Tuesday, October 19, 2010

Water Table Primer

Niether the public nor Fire River Gold shareholders are privy to the Golder Associates study on grouting and pumping at Nixon Fork. We do however have access to the environmental assessment which describes ground water conditions, something that this management apparently needs.

"There are three groundwater systems in the mine area. The first is found in the hilltops with their shallow cover of loess and weathered bedrock, which acts as an aquifer over the impermeable granitic intrusion. Surface water infiltration into the hilltops is forced to seep out of the hills as springs at high elevations. None of the early core drilling in the mine area found free water in the bedrock. However, as mining and core drilling depths increased ground water has been encountered. Ground water filters into the lower shaft of the Crystal mine at depths that varies with the season."
"The second groundwater system is found in the surface aquifers or active layers of the creek beds that thaw seasonally. Seismic investigations indicate at least 90 ft of alluvium above bedrock at one location in upper Ruby Creek. The entire cross section, however, appears to have a shallow active layer underlain by permafrost. Two exploratory wells were drilled in May 2004 in the Ruby Creek drainage to see if the area could be used for shallow injection of ground water pumped from around the mine workings. Each hole encountered permafrost to bedrock and the effort was abandoned."

"The third groundwater system is the regional water table that is encountered at the base of the Crystal mine. The water elevation in the bottom of the Crystal mine varies seasonally but it has reached an elevation of approximately 475 ft (145 meters) above sea level in the mine or about 800 ft (244 meters) below the surface of the Crystal portal.

"Groundwater flow in the regional water table is likely most significant in the permeable contact zone between the granitic intrusion and the carbonate rocks. Surface water flows appear to have large losses to the subsurface at this contact zone. Based on topography, the regional water table should discharge to the major river valley streams to the west, east and south."

Golder Associates
Thomas G Krzewinski, PE, Sr. Geotechnical Engineering
Jan F. Deick, Sr. Project Hydrogeologist
Bob Dugan, Office Manager
Steve Anderson, P.E., Senior Project Engineer