Systems and methods for processing earthen slurries such as slurries of earth cuttings and, in particular, systems and methods that involve two separation units for dewatering the slurry or that involve additive mixing units are disclosed. The systems and methods may include a conveyor such as a drag-slat conveyor that removes slurry from a holding tank at which the material is dumped and toward the separation units to allow the material to be continuously processed and dumped into the holding tank.