Open-Pit Dewatering: How It Works, and What Pump to Use

  • Post category:Dewatering

There’s more than just water down there.

Large amounts of water on a construction site stops progress in its tracks. Open-pit dewatering pumps pull water out from the bottom of a construction excavation area. Look for high-head drainage pumps to do this quickly and efficiently. They do it best when suspended from underneath a single float or raft.

There’s more to it than removing the water in the pit. You’ve got to lower the groundwater table outside the pit to prevent any of that groundwater from filling the open pit again. Here’s how this dewatering process works, and which pumps do the best job.

Getting it out, and keeping it out.

General rule of thumb: The deeper the pit, the more water you’ll encounter. You need to get it out, and keep it out.

There are two steps. Both need solutions, and these solutions are mutually exclusive. The water in the open pit has to be removed, but it’ll return unless you also lower the groundwater level. A wellpoint dewatering system around the perimeter of your construction site will take care of lowering the groundwater level.

With that solution underway, it’s time to focus on dewatering the pit. If the solid content of the water is high, choose submersible slurry pumps. Here’s why.

Submersible slurry pumps

Either diesel or electric drive units can power these hydraulic submersible trash pump dewatering solutions. Diesel might be the preferred option if you’re not close to a reliable source of electrical power. These pumps can be lowered into the pit to remove the standing water.

Give heavy consideration to the DuraFlo™ hydraulic submersible trash pump line by MWI. These hydraulically driven water pumps offer an admirable combination of ruggedness, reliability, and performance.

DuraFlo™ pumps can be skid mounted or trailer mounted, giving them the portability you will need to move them around on the construction site. They’re meant to take a beating (which is why they’re called trash pumps) so you can feel comfortable about renting them.

Dry-priming trash pumps

These pumps are reliable and inexpensive to operate. They’re often part of an open-pit dewatering plan. MWI PrimeRite™ pumps feature oil-filled bearing boxes and a mechanical seal in an oil bath. They can run dry for extended periods, making them a good choice for handling the inconsistent flows often found at job sites. The open impeller design is ideal for dealing with the debris commonly found in open-pit water.

Dry-priming trash pumps like the PrimeRite™ can “snore.” This means the pump primes and re-primes itself automatically using an assembly that draws water into the pump.

Where does this water go?

The groundwater and standing water in open pits at a construction site must be removed before foundation work can get underway. There’s no getting around this. But, the process of drying out your construction site can generate massive amounts of water. It has to be moved, and it can’t just be dumped. The quality of the water may have adverse environmental impacts. If it contains contaminates, you’re required to properly dispose of this water.

Look to your pump rental source for assistance. They should be your partners in the complete process of construction site dewatering. If all they can do is rent you the pumps, keep looking.

At MWI, we offer our clients full assistance regarding their rental needs. Feel free to contact us with any questions you may have.