Sump/Open Pumping Dewatering
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What is Sump Pumping?
Sump pumping is the simplest, most cost-effective dewatering solution. Groundwater seeps into the excavation area, where it collects in sumps. Solids handling pumps then pump the collected water out of the excavation to a discharge point. This method is used in shallow excavations or when the soil has a high content of fine-grained material (ie. Clay/silt).
Sump Pump Design
Sumps are pits that are dug in the drainage area. In some cases, trenches in the excavation may be used to direct water to the pit. The sump is filled with rock and a screen/casing to house a pump. The pump is then set, and pumping begins.
For larger excavations, multiple sumps may be constructed around the project site to assist with drainage. In some instances, sump screens/casings can be drilled into place from the surface, prior to excavation, and utilized as the project progresses.
Advantages & Limitations
Advantages
- Useful drainage method in low permeability soils
- Dewatering small excavations when there is minimal water to be pumped
- Excavation subgrade is near/in bedrock
- Cost-effective alternative to other pre-drainage dewatering systems
Limitations
- Sumps can produce high total suspended solids in the discharge water
- Pumping of fines can increase the settlement/slope collapse risk
- Limited drawdown/flow capability due to shallow nature of the sumps
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