I dunno, concentrating the environmental impact of 20GW of gas based power generation would be the equivalent of 6-9 Million cars running... All in the space of a corner of a small city

That sounds much worse than I had expected. Is this enough consumption to significantly affect the local price of gasoline?

Edit: Why don't they have lower-emission power sources?

We do have lower emission alternatives, but not at the cost point... Remember these are corporations trying to make the largest profit possible