According to the methods, a site is investigated for possible selective removal of sediment containing a contaminant. The dumbbell stanchion comprises a tubular structure 16 having a base portion 38 extending transversely to its distal ends, forming vertical stanchions. The interface enable an application to set the type of input and output data formats of a processing module and control when the processing module processes input data and generates output data. The feedback waveform and the corresponding reference waveform are both divided into a plurality of sub-waveforms. A restraining device prevents freewheeling over run of the rollers. Discharge means, including a removal device and at least one discharge chute, discharge correctly oriented closures from the discharge area.