A major mine needed to dispose of 5000 acre feet of tailings impoundment water in order to close the mining operation. The system needed to evaporate 1000 acre feet of water a year for five years.
The Rain for Rent engineering department worked closely with the mine's engineering group to develop a system that would meet all environmental and design criteria.
The primary pump station located at the tailings impoundment pond consisted of a variable-frequency drive Cornell 10RB pump with an electric priming unit. The design point was 4100 GPM at 95 feet of head. This particular pump has a very flat curve and was well suited to the system's requirements.
A system flow meter and totalizer monitored the system and also provided input to the leak detection system.
All piping was fusion welded HDPE (high density, polyethylene). Pipeline flow velocities were kept below 8 ft/sec. Distribution piping 14" OD and 12.75" OD had a 2:1 pressure safety rating and surge pressure safety rating of 1.5X working pressure. Continuous acting and large orifice (vacuum) vents were installed every 1/4 mile to protect the pipelines from collapse and bursting (high pressure surges).
The maximum pressure in the mainline system was 260 PSI. Infield spray nozzles were designed to operate at 60 PSI with a flow rate of 3.18 GPM. Typically, 20 nozzles were on each lateral "sprinkler" line. One seventh of a block was watered every day, thus completing a full "irrigation/evaporation" cycle once a week for the full 400 acres.
Rain for Rent has considerable experience with mine leachate and tailing water evaporation systems. This particular land application system was the largest we have designed and installed. "I am particularly proud of our Nampa, Idaho branch personnel who worked very hard to ensure that our customer was satisfied," said John Lake, President.