Question

Surface water is pumped into a design well for 5 days to a confined aquifer (T=97840 gpd/ft, Sc= 2 X10^-4 ) in order to preserve surface water. The well diameter is 12 inches. Determine the maximum injection rate (gpm) such that groundwater level increase in the well will not exceed 10 feet during the 5-day injection.

Answer 1

Answer: To determine injection rate (Q) for 5 day pumping in a 12 in. diameter well so that head will not exceed 10 ft we can use the expression Q=CAH.

Where C=Specific capacity of a well = (1/t)ln(h1/h2)

t=time in days =5 days

h1= depth of well before pumping =assume 15ft

h2 =depth of well after pumping = 10 feet head it becomes 5 ft

C=(1/5) ln(15/5)=0.22/day.

A= area of the well =/4 d2=  /4 x 12 =0.7854ft2 (d=12in=1ft)

H= head to be pumped in 5 day =10ft

injection rate Q= 0.22 x 0.785 x 10 =1.72ft3/day =0.009gpm