Frequent Questions

What is the Hazard Ranking System (HRS)?

The Hazard Ranking System (HRS) is a scoring system used by EPA to assess the relative threat associated with actual or potential releases of hazardous substances at sites. The HRS is the primary way of determining whether a site is to be included on the National Priorities List (NPL), the Agency's list of sites that are priorities for long-term evaluation and remedial response, and is a crucial part of EPA's program to address the identification of actual and potential releases.

An HRS score is determined for a site by evaluating three migration pathways

  • Ground water migration pathway
  • Surface water migration pathway (including surface water to ground water migration pathway), and
  • the Air migration pathway

An HRS score is also determined by evaluating one exposure pathway - the soil exposure pathway.

The HRS is used to assess both human health risks (e.g., drinking water threat, human food chain threat, threat to residential population, threat to worker population) and environmental risks (e.g., sensitive environments, resources) associated with actual or potential contamination of the ground water, surface water, and air migration pathways and soil exposure threat.

To learn more, please see Introduction to the HRS.

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