Sub catchment
Heritage Minerals activities
Potential Scenarios
Shepherds
Mining Shepherds tailings
Improved surface water drainage reducing infiltration and subsequent poor-quality seepage via removal of ARD generating mine waste (tailings). Potential for seepage water quality to improve in short term (ARD source removal), draining and expressing to Shepherds sumps. Likely reduced poor-quality seepage volumes to Shepherds sumps in medium to long term (reduced recharge). Improved surface water drainage reducing infiltration and subsequent poor-quality seepage via careful placement, compaction, shaping and capping of ARD waste rock by placement of overlying NAF waste rock. Potential for seepage water quality to further degrade in short term (reduced recharge), draining and expressing to Shepherds sumps. Likely reduced poor-quality seepage to Shepherds sumps in medium to long term (reduced recharge).
Remediation of Shepherds Outer Dump
In summary, there is likely to be reduced inflows into existing sumps from groundwater and sub- surface flows in comparison to those under existing conditions. This is expected to result in improved performance of the existing seepage interception system and reduction in poor quality seepage expressing to the receiving environment i.e. Dee River. Overall, the removal of latent tailings and operation of TSFs is expected to result in the reduction of contaminant sources via the reprocessing of mineralised tailings dams and remediation of operational areas, which will reduce the volume of mine affected seepage. As a result, it is anticipated that groundwater quality will improve during and post mining. 6.6.7 Site Wide Groundwater Recharge and Discharge The primary source of recharge to the groundwater system is seepage from the flooded OCP / Sandstone Gully TSF and net infiltration into the various mine waste units (waste rock dumps and tailings impoundments) (Robertson GeoConsultants, 2011). It is noted that the Sandstone Gully footprint is proposed to be dewatered to facilitate mining of latent tailings. In general, groundwater levels in low-lying areas of the model domain are far less sensitive to the (assumed) recharge than groundwater levels at higher elevations. This is characteristic of high relief watersheds in which topography (and drainage) strongly controls groundwater levels with much less seasonal variation in the valley floors compared to the valley ridges. As part of the groundwater modelling, Robertson GeoConsultants estimated the recharge of each mine feature which is displayed in Figure 45 with the inferred location of Upper Mundic Gully TSF drawn as a red square. Seepage from the OCP / Sandstone Gully TSF is the major source of recharge and contaminant loading to groundwater in the Mundic Valley/Linda Gully sub- catchments, however most of this seepage and Chemicals of Concern (COC) load is currently intercepted in the interception system (primarily in Mundic West). Of significance to this amendment, the recharge potential within the Upper Mundic Gully TSF area is considered minor at 10 mm/yr whilst the recharge of the adjoining Western Dump is approximately 100 mm/yr.
Project number: 25B061
Page 123
Powered by FlippingBook