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Hydraulic Conductivity from Pump Test

Hardgroundwaterwellsdupuit
An unconfined aquifer has a saturated thickness of 20 m above an impermeable layer. A well pumped at a steady 0.04 m3/s produces a drawdown of 8.0 m in an observation well 10 m away and 2.0 m in a second observation well 100 m away. The hydraulic conductivity is most nearly:
  1. A10.6 m/day
  2. B14 m/day
  3. C42 m/day
  4. D44 m/day
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Answer: B. 14 m/day

For steady radial flow to a well in an unconfined aquifer the Dupuit equation applies, and the heads are measured from the impermeable base: h₁ = 20 − 8.0 = 12.0 m and h₂ = 20 − 2.0 = 18.0 m. Then K = Q ln(r₂/r₁)/[π(h₂² − h₁²)] = 0.04 ln(10)/[π(324 − 144)] = 1.63×10⁻⁴ m/s ≈ 14 m/day. Applying the confined-aquifer form, which is linear in head, gives 10.6 m/day. Substituting the drawdowns for the heads gives about 42 m/day.
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