Your Answer : (Not Answered)

Correct Answer : B

Salt water intrusion is an entry of saline water in a freshwater aquifer.

In coastal aquifers fresh groundwater normally floats on and pushes back the denser sea water. When wells pump out fresh water faster than it is recharged, the water table falls and the boundary moves inland, so sea water enters the aquifer and the wells turn brackish. Over-pumping along the coasts of Gujarat and Tamil Nadu has caused this.

The movement of sea water up a river in a delta, or through an estuary on to land, is tidal or surface salinity ingress, not intrusion into an aquifer. Salinity from waterlogging is a problem of irrigated soils, where rising groundwater brings salts to the surface.

Your Answer : (Not Answered)

Correct Answer : C

The Ghyben-Herzberg relation says that for every metre of fresh water head above mean sea level, the fresh water zone extends about 40 metres below it.

Fresh water (density about 1.000 g/cm\(^{3}\)) floats on sea water (about 1.025 g/cm\(^{3}\)) in a coastal aquifer. Balancing the pressures at the interface gives

\[ \begin{aligned} z &= \frac{\rho_f}{\rho_s - \rho_f}\,h \\ &= \frac{1.000}{0.025}\,h = 40h \end{aligned} \]

where h is the water-table height above sea level and z the depth of the interface below sea level. The 14 m figure has no basis, and the options with 40 m or 10 m of head giving 40 m of fresh water have the ratio wrong by factors of 40 and 10. This is why over-pumping that lowers the water table by 1 m lets salt water rise by about 40 m.

Your Answer : (Not Answered)

Correct Answer : D

The ratio is the hydraulic diffusivity.

Hydraulic diffusivity is

\[ D = \frac{T}{S} \]

where T is transmissivity and S the storage coefficient. It appears in the groundwater flow equation and controls how fast a change in head, such as the drawdown from a pumping well, spreads through the aquifer.

Hydraulic conductivity is transmissivity divided by aquifer thickness, not by storativity. The hydraulic gradient is the change of head per unit distance. Hydraulic viscosity is not a standard aquifer parameter.

Your Answer : (Not Answered)

Correct Answer : D

The key gives (b) and (d).

Statement (d) is the definition of the storage coefficient (storativity): the volume of water an aquifer releases from, or takes into, storage per unit area for a unit change in head. Statement (b) is the usual account of where that water comes from in a confined aquifer: when the head falls, the aquifer skeleton is compressed and the pore water expands slightly, and the two together release water.

Statement (c) is wrong because the skeleton is compressed, not expanded, when pore pressure falls. Options A, B and C each include (a) or (c) in a pairing the key does not accept.

What could not be confirmed: statement (a) speaks of the compressibility of the pore water, which is the property the groundwater formulas use for water, so (a) is a looser wording of the same physics as (b) and option C ((a) and (d)) cannot be ruled out on physical grounds. D is taken because (b) repeats the textbook phrasing, compression of the skeleton and expansion of the water, and it is the keyed answer.

Your Answer : (Not Answered)

Correct Answer : A

The specific capacity is 166 lpm per metre of drawdown.

Specific capacity is the pumping rate divided by the drawdown, the fall from the static water level to the pumping level:

\[ \begin{aligned} s &= 6.50 - 5.00 = 1.50\ \text{m} \\ SC &= \frac{249}{1.50} = 166\ \text{lpm/m} \end{aligned} \]

Dividing by the pumping water level instead (249/6.5) gives about 38, and dividing by the static level gives about 50, so neither produces another option. 373.5 is the pumping rate multiplied by the drawdown rather than divided by it.

Your Answer : (Not Answered)

Correct Answer : A

The answer given is the Bicarbonate Province.

India's groundwater is grouped into hydrogeochemical provinces by the dominant anion. The Narmada valley and the basaltic and crystalline hills of western and central India are places where water meets silicate rocks (Deccan basalt, Archaean crystalline rocks and alluvium), and groundwater there is typically of the calcium-magnesium bicarbonate kind. A 2023 study of 305 groundwater stations in the Narmada basin found bicarbonate to be the dominant anion throughout the basin, with calcium dominant among cations in the upper and middle basin.

The chloride and the mixed bicarbonate-chloride provinces correspond to areas where sodium chloride salts are important, such as arid, coastal or saline-affected tracts, which is not the character of this valley.

What could not be confirmed is the formal province map itself: no source found names the province boundaries, so the match with the key rests on the dominance of bicarbonate in the valley's groundwater.

Your Answer : (Not Answered)

Correct Answer : A

(I) is true, (II) is false.

The height of capillary rise is inversely proportional to the radius of the pore or tube:

\[ h = \frac{2\gamma \cos\theta}{\rho g r} \]

so narrower pores raise water higher, as statement I says.

It follows that statement II is false. Clay-grade soils have very fine pores, so water rises much higher in them and their capillary fringe is thicker (up to a metre or more), while coarse sand, with large pores, has a thin fringe of only a few centimetres.

Your Answer : (Not Answered)

Correct Answer : D

The key's answer is a semiconfined aquifer.

A semiconfined (leaky) aquifer is bounded above and below by semi-pervious layers, aquitards, through which water leaks slowly to or from the neighbouring aquifers. The paper describes the system as an aquifer between other water-bearing layers, which is how the key reads it: water can move between them, so the middle aquifer is neither fully confined nor free.

A confined aquifer is sealed by impermeable layers (aquicludes). A phreatic (unconfined) aquifer has the water table as its upper surface, and a perched aquifer is a local saturated zone held above the main water table by a lens of impermeable material.

Your Answer : (Not Answered)

Correct Answer : C

A hydrograph shows the change in discharge with time.

A stream hydrograph plots the discharge of a river (volume of water per unit time, in m\(^{3}\)/s) at a gauging station against time. A storm hydrograph shows the rising limb, the peak discharge, the lag time after the rainfall and the recession limb, and is used in flood studies.

Water level (stage) is plotted on a stage hydrograph and converted to discharge with a rating curve, but the standard hydrograph is of discharge. Volume and velocity alone do not describe flow past a point over time.

Your Answer : (Not Answered)

Correct Answer : A

The problem is saltwater incursion, usually called saltwater intrusion.

In coastal aquifers fresh groundwater floats on denser seawater, and its pressure keeps the seawater back. When wells pump out fresh water faster than it is recharged, the water table falls and seawater moves inland and upward into the aquifer, making the wells saline. Coastal Gujarat and Tamil Nadu suffer from this.

Pumping does not deposit sand or reduce the permeability of the aquifer, and artesian recharge refers to replenishment of a confined aquifer under pressure, not a problem caused by pumping.

Your Answer : (Not Answered)

Correct Answer : B

Fluorosis is caused by fluoride in drinking water.

Drinking water with fluoride above about 1.5 mg/L over long periods causes dental fluorosis, with mottled and stained teeth, and at higher levels skeletal fluorosis, with stiff, painful joints and bone deformities. Fluoride-bearing minerals such as fluorite and fluorapatite in granites and gneisses release it to groundwater, a problem in Rajasthan, Andhra Pradesh, Telangana and other states.

Arsenic causes arsenicosis, high nitrate causes methaemoglobinaemia (blue baby syndrome), and sulphate mainly gives a laxative effect and bitter taste. None of them causes fluorosis.

Your Answer : (Not Answered)

Correct Answer : A

The statement is Darcy's law.

Henry Darcy found in 1856 that the discharge of water through a sand column is

\[ Q = K A \frac{h}{L} \]

where \(K\) is the hydraulic conductivity, \(A\) the cross-section, \(h\) the head loss and \(L\) the length of the flow path. Flow is thus proportional to head loss and inversely proportional to path length. It is the basic law of groundwater flow.

Newton's law of viscous flow relates shear stress to velocity gradient in a fluid, and Poiseuille's law gives laminar flow through a single tube, depending on the fourth power of its radius. Neither is the law for porous media.

Your Answer : (Not Answered)

Correct Answer : A

One darcy is about \(0.98 \times 10^{-12}\ m^{2}\).

The darcy is a unit of permeability, which has the dimensions of area. A medium has a permeability of one darcy when a fluid of viscosity 1 centipoise flows through it at 1 cm³/s across 1 cm² under a pressure gradient of 1 atm per cm. Converted to SI units this is

\[ \begin{aligned} 1\ \text{D} &\approx 9.87 \times 10^{-13}\ \text{m}^{2} \\ &\approx 0.987\ \mu\text{m}^{2} \end{aligned} \]

which is the first option. The options in m and km have the dimension of length, not area, so they cannot be a permeability, and \(2.3 \times 10^{-15}\ m^{2}\) is a few millidarcies.

Your Answer : (Not Answered)

Correct Answer : D

The formation is an Aquifer.

An aquifer is a saturated formation that is both porous and permeable enough to store, transmit and yield useful quantities of water to wells and springs. Sands, gravels, sandstones and fractured or karstic limestones are typical aquifers.

An aquiclude can hold water but cannot transmit it in useful amounts, as with clay. An aquitard transmits water only slowly and does not yield it freely. An aquifuge, such as massive unfractured granite, neither holds nor transmits water.

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Correct Answer : B

Such a layer is a Confined aquifer.

A pervious, water-bearing layer sandwiched between two clay layers is confined, because clay acts as an aquiclude that holds the water under pressure. The water in a well drilled into it rises above the top of the aquifer, and where the pressure is high enough it flows freely as an artesian well.

An unconfined aquifer has no confining layer above it. Semi-confined (leaky) aquifers are bounded by aquitards that let some water through, whereas the paper describes clay layers as full confining beds. 'Semi-unconfined' is not a standard category.

Your Answer : (Not Answered)

Correct Answer : B

An aquifer bounded by aquitards is a Leaky aquifer.

An aquitard is a poorly permeable layer that slows but does not stop the movement of water. An aquifer overlain or underlain by such a layer receives or loses water through it when pumped, so it is called leaky or semi-confined.

An artesian (confined) aquifer is bounded by impermeable aquicludes, so it does not leak. An unconfined aquifer has the water table as its upper surface, with no confining layer above. A perched aquifer is a local body of groundwater held above the main water table by a small impermeable lens.

Your Answer : (Not Answered)

Correct Answer : C

It is the zone of aeration.

Below the ground, the zone between the surface and the water table has pores holding both air and water. This is the zone of aeration (the vadose or unsaturated zone). Below the water table every pore space is filled with water.

That lower zone is the zone of saturation, which has no air in its pores. The zones of accumulation and wastage are terms from glaciers, the areas where ice is gained and lost, not from groundwater.

Your Answer : (Not Answered)

Correct Answer : C

It is connate water.

Connate water (from Latin for 'born together') is water trapped in the pores of a sediment when it was deposited and sealed in as the rock formed. It is usually old and saline, and occurs, for example, alongside oil and gas in reservoir rocks.

Meteoric water comes from rain and snow and enters rocks from the surface. Juvenile water is new water released from magma, reaching the surface for the first time. Pellicular water is the thin film held on grains by molecular attraction in the unsaturated zone.

Your Answer : (Not Answered)

Correct Answer : C

The process that is not part of the hydrologic cycle is calcium carbonate dissolving in soil water and ground water.

The hydrologic cycle is the movement of water itself between the atmosphere, the land surface, the ground and the oceans: evaporation, condensation, precipitation, infiltration, runoff and groundwater flow. Dissolving calcium carbonate is a chemical weathering reaction, part of the carbon and rock cycles; the water involved moves anyway, but the dissolution is not a step in the water cycle.

Infiltration into soil and bedrock, evaporation from a lake, and water draining into creeks and streams after rain are all stages of the hydrologic cycle.

Your Answer : (Not Answered)

Correct Answer : B

This water is called Runoff.

Runoff (stream flow) is the water that reaches and is discharged by streams. It is made up of surface or overland flow, interflow through the soil, and baseflow from groundwater, which keeps streams flowing between rains.

Precipitation is the water falling from the atmosphere, transpiration is water released by plants through their leaves, and evaporation is the change of surface water to vapour. These supply or remove water but are not the water discharged through streams.