Question

1. (2 points) A well in a uniform, homogeneous, isotropic confined aquifer is pumped at a rate of 815 L/min. After 3 days it looks as if the water levels have stabilized in observation wells at

distances of 20 m and 200 m from the pumping well. The drawdown in the well at 20 m is 6.5 m and the drawdown in the well at 200 m is 3.5 m.

a) Use the Thiem solution to determine the aquifer transmissivity. Report your answer in m^2/min.

b) If the aquifer is 45 m thick, what is the hydraulic conductivity of the aquifer material? Report your answer in m/min.

c) If the aquifer is composed of unconsolidated sediment, is the sediment most likely to be gravel, sand or silt?

Explain your reasoning.

Answer 1

Q =815L/min=0.815m3/min

r1 =20 m

r2 =200m

s1=6.5 m

s2=3.5 m

Q = discharge rate of well (m3/min)
T= transmissivity of aquifer (m²/min)
r₁, r₂ = distances from the pumping well (m)
s₁, s₂ = steady-state drawdowns in (m)

Substituting the values in the above equation we get

T=0.099 m2/min

Hydraulic conductivity,K=T/h

                                     =0.099/45

                                    =0.00221m/min=0.00003689 m/sec

It can be silt or sand .But it cannot be gravel.The value of K for different type solils are given below

Silt, Loess	10-9 - 10-5 m/sec
Silty Sand	10-7 - 10-3m/sec
Clean Sand	10-6 - 10-2m/sec