Two piezometers were installed at the Blackwater mine water treatment site to serve multiple purposes concerning both system design and continued monitoring. By drilling into the mine void, we were able to verify that the old mine workings are indeed open and hydraulically connected. This will be important when solids removed during treatment are pumped into the mine during normal operation of the treatment plant. Additionally, the piezometers are used to verify the mine pool elevation which is critical as the treatment system relies on gravity to feed water from the mine to the treatment system. Any change observed in the mine pool elevation now or during treatment could indicate changes in hydrologic conditions that may require alterations to treatment design or operations. (see piezometer diagram below)

The Piezometers were constructed by first creating an access road and drill pads on property owned by Western Pocahontas Properties, LP. The Piezometers were drilled using a truck mounted rotary air drill rig. The 6” diameter holes were drilled until mine void was encountered and the depth to the mine floor could be verified. 4” SCH40 PVC pipe was used to case the hole including a custom cut 10’ long well screen used within the mine void area to allow for a downhole camera to be inserted into the casing and view the mine void. Rubber shale traps were installed directly above the void space between the casing and the overlying bedrock. Bentonite clay was placed directly on the shale traps to seal the annulus prior to grouting. Grout was pumped down the well through a 1” PVC pipe to fill the annular space from just above the mine void up to the surface to hydraulically seal the mine from other rock units. Finally, a lockable cap was placed on the wells.

Active drilling operations showing the drill rig and, in the foreground, the drill bit used to drill the piezometers. Driller: Wayne’s Water ‘N Wells, Oakland, MD.

What the heck is a piezometer?