Dewatering is one of the first steps in construction projects. It is the process of removing surface or groundwater from a construction site, before the ground is prepared for excavation. The process involves pumping out or evaporating the water to lower the water table on the site to prepare a safe environment to work.
Why is Dewatering Important?
Construction areas are one of the most dangerous workplaces. Lack of proper safety measures can lead to serious injuries. Site safety is of the utmost importance for which de-watering is an important process. It controls groundwater to prevent flooding in the excavated area that can damage construction materials and endanger workers. Once the construction is over, de-watering is stopped to restore the original watering table. Nearly all construction sites need de-watering as water tends to accumulate in trenches and excavation sites.
There are four commonly practiced dewatering methods. It is important to select the right technique for dewatering based on soil conditions and the water table.
- Wellpoint: This method is suitable for grounds that are up to five to six metres deep. A series of impermeable or low permeable wells are built along the excavation area to prevent water from entering the site. The Wellpoints are connected to riser pipes that, in turn, connect to a main pipe and vacuum pump through which water is drawn out through suction. Any contaminated water is first treated to remove harsh elements before drawing the water away.
- Eductor Wells: This method is used for grounds containing a high content of low permeable clay or silt with depths up to 10m to 45m. Wells are created as above, but high-pressure water is used at the base of each well using high-pressure water pumps to reduce the water level and draw it out of the riser pipe instead of suction.
- Sump Pumping: This is the most common and economical method, best suited for shallow excavation areas in soils that have a high content of sand or gravel. Sumps are used to pump out water through wells within the excavation ground or at the perimeter. Rainwater, trapped groundwater in the cut-off area, any seepage is removed by pumping it out by sumps or through wells within the excavation area of the perimeter. A lowered water table outside the excavation area is dangerous. It can compress soil layers significantly, impacting adjacent structures such as roadways and rot piles of timber in the area. This is why city building authorities insist that dewatering is carried out inside the excavation site.
- Deep Wellpoint: Best suited to draw out large amounts of water from the well, this method relies on drilling boreholes with submersible pumps to lower the groundwater. Gravity depletes the groundwater in the water table. Casings in the retain the wells filter out sediment.
Best Ways to Dewater
De-watering methods need to be well-planned to prevent soil erosion, seepage and other problems. Adopting proper techniques is important for a successful outcome.
- Pick a discharge area that is safe to dispose water.
- Check city requirements and local permits before dewatering.
- Inspect the water table conditions before dewatering.
- Keep an eye out for soil erosion or instability during dewatering.
- Never discharge the water on the slopes.
- Try to discharge the water into a forested area or an area that has the vegetation.
- Never carry out de-watering in heavy rainfall.
- Contaminated water must never be discharged.
- Treat contaminated water containing oil, grease or harsh chemicals.
At Taber Solids Control, Edmonton, our technicians are well experienced in providing you with effective water treatment solutions. We are specialized in de-watering among other services to guarantee the safety and well-being of property, employees, equipment and the environment.
Call us to get the job done right.