(2) Bored wells. Bored wells are commonly constructed with earth augers
turned by hand or by power equipment. They are considered practical at depths less
than 100 feet when the water requirement is low and the earth overlying the aquifer
(water-bearing formation) has noncaving properties and few large boulders. Bored
wells have roughly the same characteristics as dug wells, but they may be extended
deeper into the water table. Like dug wells, they should be grouted around the casing
to at least 10 feet and should be protected from contamination by a concrete slab and
sanitary seal.
(3) Driven wells. Driven wells are the simplest and least expensive of all
well types. The driven well is constructed by driving into the ground a drive well point
that is fitted to the end of a series of pipe sections. The pipe sections and drive point
are driven by means of a maul, a drive shoe, or a piIe driver. The most suitable
locations for driven wells are areas containing alluvial deposits (clay, sand, siIt, gravel,
or similar material deposited by running water) of high permeabiIity. The presence of
coarse gravel, stones, or boulders interferes with sinking the well point and may
damage the wire mesh jacket covering the well point. For deeper wells, the well points
are sometimes driven into water-bearing strata from the bottoms of bored or dug wells
(see figure 6-6). The casing should be grouted in the same manner as in (1) above,
and provided with a sanitary seal.
Figure 6-6. Bored well driven well point.
MD0160
6-8