An exclusive project report on Groundwater. This project report will help you to learn about: 1. Introduction to Groundwater 2. Meaning of Groundwater 3. Sources 4. Groundwater-Table and Its Relation to the Curvature of the Land 5. Groundwater Pollution 6. Contamination 7. Artificial Recharge.
ADVERTISEMENTS:
Contents:
- Project Report on Introduction to Groundwater
- Project Report on the Meaning of Groundwater
- Project Report on the Sources of Groundwater
- Project Report on Groundwater-Table and Its Relation to the Curvature of the Land
- Project Report on Groundwater Pollution
- Project Report on the Contamination of Groundwater
- Project Report on the Artificial Recharge of Groundwater
Project Report # 1. Introduction to Groundwater:
This water is found under the ground and is available through hand pumps and deep wells etc. The water is found in the ground due to rains. In fact when rainfall occurs some water percolates down through the pores of the soil. At a certain depth the pore space in the soil is completely filled with water and the level at which this occurs is called the water level.
The water level generally follows the topography of the flow. There are three important formations of soil and rock in India, which have a bearing on the yield of groundwater. A very large portion of the country, nearly 120 million ha consists of consolidated hard rock formation. The yield in such areas is low.
In the semi-consolidated formation which covers about 5 million ha sedimentary rocks such as sand stones, lime stones and conglomerates occur. The yield in these areas is moderate. These formations occur particularly in Rajasthan, Gujarat and Tamil Nadu.
ADVERTISEMENTS:
There are large areas of unconsolidated formation in India consisting mainly of sand, gravel, boulder, laterites, soils and clays. These areas cover Kashmir, the Indus basin, Ganga-Brahmaputra basin etc. According to Geological survey of India, a rough assessment of groundwater resources has been attempted by the Central Ground Water Board.
The annual utilizable groundwater resources have been assessed as 422.860 km3 per year and the present utilization is 100 km3 per year which is about 24% of the total utilizable resources, the details are given in drought prone areas.
There are some draught prone areas as shown in Table 3. Here water level has gone deep into the Soil and surface water is also not available due to one reason or the other.
Groundwater quality comprises the physical, chemical and biological qualities of groundwater. Temperature, turbidity, colour, taste, and odour are the physical water quality parameters.
ADVERTISEMENTS:
Since most groundwater is colourless, odourless, and without specific taste, we are typically most concerned with its chemical and biological qualities. Although spring water or groundwater products are often called as “pure”, but their water quality is different from that of pure water.
Naturally, groundwater contains mineral ions. These ions slowly dissolve from soil particles, sediments, and rocks as the water travels along mineral surfaces in the pores or fractures of the unsaturated zone and the aquifer. They are referred to as dissolved solids.
ADVERTISEMENTS:
The dissolved solids in any water can be divided into three groups — major constituents, minor constituents, and trace elements (Table 1). The total mass of dissolved constituents is referred to as the Total Dissolved Solids (TDS) concentration.
In water, all of the dissolved solids are either positively charged ions (cations) or negatively charged ions (anions). The total negative charge of the anions always equals the total positive charge of the cations. A higher TDS means that there are more cations and anions in the water.
Except for natural organic matter originating from top-soils, all of these naturally occurring dissolved solids are inorganic constituents:
Minerals, nutrients, and trace elements, including trace metals.
In most cases, trace elements occur in such low concentrations that they are not a threat to human health. In fact many of the trace elements are considered essential for the human metabolism. Microbial matter is also natural constituent of groundwater.
Human activities can alter the natural composition of groundwater through the disposal or dissemination of chemicals and microbial matter at the land surface and into soils, or through injection of wastes directly into groundwater. Groundwater pollution (or groundwater contamination) is defined as an undesirable change in groundwater quality resulting from human activities.
Groundwater pollution works differently from surface water pollution, although they have many sources in common, such as fertilizers, pesticides, and animal wastes.
Project Report # 2. Meaning of Groundwater:
The whole process of the circulation of water between the land, sea and atmosphere is know as the hydrological cycle. When rain falls on the earth it is distributed in various ways. Some is immediately evaporated and thus returns to the atmosphere as water vapour.
Some is absorbed by plants and only gradually returned to the atmosphere by transpiration from the leaves of plants. Much of it flows directly off slopes to join streams and rivers, eventually reaching the seas and oceans.
This is known as run-off A considerable proportion of the water received from rain or snow, however, percolates downwards into the soil and rocks, filling up joints and pore-spaces and forming what is known as groundwater. Groundwater plays an important part in weathering and mass movement and is also important as a means of natural water storage. It re-enters the hydrological cycle by way of springs.
The amount of water available to form groundwater depends to some extent on climate In dry climates much precipitation may be quickly evaporated into the dry atmosphere and little moisture may percolate into the ground. In very humid conditions, where the surface of the ground may already be moist, much water may be moved as run-off.
In moderately humid areas water both runs off and sinks into the ground. The proportion of the rainfall absorbed as groundwater may depend on the season of the year.
More important, however, is the nature of the rocks and how easily they absorb and retain water. Various rocks and soils differ greatly in their porosity and permeability; the amount of groundwater present and the depth at which it lies are governed by these characteristics. Porous rocks are those, like sandstone, which have many pore-spaces between the grains.
Water is easily absorbed by such rocks and may be stored in the pore-spaces. Permeable or pervious rocks are those which allow water to pass through them easily (Fig. 4.6).
Thus most porous rocks are also permeable. However some rocks are porous but impermeable. Clay, for example, is highly porous since it is made up of innumerable very fine particles with pore-spaces between them. It thus absorbs a great deal of water. However, the pore-spaces are so small that the water does not move easily through the rock, which is thus impermeable.
On the other hand, granite which is a crystalline rock and consequently non-porous is often pervious. Its individual crystals absorb little or no water but the rock may have numerous joints or cracks through which the water can pass, rendering it pervious or permeable. Some granites are, however, far more pervious than others.
Project Report #
3. Sources of Groundwater:
(i) Springs:
The groundwater stored in the rock is released onto the surface at points where the water-table reaches the surface. A spring is simply an outlet for such water. The water may seep gradually out of the rock or may gush out as a fountain. Springs are of several kinds due to the nature of the rocks and the position of the water-table.
The main types are described below:
(a) In areas of tilted strata, where permeable and impermeable rocks alternate, water emerges at the base of the permeable layers (Fig. 4.8a).
Fig. 4.8(a) Spring seeps from edge of pervious rock lying above an inclined impervious strata.
(b) In well-jointed rocks water may percolate downwards until it reaches a joint which emerges at the surface. The water may come to the surface through the joint (Fig. 4.8b).
(c) Where a dyke or sill of impermeable rock is intruded through permeable rocks, it causes the water-table to reach the surface and the water issues as a spring (Fig. 4.8c).
(d) In limestone or chalk escarpments, where the permeable rock lies between impermeable strata, water issues at the foot of the scarp as a scarp-foot spring, or near the foot of the dip-slope as a dip-slope spring, as illustrated in Fig. 4.8d.
(e) In karst regions rivers often disappear underground. They then flow through passages worn in the rock by solution, and may re-emerge when limestone gives place to some impermeable rock. This kind of spring is sometimes called a vauclusian spring but is better referred to as a resurgence (Fig. 4.8e).
(ii) Wells:
Springs are the natural emergence points of groundwater, but Man can make use of stored water below ground by sinking wells. A hole is bored through the earth until the water-table, is reached. The well must be sunk to the depth of the permanent water-table (Fig. 4.9) if a constant supply of water is to be obtained.
If the well is only sunk to the wet-season depth of the water-table, water will be unobtainable when the level drops in the dry season. When a well is bored, the water usually has to be raised by hand or by mechanical pumping. Wells are particularly important in arid areas where there is little surface water but where the underlying rocks contain groundwater.
A particularly important type of well is the artesian well, which owing to the nature of its formation is quite distinctive. Where rock layers have been down- folded into a basin shape, permeable strata such as chalk or limestone may be sandwiched between impermeable layers, such as clay.
The permeable rocks may only come to the surface at the edges of the basin, but water falling on them will gradually seep downwards by the force of gravity until it reaches the lowest part of the basin (Fig. 4.10).
The impermeable layer below prevents the water from passing downwards while the impermeable layer on top prevents any possibility of the water escaping upwards. The aquifer is thus saturated to the brim of the basin.
The water is thus trapped in the aquifer under great pressure and when a well is bored, the pressure of water downwards from all around the basin is sufficient to force the water up the bore-hole so that it gushes onto the surface like a fountain. After a time the pressure decreases and it is necessary to pump up the water.
The depth of artesian wells varies from place to place, from a few feet to thousands of feet. The water may be used to supply the needs of an entire village as in the Great Plains of U.S.A. or for sheep farming as in Queensland and other parts of Australia.
Fig. 4.11 shows the distribution of artesian wells in Australia. But the water is sometimes unsuitable for agricultural or irrigation purposes as it may be hot or contain an excessive amount of mineral salts.
Artesian wells are most valuable to Man when they can be used in desert areas, e.g. in parts of the Sahara and in Australia. The aquifers receive water in areas of higher rainfall, but the water accumulates in basins underlying arid regions.
All wells bored by Man tend to deplete groundwater resources because the water is extracted faster than under natural conditions and also much faster than it can be replenished by rainfall. In many areas groundwater supplies have been greatly reduced or even exhausted by Man as a result of carelessness and overexploitation.
Project Report # 4. Groundwater-Table and Its Relation to the Curvature of the Land:
Water which seeps through the ground moves downward under the force of gravity until it reaches an impermeable layer of rock through which it cannot pass. If there is no ready outlet for the groundwater in the form of a spring, the water accumulates above the impermeable layer and saturates the rock.
The permeable rock in which the water is stored is known as the aquifer (Fig. 4.7). The surface of the saturated area is called the water-table.
The depth of the water- table varies greatly according to relief and to the type of rocks. The water-table is far below the surface of hill-tops but is close to the surface in valleys and flat low-lying areas where it may cause water-logging and swampy conditions.
The depth of the water-table also varies greatly with the seasons. When plenty of rain is available to augment groundwater supplies the water- table may rise, but in dry periods, no new supplies are available, and the water-table is lowered as groundwater is lost through seepages and springs (Fig. 4.7).
Project Report # 5. Groundwater Pollution:
Groundwater is polluted by a number of reasons, viz., geological reasons, industrial contamination or even by man-made cultural activities. The major geological conditions and the potential groundwater contamination is shown in Table 27.1.
The common groundwater contaminants are iron, arsenic, fluoride, nitrate and several other trace metals. Urban and industrial waste dump sites also contaminate the groundwater. Subsurface shallow groundwater is also contaminated with pathogenic bacteria and parasites.
There are various possibilities of groundwater sources by landfill sites through leaching processes as shown in Fig. 27.7:
In coastal areas, man-made activities like aquaculture induces the salt water intrusion to groundwater aquifers. This is primarily due to change in water table by rapid withdrawal of groundwater (Fig. 27.8).
Project Report # 6. Contamination of Groundwater:
i. Efficiency of Soil Adsorption:
The efficiency of soil adsorption is how much various parameters in the effluent from the source were reduced compared to the influent. Many factors are involved in the efficiency of soil adsorption. Such factors as climate, soil type, hydraulic conductivity, precipitation, porosity, etc. all contribute to how the effluent concentration is reduced in the soil.
Groundwater contamination has occurred were there have been high densities of septic systems. Studies have shown that the groundwater has been contaminated by high amounts of organic contaminants from septic systems. Problems with septic systems are worsen when communities that rely on subsurface disposal systems also depend on private well for drinking water.
The volume of water that flows into an average septic tank is on the order of 140 to 150 gallons per day per person. This amount can be broken down into percentages from typical household sources.
On a percentage basis the sources can be broken down as follows:
Toilets 22-45%; Laundry 4-26%; Baths 18-37%; Kitchen 6-13%; and other sources 0-14%.
As many as one-half of all septic tanks in operation are not functioning correctly. A common failure of a system is when the capacity of soil to absorb effluent is exceeded. When this happens the wastewater from the drain lines makes its way to the surface.
This type of failure occurs when the soil is clogged with waste particles or other substances and it is harder for the water to move through the soil. When the system fails in this way and wastewater makes its way to the surface, water runoff from rain may wash the contaminants into surface waters or into inadequately sealed wells down gradient.
A more significant failure is when pollutants from the drain field move too quickly through the soil and potentially into the groundwater. When there is large volume of wastewater moving through the system, soils with high permeability can be rapidly overloaded with organic and inorganic chemicals and microbes, allowing rapid movement of pollutants into the groundwater.
Special attention must be directed to the transport and fate of pollutants in the soil absorption phase when considering contamination of groundwater. Suspended solids in the effluent are removed by filtration as the waste water moves through the soil.
This process of filtration varies with the soil type, the size of the particles, soil texture, and the rate of the water flow. The key chemical processes governing the movement of particles from the effluent through the soil are ion exchange, adsorption, and chemical precipitation.
ii. Inorganic Contaminants:
Some potential inorganic contaminants include nitrogen, chlorides, phosphorous, and metals.
(i) Nitrogen:
The organic form of nitrogen is converted to the ammonium, as anaerobic conditions occur in the septic tank. The amount of nitrogen in the effluent from the tank averages about 40 mg/L and consists roughly of 75% in the NH+ and 25% in the organic form. Nitrogen contamination is of concern because it causes eutrophication in surface waters and is hazardous to human health if ingested in high concentrations.
The fate and movement of nitrogen in the soil from septic systems is dependent on the form of the nitrogen and biological conversions that may take place.
The most common form of nitrogen entering the soil is ammonium (NH+4) form that undergoes the process of nitrification. In the process of nitrification, ammonium is converted to nitrite and then into nitrate (NO–3). This process is an aerobic reaction carried out by obligate autotrophic organisms.
Denitrification also occurs in the soil under the septic system. Denitrification is the reduction of NO–3 to N2O or N2 by obligate facultative heterotrophs. In the absence of O2, NO–3 acts as the acceptor of electrons generated in the microbial decomposition of an energy source. Since ammonium is the most common form of nitrogen present, nitrification must occur before denitrification can.
Nitrate NO–3 is the most mobile form of nitrogen in both saturated and unsaturated soil conditions. The immobilization of nitrates is done by the uptake of it by plants in the immediate area. The nitrates move with water with little transformation and can travel long distances if the right conditions are present.
(ii) Chlorides:
Chlorides are very common and are naturally present in surface and groundwater, and are also found in wastewaters.
Chlorides are difficult to remove from wastewaters and both septic systems and wastewater treatment plants are unable to remove them. The concentration of chlorides in wastewater varies with the natural quality of the water supply. Since chlorides are anionic and mobile, they can be used as tracers of septic tank system pollution.
(iii) Other Inorganic Contaminants:
The soil type is an important factor in all heavy metal fixation reactions. Both soil texture and pH are important in the fixation of metals by the soil. Finer textured soil immobilizes trace and heavy metals to a greater extent as compared with those with coarse texture.
Finer textured soils usually have a greater cation exchange capacity due to their larger surface area. The transport of lead, zinc, mercury, and nickel has been linked to the texture of soil. The degree of fixation is a function of the pH. Soil pH influences the immobilization of lead, mercury, copper, and zinc.
Metals in the effluents from septic tank systems may be responsible for the contamination of shallow water supply sources, such as where there is a high groundwater table. In some areas, the levels of arsenic, iron, lead, mercury, and manganese were found at levels higher than what is recommended.
(iv) Microorganisms:
Microorganisms usually do not contaminate groundwater sources. The main limitation to movement of microbes through the soil is the physical filtration of bacteria and other microbes. It is the factor that usually limits the travel distances. Soil conditions such as no nutrients, drying, and antagonistic organisms’ secretions also determine the travel distances.
(v) Septage:
Septage is the mixture of sludge, fatty materials, and wastewater present in septic tanks. The septage is periodically pumped out by licensed companies. Septage can only contaminate groundwater if the septic tank is damaged and begins to leak or if the pumped septage is not disposed properly.
The concentration of possible pollutants is high in septage. Septage has also been found to harbor disease causing organisms.
The average values of the contents of domestic waste are shown in table:
Project Report # 7. Artificial Recharge of Groundwater:
In most low rainfall areas of the country the availability of utilizable surface water is so low that people have to depend largely on groundwater for agriculture and domestic use. Excessive groundwater pumping in these areas, especially in some of the 91 drought prone districts in 13 states of India, has resulted in alarming lowering of the groundwater levels.
The problem has been further compounded due to large- scale urbanization and growth of mega cities, which has drastically reduced open lands for natural recharge. In hard rock areas there are large variations in groundwater availability even from village to village.
In order to improve the groundwater situation it is necessary to artificially recharge the depleted groundwater aquifers. The available techniques are easy, cost-effective and sustainable in the long term. Many of these can be adopted by the individuals and village communities with locally available materials and manpower.
Advantages of Artificial Recharge of Groundwater:
Following are the main advantages of artificially recharging the groundwater aquifers:
1. No large storage structures needed to store water. Structures required are small and cost- effective.
2. Enhance the dependable yield of wells and hand pumps.
3. Negligible losses as compared to losses in surface storages.
4. Improved water quality due to dilution of harmful chemicals/salts.
5. No adverse effects like inundation of large surface areas and loss of crops.
6. No displacement of local population.
7. Reduction in cost of energy for lifting water especially where rise in groundwater level is substantial.
8. Utilizes the surplus surface runoff which otherwise drains off.
Methods of Artificial Recharge of Groundwater:
The methods of artificial recharge can be broadly classified as:
1. Spreading Method:
i. Spreading within channel
ii. Spreading stream water through a network of ditches and furrows
iii. Ponding over large area
(a) Along stream channel viz., Check Dams/Nala Bunds
(b) Vast open terrain of a drainage basin viz., Percolation Tanks
(c) Modification of village tanks as recharge structures.
2. Recharge Shafts:
i. Vertical Shafts
ii. Lateral Shafts
3. Injection Wells
4. Induced Recharge
5. Improved Land and Watershed Management:
I. Contour Bunding
II. Contour Trenching
III. Bench Terracing
IV. Gully Plugging
In alluvial as well as hard rock areas, there are thousands of dug wells, which have either gone dry, or the water levels have declined considerably.
These dug wells can be used as structures to recharge the groundwater reservoir. Storm water, tank water, canal water etc. can be diverted into these structures to directly recharge the dried aquifer. By doing so the soil moisture losses during the normal process of artificial recharge, are reduced.
The recharge water is guided through a pipe to the bottom of well, below the water level to avoid scouring of bottom and entrapment of air bubbles in the aquifer. The quality of source water including the silt content should be such that the quality of groundwater reservoir is not deteriorated. Schematic diagrams of dug well recharge are given in Fig. 27.6.
In urban and rural areas, the roof top rainwater can be conserved and used for recharge of groundwater. This approach requires connecting the outlet pipe from rooftop to divert the water to either existing wells/tube wells/bore wells or specially designed wells. The urban housing complexes or institutional buildings having large roof areas can be utilised for harvesting roof top rainwater for recharge purposes.