Test 36 - Groundwater Exploration Methods

Question 1 ప్రశ్న 1

A municipality plans a new production well field in an area having alluvium, weathered granite and possible buried faults. Which initial groundwater-exploration strategy provides the most defensible basis for selecting test-drilling sites?

A Select drilling points solely by the proximity of a highway and ignore geology. B Use the colour of the surface soil as proof of aquifer thickness and yield. C Combine geological and hydrogeological mapping, existing well records and appropriately selected geophysics before verifying targets by drilling. D Conduct pumping tests without first identifying the aquifer or installing test wells.

Question 2 ప్రశ్న 2

In a hard-rock terrain, two proposed sites lie on fresh massive granite and on a sufficiently thick, connected fractured and weathered granite zone, respectively. Which conclusion is most reasonable before drilling?

A The weathered and connected fractured zone is generally the more promising groundwater target, but its saturated thickness and transmissive connectivity require confirmation. B Massive unfractured granite must yield more water because intact crystals contain large interconnected pores. C Any mapped fracture guarantees a high-yield well regardless of depth and connectivity. D Rock hardness alone determines the chemical quality of groundwater.

Question 3 ప్రశ్న 3

Satellite imagery reveals a straight lineament crossing a proposed well-field site. What is the most appropriate hydrogeological interpretation?

A The lineament proves that a perennial underground river exists beneath the entire feature. B Every lineament must be an impermeable fault that excludes groundwater. C Lineament orientation uniquely determines groundwater salinity without sampling. D It is a possible structural or geomorphic indicator that should be checked by field mapping, geophysics and borehole evidence before being treated as a water-bearing fracture zone.

Question 4 ప్రశ్న 4

Springs occur along the contact between a permeable sandstone and an underlying less-permeable shale on a valley slope. What is the best initial interpretation?

A The springs prove that the shale is a high-permeability gravel aquifer. B Groundwater may be moving through the sandstone and emerging where the contact intersects the slope, but sustainable discharge requires investigation. C The springs show that groundwater cannot move through sedimentary rocks. D Spring occurrence establishes that all nearby boreholes will have equal yield throughout the year.

Question 5 ప్రశ్న 5

A borehole penetrates an aquifer confined between low-permeability layers, and water rises within the cased well above the top of the aquifer but remains below the ground surface. Which statement is correct?

A The observed level is a potentiometric level under confined conditions; a flowing artesian well is not implied because the level remains below ground. B The observed level must be the top of an unconfined saturated zone in all cases. C Water can rise above a confined aquifer only if a pump is operating. D The confining layers prove that the aquifer has zero groundwater pressure.

Question 6 ప్రశ్న 6

Two observation wells tap the SAME hydraulically connected unconfined aquifer and are measured at the same time under nearly steady conditions. Well A has ground elevation 160 m and depth to water 8 m; well B has ground elevation 155 m and depth to water 11 m. Their horizontal separation is 400 m. Assuming an approximately uniform hydraulic-head gradient along the straight line joining these wells, what is the gradient magnitude, and in which direction does hydraulic head decrease?

A 0.0125, with hydraulic head decreasing from B toward A. B 0.050, with hydraulic head decreasing from A toward B. C 0.020, with hydraulic head decreasing from A toward B. D 0.020, with hydraulic head decreasing from B toward A.

Question 7 ప్రశ్న 7

A water-table contour map is prepared from nearly simultaneous measurements in wells tapping one laterally connected, approximately isotropic unconfined aquifer. How is the local horizontal groundwater-flow direction ordinarily inferred?

A Along a contour toward increasing water-table elevation. B Approximately perpendicular to water-table contours, from higher hydraulic head toward lower hydraulic head. C Always parallel to the nearest surface stream regardless of head contours. D From the well having the greatest depth to water toward the shallowest well, regardless of ground elevations.

Question 8 ప్రశ్న 8

An investigator proposes combining a pre-monsoon water level from a pumped well with a post-monsoon level from an unused observation well to construct a single regional water-table map. Which change would most improve the reliability of the map?

A Use the two values unchanged because all groundwater levels are constant in time. B Convert the levels directly into rock density before contouring. C Assume that pumping lowers the regional water table by exactly the same amount everywhere. D Measure representative wells over a short common period, identify pumped or recovering wells, and use a consistent elevation datum.

Question 9 ప్రశ్న 9

A test borehole is drilled across a suspected sand aquifer beneath clay. Which combination of observations most directly verifies the lithological sequence and the interval in which groundwater enters the borehole?

A Drilling samples or cores, a depth-referenced lithological log, and observations or tests identifying water-bearing intervals. B A surface photograph alone, without recording drilled depth or material. C The rig's engine rating and drill-pipe paint colour. D A single regional topographic contour with no borehole observations.

Question 10 ప్రశ్న 10

A borehole in alluvium records 20 m of apparently saturated sand and gravel, but the proposed scheme requires a dependable long-term supply. Which next investigation best addresses the aquifer's hydraulic performance?

A Accept the well yield as unlimited because the saturated deposit is thick. B Use only the mineral colour of the recovered sand grains. C Conduct a properly designed pumping test with water-level monitoring and, where appropriate, observation wells and recovery measurements. D Compute sustainable yield by multiplying borehole diameter by the depth to bedrock without hydraulic data.

Question 11 ప్రశ్న 11

During a preliminary pumping test a well discharges 48 cubic metres per hour and produces a stabilized drawdown of 4 m at that discharge. Using specific capacity = pumping discharge/drawdown, what is its specific capacity?

A 192 cubic metres per hour per metre. B 0.083 cubic metres per hour per metre. C 4 cubic metres per hour per metre. D 12 cubic metres per hour per metre.

Question 12 ప్రశ్న 12

An electrical survey indicates a possible fresh groundwater-bearing sand body, but the area is also known to contain brackish groundwater in some wells. What additional investigation is essential before judging the suitability of the water for supply?

A Assume that electrical-resistivity interpretation directly certifies water potability. B Collect representative groundwater samples for chemical analysis and verify the water-bearing interval and yield. C Treat every conductive anomaly as proof of potable freshwater. D Measure only the seismic velocity of the ground surface and omit groundwater sampling.

Question 13 ప్రశ్న 13

Which description correctly identifies the basic measurement in a conventional four-electrode surface electrical-resistivity survey?

A Current is introduced through one electrode pair, potential difference is measured across another pair, and an array geometric factor converts measured resistance to apparent resistivity. B Groundwater is extracted from four boreholes and the total discharge is the electrical resistivity. C Two geophones measure sound travel times while the other two electrodes measure rock hardness. D The method directly counts pore spaces and yields porosity without interpretation.

Question 14 ప్రశ్న 14

A four-electrode resistivity measurement records potential difference Delta V = 0.24 V at current I = 0.020 A. The geometric factor for this specific array is supplied as K = 30 m. Using apparent resistivity rho_a = K(Delta V/I), what is rho_a?

A 12 ohm-metres. B 250 ohm-metres. C 360 ohm-metres. D 1500 ohm-metres.

Question 15 ప్రశ్న 15

A Wenner four-electrode arrangement has equal adjacent electrode spacing a = 4 m. The measured voltage is 0.080 V for current I = 0.040 A. Using rho_a = 2 pi a (Delta V/I) and pi = 3.1416, find the apparent resistivity.

A 12.6 ohm-metres. B 25.1 ohm-metres. C 100.5 ohm-metres. D 50.3 ohm-metres.

Question 16 ప్రశ్న 16

A hydrogeologist wants to investigate changes in subsurface electrical properties with depth at one locality where layers are approximately horizontal. Which field approach is most appropriate for a preliminary one-dimensional electrical investigation?

A Keep all electrode spacings fixed and only change the number of borehole casing joints. B Carry out vertical electrical sounding by progressively changing the electrode spread about the survey location and interpreting the apparent-resistivity response. C Measure the mineral hardness of outcrops without electrical measurements. D Apply a pumping test to the earth without installing a well.

Question 17 ప్రశ్న 17

An engineering team wishes to trace the lateral extent of a suspected buried channel across a floodplain at approximately comparable investigation depth. Which electrical-survey approach is especially relevant?

A Use a single hand specimen's Mohs hardness as the map of channel boundaries. B Measure one isolated voltage once and assume lateral homogeneity throughout the floodplain. C Use resistivity profiling or an appropriate multielectrode resistivity-imaging traverse, interpreting lateral apparent-resistivity variations in their geological context. D Apply seismic travel-time equations to the water pumped from an existing well rather than surveying the ground.

Question 18 ప్రశ్న 18

A surface resistivity section contains a pronounced LOW-resistivity zone at depth. The area could contain clay-rich material or sand saturated with saline water. What is the strongest defensible conclusion?

A The low resistivity is not uniquely diagnostic of a productive freshwater aquifer; both clay content and saline pore water may explain it. B The low resistivity proves the presence of clean fresh gravel with no clay. C The low resistivity proves that there is no groundwater anywhere at the site. D The zone's pumping yield is numerically equal to the inverse of its resistivity in ohm-metres.

Question 19 ప్రశ్న 19

A resistivity survey over crystalline terrain identifies a HIGH-resistivity body. Which interpretation is most appropriate without local borehole control?

A It necessarily represents saturated clay with saline groundwater. B It proves that the material has high groundwater yield and connected porosity. C It uniquely identifies the water table and determines water quality. D It may represent relatively dry, competent or otherwise resistive material, but resistivity alone cannot establish that the body is dry, massive or water-bearing.

Question 20 ప్రశ్న 20

Which principle most directly underlies a basic seismic-refraction survey used in groundwater-related geological exploration?

A Direct determination of dissolved salts by passing an electric current between four electrodes. B Measurement of first-arrival seismic travel times at geophones and interpretation of propagation velocities and refracting interfaces. C Measurement of water abstraction rate from a well against time. D Direct observation of the water table from space without drilling or geophysical interpretation.

Question 21 ప్రశ్న 21

In a simplified homogeneous near-surface layer, a direct seismic wave travels 90 m along a straight path and arrives in 0.15 s. Using velocity = distance/time, what is the corresponding seismic velocity?

A 13.5 m/s. B 135 m/s. C 600 m/s. D 6000 m/s.

Question 22 ప్రశ్న 22

A standard layered seismic-refraction interpretation is attempted where a relatively LOW-seismic-velocity unit lies beneath a HIGH-velocity unit. What important limitation should the geologist recognize?

A Such a velocity inversion may be poorly resolved or missed by conventional first-arrival refraction analysis, so independent verification or another survey approach may be needed. B Refraction always resolves low-velocity layers beneath faster layers more accurately than all other configurations. C A velocity inversion proves the presence of a freshwater aquifer and gives its pumping yield directly. D The recorded travel times cease to have units when a lower-velocity layer exists.

Question 23 ప్రశ్న 23

A proposed water-supply borehole is near a buried bedrock valley. Surface resistivity suggests a sediment-filled depression, while seismic refraction suggests a high-velocity bedrock surface beneath it. What is the most useful interpretation strategy?

A Reject both surveys because two different geophysical properties cannot be examined together. B Assume that the deeper bedrock surface alone proves a high-yield freshwater aquifer. C Compute water quality solely by dividing seismic velocity by resistivity. D Use the independent electrical and seismic contrasts together with surface geology and test drilling to constrain valley geometry and the nature of the fill.

Question 24 ప్రశ్న 24

An exploration borehole is available for downhole measurements after a surface resistivity survey produced a nonunique interpretation. How can borehole resistivity logging contribute at the appropriate engineering-geology level?

A It directly measures safe pumping discharge in cubic metres per hour without a pumping test. B It proves every low-resistivity interval is a freshwater sand bed. C It records changes in electrical response with depth that, combined with lithological and water-quality information, may help distinguish subsurface layers and fluid conditions. D It replaces the need to note borehole depth and the positions of geological contacts.

Question 25 ప్రశ్న 25

A city plans a production well and also needs to assess groundwater seepage risks near a proposed deep excavation. Which investigation sequence is most defensible?

A Drill at the strongest geophysical anomaly and immediately assign unlimited safe yield without aquifer testing. B Integrate geological mapping, well inventories and water-level observations with suitable surface geophysics; confirm by drilling, hydraulic testing and groundwater-quality assessment. C Determine aquifer transmissivity from the colour of a satellite image alone. D Use seismic-refraction velocity as a direct substitute for groundwater pressure and chemical analysis.

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