PETER WADE / FREE LEARNING RESOURCE
Before you model.
A practical checklist for starting with the scientific system, not the software.
Before opening the software, describe the scientific system. This checklist is for preparing a modelling discussion, not certifying that a model is correct.
1. Purpose and decision
What question should the model answer? What output would help you decide something? What would count as a result that does not support your initial expectation?
2. System and boundaries
Sketch what is inside the model and what is outside it. Identify materials, phases, flows, spatial extent and the relevant time scale.
3. Inputs and provenance
For every important input, record the value, unit, source and uncertainty. Distinguish measurements from estimates, assumptions and fitted parameters.
4. Processes and assumptions
Which processes are represented? Which are left out? In a geochemical model, consider your choices about equilibrium, kinetics, transport and thermodynamic data where relevant.
5. Checks before interpretation
How will you check units, conservation or mass balance, warnings and limiting cases? Which observations could you compare with an output? Keep calibration and independent evaluation distinct.
6. Sensitivity and reproducibility
Which uncertain inputs or assumptions will you vary? Record the software version, database, input files and changes between runs. Can someone else reproduce the result from your notes?
A useful next question: “What would need to change for this conclusion to no longer hold?”
For software-specific syntax and examples, use the official USGS PHREEQC documentation, alongside your course or project guidance.
Bring your next question.
These prompts are a starting point for independent study, not a replacement for course guidance or research supervision.
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