The Ebenezer Acid Mine Drainage(AMD) Abatement Project reclaimed approximately 75 acres of coal refuse and slurry and stabilized 700 feet of stream bank and slurry cell berm. The project site is located in Muhlenberg County, 2.5 miles west of Drakesboro along Pond Creek, a major tributary of the Green River. The project was divided into three main areas based upon site topography. Materials on the site were deposited by mining activities on the site in the WKY No. 11 and WKY No. 9 coal seams. Materials on the site included course and fine waste coal, shale, sandstone materials capable of producing large quantities of acid, iron, aluminum, and other minerals. Prior to this project, runoff from the site and groundwater discharges released highly mineralized and acidic water directly into Pond Creek.
The lowest elevation work area contained 6.5 acres of course refuse and 50 acres of fine slurry. The right downstream bank of Pond Creek had been built up to form a berm for the slurry on the floodplain of Pond Creek. Portions of the slurry cell berm had begun to erode due to highly acidic mine seeps and overflow across the berm creating a potential danger for the release of large quantities of acidic coal waste materials. Adding further danger was the presence of a high pressure gas line in the slurry berm that could be ruptured if the berm failed. DAML stabilized the stream bank face/berm by armoring it with limestone rocks ranging from fist size to 3’ boulders. The smaller alkaline rocks provide alkalinity to neutralize the acidic water and the large rocks will prevent erosion of the berm by Pond Creek. The course refuse pile was graded to remove gullies and drainage ditches and permanent silt traps were established across the area. In the large slurry impoundment the existing drainage channels were used was to create new rock lined channels. The entire site area was covered with 2’ of earth and vegetated. Using the existing channels maintained drainage grade on the site, followed stable drainage areas established by the site, and kept the water table low enough for heavy equipment to work without sinking into the slurry material.
The midlevel work area consisted of course refuse along a roadside. This material was highly acidic and formed soluble sulfur salts that when wetted readily formed sulfuric acid. This area served as a fill area from slurry excavated from the upper work area channels. The course refuse provided a stable base material to spread the wet slurry upon for drying. After drying the material was graded and covered with earth and vegetated. Drainage channels were established to control runoff and prevent erosion.
The upper level work area was 12 acres consisting of two slurry ponds. These ponds did not freely drain so they were saturated during construction. The contractor had to dewater the ponds prior to the creation of drainage channels and placement of the earthen cover material.
Throughout the project the contractor had to be cautious working on the slurry material because when saturated, it could easily engulf an entire bulldozer or dump truck. All water from the site had to be treated to raise the pH and remove suspended solids prior to discharge. Agricultural limestone was liberally applied throughout the site during all stages of work to ensure the maximum incorporation throughout the cover material. The final average application rate was 100 tons/acre throughout the 2.5-3’ of final cover and the first 1/2’ of the original ground surface. The heavy application of limestone will add alkalinity to groundwater that seeps upward into the cover soil or downward as rainwater percolated into the underlying materials. Across the entire site drainage channels composed of erosion control blanket, limestone rock, silt traps, cyclopean rip-rap checks, and concrete weirs were installed to control the drainage on the site and ensure the water drains without eroding into the earthen cap material. The vegetated earthen cap will decrease the production of acid from the underlying materials and will stop the direct loss of material into Pond Creek.
