How to dewater a construction site? The selected dewatering method depends on the construction site conditions and project type.
Because every construction site is unique, with different geology and hydrology conditions. But the end goal always remains the same,
Remove groundwater or surface water from a construction area.
To better understand how to dewater a construction site, we’ll first go over dewatering tips.
Important Note: dewatering protects equipment, soil, and workers. It provides dry and stable conditions for workers who operate heavy equipment. While also, protecting project budgets. Water can flood excavation areas and halt work, erode land, and destroy foundations.
For this reason, dewatering is typically done in the following instances:
- 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 foundation construction difficult
General construction site dewatering tips
The following are general dewatering tips, to ensure your project runs smoothly:
- Follow all the latest local, state, and federal agency codes and regulations.
- Apply for a permit to dump collected water.
- Limit dewatering in heavy rains, as the dewatering will not work.
- Don’t dewater areas, which show signs of erosion.
- Locate a safe discharge location before dewatering, and check for erosion.
- Investigate and learn about the water table at your construction site, to choose the best dewatering method.
- Don’t blindly discharge water into sloped terrain.
- Remove sediments from the dewatering process. Depending on the particle characteristics, you’ll need to use certain filters. For example, gravity bag filters, cartridge filters, and sand-media particulate filters.
- Test collected water for containments, to know how to dispose.
- Ensure the removal of water doesn’t compromise construction conditions. The removal of water from soil alters soil characteristics.
- Inspect the dewatering operation daily. Check filter conditions, pump operations, outlet conditions, and soil conditions.
Important Note: always first do a geotechnical and groundwater site investigation before dewatering. This will help prevent soil problems, while ensuring an efficient dewatering process.
The investigation will show if your site has surface water or groundwater. Also, you’ll know of any sediments you need to separate out and if the water has contaminants. The contaminants can include grease, oil, paint, and acids.
This is the simplest and most cost-effective method, if your project site has slopes.
You use a gravity drain to route water to your discharge area. Your created drainage channels will divert water to flow away from the high points at your site.
The downside is the long drain time, if your channel is small. This makes this method not 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 deal with small quantities of water.
For a sump pump, you first excavate an area, which is below grade. This excavated area is where the groundwater seeps 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.
Say you have a 20-foot by 20-foot excavation area. You’d first excavate 10-feet below grade for your excavation area. Next, you’d make the sump deeper than 10-feet, where the structure foundation isn’t placed. All the water will collect in the sump since it’s below the excavation area. At the same time, you continuously pump out the water in the sump as you work. You only stop the 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.
This is the common approach, when the soil is very loose and wet. In return, you prevent the sides of the sump from collapsing and blocking the inlet of the sump pump. The water can still contain some 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, you’d install wellpoints parallel to a pipeline trench, which endlessly gathers water. You first drill small wells around your excavation area. Then, you place a screen around a suction tube, placed in each well to prevent soil from entering. This tube connects to a riser pipe, which feeds into a common header pipe, 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 gather water, you can make your well only so deep. Beyond a 20 or so foot depth, this method becomes ineffective. If you want to drive down any deeper, 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 load of silt.
#4 Eductor Wells
A closed loop pressurized system, which creates a local vacuum to extract water from wellpoints.
This method utilizes the venturi principle. High-pressure water circulates through eductors at the bottom of each well. The well bottom pressure in return drops, and you can pull water through the riser pipes.
Unlike the wellpoint method though, there are no depth limits per se. You can drive down as deep as 150 feet. Plus, this method works great with soils, which don’t pass a lot of water through them, like clays and silt.
#5 Deep wellpoint
This is an aggressive dewatering method. It’s commonly used if your excavation area is below the groundwater table level. Also, when you need to repeatedly remove large volumes of water. For example, in areas where there’s highly permeable sand and gravel. In return, the groundwater quickly refills.
For install, around your excavation area, you drill wells with casings inside, to keep the form of the well. Then, you place submersible pumps at the bottom of each well shaft. The groundwater, which then falls into each well through gravity, you pump out.
#6 Heavy machinery
Sometimes you can use large machines to scoop out water to dump 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 silt only remains.
A great tip is to 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. Always start from one side of an area, and use an excavator to toss the mud into a corner. Then from the corner, scoop out the mud. Once enough open area becomes available, feed the excavator with a bulldozer.
#7 Other dewater methods at construction sites
The following is a list of other notable dewatering methods to use:
- Deep well construction
- Artificial ground freezing
- Chemical soil spraying (i.e. destabilization of fine particles to form a cake)
- Construction of a cofferdam (i.e. temporary enclosure made around a body of water)
- Geotextile tubes (i.e. large dewatering bags acting as containment structures)
- Electroosmosis (i.e. application of voltage to dewater loose soils)
In the end, there are many ways on how to dewater a construction site. The best choice comes down to the assessment of your project site and budget.
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 simple method is to discharge the water on your own land. You can then repurpose the water, or allow it to evaporate. But you can only discharge the water on-site if it’s free of pollutants.
If you decide to store the water, again, be sure it’s free of pollutants. Also, store the water in a safe and secure location on your construction site. You may even need a permit for storage, depending on your construction site location.
Discharge to nearby land
Find out who owns the land adjacent to your construction site. Then, strike an agreement to discharge the water on their land. Maybe they could use extra water…
Your agreement should include the assessment of the pollutants and sediments in the water.
Take the water to an off-site location, using containment tanks. For example, transport the water to a farm for irrigation use.
The off-site water relocation choices, highly depend on the water quality.
Sewer system discharge
This is an easy option if the water is low in pollutants. You 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 transport the water to a treatment facility, to remove the pollutants. Afterwards, you can 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 dewatering, you can 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.
So, choose the best dewatering method based on your soil conditions and water table. Then enjoy 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.