Frequently Asked Questions About Dewatering

What is dewatering?

Dewatering is the temporary removal of ground water from a construction site to allow for construction in dry conditions. Water is removed using wellpoints, eductor wells or deep wells.

Wellpoint, eductor or deep well dewatering, which is best?

Each type of dewatering system has its advantages and limitations. The selection of the best solution for your project requires the review and evaluation of many factors including the size of the excavation, anticipated flow rates, permeability of the soil and substantially dry conditions.

What is a wellpoint system?

Wellpoint systems are a series of wells connected to a common manifold and activated by a continuously primed pump. Vacuum wellpoints are highly effective when excavations extend to depth of up to 5-m below ground surface and work well in both high and low permeable soils. Vacuum wellpoint pumps come in both electrical, diesel and sound attenuated diesel configurations. Wellpoints are quick to install and easy to adapt to specific site conditions.

What are Eductors?

Eductors are a vacuum-based system where the vacuum is generated in the well with a venturi. Eductors are highly effective in stratified or low permeable soils. Eductors are not limited by the depth.

What are deep wells?

Deep wells use submersible pumps suitable for pumping large volumes of water. Deep wells are independently operated and are not limited by depth. Pumps are electrically operated. Vacuum can be introduced into a deep well system to aid in well performance.

What are the benefits of dewatering?

Groundwater control for construction projects is an essential part of the success of the project. Water entering an excavation can cause slope or basal instability. Dewatering of the site can keep projects on schedule, keep working conditions stable and provide workers safety working in dry conditions.

What is the difference between a Permit To Take Water and an Environmental Activity Sector Registry as it relates to Dewatering?

Both permits are applied in Ontario to the Ministry of the Environment, Conservation and Parks (MEC). The volume of water and application process are the main differences between the two. Generally, an Environmental Activity Sector Registry (EASR) is appropriate for construction sites that expect between 50,000 and 400,000 liters of water per day to be removed from the site during construction. For volumes over 400,000 liters per day during construction or for pumping over 50,000 liters per day post construction, a Permit To Take Water (PTTW) is required.

An EASR requires an online submission to the Ministry of the Environment, Conservation and Parks which involves a signoff from a qualified individual at the time of submission. From the time of submission to the time the permit is received is generally complete on the same business day. For a PTTW, a submission is sent to the MECP which does a detailed review of the application before a permit is issued. The PTTW process from the time of submission to the permit being issued is typically about 90 days.

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