At the moment GT++ Geothermal Generators do not show how much pollution they produce. Also, I do believe the amount is extremely high, like 2000/sec. The tooltip's missing the exact amount though, but it should say so. Also it might be worth taking that down to, say, the same as an HV Combustion gen? Or not. Either way, it should say so, I would have reconsidered making some because half my base is only sometimes habitable, heh...