The method
Before using the result
- Common datum and representative timed readings. Logs do not fit an aquifer model or establish sustainable well yield.
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
Keep timed pumping and post-stop recovery measurements on a common datum. Plot the observed response without fitting an unsupported aquifer model.
- Test date
- 2026-10-01
- Static water depth below datum
- 10 m
- Pump-stop elapsed time
- 60 min
Supplied test measurements
| Elapsed time (min) | Depth below common datum (m) | Measured pumping flow (L/s) |
|---|---|---|
| 0 | 10 | 2 |
| 30 | 14 | 2 |
| 60 | 15 | 0 |
| 90 | 12 | 0 |
- Drawdown = measured depth − 10 m.
- Pump stop at 60 elapsed minutes.
- Measurements: 4
- Test date: 2026-10-01
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.
- Test date
- 2026-10-01
- Static water depth below datum
- 9 m
- Pump-stop elapsed time
- 60 min
Supplied test measurements
| Elapsed time (min) | Depth below common datum (m) | Measured pumping flow (L/s) |
|---|---|---|
| 0 | 10 | 2 |
| 30 | 14 | 2 |
| 60 | 15 | 0 |
| 90 | 12 | 0 |
- Drawdown = measured depth − 9 m.
- Pump stop at 60 elapsed minutes.
- Measurements: 4
- Test date: 2026-10-01
Check your understanding
1. Which relationship is used?
Drawdown at each time = measured depth − static depth; label pumping/recovery using the supplied pump-stop time.
2. Which assumption should you check first?
Common datum and representative timed readings. Logs do not fit an aquifer model or establish sustainable well yield.
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.