Perfect, supernerd! The question asks us to strengthen the author's position, so we should focus on what the text told us about those risks, and the text said nothing about the risks associated with transportation of waste. But the author did tell us that one of the risks is that we can't be sure how the geological features will act upon those wastes, and as you pointed out, answer D supports that claim.
The best way to go about answering a question like this is to start by doing a little research in the passage before looking at the answer choices. Go to the sections where the author talks about the risks, and remind yourself of what those risks were. The first line of the last paragraph sums them up nicely:
significant uncertainty about where injected wastes will flow, along with the possibilities of mechanical failure and human error
Now, with that simple list in mind, go to the answers and find one that supports that there could be mistakes, mechanical failures, or problems with unpredictability. Answer D stands out and is the winner! Research and prephrasing are worth the time they take because they eliminate uncertainty and protect you from being suckered by attractive wrong answers.
Adam M. Tyson
PowerScore LSAT, GRE, ACT and SAT Instructor
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