Construction and Mine DewateringLearn about dewatering techniques and some things to look out for when starting a dewatering project.
What is Dewatering?
Dewatering refers to the act of removing or displacing groundwater or surface water from a work site. Primarily, pumps and evaporation techniques are used for the dewatering process which is usually performed before excavation for footings or to lower the water table that may cause issues during subsequent excavations.
Often times in industrial or construction work sites, accumulated water in trenches and excavations which, if left alone, can cause downtime due to work areas being inaccessible due to flooding. These areas must be dewatered so work can continue at a steady pace, and to provide additional safety for the crew operating the job. It is necessary before any excavation that dewatering is done so that the construction crew has dry land to stand on and also to lower an area’s water table that may cause problems when the excavation work is begun.
Where Does Water Accumulate?
The top two reasons for water accumulation are rain and the area having a high water table. In construction sites, water can build up in excavations, trenches, sloped areas, or if the location of the site is in an area with a high water table.
Dewatering Precautions / Things to Know
To avoid further disruption of the environment such as soil eroding, it is imperative that the dewatering process is done properly. It is also important to select the best location for the discharge line, even when you might be a long distance from any bodies of water. When choosing discharge areas for your dewatering, keep in mind:
- Water should never be pumped directly into slopes which can cause erosion or leave a potential for landslides.
- It is important to look for signs of erosion in the area and discontinue dewatering if any is found.
- If possible, water should be channeled into wooded or heavily vegetated areas.
- Avoid dewatering during heavy rains because the infiltration rate is so low that water will move very slowly, basically stopping the entire operation.
- Never discharge water contaminated with grease, oil, or caustic chemicals directly into the ground to prevent contaminating the local environment.
- Additional permits may be needed from local, state, or federal governments.
- Understanding of the water table conditions in your work area can dictate how well the process will go.
- Sump pumps are the most common dewatering technique, however, they are limited by how much volume they can process so are not suited for large jobs.
In most cases, dewatering from open trenches or excavation can be done a variety of different ways. The most simple method uses the omnipresent power of gravity. By creating drainage channels, water is carried away from the work site to the discharge point. Channels used for dewatering are usually protected with ditch linings to ensure the (sometimes contaminated) water does not seep into the ground soil.
Some of the other common dewatering techniques involve submersible dewatering pumps, siphoning, or using large machinery buckets to catch the water and dump off-site. These techniques are performed when the water that needs to be removed is below the designated discharge area.
Dewatering bags are large, durable bags made of geotextile fabric used to filter water by removing oils and sediments. They are used by hooking up the discharge line to the inlet line on the bag. As the bag fills with water, the sediment is trapped in the fabric of the bag, allowing the water to drain into the environment. Dewatering bags are also found in other areas with high water table like dredging. When using dewatering bags, avoid multiple pipe discharges as it can cause the filter bag to fail. It is best to guide the water runoff into a nearby storm inlet.
Additional Dewatering Applications
Dewatering is also done in mining excavations, particularly in rock mines and borrow pits. It is also conducted in lake excavations for making stormwater management systems. Installation of utility lines such as sewers, water, telephone, and electricity also requires dewatering.
Dewatering often deals with solid laden materials, often filled with abrasives. Need a non-clogging pump design that can handle high solids liquids which will end up clogging or damaging traditional centrifugal pumps.
Submersible Pumps are a good choice for dewatering applications because they can be fully submerged in the water that needs to be transferred, allowing an easy method of removal. The submersible pump would also need to be built for withstanding some abrasive solids content and not be prone to clog.
Self Priming Pumps are excellent choices for dewatering pump solutions because they can provide some advantages over a standard pump. Self-priming pumps have the ability to keep the pump primed in instances where the pump cannot be submerged, saving time and potential damage to the pump. The EDDY Pump Self Priming Pump is designed for heavy-duty applications equipped with a non-clogging design and high reliability which will result in constant flow and little to no downtime.
Advantages of a Self-Priming Pump
Main advantage comes in the form of mobility – Imagine a situation where a farmer has a series of five large tanks that store material for transfer. Instead of installing five costly fixed submersible dewatering pumps on the bottom of each tank, the farmer could instead invest in a single self-priming pump which can be used for unloading the five large tanks individually, a self-priming pump can be mobilized to pump all five of these tanks on its own. However, if the tanks need to be pumped 24/7, then a dedicated pump would best be served for this purpose.
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