The government has spent heavily to clean groundwater contaminated by toxic chemical spills.
Main Conclusion
More of the government's budget should be redirected to preventing spills.
Intermediate Conclusion
It makes little sense that the entire yearly budget for chemical spill prevention is less than the amount spent annually on one typical cleanup site.
Evidence
Prevention is far more effective than cleanup. The government has spent a ton already to clean spill sites, not even one of them is completely cleaned, and the amount spilled each year surpasses the amount cleaned.
Evaluate
When we do Role and Main Conclusion, we read the paragraph with the awareness that on most of these, the Conclusion comes earlier, Support comes after / last.
We also know to be more on guard when it comes to possible Intermediate Conclusions.
The "yet" indicates an Author's Pivot (but, yet, however, after all). She starts by complaining about clean-up efforts.
Then we get the big Opinion Indicator "should" in the 3rd sentence. Since this is a prescriptive recommendation (yes, that was redundant), it feels like our author's main purpose in writing the paragraph.
Does our author Support this opinion? Why should more of the government's budget be redirected to preventing spills.
Because, the cleanup effort is not even keeping pace with rate of new spills, they currently spend less on prevention each year than they spend on just ONE cleanup site each year, and prevention is far more effective than cleanup.
The word "Since" (of FABS fame .. for, after all, because, since) indicates that the 1st half of the last sentence is a Premise supporting a Conclusion in the 2nd half.
But we could only call this an Intermediate Conclusion, since it was still part of the Support for the overall Main Conclusion, .
Goal
The claim the question stem is asking us about is that 3rd sentence, which is our Main Conclusion.