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I and J Indices

I and J indices evaluate the additive effects of multiple contaminants. They are applied if no hazardous substance at a sampling location individually equals or exceeds a benchmark concentration, but more than one hazardous substance meet the criteria for an observed release.

  • The I index reflects the additive threat of cancer posed by a hazardous substance (cancer risk screening concentrations).
  • The J index reflects the additive threat of non-cancer related health effects (reference dose screening concentrations).

The equations for calculating the I and J indices are presented in the HRS Guidance Manual, Page 158. If the final value of either the I or J index is greater than or equal to 1, Level I contamination is established.

The I and J indices can be calculated using the highest concentrations of each hazardous substance among a set of comparable samples. In Highlight 7-28 of the HRS Guidance Manual, an example of the application of the I and J indices is presented for a single well.

What is the level of contamination for this well? ANSWER.

The HRS provides examples of how to score the I and J indices for each of the four pathways in their respective chapters. The calculations for the other pathways are identical to the example provided.

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