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sewage. Its sources include an ever-increasing number of septic tanks, as well as inadequate or
broken sewer systems and farm waste. If sewage water that is contaminated with bacteria enters
the groundwater system, it may become purified through natural processes. The harmful bacteria
may be mechanically filtered by the sediment through which the water percolates, destroyed by
chemical oxidation, and/or assimilated by other organisms. For purification to occur, however,
the aquifer must be of the correct composition. For example, extremely permeable aquifers (such
as highly fractured crystalline rock, coarse gravel, or cavernous limestone) have such large
openings that contaminated groundwater might travel long distances without being cleansed. In
this case, the water flows too rapidly and is not in contact with the surrounding material long
enough for purification to occur. This is the problem at Well 1 in FIGURE 7.1. In contrast, when
the aquifer is composed of sand or permeable sandstone, the water can sometimes be purified
after travelling only a few dozen meters through it. The openings between sand grains are large
enough to permit water movement, yet the movement of the water is slow enough to allow ample
time for its purification (Well 2, Figure 7.1).

Task 2. Look at Figure 7.1. Talk about the pollution of groundwater at Well №1 and
Well №2.
Task 3. Build up a glossary to the most important terms used in the text.

Task 4. Answer the questions:
1. What are the most important environmental problems associated with groundwater?
2. What do you know about the problem of contamination?

Task 5. Give a short report about the following problems associated with
groundwater (you may use all the possible Internet Webs):
 springs;
 wells;
 artesian wells;
 hot springs and geysers;
 geothermal energy.

TEST YOURSELF

Task 1. Tell whether the sentences are true or false. Correct the false ones.
1. Because gas and oil are heavy in density compared to the water that also occurs in the
pores of the subsurface rocks, petroleum falls.
2. Carrier beds are rock layers that are very permeable and transmit fluids.
3. If there is a trap along the migration route, the gas and oil cannot accumulate in the trap.
4. The trap must be in position after the gas and oil migrate through the area.
5. The most common trap is a saturated pool.
6. An unsaturated pool has a free gas cap.
7. A caprock is an impermeable rock layer that does not allow fluids to flow through it. t
8. A field is a subsurface zone that produces oil and gas but does not communicate with
other reservoirs.
9. A reservoir is the surface area directly above one or more producing reservoirs on the
same trap.
10. Groundwater is an endlessly renewable resource.
11. The pollution of groundwater is a serious matter especially in areas where aquifers are a
large part of the water supply.
12. Sewage water that is contaminated with bacteria can never become purified through
natural processes.