Chapter 28A Groundwater Resources

NIOS Class 12 Environmental Science Chapter 28A

INTEXT QUESTIONS 28.1

1. What is groundwater?

Ans: Groundwater resources are the water found underneath the soil.

2. Where does it come from?

Ans: Part of rainwater that infiltrates the earth’s surface slowly seeps downward into extensive layers of porous soil and rocks.

3. What is an aquifer?

Ans: Under groundwater body created is called an aquifer.

4. What do you mean by water table?

Ans: The Water table is the upper level of an underground surface in which the soil or rocks are permanently saturated with water.

INTEXT QUESTIONS 28.3

1. State two ways each for saving water.

(a) in bathrooms

(b) in the kitchen

Ans:

(a) In Bathrooms
- i. Use a mug while shaving or brushing teeth.
- ii. Take short showers
- iii. Turn off the water while soaping or shampooing.
(b) In Kitchens
- i. Detect and repair all leaks in the irrigation system.
- ii. Use properly treated water for irrigation (any other)

2. Suggest two ways of judicious use of water while gardening and landscaping.

Ans:

Detect and repair all leaks in the irrigation system.
Use properly treated wastewater for irrigation wherever available.

3. Give any two other judicious uses of water.

Ans:

Designate a water efficiency coordinator.
Develop a water efficiency plan
.Calculate and involve employees, residents & school children in water efficiency efforts.

INTEXT QUESTIONS 28.4

1. What is artificial recharge?

Ans: Artificial recharge is a process by which excess surface water is directed into the ground, either by spreading on the surface by using recharge wells, or by altering natural conditions to increase infiltration.

2. State two methods by which groundwater can be recharged artificially.

Ans:

Spreading basins involves the surface spreading of water in basins that are excavated in the existing terrain.
Artificial recharge systems, such as pits and shafts, could be effective in areas of low permeability between the land surface and water table.

3. Give two advantages and disadvantages of artificial recharge?

Ans: Advantages of artificial recharge

While recharging, rain and surface water infiltrate the soil and percolate down through the various geological formations, and are naturally cleansed.
Very few special tools are needed to dig drainage wells.

INTEXT QUESTIONS 28.5

1. How do mining activities affect groundwater?

Ans:

Mine drainage discharge.
Process water, sludge lagoons.
Solid mine tailings.
Oilfield spillage at group gathering stations.

2. Name any two contaminants of groundwater.

Ans: Nitrates, pathogens, trace metals, and organic compounds.

3. State two reasons for the decline in the quality of groundwater.

Ans: A vast majority of groundwater quality problems are caused by contamination, over-exploitation, or a combination of the two. All kinds of activities, urban, industrial, or agricultural, carried out on land have the potential to contaminate groundwater. Industrial discharges, landfills, and subsurface injection of chemicals and hazardous wastes are obvious sources of groundwater pollution.

INTEXT QUESTIONS 28.6

1. State two reasons for the reduction in the water table.

Ans:

Water level in several parts of India has been falling rapidly due to an increase in extraction.
The number of wells drilled for the irrigation of both food and cash crops has rapidly and indiscriminately increased.
India’s rapidly rising population and changing lifestyles have also increased the domestic need for water.

2. Give two reasons for the lowering of the water table.

Ans:

Intense competition among users in the agriculture, industry, and domestic sectors is steadily lowering the groundwater table.
The quality of groundwater is getting severely affected because of the widespread pollution of surface water.
Besides, discharge of untreated wastewater through bores and leachate from unscientific disposal of solid wastes also contaminates groundwater, thereby reducing the quality of fresh water resources.

3. Mention two risks of reduced water table and contaminated groundwater.

Ans:

Falling water tables in several states now threaten agricultural sustainability.
During the rainy season, the availability of water from precipitation is far in excess of natural and man-made holding capacity, which results in floods.
During the non-rainy period, high evaporation rates coupled with high water demands cause drought conditions requiring the import of water.
Abstraction of excessive quantities of groundwater has resulted in the drying up of wells, saltwater intrusion, and drying up of rivers that receive their flows in dry seasons from groundwater.

TERMINAL EXERCISE

1. State three important differences between groundwater and surface water.

Ans:

Surface water	Groundwater
Surface water is the water that remains on the surface of land in the form of streams, rivers, ponds, or lakes.	Groundwater is the water that is normally found underground and is obtained by digging wells, tube wells, and hand pumps.
Surface water is exposed and can be easily contaminated.	Groundwater is underground (hidden) and thus can not be easily contaminated.
Surface water often needs to be transported to the place of use and is thus expensive.	Groundwater is often available at the place of its use and need not be transported. It is thus cheaper.
Surface water can not be directly consumed as it is contaminated.	Groundwater is mostly uncontaminated and can be directly consumed.
Surface water is exposed and subject to evaporation losses and thus less dependable in times of drought.	Groundwater is underground and does not get lost due to evaporation. It is thus more dependable in times of drought.

2. What is the water table?

Ans: Water table, also called groundwater table, is the upper level of an underground surface in which the soil or rocks are permanently saturated with water. The depth at which the pore space in the soil is filled with water, and the level at which this occurs, is called the water table.

3. How can you obtain groundwater?

Ans: There are several methods to obtain groundwater.

Springs: When the water table is above the surface water level in some hilly areas, groundwater flows out as a spring. This spring water can be easily used as a source of drinking water.
Dug-well: It covers ordinary open wells of varying dimensions dug or sunk from the ground surface into water-bearing strata to extract water for irrigation purposes.
Shallow tube-well: It consists of a borehole built into the ground to tap groundwater from porous zones.
Deep tube well that extends to a depth of 100 m or more and is designed to give a discharge of 100 to 200 cubic m/h.
Handpump: Handpumps are commonly used to draw groundwater in villages and slum areas in urban centres. These are manually operated. Thus, no electricity or other power is required to operate them.

4. Describe in brief how water can be saved at home.

Ans: By using water more efficiently and by purchasing more water-efficient products, we can also help mitigate the effects of drought. Efficiency measures can also save money on water and energy bills.

Turning the taps off while brushing, shaving, etc, take short showers.
Washing veggies in a basin.
Wash only full loads of laundry.
Use soaker hoses or trickle irrigation systems for trees and shrubs.
When using a hose, control the flow with an automatic shut-off nozzle.
Wash the car with water from a bucket, or consider using a commercial car wash that recycles water.

5. What are the main groundwater quality problems in India?

Ans: All kinds of activities, urban, industrial, or agricultural, carried out on land have the potential to contaminate groundwater.

Industrial discharges, landfills, and subsurface injection of chemicals and hazardous wastes are obvious sources of groundwater pollution. These concentrated sources can be easily detected and regulated, but the more difficult problem is associated with diffuse sources of pollution like leaching of agrochemicals and animal wastes, subsurface discharges from latrines and septic tanks, and infiltration of polluted urban run-off and sewage where sewerage does not exist or is defunct.

6. Explain the natural and anthropogenic contaminants of groundwater.

Ans:

Natural Contaminants: Bacteria and viruses cause water-borne diseases such as typhoid, cholera, dysentery, polio, and hepatitis that may pass into groundwater through discharges from sewage, landfills, septic tanks, and livestock shelters.
Anthropogenic contaminants: Nitrates from sewage, fertilisers, landfills, etc, trace metals from industrial and mine discharges, and organic compounds from fertilisers and pesticides.

7. Describe the methods of artificially recharging groundwater.

Ans:

8. What are the main causes of groundwater depletion?

Ans: Causes of groundwater depletion

Groundwater crisis is not the result of natural factors:

During the past two decades, the water level in several parts of India has been falling rapidly due to an increase in extraction.
The number of wells drilled for the irrigation of both food and cash crops has rapidly and indiscriminately increased.
India’s rapidly rising population and changing lifestyles have also increased the domestic need for water.
Intense competition among users in the agriculture, industry, and domestic sectors is steadily lowering the groundwater table. The quality of groundwater is getting severely affected because of the widespread pollution of surface water.
Besides, discharge of untreated wastewater through bores and leachate from unscientific disposal of solid wastes also contaminates groundwater, thereby reducing the quality of fresh water resources.
Dependence on static storage for long periods of time results in mining of groundwater. Ideally, the age of groundwater used should be as young as possible. The greater the age, means longer the period for which mining has been carried out.

9. What are the main adverse effects of groundwater depletion?

Ans: In India and Bangladesh, millions of people are exposed to groundwater contaminated with high levels of arsenic, a highly toxic and dangerous pollutant. It has been estimated that close to 5 million people in West Bengal, India, are affected. In next-door Bangladesh, half the entire population of 120 million is exposed to elevated levels of arsenic in their drinking water.

10. How can the quality of recharge water be maintained?

Ans:

For effective artificial recharge, highly permeable soils are suitable, and maintenance of a layer of water over the highly permeable soils is necessary.
The ditches could terminate in a collection ditch designed to carry away the water that does not infiltrate. This would reduce the accumulation of fine material.
Recharge wells are suitable only in areas where a thick impervious layer exists between the surface of the soil and the aquifer to be replenished. They are also advantageous where land is scarce. A relatively high rate of recharge can be attained by this method.
Recharging with less-saline surface waters or treated effluents improves the quality of saline aquifers, facilitating the use of the water for agriculture and livestock.