Eductor Dewatering Systems

What is Eductor Dewatering?

The eductor dewatering method features a series of small diameter wells equipped with a nozzle /venturi (eductor body) that is run by an at-grade pumping station. Eductor wells are extremely low-maintenance and cost-effective as they require minimal tuning after the initial startup.

Eductors are frequently used in low permeability soils, generally pumping less than 200 GPM. This method is especially suited for deep excavations as they have no suction lift limits.

Eductor System Design

Eductor systems are a closed-loop pressurized setup that uses a high-pressure supply water stream and nozzle/venturi to create a localized low-pressure (vacuum) zone at the bottom of the well. The vacuum draws groundwater in through a foot-valve that joins the return stream and directs to a recirculation tank.

Excess water from the network (groundwater) overflows from the tank via a gravity discharge line, and a jet pump pulls water from the same tank to supply water for the system. This method is not limited by suction lift and can handle air without losing prime. However, it cannot handle large volumes of water.

1. Eductors are closely spaced (5-15ft), small diameter wells
2. Mix between deep wells and wellpoints
3. Each well is equipped with an eductor body (nozzle/venturi setup) near the bottom
4. Installed to depths ranging from 20ft to 80+ ft depending on the project/geology
5. Requires a supply & return piping system and high-pressure jet pump to deliver supply water
6. Multiple eductors can be powered by a single pump

Eductor System Installation

1. Jet/Drill boreholes at spacing designed for excavation
2. Install eductor screen/casing into boreholes and place filter pack/annular seal
3. Develop the well
4. Install the pressure and return pipes and eductor bodies
5. Connect eductors to pressure & return pipes with high-pressure hoses
6. Set the eductor pump station & tank
7. Optimize, monitor, and adjust the system
8. Lower water table
9. Excavate

Advantages & Limitations

Advantages

1. Useful in low permeability soils when close well spacing is required, or vacuum is beneficial
2. Low maintenance/tuning required once the system is optimized
3. Not limited by suction lift – Suited for deep excavations
4. Useful for dewatering stratified soils due to vacuum created in the borehole
5. Ground elevation installation eliminates the need to install from a sub-cut bench

Limitations

1. Volume limited, not typically suited for high volume applications
2. More labor-intensive due to dual supply/return line & other piping/valving
3. Pump stations can have higher power requirements