A cavity well is a specialized type of tubewell that differs fundamentally from a screen well because it:
Options:
(A) Draws water from a hollow cavity excavated in the aquifer directly beneath a strong, impermeable confining clay roof without using any well screen
(B) Utilizes three concentric slotted brass screens
(C) Cannot operate with an electric centrifugal pump
(D) Is constructed exclusively in deep unconfined gravel riverbeds
Answer Key:
A
Step-by-Step Solution & Explanation
A cavity well does not utilize a strainered/slotted pipe screen. Instead, a blind casing pipe is sunk and sealed into a strong impervious hardpan (clay roof) overlying a water-bearing artesian sand layer. Sand is pumped out from the bottom to form a hemispherical cavity below the roof, through which water enters the bottom open end at low non-scouring velocities. Option A is correct.