Processes > Inverse modelling

Good sum of residuals and delta/uncertainty, but high maximum fractional error

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**Juan Sebastian**:

Hello,

I have been working in two inverse models of acid mine drainage. In the first one, I have got 12 models with sum of residuals and delta uncertainty less than 6.00e+00, but the maximun fractional error is high (4.000e-01) in all cases .

In the second one, I have got 4 models with sum of residuals between 2.434e+00 - 3.165e+00, delta uncertainty 7.497e+00 - 9.087e+00, and the maximun fractional error is high (3.000e-01) in all cases.

I used a global uncertainty of 0.05, but I adjusted the -balances of some elementes like S(6). I realized that the excess of sulphate generate a negative charge balance (Percent error, 100*(Cat-|An|)/(Cat+|An|), for example = -70.85), so I think that S(6) influence the results of maximum fractional error.

I would like to ask if this outcoms are reliable?, considering the complex of this kind of systems.

**dlparkhurst**:

If your charge balance is -70%, you may be missing cations from your analysis. I think you need to use other analyses that have better charge balance, or determine what is the source of the imbalance in the solution that you are using. If you are missing a major cations, you might want to estimate a value for it and assign a large uncertainty.

You won't be able to decrease the maximum fractional errors, residuals, and sum of deltas until you have analyses that balance.

**Juan Sebastian**:

All right, now I am understanding more. Thank you so much for your advices!

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