Mount Morgan Mine Upper Mundic Gully TSF EA Amendment

Sub catchment

Heritage Minerals activities

Potential Scenarios

Potential for localised changes to groundwater flow directions and expressions in mine target area “pits” removing catchment from existing sumps. Likely reduced seepage volumes to 2 Mill sumps in medium to long term (reduced recharge and localised changes to groundwater catchments). Improved surface water drainage reducing infiltration and subsequent poor-quality seepage via diversion of “clean water” to site storm water drainage and “dirty water” to OCP Potential for increased risk of poor-quality seepage to Mundic West and Frog Hollow sumps from the OCP where levels are above 270 m AHD in some climate scenarios in short term. Potential for reduced risk of poor-quality seepage to Mundic West and Frog Hollow sumps. Potential for seepage water with a better quality than OCP water to migrate to OCP through embankment. Potential for seepage water with a better quality than OCP water to migrate to Dam 8, however installation of the concrete plug will reduce seepage potential. Potential for seepage water with a better quality than OCP water to migrate to OCP through embankment. Potential for high-quality seepage to Mundic West and Frog Hollow sumps. 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 Mundic and Frog Hollow sumps. Likely localised changes to groundwater flow directions and expressions in mine target area “pits” removing catchment from existing sumps. Ground inflow to mine target area “pits” will be high in the short term and will reduce along with OCP water levels. Likely reduced seepage volumes to Mundic and Frog

Linda Gully

Processing plant

Mundic Creek

Sandstone Gully TSF dewatering*

Sourcing OCP make-up for process plant water Upper Mundic Gully TSF operation

Sandstone Gully TSF operation

Mining Mundic and Red Oxide tailings

Hollow sumps in medium to long term (reduced recharge and localised changes to groundwater catchments). Reactivation of Airfield Dump 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 Mundic West and Frog Hollow sumps. Likely reduced poor-quality seepage to Mundic West and Frog Hollow sumps in medium to long term (reduced recharge).

Light of Day

Nil

Nil

Project number: 25B061

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