Makes sense to me — plug the hole up so that the fracking liquid actually WILL frack and not just, under pressure, come back up the hole that was drilled.
Maybe short lived radioactive tracers could/should be added to frack liquid just to prove to doubting Thomasinas, once and for all, that no it’s not getting into the water table.
No need. Fracking fluids have their own distinctive trace ingredients, which are on record for each well.
To date, none of these trace ingredients have shown up in the water table or anybody's well.
The only occasions of pollution by fracking fluids have occurred in surface spills -- readily remedied a carrying a clear liability.