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3.17 Well Construction 103
3.17.3 Bored Wells

Wells can be bored with hand or power augers into sufficiently cohesive (noncaving) soils.
Above the water table, the soil is usually held in the auger, which must then be raised from
time to time to be cleaned. Below the water table, sand may wash out of the auger and have
to be removed from the bore hole by a bailer or sand pump. As the well becomes deeper
and deeper, sections of rod are added to the auger stem. Bits up to 36 in. (914 mm) in
diameter have been used successfully, and wells have been enlarged in diameter up to
48 in. (1,219 mm) by reaming. A concrete, tile, or metal casing is inserted in the hole and
cemented in place before the strainer is installed.

3.17.4 Drilled Wells
High-capacity, deep wells are constructed by drilling. Because the water-bearing materials
vary so widely, no one method of drilling can be adopted under all conditions. The method
of drilling is selected to suit the particular conditions of a site. The systems of drilling used
in water-well construction are based on either the percussion or the rotary principle.

3.17.5 Collector Wells
A collector well consists of a central shaft of concrete caisson some 15 ft (4.57 m) in inter-
nal diameter and finished off below the water table with a thick concrete plug. From this
shaft, perforated radial pipes 6 or 8 in. (150 or 200 mm) in diameter and 100 to 250 ft (30
to 76 m) long are jacked horizontally into a water-bearing formation through ports near the
bottom of a caisson. The collector pipes may be installed and developed in the same
manner as for ordinary wells.

3.17.6 Pumps

Many types of well pumps are on the market to suit the wide variety of capacity requirements,
depths to water, and sources of power. Figure 3.15 shows a well pump and 190,000-gal
(719,150-L) water tank. In the United States almost all well pumps are driven by electric motors.

Figure 3.15 Well and 190,000-Gallon (719,150-L) Tank, Maui, Hawaii
(Courtesy of the Department of Water Supply, Maui County, Hawaii)