Min-Max Plume

Sometimes confidence and uncertainty just won't answer your (or your customer's) question. Just how big (or how small) might the contaminant plume be? EVS displays concentration, but what are the limits? The Min-Max Plume option directly answers those questions.

Create the network below (start with a new copy of Krig_2D).

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Open up the Kriging Parameters and choose Min-Max Plume for the Statistics Options (This feature is only available in EVS PRO). Note that the Confidencefor Min/Max Plume (percent) parameter is set to 60%.

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Choose initial_soil_investigation_full_site.apdv again as our data file and after it has run, close Kriging Parameters and open up the Display Settings.

We want to set a clamped range for outputting the min, nominal and max plumes. The limits of all three will be slightly different so we should choose values that will be compatible with all. We will set the Clamp toggle on and the Min val to -2 (equiv. to 0.01 ppm) and the Max val to 4.0 (equiv. to 10,000 ppm). Also set the Data Scaling to 20. Your parameters should match:

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Set the parameters of isolines to match the figure below and choose accept.

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Bring up the Az-El panel and set the view so that Scale = 1.10; Elevation = 45; and Azimuth = 210. Your view should now be:

Nominal Plume:

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The white outline is the nominal plume at 0.1 ppm (log value of -1.0). What does nominal mean? Nominal is the distribution where 50% of the time the predicted values are higher and 50% of the time they are lower. That means that our confidence in this plume size is never lower than 50%. Be careful, this confidence has a different meaning than the confidence discussed in the early section.

Now let's see what the minimum size plume is for our 60% confidence level. To do this we need to change both the Data Component in Krig_2D:Display Settings and the Iso Component in isolines to 60%Min:VOC (remember to hit accept in isolines also) Note a marked reduction in the 0.1 ppm plume versus the nominal plume.

Minimum Plume:

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Similarly, the maximum plume (for a 60% confidence) is:

Maximum Plume:

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What would have happened if we had set the Confidence level higher (or lower)? The Confidence parameter cannot be set lower that 50%, because by default, the nominal distribution has a 50% confidence. If it is set at 50%, the Min Plume will be the same as the Max Plume. Values below 50% don't make sense.

Similarly, a value of 100% is impossible. We can never be 100% sure of estimates. The maximum allowable value is 99.99% and we don't recommend it. Unless your site is extremely well characterized, there will be significant variation between min and max plumes at Confidence levels of 80 or 90%.

Everything we have covered on geostatistics has used two-dimensional kriging. Is that all EVS can do?..........NO!