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Types of Wells
A drilled well consists of a hole bored into the ground, with the upper part being lined with casing. The casing prevents the collapse of the borehole walls and (with a drive shoe or grout seal) prevents surface or subsurface contaminants from entering the water supply. The casing also provides a housing for a pumping mechanism and for the pipe that moves water from the pump to the surface.
Below the casing, the lower portion of the borehole is the intake through which water enters the well. The intake may be an open hole in solid bedrock (Consolidated) or it may be screened and gravel-packed (Unconsolidated), depending upon the geologic conditions.
Once the well is completed, it is pumped to develop the well and determine the yield. Many areas need further work after drilling to remove fine material remaining from the drilling process so that water can more readily enter the well. Possible development methods include compressed air (blowing), bailing, jetting, surging, or pumping. The quantity of water (yield test) is usually measured during development.
After proper disinfection, the well is capped to provide sanitary protection until it is hooked into the customer's system. Well caps require an air vent. The purpose of the vent is to equalize the air pressure between the inside of the casing and the atmosphere.. The cap must be screened to prevent the entry of foreign material such as insects into the well.
Aquifers can be classified into two types:
- Unconsolidated or aluvial consisting of sand, silt, gravel and clay
- Consolidated or bedrock consisting of rock such as granite, gneiss, sandstone, marble, and limestone.
Water forms in the fractures in the rock. The yield of bedrock aquifers may vary considerably and depends on the degree of fracturing in the rock and how they are interconnected. Some formations make drilling a well with suitable yield difficult and even wells properly constructed go dry due to:
- Lowering of the water table during periods of reduced rain
- Excessive pumping from nearby wells
- Water consumption greater that the storage capacity and yield
- Clogging or shift in the fractures
Well Water Security Alliance services consolidated wells and can assist you with any well problem.
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