Sylvania Volspruit Mine. Water Balance Simulation Results Summary

Transcription

1 Sylvania Volspruit e Water Balance Simulation Results Summary 13 January 214 Prepared for: Sylvania Compiled by: WJ Gouws (SimX Consulting CC) Dr FS Botha (Water Hunters)

2 1. BACKROUND This results summary is an excerpt from the dynamic water balance report done for Sylvania, Volspruit e. The summary highlights the prime inputs, assumptions and results for three scenarios that were simulated over a nineteen year period starting January 213. These scenarios were: 1a Base Case: o Conservative inflows to the pit areas (grouted, no faults) o Grass Valley used as buffer (both sourcing and recharging) o Irrigation of excess water to farmers apply 1b 2% Saving on TSF water losses: o Same as 1a, but additional 2% saving on water losses at the TSF 2a No irrigation (otherwise same as 1a) 2. ASSUMPTIONS AND INPUT VALUES Figure 1 Dynamic Water Balance Simulation Volspruit e in Appendix A shows the schematic flow diagram (FD) of the simulation model as set-up in Arena. The FD captures the major water infrastructure and all flows are uniquely numbered with red lines indicating the dirty water- and blue lines the clean water circuits. Major rules applied in the logic: Dewater pits at 252 m³/h only if SWD < 25% Irrigation is at constant rates while the Irrigation Dam is not empty: o 1.75 Ml/day for the first two years o 1. Ml/day for the next ten years o.75 Ml/day for the last seven years Irrigation Dam overflows to RWD OR pumps to RWD when RWD is low Grass Valley delivers o Delivers 1 Ml/day in Nov-Apr, 2. Ml/day in May-Oct while Irrig. Dam < 6% o Recharge at 2 Ml/day whenever the Irrigation Dam > 9% o The netto sourcing from Grass Valley may not exceed 1 Ml/day (sustainable yield - Grassvally mine abstraction Water Use license study) Other assumptions that influenced the three scenarios tested were: N-Pit was kept empty for at least 3-4 months every year Keep SWD empty to prevent overflows to the environment SimX Consulting /1/214

3 3. RESULTS Scenario 1a (Base Case): See graphs in Appendix C The mine had sufficient water for operations except for the period between 225 and 226 when the inflows from North Pit decreased and South Pit inflows was still low o Grass Valley could not deliver the shortage given the pump constraints above o External sources had to supply 88 m³ during the 15 month period Irrigation to farmers followed the rules set above but failed in: o 22/21 when a dry winter was simulated, and o 225/26/27 when the North-Pit inflows decreased and the South Pit inflows was still too small No overflows to the environment were recorded Scenario 1b (2% saving in TSF losses): See graphs in Appendix D Decreasing Seep/Interstitial losses at the TSF by 2% (from 42.1% to 33.7%) returns an additional 22 m³/a to the RWD for re-use. This: o Improves the irrigation dips experienced around 22 and 225 o Reduces the Take from Grass Valley by just over 22 m³/a o Negates the need for 'external sources' in 225/26 Scenario 2a (No Irrigation): See graphs in Appendix E The initial dewatering of the North Pit in the first two years (when production is still low) results in large volumes of excess dirty water available. This excess water can: Be pumped to Grass Valley for recharge (max rate of 2 Ml/day) Pumped to the farmers for irrigation water (max 1.75 Ml/day in the Base Case scenario, but this is zero in this scenario 2a) The netto Take from Grass Valley reduce to almost zero as the total sourcing and recharging are around 25 m³/a each The lack of having a drain (irrigation) however, results in: Overflows of some 55 m³ from the SWD during this period SimX Consulting /1/214

4 Appendix A Simulation Flow Diagram (FD) Figure 1 Dynamic Water Balance Simulation Volspruit e SimX Consulting /1/214

5 mm mm Appendix B Graphs pertaining to all scenarios 12. Avg monthly rainfall - Historic vs Simulated Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Historic Simulated Mth Rainfall Mth Peak Figure 2 Rainfall simulated Avg monthly rainfall - simulated vs historical values Rainfall simulated correlates well with historic rainfall data Inflows to North/South Pits (Grouted&No Faults) - monthly flow volumes Figure 3 Inflows to North- and South Pits simulated Flow 34 Flow 31 Pit inflows were taken from the Ground Water Model but the North Pit was simulated with an extended dewatering pattern that abstracted 2 5 Ml/day for a 3 month period, followed by 1 5 Ml/day for the next 9 months. This continues for the rest of operations. SimX Consulting /1/214

6 North Pit pool - monthly levels Appendix C: Result Graphs (Sc 1a - Base Case) Grass Valley water sourced - monthly flow volumes F53 to ID F51 to RWR Irrigation Dam - monthly levels Recharge to Grass Valley - monthly flow volumes Flow Return Water Dam (RWD) - monthly levels 6 Irrigation to farmers - monthly flow volumes Flow Level Storm Water Dam - monthly levels Figure 4 Result graphs for scenario 1a (Base Case) SimX Consulting /1/214

7 Appendix E: Result Graphs (Sc 2a - Base Case with NO Irrigation) North Pit pool - monthly levels Irrigation Dam - monthly levels Return Water Dam (RWD) - monthly levels Grass Valley water sourced - monthly flow volumes F53 to ID F51 to RWR Recharge to Grass Valley - monthly flow volumes Flow Irrigation to farmers - monthly flow volumes Flow Storm Water Dam - monthly levels Level Figure 5 Result graphs for scenario 1b (2% saving on TSF losses) SimX Consulting /1/214

8 North Pit pool - monthly levels Appendix E: Result Graphs (Sc 2a - Base Case with NO Irrigation) Grass Valley water sourced - monthly flow volumes F53 to ID F51 to RWR Irrigation Dam - monthly levels Return Water Dam (RWD) - monthly levels Recharge to Grass Valley - monthly flow volumes Flow 54 Irrigation Dam returns to RWD - monthly flow volumes Flow Storm Water Dam - monthly levels 12 Overflows to environment - monthly flow volumes Level Figure 6 Result graphs for scenario 2a (No Irrigation) Flow 49 SimX Consulting /1/214