EAGLE MINE
In the mid-1980s, Eagle Mine, a former zinc mine near Minturn, Colorado, was identified as a Superfund site. Accumulated mining wastes had contaminated the adjacent Eagle River. The mine produced more than 12.5 million tons of ore from the early 1900s until the early 1980s.
In 1988, a former owner began a complex site cleanup consisting primarily of relocating, consolidating, and capping several million tons of tailings materials. In late 1989, metals-contaminated mine water began seeping from the old mine workings and reached the Eagle River. A conventional water treatment plant, designed by another consultant to produce 200 gallons of treated effluent per minute, was installed to treat the collected seepage. This plant experienced extreme operational problems and was not able to treat the required volume of water consistently. It also generated heavy volumes of sludge and had no sludge dewatering facilities.
In August 1990, MWE began reviewing the conventional treatment plant to identify possible improvements or alternative treatment solutions. Following the review, a new plant was conceptualized using the new heavy metals removal process.
The project team began a laboratory study to develop a process suitable for treating the heavy metals-contaminated water. The plant had to be designed, constructed, and operational as quickly as possible. Design criteria for the new plant consisted of existing discharge permit limitations, which specified maximum contaminant levels in the discharge, and a maximum average monthly flow rate of 200 gallons per minute. MWE developed a new process, which was awarded U.S. Patent 5,266,210 in 1993, to remove heavy metals and sediment from water. It produces an effluent water quality exceeding EPA Best Available Technology levels using a single clarification step – without the need for filtration and without significant post-precipitation and scaling.
The new process is simple, easy to operate, and results in substantial cost savings. It was less than six months from the time MWE was retained to the time the plant was constructed and under continuous operation.
When compared to two other Colorado Superfund mine sites, the cost per pound of metal removed at Eagle Mine is significantly less: $1.52 compared to $7.05 and $32.93.
MWE took over operation of the plant in 1996. In 1988 MWE added a supervisory control and data acquisition (SCADA) system to the plant. This new operational system increased reliability of the process performance, reduced chemical costs, helps maintain historical plant data, automatically triggers an alarm for emergency shut-down, and allows for unattended operation of the treatment plant’s liquid-side processes.
MWE’s work at the Eagle Mine was recognized by the Colorado Mined Land Reclamation Board (MLRB) in 1993 for outstanding reclamation at a Colorado mine. This project also received an Engineering Honor Award in 1993 from the Colorado Chapter of the American Consulting Engineer’s Council.