Project Dewatering Limited

Where groundwater must be lowered further than six metres below ground and especially where the shallow aquifers include low permeability materials such as silts, muds or sands, ejectors are often the best option. Ejectors occupy a niche in the dewatering industry, where pumping levels are too deep for wellpoints but well yields are too low to allow the use of electric submersible pumps (as in classic deep wells). Ejector wells are drilled, just like deep wells, but they differ from deep wells simply in the way that the water is extracted.

Unlike electric submersible pumps, which can quickly burn out if run in a dry borehole, ejectors can pump air and water mixtures without any problems, and if the top of the borehole is sealed, the air pressure within the well will drop below atmospheric pressure and the vacuum produced by the pumping action will improve the gravity drainage towards the well as a result of the creation of this vacuum-assisted drainage path.

As such, ejectors can be used to improve the stability of low-permeability silts and fine sands. Because they use decompression of introduced water to lower pressure at the base of the borehole, ejectors can operate to far greater depths than wellpoint suction pumps. Ejectors are commonly used at depths of 30 meters, but with careful design and installation, ejectors can even pump from depths as great as 50 metres  and can even run at times of zero water entry into the well.

Project Dewatering has one of the UK’s best drilling capabilities of any groundwater company, utilising a variety of drilling methods to deal with all types of ground conditions.

They are simplistic in their surface layout, basically re-circulating supply and groundwater with any excess water, i.e. the total extracted groundwater being piped off to discharge. Returned water will enter a static tank via a common collection pipeline. This tank acts as settlement and supply tank. It contains four chambers separated by baffle plates. Chamber 1 is the entry point; water then passes in a settlement chamber before flowing over a V-notch into the supply chamber. Any excess water flows over a second V-notch to a final discharge tank, allowing the ‘total’ extracted groundwater to be discharged by gravity or pumped to a designated point.

The supply chamber is coupled to the high-pressure pump, which pumps water along the common supply pipeline, to individual supply pipes, at each ejector well. The pump is a multi-stage horizontal rotary pump, powered by a silenced diesel or electric engine. This is coupled to a standby pump that automatically starts if the duty pump fails. Plus this is an alarm facility that is triggered if the supply pressure falls below a set level.