Selecting Lines and Shading Regions

I am essentially PS illiterate but have been searching forums and tutorials trying to find a solution to my query which I would think is simple - either its not or Im just not seeing the solution I need-

I need to draw a series of cut of lines on well log cross sections, these will change and need to show various cut offs in the same spot to ideally this is done on a separate layer i can turn on or off - the problem im having is that I cant seem to copy the original line work to a new layer. Someone suggested I just trace it with the pen tool but that is extremely laborious and not a practical solution. The big issue here is that the original file is a crappy black and white grid with a even worse squiggly line which crosses back and forth (see below).

To reiterate - The black and white is the original, I need to draw the yellow vertical line and shade the portion to the left. Over time this line will move and is repeated on  several neighboring logs so if i have to change one I would prefer not to redraw the entire thing.

Any thoughts for the FNG would be much appreciated as the example below was done in paint.

EDIT [moved to correct product forum – moderator]

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