About the Data

The Superfund program was created as a result of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). CERCLA was enacted on 12/11/80, and amended by the Superfund Amendments and Reauthorization Act of 1986. These acts established broad authority for the government to respond to problems posed by the release, or threat of release, of hazardous substances, pollutants, or contaminants. CERCLA also imposed liability on those responsible for releases and provided the authority for the government to undertake enforcement and abatement action against responsible parties.
And another EPA Web page:

CERCLIS is the Comprehensive Environmental Response, Compensation, and Liability Information System. CERCLIS contains information on hazardous waste sites, site inspections, preliminary assessments and remedial status. Customers have several ways of obtaining access to CERCLIS information.
RTK NET's copy of CERCLIS does not contain all CERCLIS data fields. Only the ones that EPA chose to provide on the Web were available.

State Field

If you wish to search on the entire US, select the "ALL" value for this field.

Zip Code Field

Fill in the zip code for the area that you want. If you fill in a 5-digit zip code, the program will automatically put a "*" after it. The "*" represents any number of characters and will let your search find 9-digit zip codes that start with the 5 digits you entered. Don't fill in dashes.
Example:
If you enter 20740*
this will find

20740
207401122
207403465
etc.

NPL Status Code Field

This code allows you to select sites with a particular status on the NPL, or National Priority List. The NPL defines what is commonly known as the "Superfund" list of sites. Sites are first found, or "discovered." If closer examination warrents it, they are then proposed for listing on the NPL. If a yet closer examination warrants it, they are then listed on the final NPL. If they are then cleaned up or re-evaluated and found to be not as seriously contaminated as thought, they can be delisted from the NPL.