How to dewater a construction site? Many dewatering methods exist to accommodate different construction site conditions.
I’m going to go over all the common dewatering methods. You’ll see how they work, and when you need to use them. Because every construction site is unique with different conditions you need to consider. You’ll find the geology and hydrology vary from location to location.
In the end, there’s one goal with dewatering,
Removing groundwater or surface water from a construction area.
Before we go over how to dewater a construction site, I’m going to list dewatering tips.
Important Note: dewatering protects equipment, materials, and workers. For one, it provides dry and stable conditions for all workers using heavy equipment. But also, it protects your pockets.
Water can flood an excavation area stopping all work. Then with time being money, a construction project can quickly turn into a nightmare.
For this reason, dewatering is typically done in the following scenarios:
- The build-up of water in trenches and excavation areas
- Wet areas with limited sloped terrain
- Areas with high water tables
- The flow of rainwater into excavated areas
- Rise of subsoil water, making it difficult to lay foundations
Construction site dewatering general tips
If you don’t dewater right, you can badly destroy the soil of a construction site. The land can erode causing more damages than the water itself.
I’ve seen a project where dewatering wasn’t properly done. Several years later, the structure built on-site started to sink and tilt. The contractor was then held liable and had to later file bankruptcy.
This happened because subsoil water rose into the excavation area. Thus, the structural foundation from the start was unstable.
With that said, use the following tips at every construction site:
- Follow all the latest local, state, and federal agency codes and regulations.
- Depending on where you dump your collected water, you may need to apply for a permit.
- Limit any dewatering in heavy rains. The dewatering process may not work and you’ll do a lot of work without making much progress.
- Do not dewater areas that show signs of erosion.
- Before you dewater, locate a safe discharge location. Then check the discharge location as you dewater looking for any erosion.
- Investigate and learn about the water table at your construction site. This will help you choose the best dewatering method to use.
- Don’t discharge water into sloped terrain.
- Remove sediments from the dewatering process. Depending on the particle characteristics, you’ll need to use a certain filter. For example, gravity bag filters, cartridge filters, and sand-media particulate filters.
- If you suspect the water has containments, take a sample to the laboratory for testing. You’ll then know how to dispose of the water.
- If you’re discharging large volumes of water, always test the water first. You may find unsafe contaminated oil and/or chemicals in the water.
- The removal of water from soil alters the soil’s characteristics. Make sure any removed soil doesn’t compromise your construction work.
- Inspect your dewatering operation daily. Inspect filter conditions, pump operations, outlet conditions, and check for any erosion.
Important Note: always do a geotechnical and groundwater site investigation. This will help you set up your dewatering plan.
The analysis will show you if your site has surface water or groundwater. Also, you’ll know of any sediments you need to separate out and if the water contains contaminants. The contaminants can include grease, oil, paint, and acids.
You don’t want to ever blindly do any dewatering work at a construction site.
This is the most simple, straightforward, and cost-effective method.
You use a gravity drain to route the water to your discharge area. You can create drainage channels and the water will flow away from the high points at your site. Thus, your land needs to have some slope to it to use this method.
The downside is it takes a long time to drain an area using gravity if your channel is small. So this method isn’t ideal if you have a lot of water to drain or if your excavation area is deep.
#2 Sump pump
Sump pumping is commonly used when you’re dealing with small quantities of water. You use gravity in shallow excavation areas where there’s plenty of sand and gravel.
You excavate an area that’s below grade, and you allow groundwater to seep in. The collected water in the sump is then pumped out.
The downside is the risk of the sides of the sump collapsing from a high head or steep slopes. Also, it’s not well suited if you have heavy rains and inflows.
But I find it works great when you want to quickly lay footing in a wet area. Let’s say you have a 20-foot by 20-foot excavation area.
First, dig 10-feet down, and make the sump deeper than 10-feet where the foundation isn’t placed. All the water will then collect in the sump since it’s below 10 feet. At the same time, continuously pump out the water in the sump as you work. You can stop pumping once the foundation’s concrete sets in.
Important Note: for clearing water from an excavation, dig a small sump. Next, place a perforated pipe inside the sump and surround it with a suitable grade of stones. Then place the sump pump inside the perforated pipe.
I see this commonly done when the soil is very loose and wet. This will prevent the sides of the sump from falling and blocking the inlet of the sump pump. The water may still contain silt though.
#3 Wellpoint system
Used for most soil and hydraulic conditions to lower the groundwater table levels. It’s commonly used in construction projects where you need to perpetually discharge water. For example, install wellpoints parallel to a pipeline trench that endlessly gathers water.
You first drill small wells around your excavation area. Next, you place a screen around a suction tube that you place in each well to prevent soil from entering in. This tube then connects to a riser pipe that feeds into a common header pipe that’s connected to a vacuum pump. The vacuum pump then sucks up the water from each of the connected wellpoints.
Since this method uses suction to pick up water, you can make your well only so deep. After a certain depth, this method becomes ineffective. This depth is typically 20 feet or less.
If you want to drive down any deeper than 20 feet, you need to use a multi-stage wellpoint system.
Important Note: with all pumps, ensure the pump outlet faces away from the excavation area. This will prevent water from running back into the excavation area.
Also, turn off the pumps when the well is near empty. Otherwise, the pump will suck up a lot of silt.
#4 Eductor Wells
This method is like the wellpoint method. Except, you use high-pressure water instead of a vacuum to pull up water from the wellpoints.
This method utilizes the venturi principle. High-pressure water circulates through eductors at the bottom of each well. This drops the pressure. The reduction in pressure then pulls water through the riser pipes.
Using this method, there aren’t really any limits in well depth. You can even go as deep as 150-feet.
What’s more, this method works great with soils that don’t pass a lot of water through them like clays and silt.
#5 Deep wellpoint
This is an aggressive dewatering approach. It’s commonly used if your excavation area is below the groundwater table level.
Around your excavation area, drill wells with casings inside to keep the form of the well. Then place submersible pumps at the bottom of each well shaft.
The groundwater that falls into the wells due to gravity is then pumped out.
This method is commonly used when you need to repeatedly remove large amounts of water. For example, in areas where there’s highly permeable sand and gravel. As a result, the groundwater quickly refills in your excavation area.
#6 Heavy machinery
Sometimes you can use large machines to scoop out water and dump it elsewhere.
If you have machines on-site and the excavation area isn’t too deep, this becomes an option. Especially when most of the water is already pumped out and you only have silt left.
You can use a bulldozer to push the softer silt to one side of the construction area. Then, use a loader to relocate the silt.
Important Note: when using heavy equipment, be careful the machinery doesn’t get stuck. So start from one side and use an excavator to toss the mud into a corner.
Then in the corner, scoop out the mud. Once enough open area becomes available, you can feed the excavator with a bulldozer.
#7 Other dewater methods at construction sites
The following is a list of other notable dewatering methods that you can use:
- Deep well construction
- Artificial ground freezing
- Chemical spraying soil (destabilization of fine particles to form a cake)
- Construction of cofferdam (temporary enclosure made around a body of water)
- Geotextile tubes (large dewatering bags acting as containment structures )
- Electroosmosis (application of voltage to dewater loose soils)
In the end, there are many ways on how to dewater a construction site. It comes down to properly assessing your project site to choose the best method. Also, your project budget is a big consideration.
Water discharge location options
You always have several options on where to discharge your water. But each option has pros and cons, with associated costs.
The following are some of your options and what you need to consider:
The easy method is to discharge the water on your own land. You can then repurpose the water, or let it evaporate. But you can only discharge the water on-site if it’s free of pollutants.
Also, if you decide to store the water, be sure the water is free of pollutants. And, store the water in a safe secure location on your construction site. You may even need a permit for storage depending on where your construction site is.
Discharge to nearby land
Find out who owns the land adjacent to your construction site. Then strike an agreement to discharge the water in their land. Maybe they could use extra water.
Your agreement should include the assessment of the pollutants and sediments in the water.
Taking the water to an off-site location using containment tanks. For example, you transport the water to a farm for irrigation use.
The off-site choices for the water highly depend on the quality of the water though.
Sewer system discharge
This is an easy option if the water is low in pollutants. You can simply channel the water through the local sewage system. You’ll need to first test the water and receive a permit from the local ruling authorities though.
If you find dangerous pollutants in the water, off-site treatment is your only option. You’ll need to take the water to a treatment facility to remove the pollutants. After you treat the water, you can then decide on what to do.
“How to dewater a construction site?” wrap up
Dewatering is an important part of almost every construction project. In fact, by skipping the dewatering step you could compromise an entire project.
Water can flood excavated areas, damage equipment, and cause structures to collapse. This then puts the life of workers and later the public at risk.
Thus, choose the best dewatering method based on your soil conditions and water table. Then enjoy having a safe and ready-to-go construction site to do your work.
How do you dewater a construction site? What challenges have you encountered in the dewatering process?
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Koosha started Engineer Calcs in 2020 to help people better understand the engineering and construction industry, and to discuss various science and engineering-related topics to make people think. He has been working in the engineering and tech industry in California for over 15 years now and is a licensed professional electrical engineer, and also has various entrepreneurial pursuits.
Koosha has an extensive background in the design and specification of electrical systems with areas of expertise including power generation, transmission, distribution, instrumentation and controls, and water distribution and pumping as well as alternative energy (wind, solar, geothermal, and storage).
Koosha is most interested in engineering innovations, the cosmos, our history and future, sports, and fitness.