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HRS Guidance Manual, Page 158

Equations for Calculating the I and J Indices

(4):Calculate the I and J indices for all hazardous substances for this well that meet the observed release criteria. Make two lists of substances that meet the observed release criteria: hazardous substances with screening concentrations for cancer risk; and hazardous substances with screening concentrations for non-cancer effects. Each hazardous substance may be on one, neither, or both of the lists. If more than one sample has been taken from a well and these samples are comparable (e.g., taken in the same time frame, collected using the same field techniques, analyzed by the same methods), for each hazardous substance, select the highest concentration to use in the calculations below.

  • Calculate the I index for all hazardous substances with screening concentrations for cancer risk that meet the observed release criteria, using the following equation:

equation no. 1

where:

Ci = concentration of substance i in well;

SCi = screening concentration for cancer risk, which is the concentration corresponding to 10-6 individual cancer risk for oral exposure for hazardous substance i; and

n = number of hazardous substances that meet observed release criteria and for which an SC is available.

  • Calculate the J index for all hazardous substances with screening concentrations for non-cancer effects that meet the observed release criteria, using the following equation:

equation no.2

where:

Cj = concentration of substance j in well;

CRj = screening concentration for non-cancer effects, which is the concentration corresponding to the reference dose for oral exposure for hazardous substance j; and

m = number of hazardous substances (1) that meet observed release criteria and (2) for which a CR is available.

  • If either the I or J index is greater than or equal to 1, score the well as Level I. If both the I and J indices are less than one, score the well at Level II. An example of calculating the I and J indices is presented in Highlight 7-28.

 

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