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I am trying to use some interpolation tools for analytical data of concentrations of Benzene for monitoring wells. A decent amount of our values for Benzene are '<1' (not 0.943 or 0.345) because of how our sampling works here. Therefore, when I convert my excel tables to points, it classifies my Benzene column as a string and I can't use it as the Z value field. Is there anything I can do so I can still accurately run IDW (or a different interpolation tool) using my Benzene concentrations?

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    You need to clean up your data prior to loading it into QGIS. I would do this either by removing the data points by giving them a specific value (either something negative (e.g. -9999) and set QGIS to remove them when running your IDW or an amouint agreed upon for describing a trace amount (e.g. 0.5) ). The application needs to know how you want to treat these values and will only work with real numbers. – Trevor J. Smith Apr 30 at 18:07
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    I figured that was the only way I'd be able to do it. Just trying to figure out the most accurate way to go about it. Thanks so much!! – mv9916 Apr 30 at 18:09
  • Glad to be of help! I'll post my comment as an answer below so the question can be closed. – Trevor J. Smith Apr 30 at 18:40
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You need to clean up your data prior to loading it into QGIS. I would do this either by removing the data points by giving them a specific value (either something negative (e.g. -9999) and set QGIS to remove them when running your IDW or an amouint agreed upon for describing a trace amount (e.g. 0.5)).

QGIS needs to know how you want to treat these values and it will only work with real numbers.

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