Dewatering - Hoelscher Dewatering Inc.

Hoelscher Dewatering Inc.

Dewatering Services

Our specialists know how to get groundwater and surface water away from your site, and keep it away permanently. Whether your construction project is a straightforward residential development or a complex industrial facility, our expertise in the areas of pipeline, sewer, tunnel and mass transit construction is invaluable. We offer a wide spectrum of services, including preliminary consultations and conception, drafting of special proposals, expert project execution, and computer-controlled monitoring and documentation.

Eductors

Eductor wells are effective for situations where pumping levels are too deep for wellpoints, yet well yield levels are too low to rely on electric submersible pumps alone. While not suitable for depths greater than 45 to 50m, educator wells are an ideal dewatering solution for projects that require groundwater to be lowered more than six metres below ground in lower permeability soils.

Eductors are drilled and installed like deep wells, but differ in the way they extract water. Unlike electric submersible pumps, which burn out quickly if run in dry boreholes, educators pump air and water mixtures without issue. Sealing the borehole on an educator well also creates a vacuum assisted drainage path towards the well.

Eductors systems require a high-pressure supply and low-pressure return header main following the line of the wells. They also often require more experience and maintenance to operate at maximum performance.

To help, Hoelscher Dewatering provides double pipe or concentric pipe educator systems, depending on project requirements; and its 30-plus years of installation, monitoring, control, and maintenance experience with educator wells guarantees optimal performance every stage of site dewatering.

Deep Wells

Deep wells are most commonly used for site dewatering and created by drilling boreholes down to depths of up to several hundred metres. They can be drilled using dry or straight-flush rotary drilling depending on site conditions, intended depth, and diametre, which can range from 300 to 2000mm.

Once drilled, boreholes are lined with a wellscreen / casing assembly. Gravel is then added to fill the annular void around the assembly, and a bentonite seal is placed to protect the borehole against surface water and/or contaminants. Finally, a multi-stage submersible pump is installed within the deep well to begin groundwater extraction, and discharge lines are used to carry the groundwater to a discharge point at the surface. Together, this system works to lower the water table to a project’s desired depth.

Vacuum-extracted deep wells share are similar to standard deep wells, but use a partial vacuum to provide faster, more wide-ranging groundwater extraction in soils with low permeability. This is achieved through the installation of a vacuum pump aggregate installed at the upper edge of the well which can achieve of up to 28” of vacuum. Vacuum-extracted deep wells are typically made with boreholes at depths up to 50m and diametres between 300mm and 700mm, and are effective in aquifers with permeability coefficients ranging from 1X10-5 m/s to 1X10-7m/s.

Vacuum Deep Wells

Deep wells are most commonly used for site dewatering and created by drilling boreholes down to depths of up to several hundred metres. They can be drilled using dry or straight-flush rotary drilling depending on site conditions, intended depth, and diametre, which can range from 300 to 2000mm.

Once drilled, boreholes are lined with a wellscreen / casing assembly. Gravel is then added to fill the annular void around the assembly, and a bentonite seal is placed to protect the borehole against surface water and/or contaminants. Finally, a multi-stage submersible pump is installed within the deep well to begin groundwater extraction, and discharge lines are used to carry the groundwater to a discharge point at the surface. Together, this system works to lower the water table to a project’s desired depth.

Groundwater abstraction is realized by a multi-stage submersible pump installed in the completed well. Discharge lines carry the groundwater to a discharge point at the surface, therefore lowering the water table to the desired depth.

The groundwater removal is also assisted by a partial vacuum drawn by a vacuum pump aggregate at the upper edge of the well. The vacuum achieved can range up to 0.9 bar (13 psi). The vacuum provides faster and more wide-ranging drainage even in soils with low permeability, therefore stabilizing the surrounding soil layers.

Well Point Systems

Durable, easy to install, and reliable, Hoelscher Dewatering’s MicroWell wellpoint systems are ideal dewatering solutions for shallow excavations up to 6m in depth.

Installation requires drilling a borehole of approximately 110mm in diametre to a depth of 8m. After, a plastic pipe 50mm in diametre is inserted and centre into the borehole, the bottommost layer of which is perforated with slots measuring 0.3mm in width. The annular space around the pipe is backfilled with filter gravel and sealed with clay sealant.

Above ground, individual wellpoints are connected to a peripheral header main via PVC vacuum hoses. Vacuum pumps are then used to create a powerful vacuum in the header main up to 28” of vacuum. The vacuum on the pump’s inlet side pulls the water through the wellpoints, draining and stabilizng the surrounding soil layers.