 was calculated in percentage of fill height and is up to 0.7 % of the fill depth. The measured deformations are within normally expected values for embankment fill. Deformations over the last 7 years have been very small. Markers with the greatest settlement to date had very little settlement since 2013. The slowing down in settlement with time is expected. The maximum horizontal deformation is 53 mm on Storage 2. The vectors of horizontal movement are shown in Figure 29. Movements less than 15 mm are not shown as this is the accuracy limit of the survey. The maximum horizontal deformation of 53 mm is small compared with the size of the embankment. It is also localised and not directly downhill suggesting it is local surficial movement, possibly from disturbance from a vehicle or could be due to
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