How do I make a constant slope elevation model in arcMap?

I am currently working with ArcMap to develop an elevation model of a quarry showing how the terrain at the quarry site would look post-closure. One of the requirements is that the slopes placed along the benches should be 30 degrees exactly. I have an elevation model of the site and a shapefile showing all the quarry leases. One of the assumptions is that the boundary elevation shall remain the same in the future and all of the rock within the boundary would be extracted. The final base elevation is assumed to be 100m for the time-being; i.e. elevation of the pit surface post closure.

To start, I extracted the elevation points of the boundaries where the slopes shall be put in; using "Extract by Mask" and "Sample" to tabulate the values and then import them into a new template. I was wondering if it would be possible to create the points at the base of the slope using Excel; i.e. design some sort of an algorithm that will determine the XY coordinates of a point inside the boundary such that:

1. 
   

   The distance between a point on the boundary and the corresponding point inside the boundary is (Boundary Elevation - 100)/tan 30deg.

   
   


2. 
   

   The point inside the boundary is such that it's on a line perpendicular to the line where the boundary point is situated.

   
   

However I'm pretty sure this would take quite a lot of time and would not be the optimal way of going about the problem. As the final base elevation is subject to change, it would be better to have a solution that doesn't require much effort.

What would be the optimal way of creating the elevation model?

I have gone through some of the forums in ESRI as well as stackexchange but haven't been able to understand the methods suggested, particularly those involving python as I don't have any experience working with Python. So I was wondering if it will be possible to work on it without using python or if it does require the use of python, could anyone explain to me how the script can be written?

The method suggested for this question for instance: How can I create a constant slope DEM?