Sorry, but it generally has less than 1% by volume, but certainly less than 5%. IIRC, the initial limit your article mentions is 1.3% and then 0.6% later.
And some concerns about benzene in water is that the ingestion of contaminated water takes in more than the inhalation pathway, plus the intrusion of benzene vapor into occupied structures, where the exposures are concentrated because of low air-exchange.
BWHAHAHA! I believe your numbers are closer, but I didn’t take the time to find any better data. It has been many years since I did any LUST work, but I always remember the people that complained about cleaning up their leaks because they were breathing benzene every time they filled their car up. I did a little better research and found this:
“overall average reported benzene levels are expected to decrease from 1.05 volume percent (vol%) in 2007 to 0.59 vol% in 2015”
http://www.epa.gov/oms/regs/toxics/420r08022.pdf
As for the toxicology of benzene, I agree I would much rather breath a little than drink a little. I did notice when I Googled that there were a few studies of service station attendants versus benzene exposure.