"July 1986"--T.p. "MTR-86W101"--T.p. "Sponsor: U.S. Environmental Protection Agency"--T.p. "Contract no.: EPA 68-01-7054"--T.p. EPA 540-2-87-519, per NSCEP's publication title list. Includes bibliographical references.

This report deals with the question of what criterion should be used to establish that the concentration of a released uncontrolled hazardous substance is "significantly higher than the background." The criterion would be used in determining an observed release under the Hazard Ranking System (HRS), and Appendix to the National Contingency Plan (NCP) for oil and hazardous substances created by the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA). The report examines options for HRS revision including definitions of significance based on the limits of detection and quantitation to discriminate between contaminant levels at or in the vicinity of an uncontrolled hazardous substance facility and background levels. The report also examines the relevance of EPA responses to public comments relating to significance issues, general concepts and tests of significance, detection limits, and the nature and amount of data available for determining and observed release.