71. Percussion drilling is unsuitable in

A. unconsolidated sand

B. unconsolidated gravel

C. quick sand

D. consolidated rocks.

72. The-maximum non-verticality of the bore of a well 200 m deep, may be permitted up to

A. 25 cm

B. 50 cm

C. 75 cm

D. 100 cm

73. For least effect on the water table, the tube wells must be dug one in every

A. 0.5 sq km

B. 0.75 sq km

C. 1.0 sq km

D. 1.5 sq km.

74. Pick up the correct statement from the following :

A. Deposition of calcium carbonate on the inside of the well pipe, causes incrustation of the pipe

B. Incrustation of the pipe reduces the discharge

C. Acidic waters cause corrosion of the pipes

D. All the above.

75. Corrosion of well pipes may not be reduced by

A. reducing the draw down and the pumping rate

B. reducing the flow velocity

C. using thicker pipes

D. using screens having larger area of openings

76. Derivation of Thiem's formula 271T (s1 - s2) Q =2.3 log10 is based on the assumption

A. the aquifer is homogeneous, isotropic and of infinite depth and area

B. the well is sunk through the full depth of the aquifer

C. the flow lines are radial and horizontal, and the flow is laminar

D. all the above.

77. The discharge Q -for the confined tube 2.3 logioiTv well is obtained from

A. Thiem's formula

B. Darcy's formula

C. Tolman's formula

D. Dupuits formula.

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