Dewatering
CSI Division 31, Earthwork
The process of removing groundwater from an excavation, using well points, sump pumps, or deep wells, to keep a construction area dry enough to work in, required whenever an excavation extends below the local water table and often triggering its own separate discharge permit for where the removed water actually goes.
Why it matters
Dewatering doesn't just make an excavation dry, done incorrectly it can draw down the groundwater table enough to cause settlement in nearby existing structures, so a dewatering plan on an urban site has to account for its effect well beyond the excavation's own footprint.
On a real project
A contractor excavating for a below-grade parking structure installs a ring of well points around the excavation's perimeter, pumping continuously to keep groundwater below the working elevation while monitoring nearby buildings for any settlement the dewatering might cause.
Who this matters most to
A Civil Engineer designs the dewatering plan based on the site's geotechnical conditions. An Equipment Operator or specialty dewatering contractor installs and runs the well points and pumps.
Where this goes wrong
A contractor's dewatering plan underestimates how far the pumping will actually draw down the groundwater table, based on a drawdown radius calculated from limited geotechnical data. Within weeks, a private well serving a home two lots away runs dry, well outside the radius the original plan accounted for, forcing the contractor to supply temporary water to the homeowner while the well is investigated and the dewatering plan is revised.