I recently ran across an article that was written by an experienced Surfer user, Joseph A. Ricker. The article, A Practical Method to Evaluate Ground Water Contaminant Plume Stability, provides a workflow for determining the average contaminant plume concentration that I thought our Surfer community may find interesting. Below, I've summarized the workflow outlined in Mr. Ricker's article and provided the exact steps required to duplicate this in Surfer 14.
First, grid the contaminant concentration data using Surfer. In Mr. Ricker's example the values range from non-detectable (0) to 9400 µg/L so applying a Log, save as linear Z transform would be recommended. This prevents the areas of high concentration from being ignored, or from having too large an effect on the surrounding area. Since we are gridding concentration data, a minimum Z of 0 can also be defined to prevent the grid z values from becoming negative. To grid the data with these options:
Next, calculate the volume of the plume where the concentration is above the accepted safe level.
Finally, divide the volume (in units of µg/L*m2) by the planar area (in units of m2) to get the average plume concentration above the cutoff or safe concentration.
This workflow is a great example of the many ways Surfer's gridding algorithms and grid-based calculations are used in the field.