The lake is massive. Thousands of gallons of freon would barely register as a contaminant. Moreover, the pressure of the water would tend to push up through the borehole (although Freon is slightly denser than water so some will likely seep down through the water column).
The real issue isn't potential chemical contaminants, but biological contamination. It's thought that the lake has been cut off from the rest of earth's biosphere for millennia. It's likely a biological time-capsule, but breaching the seal could expose it to modern life that could take over.
> Moreover, the pressure of the water would tend to push up through the borehole
That's the plan actually! The water would rush up and then freeze sealing the opening and keeping the ecosphere uncontaminated. It is not the freon that would be the problem but the bacteria that they would introduce in the lake. Now hopefully they have some contingency plan for bacteria contaminating our side of the ecosphere ;-)
I had read in an earlier article that their approved methodology was to pull back the instant they detected liquid water---which, due to the pressure of the ice sheet, would flow out of the hole---and withdraw the drill and go away for the winter; then come back in November and drill out cores from the now-really-well-frozen water that would have risen from the hole. Basically, using the lake's water to plug their borehole and protect the lake.
So I'm not sure what this kerosene and freon business is about.
I think this was the old borehole, they specifically didn't penetrate the lake so as to not contaminate it. They're using a different method or an adjacent hole with a sanitized drilling apparatus now. This is based on stories I've read about Vostok over the years, I don't have any extra knowledge on the situation there today.
that jumped out at me too, but one has to think that a bunch of clearly dedicated scientists (I'd have gone home at -10) would have given thought to pumping CFC's into a pristine lake.
Actually CFCs are not at all bad. They are incredibly stable chemical compounds that won't normally react with anything else.
The problem with CFCs is that you get a stable compound by reacting really reactive things together, and now they can't find anything they want to react with more. So when they get into the upper atmosphere and get broken apart by hard radiation, you now have really reactive stuff mixed in with the fragile ozone layer. And they act as a catalyst to break down ozone.
But you can breathe them all you want, and (assuming you got enough oxygen) will suffer no ill effects.
I wouldn't be so hopeful. One of my professors who works in Antarctica and drills lots of ice cores was bemoaning the Russian mismanagement of the Vostok drilling project.
The explorers now face the question: How do we go where no one has gone before without spoiling it [...]"
Oh, I don't know... how about start by not dumping in thousands of gallons of _freon_?