Assigned: 10/04/17 GEOL 410/614-Problem Set #4 Due: 10/13/17 Hydrualic Conductiv

Question

Assigned: 10/04/17 GEOL 410/614-Problem Set #4 Due: 10/13/17 Hydrualic Conductivity, Potentiometric Surfaces, Hydraulic Gradient and Equations of Groundwater Flow in Unconfined and Confined Aquifers 1) (20 pt) In a preliminary study your company wants you to estimate the hydraulic conductivity of a vertical core samples of silt taken from an important aquitard underlying a toxic waste site. (a) The diameter of the vertical core is 8 cm and the length is 20 cm. The porosity is 0.3. You perform a falling head permeameter test to determine K. The initial head in the falling head tube 50 cm. After 4.5 hours the level had dropped to 28 cm. Given that the tube diameter is 1 cm calculate the hydraulic conductivity of the vertical core in units of m/day. (b) The difference in hydraulic head across the aquitard was observed in the field to be 1 m. If that's the case, how long would it take groundwater to cross the aquitard if it is 5 m thick? Give your answer in both days and years. de

Explanation / Answer

For falling head permeameter:

K=rt2L/rc2t In h1/h2

h1=initial head of tube=50 cm=0.5m

h2=final head of tube=28 cm=0.28m

rt=radius of falling tube=1/2cm=0.5 cm=0.005 m

rc=radius of cylindrical tube=8/2 cm=4 cm=0.04 m

L=length of tube=20 cm=0.2m

t=time interval for the water level in the tube to fall from h1 to h2 =4.5 hours=0.1875 days

K=hydraulic conductivity=??

K=0.0052*0.2/0.042*0.1875 In 0.5/0.28

K=2.5*10-5*0.2/1.6*10-3*0.1875 In 1.785

K=0.5*10-5/0.3*10-3 *0.579

K=1.66*10-2*0.579

K=0.961*10-2

K=0.00961 m/day

Therefore hydraulic conductivity of vertical core is=0.00961 m/day

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