Question

1) If the water level in a 5-cm-diameter piezometer recovers 90% of its bailed drawdown in 20 h, calculate the hydraulic conductivity of the system. The well screen is 0.5 m long and the same diameter as the well casing. Assume that the requirements of the Hvorslev point test are met.

Answer 1

Diameter of piezometer = 5cm It recovers 90% of its bailed drawdown in 20hrs. length of well screen = 0.5m Diameter of well screen = Diameter of well casing Huorsles equation hdds if length of piezometer is more than 8 times the radius of the well screen (Le/rw] > 8 Hydralic conductivity of the system k = vc^2 ln [le/rw]/2Le where, rc is the radius of well casing, (m) Le is the length of well screen (m), rw is the radius of the well screen (m), to (s) is the basic time lag (sec). \r\n Le/rw > 8 rightdoublearrow 0.5/rw > 8 rw < 0.5/8 = 0.0625 m Take rw = 0.0625 m therefore since dia of well screen 2 dia of well casing. Therefore rw = rc = 0.0625 m. k = 0.0625^2 ln [0.5/0.0625]/2 times 0.5 times 2 times 3600 = 1.128 times 10^-7 m/sec therefore Hydraulic conductivity of the system (k) k = 1.128 times 10^-7 m/sec