Well Contractor Exam · Free practical tool

Drawdown and specific capacity calculator

Measure static and pumping depths from one reference datum. Use drawdown and test flow to describe specific capacity without claiming a sustainable yield.

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The method

Drawdown = pumping depth − static depth; specific capacity = flow/drawdown.

Before using the result

  • Use depths measured downward from the same datum at the documented test time. Specific capacity is not a sustainable-yield assessment.

Worked examples

These original training examples illustrate the method for NGWA Certified Well Driller (CWD) General Drilling Examination. Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.

1. Worked example

Measure static and pumping depths from one reference datum. Use drawdown and test flow to describe specific capacity without claiming a sustainable yield.

Static depth below common datum
10 m
Pumping depth below same datum
15 m
Volume flow
2 L/s
  1. Drawdown = 15 − 10 = 5 m.
  2. Specific capacity = 0.002 × 1000 / 5 L/s per m.
  • Drawdown: 5 m
  • Specific capacity: 0.4 L/s per m

2. Comparison example

Compare a different supplied condition using the same method. For Well Contractor Exam, the important check is that the input meaning, units and method assumptions still match the problem.

Static depth below common datum
10 m
Pumping depth below same datum
20 m
Volume flow
2 L/s
  1. Drawdown = 20 − 10 = 10 m.
  2. Specific capacity = 0.002 × 1000 / 10 L/s per m.
  • Drawdown: 10 m
  • Specific capacity: 0.2 L/s per m

Check your understanding

1. Which relationship is used?

Drawdown = pumping depth − static depth; specific capacity = flow/drawdown.

2. Which assumption should you check first?

Use depths measured downward from the same datum at the documented test time. Specific capacity is not a sustainable-yield assessment.

3. How should you verify a different unit system?

Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.

Continue with the matching exam topic

This tool connects to NGWA Certified Well Driller (CWD) General Drilling Examination free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.

Drawdown and specific capacity calculator — free with working | Well Contractor Exam