The Issues The Context Mine Water Management Water supply - PowerPoint PPT Presentation

The Issues The Context Mine Water Management   Water supply Community concerns Heaven or Hell for   Excess water Environmental protection Hydrologic Modellers?   Water quality Regulatory control Mines constantly evolve Steve Perrens 2 Water Quality Numerous sources – Different pollutants  Runoff into pit Coal dust, sediment;  Groundwater inflow Salinity, pH, iron;  Coal stockpiles Coal dust;  Haul roads Sediment, coal dust;  Vehicle maintenance Hydrocarbons;  Fuel storage Hydrocarbons;  Overburden runoff Sediment;  Overburden leachate Salinity, acid leachate;  Washery tailings disposal Sediment, salinity, pH? 3 4

Comparison of sediment dam and Mine Water Quantity & Quality drainage line water quality 500 Dam 1 Dam 2 Dam 3 Dam 4 Dam 5  450 Highly variable over time; 400 350 Total Suspended Solids (mg/L)  Pit & overburden area variable throughout mine life; 300 250  Groundwater inflow to pit variable – generally related to depth of pit; 200 150  Groundwater inflow to U/G workings variable depending of mine 100 25,000 50 Rising stage samples layout; Monthly 1 2 3 4 5 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 20,000 Percentile Total Suspended Solids (mg/L)  Runoff highly variable depending on climate 15,000 (typical annual variation: 20% - 300% of average) 10,000  Consequences of changes to mine plan 5,000 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentile 5 6 Management Issues Regulatory Issues  Sufficient supply for mine operations :  Water access licenses for incidental take  Dust suppression  Longwall operation  Unavoidable groundwater make  Coal washing  Problem when linked to ‘cease to pump’ rules in the WSP  Sufficient storage to meet operational requirements  Aquifer interference policy  Reliability of supply  Return flows not counted  Storage of excess – without compromising production  Treatment and discharge in the event of excess?  Water access licenses for supply;   Minimise discharge (zero discharge preferred) Availability of surface and groundwater licenses  Divert external catchments  Supply reliability  Enhanced use/loss (irrigation, evaporation)  Water quality (sediment, salinity)  Discharge licenses/permits  Treatment  HRSTS. 7 8

Mine Water Management Steve Perrens 10 Issues  Complex interactions between  Evolving mine landform  Rehabilitated and ‘natural’ catchments  Water management system  Storage requirements  Water balance highly dependent on climate  Increasing salinity:  Deeper pits  Underground mining 11 12

Predicted Annual ROM Supply and Issues CHPP Water Requirement (Assumes slurry disposal)  Alterations to mine plan and production 6,500 6,000  Short term variation in CHPP throughput 5,500 5,000  Operating rules for exchange of water between mines 4,500 ROM and Water Requirement 4,000  Opportunities for discharge from sites 3,500 3,000 2,500 2,000 1,500 1,000 ROM (t x 1,000) CHPP Water (ML) 500 0 0 5 10 15 20 25 Project Life (Years) 13 14 Projected Tailings Storage Requirements Mine Water Balance  Water sources (internal and external) 25  Water demands Cumulative Tailings Volume (m 3 x 10 6 ) 20  Dust suppression, 15  Coal processing,  Underground operations 10  Losses / discharge 5  Storage 0 0 5 10 15 20 25 Project Life (Years) 15 16

Water Demands Dust Suppression  Dust suppression – haul roads  Dust suppression,  Mainly achieved by water spray  Mainly achieved by water spray (chemicals in special situations) (chemicals in special situations)  Dependent on haul area and weather (rainfall and wind)  Differentiate between stockpiles and haul roads  Little benchmarked data in Australia  South African research – water required to maintain wet surface  Consistency of approaches by air quality modellers and (effects of road albedo and wheel movement) hydrologists?  Dust suppression – coal stockpiles  Underground operations  Dependent on dump height and reclaim process  Typical longwall – 1 ML/day  Dust suppression  Consistency of approaches by air quality modellers and hydrologists? 17 18 Why do we use models? Water Demands  Coal processing – dependent on  Prediction of interaction between the mine, climate and the  Mining process and source characteristics (Open-cut ± 12% fines; Underground ± 8% fines) surrounding environment  Dewatering process  Assessment (design) of the location and size of facilities Relative Water Treatment necessary to manage water Requirements Slurry disposal 100%  Understanding the risks Secondary flocculation 90% Paste thickener 60%  Ongoing management of water at an operating site: Belt press 40%  Pressure filter 30% Are predictions valid/correct? Solid bowl centrifuge 30%  Does management need to change?  Underground operations  Are new/additional facilities necessary?  Typical longwall – 1 ML/day  Dust suppression 19 20

Modelling Considerations Mine Site Models  Adequacy of supply - enough water?  System models:  Water gains and losses  Adequate storage –  Storages  Seasonal variation of rainfall and evaporation  Water conveyance (channels, pumps, pipelines)  Probability of extreme sequences of rainfall  Operating rules/triggers  Variation of groundwater make  Year-to-year carry-over of water  Process models:  Groundwater make  Discharge frequency, volume and quality  Runoff from different surfaces  Relevant timescale to characterise runoff and mine  Water uses (dust suppression, coal washing, etc) operations  Losses (evaporation, seepage)  Data requirements and availability 21 22 23 24

AWBM 25 26 Model Parameter Estimation AWBM Leave One Out Cross Validation Flow Duration 10.00  Automatic AWBM calibration for full data set with one year omitted Actual Calculated  1.00 Use estimated parameters to model runoff for missing year Runoff (mm/day)  Assess adequacy of fit between modelled and observed (Total volume, 0.10 R 2 , Nash-Sutcliffe coefficient of efficiency, flow duration, etc)  Repeat process taking out successive years of data 0.01 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Cumulative Runoff  Assess statistics of parameters and goodness of fit to select Percent of Time Runoff is Equalled or Exceeded 100% parameters for adoption Percent of Total Volume of Cumulative Runoff Actual 80% Calculated 60% 40% 20% 0% 27 28 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percent of Time over which Cumulative Runoff Volume Occurs

Groundwater Inflows to Pit and Storage Requirements – median rainfall Underground Workings Sequence: A 800  Derived from 700 Annual Dewatering (ML/year) groundwater modelling 600 500  Relatively steady day 400 to day 300  Significant variation 200 over mine life – 100 depends on mine plan 0 0 5 10 15 20 25 Mine Year 29 30 Storage Requirements – median rainfall Storage requirements – risk profile Sequence: B (± 125 years rainfall data) 31 32

174 172 170 Water quality modelling 168 Void Water Level (m AHD) 166 164  Salt balance – conservation of mass 162 160  Final void salinity – water and salt balance: 158 156  Groundwater leaching through in-pit spoil 154 0 100 200 300 400 500 600 700 800 900 1000 Years Following Mine Closure  Surface runoff from void 152  Groundwater loss from ‘lake’ (or make) 150 Void Water Level (m AHD) 148 146  Evaporation loss (accounting for depth of void) 144 142 140 Need for strong linkage between 138 136 134 surface and groundwater models 132 0 100 200 300 400 500 600 700 800 900 1000 Years Following Mine Closure 33 6,000 5,000 4,000 Salinity (mg/L) 3,000 2,000 Dr Steve Perrens 1,000 Evans & Peck Existing Climate Climate Change 0 (02) 9495 0500 0 10 20 30 40 50 60 70 80 90 100 Years Following Mine Closure sperrens@evanspeck.com 12,000 10,000 8,000 Salinity (mg/L) 6,000 4,000 2,000 Existing Climate Climate Change 0 0 10 20 30 40 50 60 70 80 90 100 Years Following Mine Closure