Chapter 6
Q. 6.4
An aquifer of 20\:m average thickness is overlain by an impermeable layer of 30\:m thickness. A test well of 0.5\:m diameter and two observation wells at a distance of 10\:m and 60\:m from the test well are drilled through the aquifer. After pumping at a rate of 0.1\:m^3/s for a long time, the following drawdowns (amount that head is lowered from the initial position) are stabilized in these wells: first observation well, 4\:m; second observation well, 3\:m. Determine the hydraulic conductivity of the aquifer and the drawdown in the test well.
Step-by-Step
Verified Solution
1. Arrangement is shown in Figure 6.5.
H=(Z–3) and h=(Z–4) as shown in Fig. 6.5
hence, (H–h)=(Z–3)–(Z–4)=1\:m
2. From eq. (6.3),
H\:\:\:\:h\:\:\:\:\frac{Q}{2πbK}\:\ln\frac{R}{r}\:\:\:\:[L] (6.3)
1\:\:\:\:\frac{0.1}{2π\:\:20\:\:K}\:\ln\frac{60}{10}
K\:\:\:\:\frac{0.1\:m^3/s}{2π\:\:20\:m\:\:1\:m}\:\ln\frac{60\:m}{10\:m}
1.43×10\:\:^3\:m/s
3. Apply eq. (6.3) between the test well and the first observation well.
H=(Z–4), h=(Z–s)
hence, (H–h)=(Z–4)–(Z–s)=(s–4)
4. From eq. (6.3),
(s\:\:\:\:4)\:\:\:\:\frac{0.1}{2π(20)(1.43×10\:\:^3)}\:\ln\frac{10}{0.25}
2.05
or s\:\:\:\:6.05\:m
