Groundwater can often delay projects from the start. These are some of the best ways to remove it ahead of construction.
Construction dewatering is necessary at most sites to lower the groundwater level. You can’t build or pour a foundation unless you’ve removed standing water. Once it’s removed, you need to keep it out of the way until any construction activities below the natural groundwater level are complete.
Soil type and construction procedures often determine the dewatering method you’ll use. There are four top methods.
This is the most common and simplest form of groundwater control. Groundwater is collected in a sump and then pumped away from your construction site. Sump pumping is inexpensive, but you must be careful of excessive seepage and ground loss. Both can lead to ground instability in other areas of the construction site.
Be sure to test the quality of the groundwater you’ve collected with this pumping method. It may not be suitable for discharge unless you treat it first.
Sump pumping works best to remove groundwater in shallow excavations. It’s suited for permeable soils. You can also use sump pumping for deeper excavations in rock, or where there’s no concern about ground stability.
Look for an automatic dry-priming trash pump. They are reliable, inexpensive to operate, and easy to maintain or repair.
Deep well system pumping
A deep well system is made up of an arrangement of drilled wells. A submersible pump is fitted in each well. Deep well pumping lowers the groundwater level at a construction site by drawing the water away in each well.
As you might expect by its name, deep well dewatering is suited to deep excavations. It works best with moderate to high soil permeability. This pumping system helps to stabilize groundwater pressure. Deep well pumps have high capacities. They can move many thousands of gallons each minute. Well depth and spacing allows you to work in restricted areas.
Look for submersible pumps that use standard commercially available seals. These are less costly than some manufacturers’ proprietary spare parts.
This century-old pumping system lowers groundwater levels with a series of small-diameter wells. A header pipe to a wellpoint pump connects them. The pump creates a vacuum in the header pipe. Groundwater is drawn up from its resting point.
Welpoints are installed along the perimeter of your construction site. They do their job in stages if the groundwater level is deeper than 18 feet. That’s the limit to the height of which a wellpoint vacuum can draw water.
Wellpoint systems work best for shallow foundations and excavations. You’ll see them often used for pipeline trench work. They can be quickly installed and are easy to maintain.
Look for a self-priming, valveless positive displacement pump. They offer reliability, a low operating cost, and rapid onsite repairs.
Ejector pump systems
This dewatering method uses air within the wells to produce a vacuum. It removes groundwater from the soil. Ejector pumps circulate high-pressure water fed from a tank and supply pumps at ground level. It’s pumped down the well into the ejector nozzle and venturi at the well’s foot. The flow of water through the nozzle creates a vacuum in the well drawing the groundwater. The groundwater is piped back up to surface level and the supply pump recirculates it. Ejector dewatering systems are best suited for sites with silt or fine sands.
Your pumps are the key
Each of these four systems removes groundwater I n a different way. You’ll select the system depending on many factors. They’ll include the type of soil, the condition of the water, and even the amount of groundwater itself.
In some instances, such as the Wellpoint method, the pump must work without stopping until you’ve completed construction. That means you need the right pump for the right job. Don’t skimp on doing just as much research on pumps as you do on selecting your dewatering method.