In Plain English
Quick Answer
Pumping water out of an excavation so construction work can be done in dry conditions.
Definition
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.
Context
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
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.
See Also
Related Terms
FAQ
Questions Contractors Ask
What factors drive the cost of dewatering in a bid?
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.
What dewatering method should be used for different soil conditions?
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.
Does dewatering require permits, and who handles discharge?
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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