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Module 3 — Design and Construction of Water Wells
There are three types of possible well completions for both drilling methods (see Figure 2,
Well Completions):
Surface casing with slotted or perforated liner
Sand screen with continuous slot openings
Single string slotted or perforated casing.
Casing Size and Type
Decisions about the diameter and type of well casing are made after the driller considers
the following:
Aquifer characteristics
Hydraulic factors that influence well performance
Drilling method
Well depth
Cost (in discussion with the well owner).
The casing must be large enough to house the pump and allow sufficient clearance for
installation and efficient operation.
If a submersible pump is going to be used, the casing must have an inside diameter of at
least 10.16 cm (4 in.), by law. It is recommended that the casing be at least one nominal size
larger than the outside diameter of the pump. The more space there is between the pump
and the casing, the easier it will be to service and repair the pump in the future.
There are two common materials used for casing: steel and plastic. Steel casing is the
strongest but is susceptible to corrosion. Plastic casing is becoming more popular because of
its resistance to corrosion.
All casing must be new and uncontaminated. Plastic casing must be made of virgin resin,
not recycled material.
Intake Design
Water moves from the aquifer into the well through either a screen or slotted or
perforated casing.
Screens are manufactured with regularly shaped and sized openings. They are
engineered to allow the maximum amount of water in with minimal entry of formation
sediments. Stainless steel screens are the most widely used because they are strong and
relatively able to withstand corrosive water. Screens are manufactured with various slot
sizes and shapes to match the characteristics of the aquifer.
Provincial regulation provides detailed
specifications for casing diameters and wall
thicknesses. All casing must meet or exceed
standards set by the Canadian Standards
Association or the American Society of
Testing and Materials (see Module 4” Water
Well Drilling Agreements”, Water Well
Casing Specifications).