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Section 6: Likelihood of Release

Likelihood of Release (LR) is the first factor category evaluated in scoring an HRS pathway. LR reflects the likelihood that there has been, or will be, a release of any hazardous substance from the site into the pathway being scored. LR is evaluated for the three migration pathways — ground water, surface water, and air. The corresponding factor category in the soil exposure pathway is the Likelihood of Exposure (LE). This change in terminology reflects the perspective that contaminants migrate through ground water, surface water, and air resulting in exposure while people migrate to locations where they are exposed to soil contaminants.

Section 6 -- Slide 6:2

The LR factor category is evaluated based on two factors: observed release and potential to release. If the criteria for an observed release have been met, then the maximum LR value of 550 is assigned to the factor category. An observed release can be documented in two ways:

  • direct observation of the release of a hazardous substance from the site into ground water, surface water, or air (as applicable).

  • chemical analysis of ground water, surface water, or air samples (as applicable) that indicate the presence of a site-related hazardous substance at a level significantly above background.

If an observed release is established through either of these criteria, potential to release is not evaluated. If no observed released can be established, the site is scored on potential to release only (maximum value: 500 points). The procedures for determining potential to release are pathway-specific and will be addressed separately for each pathway.

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