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Types of Wells/
See also:
Drilled wells. Drilled
wells are constructed by either cable tool (percussion) or rotary-drilling
machines. Drilled wells that penetrate unconsolidated material require
installation of casing and a screen to prevent inflow of sediment
and collapse. They can be drilled more than 1,000 feet deep. The
space around the casing must be sealed with grouting material of
either neat cement or bentonite clay to prevent contamination by
water draining from the surface downward around the outside of the
casing.
View videos
of the most common well drilling methods: air
rotary, bucket auger,
cable tool,,
down the hole and reverse circulation. Videos are courtesy of Sir Sanford Fleming College.
Driven wells. Driven
wells are constructed by driving a small-diameter pipe into shallow
water-bearing sand or gravel. Usually a screened well point is attached
to the bottom of the casing before driving. These wells are relatively
simple and economical to construct, but they can tap only shallow
water and are easily contaminated from nearby surface sources because
they are not sealed with grouting material. Hand-driven wells usually
are only around 30 feet deep; machine-driven wells can be 50 feet
deep or more.
Dug wells. Historically, dug wells
were excavated by hand shovel to below the water table until incoming
water exceeded the digger's bailing rate. The well was lined with
stones, bricks, tile, or other material to prevent collapse, and
was covered with a cap of wood, stone, or concrete tile. Because
of the type of construction, bored wells can go deeper beneath the
water table than can hand-dug wells. Dug and bored wells have a
large diameter and expose a large area to the aquifer. These wells
are able to obtain water from less-permeable materials such as very
fine sand, silt, or clay. Disadvantages of this type of well are
that they are shallow and lack continuous casing and grouting, making
them subject to contamination from nearby surface sources, and they
go dry during periods of drought if the water table drops below
the well bottom.
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