📋 Case Study
Small-Scale Mine Dewatering & Water Management Implementation
Sustained groundwater ingress (~8–12 L/s during wet season) threatened pit wall stability, restricted access to lower benches, and risked contamination of surface runoff with dissolved metals (Fe, Mn, As). Limited power infrastructure, remote location, and strict WA EPA water discharge limits (<0.5 mg/L total suspended solids, <0.1 mg/L arsenic) compounded complexity.
🏗️ Project Overview
A small-scale gold exploration mine in the arid Pilbara region of Western Australia, operating across a 12-hectare open pit and shallow underground adit system. Annual production target: 15,000 tonnes of ore; maximum pit depth: 42 m. Site experiences seasonal monsoonal infiltration and persistent groundwater inflow from fractured banded iron formation (BIF) aquifers.
🎯 Challenge
Sustained groundwater ingress (~8–12 L/s during wet season) threatened pit wall stability, restricted access to lower benches, and risked contamination of surface runoff with dissolved metals (Fe, Mn, As). Limited power infrastructure, remote location, and strict WA EPA water discharge limits (<0.5 mg/L total suspended solids, <0.1 mg/L arsenic) compounded complexity.
🔧 Design Approach
Phased, risk-based design integrating hydrogeological modeling (MODFLOW-SURFACT), real-time monitoring (12 piezometers + 3 automated flow stations), and modular treatment. Selected submersible borehole pumps with variable-frequency drives (VFDs) for adaptive dewatering; gravity-fed settling + cartridge filtration + pH-adjusted coagulation/flocculation (FeCl₃ + lime) followed by activated carbon polishing for trace metal removal. All systems designed for solar-diesel hybrid power and minimal civil works.
📐 Design Diagram
AI-generated project design illustration
📐 Key Calculations
Required dewatering capacity
Q_required = Q_inflow × Safety factor (1.3) + Evaporation loss compensation
Result: 15.6 L/s
Ensured pump selection accommodated peak monsoonal inflow while maintaining safe drawdown rates (<0.5 m/day) to prevent slope instability.
Retention time for coagulation basin
t = V / Q_design, where V = basin volume, Q_design = max treated flow (15.6 L/s)
Result: 24.3 minutes
Met minimum 20-min contact time per WA DER guidelines for effective arsenic co-precipitation with ferric hydroxide.
Solar array sizing for 24/7 pump operation
P_solar = (Total daily energy demand kWh/day) / (Peak sun hours × System efficiency)
Result: 42.7 kWp
Enabled >92% renewable energy coverage despite high dust loading and seasonal irradiance variability, reducing diesel consumption by 87%.
📊 Results
Metrics: Average dewatering rate: 11.2 L/s, Treated effluent turbidity: <0.3 NTU, Arsenic concentration: 0.04 mg/L, System uptime: 98.6%, OPEX reduction vs. conventional diesel-only: 34%
Achieved stable pit operations at full bench depth, eliminated uncontrolled seepage, and consistently met all EPA discharge criteria over 18 months of continuous operation. Modular design allowed staged commissioning with zero production downtime.
💡 Lessons Learned
- •Real-time piezometric feedback is critical for adjusting pump duty cycles—static drawdown assumptions underestimated localized fracture flow by up to 40%.
- •Pre-treatment sediment screening reduced cartridge filter replacement frequency by 70%, justifying added CAPEX.
- •Local operator training on VFD diagnostics and coagulant dosing calibration proved essential for sustaining performance during contractor handover.
✅ Key Takeaways
- 1For remote small-scale mines, integrated dewatering and water treatment must prioritize modularity, energy resilience, and operational simplicity—not just compliance—to ensure long-term viability.