ABSTRACT
This chapter describes the background to decommissioning and describes commonly used methods. Groundwater control systems are designed with the specific intent of manipulating or influencing groundwater flow in order to allow construction or engineering work below groundwater level. The pre-requisite for decommissioning is that groundwater control is longer required. Very low-permeability cut-off walls or zones of ground treatment are widely used as part of groundwater exclusion strategies. In some cases, particularly shallow wellpoint systems penetrating one aquifer only on uncontaminated sites, shallow wells may be left unsealed with the wellpoint riser simply cut off below surface reinstatement level. Sumps are generally relatively shallow and are commonly decommissioned by backfilling with clean, inert and non-polluting backfill materials. Dewatering wells, relief wells and sumps are sometimes located within the footprint of the structure being constructed. The flange of the steel duct is below the original groundwater level, so as water levels recover, the duct will begin to overflow.
