Goundwater Essay Research Paper INTRODUCTIONAlthough 70 percent

Goundwater Essay, Research Paper

INTRODUCTION

Although 70 percent of the Earth’s surface is covered by water, 97 percent of it is contained in the oceans and is too salty to drink (Cunningham and Saigo, 1992). Therefor, fresh water is a precious resource that in some areas of the world is so scarce, that people will fight wars over it. About 25 percent of the world’s fresh water is groundwater. Although groundwater is not as accessible as surface water (lakes, rivers and streams), people are willing to dig wells to obtain it in areas where the climate is too dry to allow much surface water. Many farmers pump water from wells to support irrigation. This is often done with windmills, a very cheap form of energy. In some dry areas like Arizona, large cities use groundwater for their entire water supply. Although groundwater is an excellent water source, there are many complications. For example, it is a resource that is difficult to assess since it is not directly visible. Therefor with out complicated measurements, it is hard to say how much water there is left in your well. It is also difficult to tell where exactly the source of recharge for your well is. Thus if an area near your well becomes polluted, the pollution may seep into the groundwater feeding your well.

The purpose of this project is to explore the subject of groundwater, its place in the water cycle, how it seeps through the ground and how it accumulates in underground pockets called aquifers. The project will also examine the many uses of groundwater in agriculture as well as environmental problems that are presently threatening the quantity and quality of groundwater reserves.

THE WATER CYCLE

The water cycle is a constant movement of water in the air, in the ground and on the surface of the Earth. It starts when water evaporates from plants, the ground, lakes, rivers and oceans. This is called evapotranspiration.

As the vapor rises, the surrounding air gets colder and colder. The dew point is the temperature at which water begins to condense (change into it’s liquid form). At the dew point, it clouds form. Clouds consist of tiny water droplets which remain suspended in the air until they become too large for turbulence to hold up. When this happens, some form of precipitation (rain, hail or snow) falls on the earth and either seeps into the soil or flows across the surface. Most of the time, it does both. Whatever doesn’t evaporate or run off infiltrates into the ground and is called groundwater. When it flows across the surface it is called surface runoff. The surface runoff goes into an ocean, river or stream where it evaporates in to the atmosphere again.

Water infiltrates deeper and deeper through the ground until it eventually reaches a water table, which is the point where water becomes saturated. The water tends to percolate through the ground in such a way to level the water table just as water tends to seek it’s own level in a lake. Water moves very slowly through the ground so the water table never really levels out, but rather, follows the topography of the landscape. The tendency for the water table to level itself results in depressions being filled with water. Thus in a depression, the water table will be above the ground. Since streams and lakes sit in depressions the ground water is constantly feeding them. Thus ground water joins the surface runoff and can evaporate again, repeating the cycle. D’arcy’s Law says that as water infiltrates into the ground and is pulled downward by gravity, it follows curved.

The rock or dirt immediately beneath the earth’s surface is made up of solids and voids. The voids are cracks in the rock, air pockets or sand. All water beneath the surface is in these spaces and is called underground or subsurface water. Subsurface water can be found in two different zones: One zone is immediately underneath the surface and contains water and air in the voids. This is called the unsaturated zone. It is almost always has a second zone called the saturated zone right beneath it. The water in the saturated zone is called groundwater and is the only water used in wells and springs.

AQUIFERS AND ARTESIAN WELLS

As water seeps through the ground, it sometimes becomes trapped in pockets called aquifers. If you dig a well into these, it could be a rich water supply. The previous paragraph shows how water seeps evenly when the ground is homogeneous, aquifers usually indicate that the ground is heterogeneous, that is it consists of layers of materials that have different permeabilities. If a layer of very porous materials like gravel or sand becomes sandwiched in between two impermeable layers of clay or silt this could be the start of an aquifer, a water bearing area under the earth’s surface.

When precipitation infiltrates into the ground, much of it will enter that layer of gravel or sand. Then, since the permeable layer is enclosed by impermeable layers, the water simply collects in the porous layer. Wells dug into the lower parts of aquifers are especially good because as the water is pumped out, new groundwater constantly replenishes them because it seeps through the permeable material very quickly.

There are two types of aquifers: Confined and unconfined. A confined aquifer is usually under pressure from the weight of the water it contains and the ground above it, whereas an unco