2 Factors affecting ground water

epgp books

 

 

 

Introduction:

 

Water that lies beneath the earth’s surface, fills in the pore spaces, cracks, and fractures in rocks and sediments found beneath the earth’s surface is termed as underground water, groundwater, subsurface water or subterranean water. Water can be termed as groundwater when it moves beneath the earth’s surface. Groundwater occurs everywhere beneath the earth’s surface, and is usually restricted to a depth of about 750 meters or less. The definition of groundwater in practice is quite complex. The groundwater includes water that is contained in the soil, which is in the intermediate unsaturated zone. It also includes water which is in the capillary fringe (zone above the water table) and which is below the water table. The soil comprises of the broken down and weathered rock along with the decaying plant debris at the surface.

 

Sources of Groundwater:

 

There are four sources of groundwater:

 

(i) Connate water:

 

It is the water which includes in the rock itself, at the time of rock formation when water gets trapped in rock strata. Because rock containing connate water is typically formed from ocean sediments, it is normal saline. In geology and sedimentology, connate waters are liquid molecules which got trapped in the pores of sedimentary rocks at their time of deposition. These waters also contain many mineral components in the form of ions in solution. The connate liquids are expelled as rocks get buried and undergo lithification. If the escape route for these fluids blocks, the pore fluid pressure builds up in the rocks leading to overpressure.

 

(ii) Meteoric water:

 

It is the water which is derived from precipitation i.e. snow and rain. It includes water in lakes, rivers, and ice melts, which has fallen from precipitation indirectly. It originates in the atmosphere by evaporation which falls as rain and ultimately becomes groundwater by the process of infiltration. This infiltrating water continues its downward journey to the zone of saturation to become a part of the groundwater in aquifers, thus forming the major part of underground water.

 

 (iii) Juvenile water:

 

It is also known as magmatic water as it originates in the earth’s interior and associates with the magmatic activities below the crust. Magmatic water rises from great depth accompanying magma intrusion. With the cooling of magma, its contents, gaseous and vapor etc. separate out from it. The water vapors gets condensed into heated water and gradually moves upward from the area of high temperature and pressure to that of low temperature and pressure. This is also called virgin water.

 

(iv) Condensational water:

 

It is the prime source which replenishes groundwater in deserts and semi-desert areas where precipitation is scanty, and there is rapid evaporation. During summers, the air over land is warmer than the air trapped in the soil, which lead to pressure difference between the two. Because of the pressure gradient, the atmospheric water vapor penetrates the rocks and gets converted into water through condensation due to falling temperature of the water vapor below. This process may lead to the accumulation of a certain amount of water in rocks in arid and desert regions.

 

Importance of Groundwater:

 

Groundwater is critical in supplying fresh water to streams and wetlands. The water is used mainly for irrigation, manufacturing, domestic and other purposes. In the United States, 80 to 90 percent of the fresh water is extracted from groundwater. Due to limited availability of surface water, there is an increased dependence on groundwater. Initially it was thought to be of an unlimited quantity and naturally protected by the soils above it. Later it was found to be of overuse and improper use with disposal of chemicals at the land surface. The proper use and protection of groundwater require an insight and an understanding of the groundwater system.

 

Out of the total earth’s water, 97% is salt water which is in the oceans; the remaining 3% being fresh water. Groundwater is a significant part of the hydrological cycle, containing 21 percent of Earth’s freshwater. Groundwater makes up about 1% of the water on the Earth (most water is in oceans). It makes up to 35 times the amount of water in lakes and streams. Groundwater is a component of the hydrologic cycle, which tells about the occurrence of water and the processes by which it moves.

   

Vertical Distribution of Groundwater:

 

A water table is the area between water-saturated ground and unsaturated ground, below which the rocks and soil are full of water. At times, below the water table are pockets of water called aquifers.

 

The region of subsurface from the ground surface to the water table is the unsaturated zone. It contains both air and water where the pore spaces do not fill with ground water. The area below the earth surface is saturated or filled with ground water, called the saturated zone. In this zone, all of the voids are full of water.

 

The water table marks the boundary between the saturated and unsaturated zone. It is the surface at which fluid pressure equals the atmospheric pressure. Thus, groundwater refers only to water in the saturated zone beneath the water table. The water zone beneath the Earth’s surface is called subsurface water. The saturated and unsaturated zones are connected, and the position of the water table fluctuates seasonally and with the effects of groundwater abstraction. All openings in the rock below gets saturated with water. With the increase in pressure, the pore spaces are reduced. The water table level is not necessarily completely level. It rises with the hills & sinks with the valleys. The water table intersects the surface in springs, rivers, and lakes. There is perched water table above the actual water table if a porous and permeable rock lies above the saturated zone (see figure 1).

    Groundwater Zones

 

The surface water seeps downward through soil, sediment, and rocks. This includes precipitation, irrigation from crops and other plants which contribute to a fluctuating water table. This process of seeping is called saturation. Above the water table, completely dry to partially wet is the Zone of Aeration. The rocks and pores that are filled with water are saturated. The water table lies on top of the saturation, or phreatic zone. The forces preventing groundwater to move downward are first, the molecular attraction between water and rocks and earth materials and second, the molecular attraction between water particles.

 

The area above the water table is called the vadose zone. The area between the soil and the water table is called as the unsaturated or vadose zone. Water moves in the downward direction through this zone to the water table. This general zone can be subdivided into the soil water zone, the intermediate vadose zone (sub-soil zone), and capillary zone. It consists of 3 separate zones (see figure 2).

 

i) Zone of soil moisture – This part is at the top and most familiar to us. It responds to the local moisture conditions and precipitation. Vegetation survives in this part. Therefore, water is mostly trapped, and lost by evapotranspiration in this zone.

 

(ii) Intermediate Zone–

 

This lies below the area of soil moisture and is generally dry. Water moves down through the this zone to the water table.

 

(iii) The capillary fringe- This extends a short distance above the water tablewhere capillary forces pull water upward into pore spaces.

 

 

Groundwater and Hydrological System

 

In the hydrological cycle the river basin forms the geographical expression and also the spatial  unit  where water  resource balances is estimated. It is here through  which pollutants are transported in the cycle.

 

Wateris found at or beneath the earth’s surface or in the atmosphere in any form-water vapor and ice. Water continually circulates between the ocean, atmosphere, and land. This continual circulation, however, thought of as the beginning in the oceans, is called the hydrologic cycle. Water evaporates from surface water like an ocean, lake, river or through transpiration from plants. The water vapor moves over the land, rises at higher altitude and condenses to form clouds. This evaporated water comes back to the earth’s surface as precipitation in the form of rain or snow. Some of the snow ends up in polar ice caps or glaciers. The rain and snowmelt flows in channels or infiltrates into the subsurface (See Figure 3). This infiltrated water gradually moves at the subsurface level under the influence of gravity, into the saturated zone thus becoming groundwater. Some of the infiltrated water gets transpired by plants and returns to the atmosphere by evaporation. The groundwater from here flows toward surface as rivers, lakes, or the ocean to begin the cycle afresh. This flow from recharge areas to surface areas is the groundwater portion of the hydrologic cycle.

 

Occurrence of Groundwater: Controlling factors

 

The occurrence of groundwater is influenced by the following factors:

 

Topography: A water table is not horizontal, but follows the topography, or upward and downward tilts, of the land above them. The water table is higher near the hilltops and lower near the valleys, because water seepage into streams, swamps and lakes cause lowering of water table near the valleys.

 

In an aquifer, the water table is mostly vertical and reflects the surface relief of the area above. This is due to the capillary effect of the soil, sediments and other porous material. In the aquifer, the flow of groundwater is in both horizontal and vertical directions and from points of higher pressure to lower pressure. The slope of the water table is known as the hydraulic gradient. This depends on first, the rate at which water adds and subtracts from the aquifer and second, the permeability of the material. At times, the water table of an area is not dependent on the topography. This may be due to variations in the underlying geological structure (e.g., folds, faults, fractures in the bedrock). Sometimes, a water table intersects with the land surface.

 

The fluctuation of the water table is due to the fact that in areas which experience monsoon climate like as in the Indian subcontinent, especially during dry seasons, the water table flattens and gradually the high water table beneath the hills decreases to the level of valleys.

 

In addition to topography, water table is influenced by many factors, including climate, land use, geology, etc.

 

Climate: In humid regions, recharge areas through which water percolates underground are found everywhere except streams, and adjacent floodplains. On the other hand, in arid regions recharge areas encompass only the mountains and adjoining alluvial fans and the streams below which porous alluvium soil is there through which water can percolate and recharge the groundwater. Groundwater is available at great depth in dry or arid regions whereas it exists at shallow depth in humid areas. Seasonally, water table rises during the rainy season and sinks in the dry season. Change in climate, for example, major increases in frequency and intensity of exceptional rainfall events in groundwater recharge areas can result in water tables rising to levels higher than previously recorded maxima, causing extensive ‘groundwater flooding’ with damage to property and crops.

 

Land use can also influence an area’s water table. Most groundwater is formed from excess rainfall percolating the land surface. Urban areas often have impervious surfaces, such as roads etc. These prevent water from seeping into the ground below. Instead of entering the zone of saturation, water becomes runoff and the water table dips. Lands having irrigation from surface water source has the greatest impact on groundwater, both quantitatively and qualitatively as excess water infiltrates into the shallow aquifers.

 

Geology often determines the quantity of water that filters below the zone of saturation, making the water table easy to measure. Porous rocks can hold more water than dense rocks. For example, an area underlain with pumice which is a light and porous rock can retain a fuller aquifer, is easier to assess than the water table of an area underlain with hard granite or marble.

 

Properties of Materials: The degree to which a body of rock or sediments will function as a groundwater resource depends on many properties. The two important physical properties are porosity and hydraulic conductivity. Transmissivity is also an important concept in knowing an aquifer’s ability to yield groundwater.

 

1. Porosity of the Rock

 

Porosity is determined by studying the shape and arrangement of soil particles. It is the amount of air space or void between soil particles. Infiltration, groundwater movement, and storage occur in these spaces. The porosity of soil is the ratio of the volume of pore space in a unit of material to its total volume. The total amount of water that can be contained in the rock depends on the proportion of the gaps in a given volume of rock, and this is called as porosity of the rock.

 

It is expressed as a decimal fraction or percentage. It is a measure of the amount of groundwater that is stored in the geological material. It can be defined mathematically by the equation:

 

n= Vv ÷ V×100%

Where,

n = Porosity, expressed as percentage

Vv = Volume of void space in a unit volume of geological materials, written as L3, cm3 or m3

V = Unit volume of earth material, including both voids and materials, read as L3, cm3 or m3

 

Porosity ranges from zero to around 60%.

 

Porosity is dependent on the type of rock which contains the water. In other words, the porosity depends upon the spacing, pattern of cracks and fractures of the rocks.

 

In sediments, the porosity of the rock depends on the grain size, shape of the grains, and the degree of sorting and cementation. The sorting or packing arrangement is most important in these rocks. The porosity of well-rounded sorted sediments is significant as they are all almost of the same size. Poorly sorted sediments generally have low porosity because the fine-grained particles tend to fill the void spaces.

 

Well-rounded coarse-grained sediments usually have higher porosity than fine-grained sediments, because the grains don’t fit together well (see Figure 4). Very fine-grained rocks make poor aquifers because of the surface tension which holds the water in them. Some shales can have up to 90 per cent of open space (Fig. 5).

    The porosity of sediments is affected by the shape of the grains. They can be of various shapes like rods, disks, or books. The fabric or orientation of the particles, if they are not spheres, also influence porosity (Figure 6).

Figure 6: Porosity of Well-Rounded Coarse-Sediments is more than the Fine-Grained Sediments

 

    The amount of cement already filling up the void spaces in highly cemented sedimentary rocks have a lower porosity (see Figure 7) as compared to the cemented void spaces.

 

In carbonate, sedimentary rocks such as limestone, groundwater occur in fractures and cavities formed as a result of the dissolution of the sediments (figure 8). Flow in the largest fractures may approach the velocities of surface water.

    In Igneous and Metamorphic rocks, which are very dense crystalline rocks, porosity is controlled by cracks, fractures, an faults. Structure of the rocks and its weathering are also important factors.   Porosity is low as the minerals tend to be intergrown, leaving little void space.

 

Higher fractured igneous and metamorphic rocks, however, could have a high secondary porosity (see figure 9).

 

Such type of extraction of groundwater from fractured rocks is there in the mountainous regions of the United States as the Sierra Nevada has carbonate rocks. Also, the Peninsular Ranges and coastal ranges have significant groundwater.

 

The arrangement or packing of the soil particles plays an important role in porosity. If the

 

      particles are stacked directly on top of each other, it is called as cubic packing. It has higher porosity than the particles which are laid on top of two other particles in a pyramid shape called as rhombohedral packing. The smaller particles could fill in the void spaces between the larger particles, which would result in a lower porosity, (see figure 10a and 10b).

 

 

 Particles exist in many shapes, and these shapes are packed in a variety of ways which increase or decrease porosity. A mixture of grain sizes and shapes result in lower porosity.

 

It is important to understand that porosity is not affected by the diameter size of the grain. Porosity is the ratio of void space to total volume. A box full of ping pong balls and other of basketballs would have the same porosity, as long as the packing or arrangements of the balls is same in both the cases.

 

Porosity is classified as primary or secondary. Primary porosity is referred to the voids present in the sediment or rock which is initially formed. Secondary porosity is referred to voids formed in the rock through fracturing or weathering after it was formed. It is the porosity of fractured rocks provided by discrete rock mass discontinuities (faults, joints, and fractures). In sediments, porosity of a rock is a function of the uniformity of grain size (sorting) and shape of the rock. Finer-grained sediments have a higher porosity than coarser sediments as the finer-grained sediments have greater uniformity of size. In crystalline rocks, porosity is more because of a higher degree of fracturing or weathering in them. As alluvial sediments become consolidated, primary porosity decreases due to compaction and cementation of the voids. Secondary porosity also increases when consolidated rock is prone to stresses that cause fracturing.

 

Table 1.1 shows that clays though have the highest porosities, make poor sources of groundwater because they yield very little water. Sand and gravel on the other hand make excellent sources of groundwater even though they have lower porosity than clay, due to the high specific yield, which allows the groundwater to flow to wells. If the rocks such as limestone and basalt are well-weathered and highly fractured, they make good quantities of groundwater. Though porosity measures the total amount of water that is contained in void spaces, the two related properties cannot be ignored.

 

Specific yield is defined as the ratio of the volume of water that moves from a water filled rock due to gravity to the total volume of rock.

 

Table 1.1: list represents porosity ranges from various geologic materials.

 

   Table 1.1: Range of Values of Porosity (after Freeze & Cherry, 1979)

 

It describes the portion of the groundwater that could be available for extraction. All of the water stored in pore spaces does not become part of flowing or moving groundwater.

 

Just as water clings to glass, water also sticks to soil particles due to surface tension, cohesion, or adhesion forming a thin film around a soil particle. Thus specific yield is less than porosity.

 

A mathematical equation to describe specific yield is:

 

Specific Yield or Sy= (Vdrained/ Vtotal) × 100

 

Unlike porosity, specific yield is determined by grain size. For example, if two soil have the same porosity, but different grain sizes (e.g., clay and sand), the soil with smaller grain size will have a lower specific yield. Clay has a greater surface area than sand. Therefore, more water will remain behind clinging to the clay particle surfaces, this have a greater specific yield.

 

Specific Retention: The portion of groundwater that remains as a film on particles or in pore spaces is called specific retention. It increases with decreasing grain size.

 

Specific yield and specific retention of the aquifer material together equal porosity. Table 1.2 shows that clays though have the highest porosities, make poor sources of groundwater as they yield very little water. Sand and gravel have much lower porosity than clay, make excellent sources of groundwater. This is because of the high specific yield of sand and gravel which allows the groundwater to flow to wells. Rocks such as limestone and basalt have significant quantities of groundwater if they are well-weathered and highly fractured. Porosity does not indicate clearly about the availability of groundwater in the subsurface. The pore spaces must also interconnect with each other and be large enough for water to move freely in the ground so that it can be extracted from a well or discharged to a water body. The term “effective porosity” refers to the degree of interconnectedness of pore spaces.

Table 1.2: Porosity (in percent) of soil and rock types

 

 

Modified from Heath (1983)

 

In finer sediments, porosity may be low due to water that is held tightly in small pores.

 

Effective porosity is very low in crystalline rocks that are not weathered or highly fractured.

 

2. Permeability

 

While porosity tells us how much water rock or soil can retain, permeability is a measure of the capability of rock to transmit water through its pore spaces. It is the property of the soil to allow water to pass through the gaps between them. Since voids are present in all the soils even in the most stiff soil clay, they all are permeable. It is a slow process, on an average being “a few centimeters per day. Without the voids or interconnected pore spaces, the liquid or gas will not flow. The size of pore space and interconnectivity of the spaces help determine permeability, so shape and arrangement of soil grains play the main role. The term hydraulic conductivity is used in explaining groundwater and aquifer properties. Hydraulic conductivity understands that water is the fluid moving through soil or rock type.

 

Water can percolate between pore spaces, and fractures between rocks. Larger the pore space, more permeable is the geological material. The sample size of mixed grain sizes which is poorly sorted has lower permeability because the smaller grains fill the openings made by the larger grains. Soil, sand, and gravel are porous and permeable. Though clay and shale are porous and can hold a lot of water, the pore spaces within these fine-grained soils are small for water to flow through them very slowly. Clay has low permeability due to small grain sizes with large surface areas and less connectivity of pore spaces. Sandstone and conglomerate are highly permeable due to the presence of large interconnected pore spaces between the grains (Table 1.3). If the permeability of the ground is uniform and there is an increasing gradient of slope of the water table, then the velocity of groundwater flow increase. This is called hydraulic gradient.

 

 

Table 1.3: Permeability for Sediments

 

In rocks with fractures, permeability is determined by the size of the openings, the degree of interconnectedness, and the amount of open space.

 

Movement of Groundwater

 

The movement of ground water is not stationary. It flows due to differences in porosity, permeability, elevation, and pressure gradient through pore spaces at extremely slow velocity driven by potential energy. The flow velocity of ground water is expressed in metres per day. Groundwater permeates through the soil layers after being activated by the force of gravity. Permeability decreases downward as the excessive weight exerted by the overlying soil makes the bottom layer compact. The vertical infiltration of water decreases, and if it is lies on a slope, groundwater deflects down the slope. The water table does not have a flat surface, but there are high and low areas as there are hills and valleys found on land. The ground water tends to move down the slope from water-table areas of higher elevation to regions of lower elevation. Such differences of the water table are known as hydraulic head. This difference results in the movement of ground water from recharge areas to discharge areas. Ground water may naturally come out from the subsurface and flows in the form of a spring, stream, lake, ocean, or seep, or by being transpired by plants. The rate at which ground water flows is dependent on the hydraulic conductivity and the rate of change of hydraulic head. The difference between hydraulic heads divided by the distance between them is the hydraulic gradient.

 

In the mid nineteenth century, Henry Darcy experimented on sand filters for water treatment. He measured the flow rate or discharge with units of volume of water per unit time; (similar to stream discharge) through porous medium, i.e., sand. He found that the amount of flow through a porous medium is directly proportional to the difference between hydraulic head values and inversely proportional to the horizontal distance between them (Fetter 2001). When combined with the hydraulic conductivity of the porous medium and the cross-sectional area through which the groundwater flows, Darcy’s law states:

 

Q = KA (dh/dl) (volume/time)

 

Where:

 

Q = flow discharging through a porous medium

 

K = hydraulic conductivity (length/time)

 

A = cross-sectional area (length2)

 

dh = change in hydraulic head between two points (length)

 

dl = distance between two points (length)

 

The hydraulic conductivity is a property of the porous medium and the fluid that represents the ability of the geologic structure to transmit water. The higher the hydraulic conductivity of a medium, easier it is for the water to flow through it.

 

This law provides the rate of volumetric flow of water. In order to calculate the average linear velocity at which the water flows, the result obtained is divided by the effective porosity. The rate of movement of ground water is very less. The tremendous amount of friction produced due to the movement of water through the spacesbetween particles of sand and gravel results in the slow rate of movement of ground water. Generally it is less than 1,000 feet/year. More steep the slope of the water table, the faster the ground water flows. In impermeable rock as the shale, ground water flows only a few centimetres a year, while in permeable gravel, ground water can flow large distances say, to hundreds and thousands of metres in a day.

 

Aquifer Depletion: Threats of Overuse

 

Groundwater is largely used by people around the world specially where availability of surface water is not there. It is under severe crisis due to it’s depletion in various areas. Aquifers can be measured by water tables. They are used to extract under ground water in order to meet the growing demands of the population such as industry, agriculture, plants etc. Pumping ground water over the long term causes problem of some water tables dropping very quickly. This process is called“aquifer depletion.” The shallow aquifers can recharge from surface water. The deep acquifers contain ancient water locked in the rocks caused by the changes in the geological structure millions of years ago. This maybe termed as “fossil water”. Once this is water is gone it cannot be recharged. Some of the adverse effects of groundwater depletion are:

 

Lowering of the Water Table

 

The excessive groundwater pumping in an area below which the ground is saturated with water has a severe consequence of the land being subsided. As water levels decline, the rate of water the well can yield may decline. Hence these wells are not able to reach groundwater.

 

 Increased costs for the user

 

As the water table lowers, the water must be pumped farther to reach the surface, using more energy. If pumps are used to lift the ground water, more energy is required to drive the pump. Using the well can become prohibitively expensive.

 

Reduced Surface Water

 

Ground water of the lakes and rivers are interconnected. When groundwater is overused, the lakes, streams, and rivers connected to groundwater can also have their supply diminished. The seepage of groundwater into the streambed discharges as running water in the streams. The proportion of stream water that comes from groundwater inflow depends on the region’s topography, geology and climate. Groundwater pumping can change the flow of water between an aquifer and a stream, or lake. This can be done by obstructing groundwater flow which discharges as the surface-water body or by increasing the rate of water movement from the surface-water body into an aquifer. The effect of ground water pumping is the lowering of groundwater levels below the depth of vegetation along the wetland. The overall effect is a loss of vegetation and wildlife habitat in that region.

 

Land Subsidence

 

A negative consequence of extraction of ground water too fast is land subsidence. Land subsidence occurs when there is a lack of support below the ground. This process is mostly caused by human activities, from the discharge of groundwater. When water is drawn out of the soil, it collapses, compacts, and drops. Without ground water filling pore space, the aquifer compacts and the surface of the land drops. This subsidence of land depends on factors as type of soil and rock below the surface. At times, aquifers are recharged artificially to prevent them from compacting. This recharging is done by pumping natural flood waters and treated wastewater back into the ground.

 

Water Quality Deterioration

 

 

One water-quality threat to ground water reserves is contamination from saltwater intrusion. Under natural circumstances, the boundary between the fresh water and salt water is relatively stable, but excessive pumping in coastal areas, can cause salt water to move inland and upward, leading to saltwater contamination of the ground water. All of the water present on the ground is not fresh water. Also, most of the very deep ground water and water below oceans is saline. It is estimated that around 12.9 cubic kilometers of saline ground water exists compared to about 10.5 million cubic kilometers of fresh groundwater.

 

In regions such as North Africa, water in aquifers are used by people faster than it can be replaced by rain or snow. Aquifers in North Africa are not used much but they are much shallower as compared to aquifers in other parts of the world. hence parts of North Africa are experiencing aquifer depletion.

 

The onset of the twentieth century sees a threat of aquifer depletion, as activities such as industry, agriculture, have drained the aquifer faster than it could naturally replenish itself. Ground water can last indefinitely only if the withdrawal rate from wells does not exceed the recharge rate. Unfortunately, this is not taking place and many aquifers are being discharged at a faster rate than they recharge.

 

Contamination of Ground Water

 

Soils and rocks have a natural ability to filter impurities out of ground water. The electrostatic charges of clay minerals attract and remove contaminant particles from ground water.

 

However, certain pollutants such as raw sewage, pesticides, fertilizers, and heavy metals can pose problem if they enter the ground water. The contaminants are added by chemical storage facilities, landfills, mines, and factories. Low-density contaminants float on water and occupy the upper level of an aquifer, whereas denser contaminants fall at the bottom of the aquifer.

 

Contaminants may also dissolve in the water. Salt water intrusion, a type of natural contamination can be a result of heavy pumping of wells near the seas and oceans. These impurities mixed with ground water are difficult and expensive to remove. They may be removed by pumping or in certain instances given chemical treatments.

   Conclusion

 

Groundwater is the subsurface water found in pore spaces, cracks, etc. beneath the earth surface. It makes up more than 90 percent of earth available fresh water. Water from various sources seeps down the top layer and collects above the bedrock deep down the earth. It is a finite resource and gets replenished if extraction rate exceeds recharge rate. Also, contamination of groundwater can take place. Therefore, it is important to minimise activities that can affect quality and quantity of groundwater available to humans and the environment.

 

you can view video on Factors affecting ground water

 

References