Reference
Parameters and their limits, units, the derivative, the fitting method, the example tests and the engine.
Parameters
| Name | Meaning | Fitted between |
|---|---|---|
| T | Transmissivity | 1e-8 and 1e8 m2/d |
| S | Storativity (elastic) | 1e-10 and 1 |
| B | Leakage factor, Hantush-Jacob | 0.001 m and 1e8 m |
| Sk | Skin factor, Papadopulos-Cooper | -5 and 100 |
| rc | Effective casing radius, Papadopulos-Cooper | 0.0001 m and 10 m |
| Sy | Specific yield, Neuman | 1e-5 and 0.6 |
| Kd | Anisotropy ratio Kz / Kr, Neuman | 1e-6 and 1000 |
All parameters but Sk are searched on a logarithmic scale. A parameter that ends within half a per cent of a limit, on that scale, is reported as at its limit.
Units
Readings, distances and rates are entered in the units chosen in Data > Test and units.... Calculations are done in metres, days and cubic metres per day, and parameters are stored that way, so changing the display units never moves a result. Lengths in the results (B, rc, RMSE) are shown in the length unit of the test.
Fitting method
Least squares on drawdown, unweighted, over all included readings, with several starting points. Standard errors are linearised from the fit at its optimum and assume independent residuals. AICc = n ln(SSR / n) + 2k + 2k(k + 1) / (n - k - 1), for n readings and k fitted parameters. The derivative is that of Bourdet et al. (1989), over neighbours at least 0.2 natural-log units of time apart.
Example tests
- Gridley, Sioux Flats and Texas Hill: from the AQTESOLV manual (Duffield 2007), as digitised for the TTim documentation (MIT licence). Published parameters: the AQTESOLV values reported by Yang (2020).
- Lauswiesen B2 to B5: Leven (2020), doi:10.57754/fdat.hma1z-00r32, licensed CC BY-SA 4.0. Published parameters: the welltestpy analysis of Mueller et al. (2022).
The engine
The solutions, fitting and straight-line methods are those of pumptest (github.com/GeoPilot-AI/pumptest, MIT licence), run unchanged in the browser. Its comparisons with AQTESOLV and welltestpy on the example tests, and with independent evaluations of the published solutions, are on its validation page. The version in use is shown in Help > About PumpPilot.
Not yet in PumpPilot
Partially penetrating pumping wells, hydraulic boundaries, storage in the aquitard, fractured and double-porosity aquifers, and slug tests have no solutions in PumpPilot yet.