Environmental Assessment Chapter 8 Surface Water

Environmental Assessment Chapter 8 Surface Water 8.2.7 Rainfall and Evaporation Based on recorded data for the area of interest, the mean annual rainfall is about 700mm, with maximum monthly rainfalls occurring during the summer months. Mean annual evaporation is 1613mm, which is substantially higher than rainfall. 8.2.8 Catchment Runoff The runoff characteristics of mine site catchments were simulated using the AWBM rainfall-runoff model. Natural catchment runoff was simulated by calibrating the AWBM model to recorded streamflow data for Glennies Creek. Different sets of model parameters were then derived to represent the runoff characteristics of areas disturbed by mining and dumped overburden material (spoil). Simulated catchment runoff generated by the AWBM model was used as an inflow to the IQQM model. 8.2.9 Pumping Rules The operational strategy for the mine s water management system is represented in the water balance model as a set of pumping rules that describe the interactions between the various storages. The pumping rules are based on the following operating strategy. The Portal Sump water level is kept as low as possible by pumping to D1 and to the Possum Skin Dam. The Possum Skin Dam level is kept as high as possible to maximise dirty water disposal by evaporation. Water accumulating in Dams D2 and D3 is pumped to D1 when these dams reach their maximum operating level. The Northern and Southern Dirty Water Containment Dams at the proposed North Open Cut are pumped dry. Water is drawn from the clean water system only when D1 drops below 10% of capacity and additional water is not available from other storages, such as the Portal Sump and Possum Skin Dam. Open cut pits are pumped dry, subject to available capacity in D1. 8.2.10 Model Results - Existing Conditions Table 8-3 provides a summary of the water balance model results for the existing conditions. Note that the value shown for pumping from the South Pit includes both seepage inflow and surface runoff collected within the pit. 8-11

Chapter 8 Surface Water Environmental Assessment Table 8-3 Water Balance Model Results, Open Cut Project, Existing Conditions Mean Annual Volume (ML) Inflows Seepage to Portal Sump 511 Seepage to D1 292 Pumping from South Pit 433 Net Inflow from Underground 110 Surface runoff dirty water system (excluding pit) 324 Harvest from clean water system 253 Total 1923 Outflows CHPP 1076 (98% reliability) Dust Suppression 439 (85% reliability) Ashton 343 (85% reliability) Net evaporation from storages 69 Spills from D1 0 Spills from PSD 0 Total 1927 Note: difference between total inflow and total outflow is due to change in storage over the simulation period. The water balance model results for existing conditions showed that under the assumed pumping rules, the water management system allows operations while ensuring no spills from the dirty water system. The CHPP demand is met 98% of the time. The demand for dust suppression is met 85% of the time. During dry years when insufficient water is available to meet onsite demand it is possible for the water shortfall to be sourced from Integra s water allocation from Glennies Creek. The simulated water storage levels indicated that most storages remain within normal operational ranges. The 95 th percentile water volume in the existing South Pit was 215ML which would be able to be accommodated without significant impacts on production. Any excess water in the system is managed by allowing a temporary rise in water levels in other mine storages or by holding water temporarily in the open cut pits. It is also possible that additional water could be delivered to the Rix s Creek or Ashton Mines, helping to reduce the dirty water storage requirements. 8.3 Assessment of Impacts The Extended South Pit and its final landform (Figure 8-5) will have impacts on the local drainage network, the water management system and the site water balance, each of which is discussed below. 8.3.1 Local Drainage Network Impact of Mining Figure 8-4 shows the approximate extent of the surface water catchments captured within the existing integrated mine water management system, together with those associated with the North Open Cut and the proposed extension to the South Pit. The eastern portion of the North Open Cut will intercept runoff from the Reedy Creek catchment. A number of diversion bunds and excavated channels would be used to divert clean catchment runoff around areas disturbed by mining operations. Table 8-4 shows the areas removed from various natural catchments by mining operations for the North Open Cut and the proposed extension of the South Pit. 8-12

Environmental Assessment Chapter 8 Surface Water Table 8-4 Impacts of Mining on Local Drainage Network Catchment Total Catchment Area Pre-Mining (km 2 ) Area Removed from Catchment by Mining Operations (km 2 ) Existing Mine Existing + North Open Cut + Extension to South Pit Glennies Creek (excluding Station Creek and Reedy Creek) 474 0.5 1.3 Station Creek 24 6.6 8.3 Reedy Creek 14 0 0.3 Total 7.1 9.9 The existing mining operations capture runoff from a total area of 7.1km 2. Though reducing the Station Creek catchment by some 28%, the existing mining operations have had a negligible impact on the area draining directly to Glennies Creek. Capture of water from the proposed Mine Area and the North Open Cut during mining operations would reduce the area of the Station Creek Catchment by a further 7%. The North Open Cut would reduce the catchment area draining to Reedy Creek by only 2%. 8.3.2 Water Quality Impact of Mining Backfilled South Pit An assessment of the potential ph and salinity of waste rock leachate within the backfilled Extended South Pit was obtained through coarse crushing and batch leachate testing of selected Foybrook Formation overburden and minor coal seam core samples from bores located within the proposed Mine Area (Full Pit Extent). The assessment was undertaken by Geoterra Pty Ltd with reference to the Australian Standard Leaching Procedure (Standards Australia (1997) AS4439.3-1997 and the ARD Test Handbook (Amira International 2002). Following five months of leaching, the pore space waters were combined in relative proportion to the anticipated proportion of each lithology in the overall overburden that may be placed back in the backfilled open cut. The combined pore space waters indicate the overall waste rock backfill leachate, prior to any evaporation effects, would have an approximate ph of 8.37 and salinity of 2600µS/cm. Groundwater Samples taken from piezometers drilled adjacent to the Open Cut Area indicate the potential inflow to the Extended South Pit could have a ph of between 7.32 and 8.40 and a salinity ranging from 9,340µS/cm to 12,070µS/cm, without accounting for evaporation. Final Void Results from the waste rock batch leach testing, along with the potential groundwater inflow, clean water in-pit rainfall and runoff, tailings dam leachate and evaporation, were used to provide a first-pass indication of the potential final void water body quality that may develop after rehabilitation of the Extended South Pit. Using an adapted mass balance method involving the proportional mixing of waste rock and tailings dam leachate inflow, groundwater quantities and qualities as well as in-pit rainfall 8-13

Chapter 8 Surface Water Environmental Assessment sources, the final water quality was predicted to exhibit a ph of 8.5 and an electrical conductivity of 11,350µS/cm. It is noted, however, that the final void water quality is highly dependant on the degree of clean water dilution provided from surface runoff, as the groundwater input is relatively constant. Downstream Water Quality The results of the water balance model indicate that the proposed water management strategy will ensure that no discharge of dirty water from areas disturbed by mining will occur under historical climatic conditions. Hence, it is not expected that the proposed Open Cut Extension project will pose any threat to downstream water quality or the long-term integrity of surface water resources. Whilst the dirty water management system is designed to prevent spills, it is possible that spills could potentially occur due to: an extreme event or sequence of events more severe than represented in the historical climate record used for the water balance modelling, or failure of the water management system through operator error, equipment malfunction or infrastructure damage. During an extreme event, spills from D1, the main dirty water storage on the site, would be diluted by clean water stored in downstream clean water dams C3 and C4, as well as runoff from the clean water system. The combined storage volume of downstream clean water storages C3 and C4 is almost 200 ML, close to half the capacity of D1. Dirty water storages D1 and D3 collect runoff from disturbed areas of about 40 ha, within a clean water catchment area of about 1200 ha. Hence, during an extreme event when all catchment surfaces would be saturated, overflows from D1 are likely to be diluted by a factor of about 30 to 1. Dry-weather spills from D1 or D3 would be captured in C3 and C4 if storage capacity is available in these storages (up to 200 ML if both storages are empty). If C3 and C4 are full, spills from D1 or D3 would be diluted by clean water held in C3 and C4. Spills from Possum Skin Dam would discharge directly off the mine site. However, since the external catchment draining to Possum Skin Dam is minimal, spills from this storage are very unlikely provided that pumped inflows cease at a Maximum Operating Level that allows sufficient storage for an extreme rainfall event, such as a 1 in 100 years average recurrence interval (ARI) event. Excluding catastrophic failure of the dam embankment, the volume of any spill from Possum Skin Dam would be likely to be small, consisting of either pumped inflows only (in the event of unplanned pumping to a full storage) or the additional water above a 100 year ARI event. It is likely that the quality of spills during an extreme event would be better than the typical water quality of Possum Skin Dam because fresh water inflows from rainfall would be likely to remain on the surface of the more saline dirty water in the dam. The small risk of spills from the site, combined with the dilution potential of the clean water system will ensure that the risks of any adverse impacts on the quantity, quality and long-term integrity of off site surface water resources are extremely small. Proposed management measures to deal with a spill or potential spill of dirty water from the site are provided in Section 8.4.2. 8-14

Environmental Assessment Chapter 8 Surface Water 8.3.3 Water Management System The extension to the South Pit will contribute additional water to the existing dirty water system by increasing disturbed areas, as well as collecting additional groundwater inflows. Although, the configuration and operation of the existing water management system as presented schematically in Figure 8-2 will essentially remain the same, it has been assumed that D2 will no longer be available for water storage. On completion of tailings disposal to TD2 around mid 2009, tailings disposal is planned to commence in D2. Use of D2 (also referred to as TD3) for tailings disposal was conditionally approved under DA 86/2889 and has subsequently been approved for use as an emplacement by DoP, and DPI under s.100 of the Coal Mines Health and Safety Act 2002. D2 has a capacity of 1.5Mm 3 and will provide storage for tailings from the existing Integra Open Cut (South Pit) and Underground operations, together with the forecast tailings production from the North Open Cut and Extended South Pit (if approved) through until 2011. Figure 8-6 presents the amended mine water management system. 8.3.4 Water Balance As described in Section 8.2.5, a daily numerical water balance model for the Open Cut Extension and Underground operations was developed using the IQQM model. Models were developed for Year 4 and Year 8 of the Open Cut Extension. During Year 4, mining would be occurring both within the North Open Cut and the Extended South Pit whereas by Year 8, mining activities in the North Open Cut will have ceased. The results for the modelled scenarios in Year 4, Year 8 and the Final Void are presented below. 8-15

Legend: Final Void Catchment Boundary Open Cut Project Area Note: Specific Drainage Structures on the Final Landform Extended for Clarity. NN 0 250 500 meters Source: Integra Coal Operations Pty Ltd WRM Water & Environment Pty Ltd Drawn: AO Approved: RO Job No: 43177507 Date: 19/02/2009 File: 43177507.071.wor Client This drawing is subject to COPYRIGHT. It remains the property of URS Australia Pty Ltd. INTEGRA COAL OPERATIONS PTY LTD Project INTEGRA OPEN CUT PROJECT Title EXTENDED SOUTH PIT FINAL LANDFORM Figure: 8.5

D2 (TD3) Source: WRM Water & Environment Pty Ltd Drawn: AO Approved: RO Date: 17/06/2009 Job No: 43177507 File: 43177507.068.wor Client INTEGRA COAL OPERATIONS PTY LTD This drawing is subject to COPYRIGHT. It remains the property of URS Australia Pty Ltd. Extended South Pit Project Title Figure: INTEGRA OPEN CUT PROJECT CONCEPTUAL ILLUSTRATION OF THE MINE WATER MANAGEMENT SYSTEM - WITH OPEN CUT EXTENSION 8.6 T:\JOBS

Chapter 8 Surface Water Environmental Assessment Model Results Year 4 Open Cut Extension Table 8-5 provides a summary of the water balance model results for Year 4 of the Open Cut Project. Table 8-5 Water Balance Model Results, Open Cut Project, Year 4 Inflows Outflows Mean Annual Volume (ML) Seepage to Portal Sump 511 Seepage to D1 292 Pumping from South Pit 521 Pumping from North Open Cut 102 Net Inflow from Underground 336 Surface runoff dirty water system (excluding pits) 338 Harvest from clean water system 110 Total 2210 CHPP 1096 (100% reliability) Dust Suppression 643 (97% reliability) Ashton 381 (95% reliability) Net evaporation from storages 95 Spills from D1 0 Spills from PSD 0 Spills from proposed Dirty Water Containment Dams 0 Total 2215 Note: difference between total inflow and total outflow is due to change in storage over the simulation period. The water balance model results show that, with mining activities being undertaken in both the North Open Cut and the Extension area as typified by Year 4 operations, the water management system can be operated to ensure no spills from the dirty water system. The CHPP demand can be fully met from on-site water sources and the dust suppression demand can be met with a reliability of 97%. The extra water generated through increased surface water runoff and seepage to the North Open Cut would mean that the mine site storages would operate at a higher level than for the existing system and that a substantial volume of water would accumulate within the Extended South Pit (and / or North Open Cut) excavation during extended wet periods, potentially affecting production. 8-18

Environmental Assessment Chapter 8 Surface Water Model Results Year 8 Open Cut Extension Table 8-6 provides a summary of the water balance model results for Year 8 of the Open Cut Project. Table 8-6 Water Balance Model Results, Open Cut Project, Year 8 Inflows Outflows Mean Annual Volume (ML) Seepage to Portal Sump 511 Seepage to D1 292 Pumping from South Pit 491 Pumping from North Open Cut 99 Net Inflow from Underground 206 Surface runoff dirty water system (excluding pits) 335 Harvest from clean water system 190 Total 2124 CHPP 1096 (100% reliability) Dust Suppression 608 (91% reliability) Ashton 359 (89% reliability) Net evaporation from storages 67 Spills from D1 0 Spills from PSD 0 Spills from proposed Dirty Water Containment Dams 0 Total 2130 Note: difference between total inflow and total outflow is due to change in storage over the simulation period. The water balance model results show that during Year 8 operations, the water management system can be operated to ensure no spills from the dirty water system. CHPP demands can be fully met, and dust suppression demands can be met with 91% reliability. The water volumes within storages would be slightly less than for the case with the new North Open Cut operating because the progressive infilling of the South Pit with mined overburden reduces the disturbed / compacted area within the pit, i.e. that component of the catchment that produces the largest amount of runoff. As with the Year 4 scenario, a substantial volume of water would accumulate within the Extended South Pit excavation during extended wet periods, potentially affecting production. Extended South Pit Final Void A water balance model was also undertaken for the Extended South Pit Final Void. Adopted inflows consisted of surface runoff and a groundwater inflow of 0.32ML/d. The only outflow from the final void would be evaporation. An adopted relationship between elevation, surface area and stored volume of the final void was used to determine storage availability. The results of the water balance model indicate a steady long-term storage volume of around 7,000ML and a water level at about -50mAHD which is well below the natural surface level. By comparison, the available water storage capacity (to spill level at 70m AHD) within the final void would be approximately 34,000ML. However, WRM consider that evaporation at the -50mAHD 8-19

Chapter 8 Surface Water Environmental Assessment level may be lower than at the natural surface level and that the long-term equilibrium storage volume would be greater than 7,000ML. Ultimately the final storage volume will depend upon the relationship between the water level within the void and the evaporation rate. Without detailed information on this relationship, WRM concluded that it is not possible to accurately determine the equilibrium water level, noting that it is possible that the equilibrium water level may be much higher than the predicted -50mAHD determined when assuming full evaporation. However, a sensitivity check assuming a 30% reduction in evaporation over the full depth of the final void indicated that although water levels would rise to within about 20m of the natural surface over a period of the order of 1000 years, water would not spill from the final void. 8.4 Mitigation Measures 8.4.1 Stormwater Management The conceptual arrangements of clean and dirty water diversion drains and sedimentation basins for Year 1 and Year 4 of mining operations for the Full Pit are presented in Figures 8-7 and 8-8. The following management structures would be constructed. Clean water diversion drains to divert runoff from undisturbed areas around the Mine Area and topsoil stockpiles. Dirty water diversion drains to collect stormwater runoff from disturbed areas and deliver it to sedimentation basins. Sedimentation basins to treat disturbed area run off prior to discharge. The sediment dams would generally be designed to capture run-off from a 1 in 50 year ARI storm event and would be monitored for performance and adequacy during and after construction. All water management structures would be designed and implemented as per Landcom: Soils and Construction - Managing Urban Stormwater, 2004. In the event of a spill from the sediment dams, water samples will be collected at the overflow from the sediment dam and at the surface water sampling locations along Station Creek. Extended South Pit Final Landform The proposed final landform of the Extended South Pit is shown in Figure 8-5. The eastern and northern components will be filled with overburden material and rehabilitated to a finished level above the natural surface. The south-western component of the proposed Pit will remain as a final void which will fill with water to a stable long-term level where groundwater inflows, surface runoff from the rehabilitated spoil and direct rainfall are, on average, equivalent to evaporation. All water from the final landform (above the natural land surface) would be captured in a series of diversion drains (graded banks) and diverted into the existing surrounding waterways and drainage lines. Prior to the successful rehabilitation of the landform, all water would be passed through appropriately designed sediment basins before release from the site. Where possible the use of rock-lined drains would be avoided. All water below the natural land surface would report to the final void. As discussed in Section 8.3.4, the void would gradually fill with water from the landform and groundwater ingress to an approximate level of -50mAHD. The construction of drainage works would closely follow the completion of reshaping activities to minimise the potential for surface degradation from heavy storm events that may occur prior to vegetation being established. After the construction of drainage works, the area would be topsoiled and revegetated using 8-20

Environmental Assessment Chapter 8 Surface Water a combination of pasture grasses and cover crops that seek to stabilise the ground surface as soon as possible. Following rehabilitation, rehabilitated landforms above ground level would feature drainage provisions designed to effectively capture and divert surface water run-off to stable disposal areas prior to being discharged into surrounding watercourses. The drainage works would include contour banks or diversion drains at regular intervals down the rehabilitated slope that would release water into sedimentation dams with sufficient capacity to allow for the settling of suspended solids. Suitable structures would be used to ensure the stability of water discharge points such as level sills, rock lined drop structures and/or energy dispersion measures. The contour banks and dams would generally be designed to capture run-off from a 1 in 50 year ARI storm event and would be monitored for performance and adequacy during and after construction. All water management structures would be designed and implemented as per Landcom: Soils and Construction - Managing Urban Stormwater, 2004. Further details on final landform surface water management are presented in detail in Appendix J Rehabilitation and Decommissioning Strategy. 8.4.2 Spill Response The following management approaches will be implemented on the site to deal with the risk of dirty water spills: All pumped inflows to dirty water storages will cease when the storage water level reaches a defined Maximum Operating Level. If the weather outlook indicates future significant rainfall, water will be pumped out of any dirty water storage that is within 100 mm of spilling, provided that a safe storage location is available elsewhere on the site. In the event of a spill, water samples will be collected at the overflow from the spilling storage and at the surface water sampling locations along Station Creek (for spills within the Station Creek catchment). For a spill from Possum Skin Dam, a sample will be collected at the discharge point and at the point of inflow to Glennies Creek. An incident report will be prepared which documents the circumstances leading to the spill, the measures taken to prevent the spill, the estimated spill volume and duration, and the measured water quality results. Any spillage would be reported to DECC in accordance with the requirements of the site s Environment Protection Licence. 8-21

This drawing is subject to COPYRIGHT. It remains the property of URS Australia Pty Ltd. Source: WRM Water & Environment Pty Ltd Client Project Title INTEGRA COAL OPERATIONS PTY LTD INTEGRA OPEN CUT PROJECT YEAR 1 - CONCEPTUAL SURFACE WATER DRAINAGE PLAN Drawn: Job No: AO Approved: RO Date: 20/11/2008 43177507 File No: 43177507.068.wor Figure: 8.7

Source: WRM Water & Environment Pty Ltd This drawing is subject to COPYRIGHT. It remains the property of URS Australia Pty Ltd. Client Project Title INTEGRA COAL OPERATIONS PTY LTD YEAR 4 - INTEGRA OPEN CUT PROJECT Drawn: AO Job No: 43177507 Approved: RO File No: 43177507.068.wor Date: 10/02/2009 Figure: 8.8 CONCEPTUAL SURFACE WATER DRAINAGE PLAN

Chapter 8 Surface Water Environmental Assessment 8.4.3 Surface Water Monitoring Integra currently has a surface water monitoring program which measures a range of water quality parameters at some 20 locations in the area surrounding its mining operations. The locations of surface water sampling points are shown in Figure 7-2 (Chapter 7 Groundwater). Water quality samples are collected on a monthly basis and sent for laboratory testing to determine a range of water quality parameters including ph, EC, TSS and TDS. As the proposed Open Cut Extension lies within the Station Creek Catchment and areas covered by the existing surface water monitoring system, the existing sampling locations would be adequate to monitor water quality impacts downstream of the Open Cut Project Area. Notwithstanding, Integra would implement the refinements to the surface water monitoring program recommended by WRM, namely: collection of grab samples along ephemeral watercourses such as Station Creek, during or immediately after surface runoff events; monthly water quality sampling of water storages on the site; and regular collection of data on water quality, storage water levels (including the Portal Sump) and pumping volumes between storages as this data would be of assistance in the future validation of the existing water balance model and management of water within the dirty water circuit. 8.5 Open Cut Project Area The concurrent development of the approved North Open Cut and expansion of the South Pit will increase the volume of dirty water generated within the Project Area through the addition of disturbed catchment areas to the dirty water management system and collection of additional groundwater inflows into the pits. Modelling has shown that by using a similar operational strategy to that currently employed, the water management system can still be operated to ensure no spills from the dirty water system. Although average water levels within all storages will be higher than under existing conditions and the Open Cuts may be required to hold substantial quantities of water during extended wet periods, the water management system provides some flexibility to manage these impacts through short-term variations in the long-term operational strategy (such as pumping rules). 8.6 Statement of Commitments Integra s commitments with respect to surface water management and mitigation are summarised in Chapter 17 Draft Statement of Commitments. 8-24