Oh, so government geniuses bought perfectly good oil and contaminated it...
I assume that the Corps of Engineers would have "built" (or contracted to others) the storage facility, and I'll bet that they used a consulting firm for the design effort.
Maybe they got bad geotechnical data on the sulfur distribution below ground. Anyway, a lot of opportunities to screw up.
Then again, maybe the gummint just bought bad oil, like you originally suggested!