No. It's completely positive. Methane has almost no pollution, and far less CO2 than any other large scale energy source.
The "contamination" is methane in water, which is harmless even if you drank it, and trivial to remove.
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[0] http://epa.gov/climatechange/ghgemissions/gases/ch4.html
He picked the ones that seemed most dangerous to him, and they are all harmless. (But I haven't checked if there are others.)
Don't forget these chemicals are injected deep underground, so unlike lighter-than-air methane they won't easily get to water.
(PS. It's not "dumping" if you are actively using them. Dumping is the waste you don't need, no need for inaccurate emotive language.)