The North Fork of the Blackwater River and the nearby Upper North Branch of the Potomac River suffer severe AMD pollution originating from underground mine pools of the Coketon/Kempton Industrial Complex. Situated in Garrett County, Maryland and Tucker and Preston Counties, West Virginia both the Kempton and Coketon mine pools trace their history to early 1900s – 1950s, when the Davis Coal and Coke Company mined the Freeport coal seam in both locations. The two underground mine complexes eventually became interconnected underground, separated only by an unmined coal barrier. When the mines were closed, and pumps that kept mines dry during mining where turned off and the mine voids became filled with water. The Kempton pool is now an underground lake covering 1,800 acres and discharging an average of 3.5 million gallons of acidic water per day into the North Branch of the Potomac via Laurel Run (one of several Laurel Runs in the watershed.) The Coketon pool covers 1,110 acres and discharges an average of 2 million gallons of water per day into the North Fork of the Blackwater River. The pHs of both discharges is in the 3.0 range and have heavy concentrations of dissolved iron and aluminum. In addition to the underground mine pools, there are numerous surface sources of AMD associated with these mining complexes. These include strip mines, highwall mines, and gob piles (piles of waste rock).