methyl tertiary butyl ether, or MTBE, and tert-butyl alcohol, or TBA, according to this article in the Merced Sun-Star.
Merced, California sues oil companies for MTBE contaminationThe city contends that the companies sold gasoline containing the substances to local service stations and those stations improperly handled them, causing them to be released into the environment. The main avenue to the ground water was leaking underground storage tanks. The city also linked the oil companies deeply to the contamination by alleging they promoted the additives as being environmentally beneficial but failed to disclose it would make water undrinkable. The contamination supposedly occurred between 1992 and 2002. The city also alleges the defendants were "negligent, careless, reckless or intentionally failed to prevent leaks of MTBE or TBA through the use of appropriate technology, installation and maintenance of gasoline delivery systems that could prevent leaks or monitor and discover them as soon as possible."
MTBE continues to be a growing contaminant in water supplies across the country, according to the EPA. Even very low amounts of it make water smell like turpentine and taste like chemicals, and in high amounts it is a suspected carcinogen. MTBE is water-soluble and doesn't cling to soil very well, so it migrates quickly to ground water. TBA is used in gasoline to boost the octane rating, but what many people may not be aware of is that it has also been used to coat metal food containers. Studies done with rats, as reported by California, have shown this chemical to be a potential carcinogen.