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Sitework & Earthworkaka: pumpingaka: groundwater control

Dewatering

In Plain English

Pumping water out of an excavation so construction work can be done in dry conditions.

Definition

The removal of groundwater, surface water, or accumulated rainwater from an excavation to maintain dry working conditions. Dewatering methods include open pumping (sump pumps), wellpoints, deep wells, and eductor systems, chosen based on soil conditions and the depth and extent of the excavation. Proper dewatering protects workers, prevents soil instability, and allows construction to proceed below the water table.

Why It Matters in Bidding

Dewatering is a frequently underestimated sitework cost whose price swings widely with the water table, soil permeability, and how long the excavation stays open. Because the method and duration depend on subsurface data that may be limited at bid time, it is a significant risk item that estimators often address with unit pricing or explicit assumptions. Inadequate dewatering also stalls the schedule and can trigger excavation instability and safety exposure.

Example

On a high-water-table site, the estimator prices a wellpoint system based on the geotech report, then qualifies the bid by stating the dewatering allowance assumes the system runs for the 90-day excavation period.

Related Terms

ExcavationShoringSubgradeFrench Drain

Frequently Asked Questions

Key drivers are the depth of excavation below the water table, soil permeability, the chosen method, the duration the system must run, and discharge permitting or treatment requirements. Because these depend on subsurface conditions, estimators often price dewatering with stated assumptions or unit rates to manage the uncertainty.
Open pumping with sumps suits shallow excavations in less permeable soils. Wellpoints handle moderate depths in sandy soils. Deep wells and eductor systems address deeper excavations or high flows. The geotechnical report guides the selection, since the wrong method can fail to control water and stall the work.
Pumped water often cannot simply be discharged onsite; many jurisdictions require permits and may mandate sediment or contaminant treatment before discharge to storm drains or waterways. Estimators should confirm permitting and treatment scope, since these requirements add cost and schedule and are easy to overlook when pricing earthwork.

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