Create contours where two surfaces meet

You would like to be able to create contours where your two surfaces meet in Autodesk® AutoCAD® Civil 3D®.   
The goal is to extract a polyline or find some way to create a polyline at the intersection of two surfaces (where they cross each other 3 dimensionally). 

The two surfaces being compared here are the Existing surface and the Finished ground surface. All other surfaces are set to no display. 

Causes:

Basically the zero contour line of a volume surface is the intersection line between the two surfaces. Use a contour line style and extract features from surface to get 3D Polylines of contours.

Solution:

1. Create new style showing only Custom Contours and border, adjust styles as desired 
2. Create volume surface by comparing your Existing and Finished Ground surfaces applying the style you created earlier to your volume surface 
3. From volume surface properties go to Analyze tab and run analysis using Custom contours with elevation of zero (this will create the contours where the surfaces meet) 
4. Select surface and choose extract objects from contextual ribbon and select “All contours” and Border if you need to. This will turn your user defined contours into polylines 
5. Now that you have your polylines you can turn them into feature lines by projecting them onto the surface of your choice such as Existing. You can do that by “create feature lines from objects” and selecting all your polylines. You would choose “assign elevation” and “from surface” and select desired surface. 
6. This should create feature lines with elevations matching where surfaces meet