Program: David Bardsley, P.G. will present a case study of dewatering a tailings pond with unique challenges and conditions that could lead to a catastrophic toxic release. In this case, the Maine Department of Environmental Protection looked to horizontal wells to address their challenges.
The Maine mine tailing site provided several challenges. One, the remote location and rugged terrain limited equipment access. Two, the impoundment’s embankments were constructed of mine waste including boulder and cobble materials. Three, little field data was available as to composition and water content of the sludge at the bottom of the pond.
To treat the tailings drainage a gravity-fed bio-reactor was to be constructed down gradient of the impoundment. The future site of the bio-reactor and the improved roads leading to it provided a logical location for drilling activities. By setting up in this location and drilling under the clay and rock embankments the first two challenges could be overcome.
The third challenge required a unique solution. By drilling under the embankment and then up through the floor of the pond a potentially uncontrollable drain may develop. Depending on the water content or slurry composition this could lead to a catastrophic toxic release. During the design phase of this project this became poignantly clear with the Gold King Mine release into the Animas River, Colorado.
To avoid a similar release several controls were implemented at the Maine site. Notably casing was driven under the embankment with the drilling going through the length of casing. The casing provided support to the overlying embankment and also focused any potential discharge through this one control point. A plug at the exit of the casing controlled flow out of the tailings pond.
A gravity-fed dewatering drain was successfully installed via horizontal directional drilling. Drilling operations worked down gradient of the impoundment toe, drill under the clay embankment and up into the lower levels of the impoundment. When taking this approach thorough planning and preparations are necessary to avoid an uncontrollable release of tailings liquids. Takeaway lesson from this project is that with proper planning mine tailings can effectively be drained using horizontal wells.
Include for EACH Person (badge will be printed as provided):
$27 SME Tucson members who reserve by deadline.
$35 non-members who reserve by deadline.
Add $3 to above ($30/$38) for late RSVPs if space allows.
Free for current UA mining students who are UA SME members.
Payable at the door by cash or check payable to SME TucsonCost does not include bar drinks. Cash bar is available.