Covering of soft mine tailings

The historically ponded (HP) area of the Consolidated Tailings Pile (CTP) at the Eagle Mine Superfund site presented difficult (but not unusual) conditions for completion of the required covering and capping activities. The extremely high moisture content and low strength of the soft tailings would not even support low ground pressure construction equipment. Closure of the HP area required the placement of 2 to 12 feet of regraded and relocated material and, after 90 percent of the primary settlement was achieved, installation of a multi-layer cap. After a field test with a woven geotextile was unsuccessful, a plan to use a geogrid material with a drainage layer was developed for winter placement using the frozen surface to support the geogrid and drainage layer. The successful placement of that initial HP area cover provided access for additional material (fill) placement and, after the required settlement had occurred, offered a stable base for cap placement.