Groundwater Development for Portable Water Supply
CHAPTER ONE
OVERVIEW
Groundwater development dates from ancient times the Old Testament contains numerous references to groundwater, springs, and wells, other that dug wells, groundwater in ancient times we supplied from horizontal wells known as QAUNATS. These persist to the present day and can be found in a band across the regions of the South Western Asia and North Africa extending from Aghanistan to Morocco. A cross section a long a qanat ie shown in fig 1.1 typically, a gently sloping tunnel dug through alluvial material leads water by gravity flow beneath the water table at its upper end to a ground.
CHAPTER TWO
IMPORTANCE OF GROUNDWATER
Groundwater plays an important part in the petroleum engineering. Groundwater is an important source of water supply throughout the world. Its use in irrigation, industries, municipalities, and rural homes continues to increase. For instance in Indian village there is high rate of dependence of its water source from a single dug well. Cooling and air – conditioning have made heavy demands on groundwater because of its characteristics uniformity in temperature. Shortages of groundwater in areas where excessive withdrawals have occurred emphasized the need for accurate estimates of the available subsurface resources and the importance of proper planning to ensure the continued availability of water supplies.
There is a tendency to think of groundwater as being the primary water. Source in a rid regions and of surface water in humid regions. But a study of groundwater use in the United States, for example reveals that groundwater serves as an important resource in all climatic zones.
Reasons include
- Its convenient availability near the point of use
- Its excellent quality (which typically requires little treatment) and
- Its relatively low cost of development
Furthermore, in humid locales such as Barbados, Jamaica, and Hawaii groundwater predominates as the water source because the high infiltration capacity of the sale sharply reduces surface run off.
During the dramatic drought of 1976 – 1977 in California, surface water resources all but disappeared in many areas. Emergency measures of many types were instituted to sustain public water supplies, but the drilling of thousands of new wells became a key factor in meeting restricted water demands during the critical period
See fig 1.2 estimates of water use in the U.S as of 1975 were prepared by the U.S geological survey. The largest single demand on ground water is irrigation, a mounting to 71 percent of all ground water use. More than 90% of this water is pumped in the western states.
CHAPTER THREE
SEARCHING/EXPLORATION OF GROUNDWATER
Although groundwater cannot be seen on the earth is surface, a variety of techniques can provide information. Concerning it’s occurrence and under certain condition even its quality from surface or above surface locations. Surface investigation or exploration of groundwater is seldom more than partially successfully in that results usually leave the hydrogeology picture incomplete. However, such methods are normally less costly than subsurface investigations. Geologic methods, involving interpretation of geologic data and field reconnaissance. Represent an important first step in any groundwater investigation. Remote sensing from aircraft or satellite has become an increasing valuable tool for understanding subsurface water conditions. Finally geophysical techniques, especially electric resistively and seismic retraction method.
CHAPTER FOUR
DRILLING FOR GROUNDWATER (WELLS)
These are holes or shaft, usually vertical excavated in the earth for bringing groundwater to the surface of occasionally these holes
gotten or wells serves other purposes, such as for subsurface exploration and observation, artificial recharge, and disposal of waste waters. Many methods exist for constructing wells, selection of a particular method depends on the purposes of the wells, the quality of water required, depth to groundwater, geologic conditions and economic factors. Shallow wells are dug, bored, driven or jetted; deep wells are ods. Attention to proper design will ensure efficient and long lived wells. After a well has been drilled, it should be completed, developed for optimum yield, and fasted. Wells should be sealed against entrance of surface pollution and given periodic maintenance. Wells of horizontal extent are constructed where warranted by special ground water situations.
CHAPTER FIVE
COMPLETION OF WELLS
After a well has been drilled, it must be completed. This can involve placement of casing, cementing of casing, placement of well screens, and gravel packing, however, wells in hard rock formations can be left as open holes so that these components may not be required.
WELL CASINGS
Well casing serves as a lining to maintain an open hole from ground surface to the aquifer. It seals out surface water and any undesirable groundwater and also provides structural support against caving materials outside the well. Materials commonly employed for well casing are wrought iron, alloyed or unalloyed steel, and ingot iron. Joints normally consist of threaded couplings or are welted, the object being t o secure water tightness.
CEMENTING
Wells are cemented in the annualar space surrounding the casing to prevent entrance of water of unsatisfactory quality to protect the casing against exterior corrosion and/or to stabilize caving rock formations. Cement grout, consisting of a mixture of cement and water and sometimes various additives, can be placed by a pump bailer, by a tremie pipe, or by pumping. It is important that the grout be introduced at the bottom of the space to be grouted to ensure that the zone is properly sealed.
SCREENS
In consolidated formations, where the material surrounding the well is stable, groundwater can enter directly into an uncased well. In unconsolidated formations, however, wells are equipped with screens. These stabilize the sides of the hole, prevent sand movement into the well and allow a maximum amount of water to enter the well with a minimum of hydraulic resistance.
Screens are made of a variety of metals and metal alloys, plastics concrete, asbestos cement, fibre glass reinforced epoxy, coated base metals and wood. Because a well screen is particularly susceptible to corrosions and incrustation, nonferrous metals alloys and plastics are often selected to prolong well life and efficient operation.
REFERENCES
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- Groundwater Hydrology John Wiley & Son, New York, 284 pp 1963
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