Wellpoint Dewatering
Utilizing wellpoints to manage groundwater near excavations is an overall efficient and popular option. A complete wellpoint system uses a series of small diameter PVC pipes vertically installed in the ground. These pipes can be installed up to roughly 20 ft deep and feature a slotted screen at the bottom, which allows water to flow in while a specifically designed filter pack prevents the pumping of fines. After they’ve been installed, the pipes get connected to a suction header, which is a larger PVC pipe that horizontally collects the water from multiple wellpoints.
The suction header is connected to the vacuum pump, or the wellpoint pump, creating the required strength to draw water upwards from the ground. Since this operates by a vacuum system, watching out for air leakage is critical, as any amount could negatively impact the overall performance of the system. To minimize the chances of air leakage, we use components such as rubber grommets and Fernco boots which help seal connections throughout the system.
Sock Tile Dewatering
This method typically starts with a 5” perforated corrugated tile wrapped in a geofabric sock, which acts as a filter, being laid horizontally at the bottom of a trench created by our one-pass trencher. The tile is connected into a non-perforated header tile, which is brought up to surface and tied into a vacuum pump. Usage of the vacuum pump at surface limits the vacuum depth capability to no greater than ~ 20 vertical feet deep (depending on the location), and a max of ~ 800 linear feet of header per pump (dependent on-site soils and potential volume).
Deep well Dewatering
A single deep well consists of a well casing with a screen at the bottom, which can vary in size. An electric submersible pump is then lowered into the casing, set near the bottom, and is connected to a riser pipe that brings water to the surface. After the submersible is set into place, the riser pipe manifolds to a discharge system using a rigid hose. As no vacuum is applied in this application, it relies on gravity to bring water through the soil to the submersibles. A specifically designed filter pack surrounds the well screens to prevent the pumping of fines. Most systems involve multiple wells surrounding an excavation.
Eductor Dewatering
Eductor dewatering begins with a high-head pump connected to a water reservoir that pumps pressurized water through a supply line into a wellhead with two ports. From there, the water is forced into the outer PVC casing and through a venturi located at the bottom of each well. The venturi creates a vacuum that draws in surrounding groundwater from a lower drop tube, which extends to a screened section at the base of the well. The combined recirculated and extracted water is then forced up an internal riser pipe to the surface, where it re-enters the reservoir tank through a return line. While this is a closed system, after some time, the addition of groundwater causes the reservoir to overflow, and be discharged out of the tank. A full system consists of multiple eductor wells manifolded together.
Conclusion
Whether you need the depth capabilities of a deep well or efficiency of wellpoints, understanding the operations of each method will help you to secure a workably dry site. At Mersino Water Solutions, we pride ourselves on being experts in all things dewatering – so if you require any of these services for your next project, contact us via phone call or by filling out an inquiry form.
