In March 2012 a drill intersected water flows of approximately 80 l/s at high pressure (5200 kPa) and high temperature (49 degrees Celsius) 825 m below ground level during development of the access to the shaft. Had not previously mined in this area although water was expected from previous exploration holes. Required to mine an additional 600m. No knowledge of how far the water zone extended. Drilling through valved standpipes mitigated the risk of uncontrolled water inflows from drill holes in declining development. This was very slow. A rapid drop in the water table was highlighted from Hydrograph analysis of installed piezometers. A strong aquifer compartmentalization was postulated. Based on the hydrograph response as well as through the identification of boundary structures a total of eight aquifer zones were identified at EHM with different degrees fracture connectivity. Targeting the zone with the highest hydraulic conductivity for dewatering allowed dropping the water pressure at the current main development heading from 4200 kPa to 700 kPa within two months. Dewatering and optimization of standpiping and grouting methods allowed a sequential reduction in the cycle time for mine development through high water risk areas.
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