The primary methods of pre-drainage are wellpoints and deep wells. Applying these methods in an engineered design is proving to be a faster, safer and more reliable method of expediting ash pond closure than traditional rim ditching and sumping which can result in instability and running ground conditions in the ash.
Wellpoints are very effective in soils and ash of low hydraulic conductivity and when close spacing is required. A deep well system can be installed to much greater depths than wellpoints and is best suited to material of high hydraulic conductivity such as bottom ash or where the ash extends to significant depths. Where subsurface conditions dictate, deep wells can be utilized around the pond perimeter, with interior dewatering accomplished by wellpoints.
Moretrench has successfully applied pre-drainage dewatering techniques to a number of ash ponds, with the resulting stabilized material proving to be readily and rapidly excavated in tall, near vertical lifts with conventional track-mounted and rubber tire equipment.