structures at EHM, the Footwall Shear Zone (FWSZ), shows disconnection. Disconnection is highlighted through different pressure responses below and above the FWSZ. Connection within aquifer zones were shown by similar pressure responses for all piezometers within a zone. An example of high intra zone connectivity is given in Figure 1b. Here hydrographs of 4 multilevel grouted piezometers all show a very similar response highlighting a well connected fracture system. Figure 1: a) Hydrograph of GT1-Piezometer 1 to GT1-Piezometer 6, Piezometer 5 and 6 are below the Foot Wall Shear Zone (FWSZ), which was identified as a boundary structure in the fractured aquifer, b) Hydrograph in aquifer zone 5, all 9 piezometers in this zone show a very similar response. The identification of aquifer zones allowed assigning a degree of water risk for each zone. The majority of water intersects recorded during development occurred in aquifer zone 5 (Figure 2), which also showed a large degree of similarity in hydrograph response (Figure 1b). The combination of a large number of recorded water intersects and the almost identical response in the hydrographs of all piezometers located in zone 5 highlight a well connected fracture network that is capable of producing large flows when intersected during mining. Aquifer zone 5 was consequently identified as the major water risk zone at EHM. Figure 2: a) EHM as built, b) EHM as built with all recorded water intersects (in green: flows <5 l/s, in yellow: flows 5-<10 l/s, in orange: flows 10-<20 l/s, in red: flows >20 l/s), c) EHM as built with all recorded water intersects and aquifer zone 5. In addition to predicting the risk of water intersects, the improved understanding of the compartmentalization of the aquifer allowed a dewatering strategy targeting only the aquifer zone with the largest water risk (zone 5). A total of 6 dewatering holes of 30 m length were drilled with a production drill rig from two locations (775 and 825 m below ground level). The total drilling time was less than a week. Dewatering of the formation by passive pressure head driven drainage allowed lowering the water pressure at the main development heading (825 m below ground level) from 4200 kPa to 700 kPa within 2 month. Further reduction in water pressure is expected through the drilling of two additional dewatering holes at the bottom of the current mine development (975 m below ground level). A diamond drill rig is scheduled to carry out this drilling in August 2013. The additional reduction in water pressure will aid development at the next priority heading at greater depth. STANDPIPING AND GROUTING METHODS
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