The substances found at Superfund sites have been designated by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) as 1) causing or contributing to an increase in mortality or in irreversible or incapacitating illness, or 2) posing a substantial present or potential hazard to human health or to the environment when improperly treated, stored, transported, disposed of, or otherwise managed.
More than 800 substances are currently designated as hazardous
(http://www.epa.gov/oswer/riskassessment/glossary.htm#h), and many more as potentially hazardous. These substances do not include petroleum or natural gas.
A list of Superfund chemicals
found in TOXMAP can be found at http://toxmap-classic.nlm.nih.gov/toxmap/main/sfChemicals.jsp.