This was an interpolation exercise dealing with fecal coliform for the Galveston Bay in Texas

This is the study area.

There was an excel document containing points from GPS from the sample points. I used the "Display X Y  Data"  and adjusted the coordinates to get right projection for the study area, and set the z- value to the Fecal Coliform data that was in the spreadsheet.  When everything was generated, I got these points.

Everything was pretty simple from this point.  All that had to be done was just find the IDW tool, which interpolates the study area from the points.  Also, you have to mask the area so it focuses on just one portion of interest.  You do this by going in the "Environment setting" and under the "Raster Analysis" you set your mask to the study area and I came up with this.

I used the same step from the IDW.  This the Kriging with the default settings.

This is the Spline.  I used the TENSION type with a weight of  5 to get  the smoothness of the curve better.  
The three different interpolation methods showed that from the sample points of the fecal coliform there were a lot more influence toward the upper left where the downtown of the area is located with mostly impervious surfaces. This could mean that the runoff from the city goes into the Galveston Bay would have more of a change then the other parts of the Bay.