Ten proactive measures to help you plan and maintain a dry, working quarry.
by David Stewart and Stephanie Hassler
To an outsider, an open pit mine may appear to be nothing more than a fancy hole in the ground. But mining insiders know the level of detail involved in mine planning, including efforts to keep water from stopping production. Consider taking the following proactive measures to keep your pit floor as dry as possible.
- Be sure that your mine plan includes engineering and location of a sump. Obviously, the larger the sump hole, the greater the chance to handle storm surges. Create a sump hole with the capacity to handle a daily maximum of 2 inches of rain, and calculate the resulting gallons over the square footage of surface area with the goal of ensuring that the sump hole does not fill immediately during rainfall.
- When benching, continue your ramp another 10 to 20 feet in depth below the surface to create a sump hole, which would be of minimal additional cost and maximum overall benefit, since you’d eventually be benching down even lower. This practice pulls water down.
- When sub-drilling, if you get the sump below the sub-drill, you effectively create a French drain that allows the material to drain out, absorbing the stormwater.
- To divert as much run-off water as possible, consider digging a trench wall or creating a berm/terrace to collect water that would otherwise enter your pit.
- Fill in wet spots to maintain the level of your pit floor.
- Use a good pump. When selecting a pump, particularly for stormwater management, consider the availability of automatic controls. Automatic controls can serve two purposes: the first is to automatically start and stop the pump in conjunction with level floats; and the second is to perform the starting and stopping slowly, in an effort to eliminate unnecessary engine wear and tear caused by bringing a pump online at full throttle.
- Pump performance is particularly important. Make sure you size the pump for the volume of water you anticipate. This will help the pump operate in the most efficient part of the pump curve and increase pump longevity. In addition, make sure you position the pump safely and as close to the water source as possible. Check the impeller for wear or cavitation at every maintenance interval (at roughly 250-hour intervals). Also be sure to clear the impeller of obstructions. You can do this by removing the suction line.
- Be sure to consider discharge pipe size for your dewatering system. For example, you can achieve a greater discharge capacity from an 8-inch hose connected to a 6-inch pump than you can on a strict 6-inch to 6-inch connection. Larger pipe increases discharge capacity.
- Check discharge piping and remove all leaks.
- Consider having a lead and lag pump to supplement stormwater management.
- If the pit is particularly wet, consider drilling wells around the perimeter to intercept the water and draw down the phreatic surface below the pit floor.
- Build a waterfill station in the pit for your water truck. This will save energy and trips on your water truck.
- Make sure sediment ponds and process ponds are not leaking into the pit. Relocate to avoid leading additional water into the pit sump.
10. Pipe large amounts of water that could enter the pit to a sump away from loading and travel ways. Productivity is cut drastically if the material is wet. In addition, a wet pit floor can wreak havoc on rubber tires, particularly on front-end loaders.
David Stewart is the plant manager of Lafarge’s Cummings Quarry in Cummings, Ga.; Stephanie Hassler is corporate communications manager, Godwin Pumps, headquartered in Bridgeport, N.J.