Project Dewatering Limited

A deep well typically consists of a borehole fitted with a slotted liner and an electric submersible pump. As water is pumped from a deep well, a hydraulic gradient is formed and water flows into the well forming a cone of depression around the well in which there is little or no water remaining in the pore spaces of the surrounding soil. Deep wells work best in soils with specific permeability profiles (k=1x10-3m/s to 1x10-5m/s) and the amount of drawdown that a well can achieve is limited only by the size of the pump

Deep wells can be installed in a ring around an excavation to lower the water level and maintain a safe, dry site. Several equations can be used to design deep well dewatering systems, but many of these are based on experimental data and therefore can occasionally fail.

This is where our knowledge and practical experience come into play; Project Dewatering’s past experiences and practical application of tried and tested methodologies can significantly improve the success rate of your deep well project.

Greater drawdown levels and the ability to overcome the limited suction lift of wellpoints can be made by the installation of Deep Well Dewatering systems. Deep Wells are also advantageous where there is limited space to install wellpoints close to an excavation, as Deep Wells can be located at a distance to generate the required drawdown. Deep Wells are also used for water extraction wells, groundwater remediation and as a point of recharge in pumping systems.

Project Dewatering offer effective and innovative sub-contract solutions to groundwater problems using deep wells, offering a professional turnkey service from initial design, drilling, supply and installation of pumping equipment together with site management throughout.

Design Considerations and Pumping Test Data.

The design of Deep Well and Ejector Dewatering Systems are more complex than for wellpoint schemes.

Because of the remote locations, deep wells rely on the interaction of individual drawdown profiles to produce the desired total drawdown. The normal spacing of Deep Wells is between 5m to 25m., with the terminal depth of a deep well being dependent on the required individual well yield and the drawdown profile. This in turn is a function of soil permeability and characteristics, target drawdowns and spatial parameters. To ensure a successful installation, Pumping Test Data is needs to be gathered and analysed to provide the necessary information to develop good initial design parameters.

Deep Wells typically consist of vertical or inclined bores, usually in the order of 200mm to 300mm diameter placed through the strata requiring dewatering or pressure relief. A suitable uPVC liner will be placed in the borehole, consisting of screened and cased sections. An adequate filter pack is installed to both maximise well yield and inhibit the movement of fines. After well development, typically airlifting in granular soils, or acidisation in hard Chalk, a suitable electric submersible borehole pump is installed.

A Deep Well Field

Deep Well Site	Deep Well Pipework

Project Dewatering Ltd has probably the best drilling capability of any groundwater control company in the UK. We can use a variety of drilling methods to deal with all ground conditions such as Cable Percussive (Shell & Auger) Auger and Rotary drilling techniques using polymer, water and air flush methods.

For a project to be successful it is imperative that the best possible well is deployed, as the best deigns can fail if a poorly constructed and installed well is used.