How could it get into groundwater unless the underground gas tanks were leaking? Just because mom and pop gas stations don't have deep pockets, they want to sue the maker. Anyway, most gas stations are owned by oil companies and could afford to pay, if negligent.
What they didn't tell you: originally gasoline, while obnoxious for a short period, was not a pollutant, as when released into the ground it was quickly reduced by natural processes to benign compounds.
Steel underground tanks would deteriorate by rusting and leak some gasoline into the ground, and those tanks would be detected and replaced. But this wasn't good enough for government money burners, everybody had to replace all the tanks immediately. No more worries, as the new tanks would be rustproof Fiberglas (plastic) construction, impervious to gasoline. The government idiots didn't bother to find out if the new tanks resisted ALCOHOL (MTBE and ethanol) which, of course, they didn't. And of course the pollutants in gasoline that DON'T break down in the environment are the late model additives and MTBE. So the new tanks began leaking real pollutants very quickly.
Bottom line the government mandated that we spend billions to go from no problem to huge problem. Enviroterrorists have been in government for a long time.
Not certain of this but - I believe that MTBE when burned with gasoline becomes airborne and when rain washes it to the ground it seeps in, resulting in groundwater pollution.