How Does Barium Get Into an Aquifer During Gas Drilling Operations?

Dr. Anthony Ingraffea answered this question:

Barium occurs naturally in marcellus shale, and is also used in a drilling compound, as barium sulfate.

From either source, it can contaminate an aquifer (underground), while underground, or it can spill on the surface from either source and leach down into the aquifer.

For example, during drilling, the drilling mud containing barium sulfate, is in direct contact with the aquifer, while drilling through it.
If there is a cement failure, flowback fluid containing barium can migrate into the aquifer.

Or, frac fluid containing barium from the formation can migrate upwards through faults, abandoned wells, or the overlying formation.

My comment is this:  Did you ever think about it this way?  As the hole is drilled in the ground on the well pad, the drilling mud is in direct contact with the aquifer.  I think this flies  in the face of industry people who say they are drilling so deep that they never affect the aquifer.  They are drilling right through the aquifer.  What are they talking about?  Before the cement is put in around the well bore,  the aquifer has already been penetrated and disturbed.