Question

Read the text and fill in the gaps with the appropriate words and phrases given below: Saltwater Contamination

In many 1) areas the groundwater resource is being threatened by the encroachment of salt water.

Since 2) is less dense than salt water, it floats on the salt water and forms a large, lens shaped body that may extend to considerable depths below sea level. In such a situation, if the 3) is 1 meter above sea level, the base of the freshwater body will extend to a depth of about 40 meters below sea level. Stated another way, the depth of the fresh water below sea level is about 40 times greater than the elevation of the water table above 4) . Thus, when 5) lowers the water table by a certain amount, the bottom of the freshwater zone will rise by 40 times that amount. Therefore, if groundwater 6) continues to exceed 7) , there will come a time when the elevation of the salt water will be sufficiently high to be drawn into wells, thus contaminating the freshwater supply. Deep wells and wells near the shore are usually the first to be 8) .

In urbanized coastal areas, the problems created by excessive pumping are compounded by a decrease in the rate of 9) . As more and more of the surface is covered by streets, parking lots, and buildings, 10) into the soil is diminished.

In an attempt to correct the problem of 11) of groundwater resources, a network of recharge wells may be used. These wells allow 12) to be pumped back into the groundwater system. A second method of correction is accomplished by building large 13) . These basins collect surface drainage and allow it to seep into the ground.

Although contamination of 14) by salt water is primarily a problem in coastal areas, it can threaten noncoastal locations as well. Many ancient sedimentary rocks of 15) were deposited when the ocean covered places that are now far inland. In some instances, significant quantities of seawater were trapped and still remain in the rock. These 16) sometimes contain important quantities of fresh water and may be pumped for use by people. However, if fresh water is removed more rapidly than it is 17) , saline water may 18) and render the wells unusable.

Coastal, freshwater aquifers, fresh water, encroach, sea level, marine origin, withdrawal, excessive pumping, affected, natural recharge, infiltration, saltwater contamination, recharge, basins, waste water, strata, replenished, water table.