From the article:
"Armstrong said about a third of the 32 million gallons referred to in the letter was straight diesel fuel."
Essay, Skip - that's a pretty easy appoximate ppm to calculate. Although the context still seems unclear in terms of how this was spread across how many wells. They mention this happening in up to 19 states.
The industry obviously has a valid point in terms of when the EPA may have gained jurisdiction over this, but being technically correct may win the legal skirmish but not necessarily the publicity war.
I would prefer someone besides the industry decide just how close to aquifers the technique can be used (and if and when it is or is not okay). As the article states - the industry does not do this with coalbed methane due to greater proximity to aquifers, but exactly what is too close? Ultimately if the industry can find an acceptable substitute that eliminates any question of harm to drinking water, it would be better off in the battle of public perception.