●Defined at 42 U.S.C. § 9601(14).
●Covers a staggering array of substances.
●Only substances specifically excluded are natural gas and oil.
●Pursuant to 9601 (14)(B), EPA has designated over 700 hazardous substances (See 40 C.F.R. § 302.4).
●Does not impose any quantitative requirement or concentration level―rather substance must simply fall within one of the designated categories.