What is dewateringin construction?

A sump collects water that has already entered the excavation in a low pit and pumps it out, which works for rain, perched water, and minor seepage. A wellpoint system lowers the water table before the water reaches the cut: dozens of small wells around the excavation connect to a header pipe and vacuum pump and pull the groundwater down. Permeable soil with a high water table generally needs wellpoints; sumps alone just chase the inflow.

As setup plus run time. Setup is the fixed cost: mobilization, wellpoint and header installation, sumps, and discharge piping. Run time is the operating cost per day or week the pumps run: rental, fuel or power, and monitoring. Duration moves the number most, and it comes from the construction schedule rather than the drawings, so the estimator should state the assumed weeks of pumping right on the line item.

Usually, yes. Pumped groundwater typically has to pass through sediment controls, a tank, filter bag, or basin, before discharge, and most jurisdictions regulate where it can go; storm systems often require approval and sanitary sewers usually prohibit it without a permit. On projects disturbing an acre or more, the discharge points and controls belong in the SWPPP. Carry treatment and permit costs with the dewatering line instead of assuming free discharge to grade.