Trench dewatering is one of the most routine yet consequential activities in horizontal infrastructure construction. Every metre of buried pipeline, cable duct or culvert laid below the water table depends on a temporary, well-managed drop in groundwater level to allow safe, dry, compactable working conditions. The methods used to achieve that dry condition, however, have changed little in half a century. Vacuum-primed dewatering spears feeding water to surface settling tanks remain the default approach on most sites, despite well-known limitations around priming reliability, cavitation, plant footprint and discharge water quality management.

This paper sets out the case for a step change in that practice through the adoption of Changing State Technologies' (CST) MPR pump — a Stable Vapour Cavity technology capable of drawing water from existing in-ground dewatering spears without priming, without cavitating under mixed air-water suction conditions, and without the need for an intermediate settling tank. In place of the traditional four-stage water handling train — spear, vacuum pump, settling tank, sediment treatment — the MPR approach compresses this to two stages: spear and pump, discharging directly through consumable filter bag screens.