Summary: Output from the risk calculator will include 2 to 3 boxes. The first output box summarizes all cancer risk. Subsequent output boxes provide non-cancer information for each exposed party that has been selected. The basic interpretation of the risk calculator output is simply that values associated with "cumulative cancer risk" and non-cancer "sum" that are less than or equal to 1.00 are within acceptable cumulative risk levels.

Cancer Risk: The first output box displays cancer risks. All values presented in this box are expressed as factors of 1 x 10-4 (e.g., a value of 0.32 = 3.2 x 10-5). Cumulative cancer risk for each exposed party that has been selected will appear at the bottom of the box. A cumulative cancer risk shown as a value less than or equal to 1.00 (a value of 1 being equivalent to a 1 x 10-4 cancer risk) represents an acceptable cumulative cancer risk for that exposed party.

The values for each selected chemical in the various columns represent the cancer risk associated with a particular medium (e.g., soil) for a particular exposed party (e.g., site worker). Cumulative risks to exposed parties are determined as follows:

Cumulative Cancer Risk Site Resident = cancer risk associated with Resident Groundwater + Resident Soil + Resident Air

Cumulative Cancer Risk Site Worker = cancer risk associated with Site Worker Groundwater + Site Worker Soil + Site Worker Air

Cumulative Cancer Risk Construction Worker = cancer risk associated with Construction Worker Soil + Construction Worker Air

Non-Cancer Risk: All output boxes after the "Cancer Risk Output" display non-cancer risks. Unlike the cancer output, a seperate non-cancer output box appears for each selected exposed party. All values presented in the "Non Cancer Risk Output" boxes, except for the "Sum" values, are expressed as hazard quotients. A hazard quotient is the ratio of the contaminant concentration divided by the concentration below which no adverse health impact is expected. The hazard quotients for all chemicals and media of concern (i.e., groundwater, soil, and/or air) are summed for each target organ (e.g., heart) and shown at the bottom of each non-cancer output box. The "Sum" value for each target organ must be less than or equal to 1.00 to achieve compliance with the cumulative non-cancer risk criterion.


Public Water Supply Impact: The groundwater exposure scenario for the site resident assumes that an on-site well is used for water supply only by the site resident for the 30-year period that the resident lives at the site. If contamination from the site impacts or potentially impacts a public water supply that is used by the site resident, in addition to other residents of the community, the exposure point concentration from the public well should be used in the risk calculator and the cancer output values should be multiplied by 1.84 to account for possible lifetime exposure to the same water supply in lieu of the 30-year exposure assumed in the risk calculator. No change to the non-cancer output is necessary. For a similar situation involving the site-worker scenario in lieu of the site-resident scenario, an adjustment of the cancer output by a factor of 9.09 would apply.

Additional Compliance Requirements: Demonstration of compliance is specified in rule 567 IAC 137.10 (455H). Cumulative risk is not the only compliance criterion in the Land Recycling Program. Compliance with cumulative risk criteria does not guarantee compliance with all compliance criteria. For example, compliance with the cumulative-risk criteria based on exposure to on-site groundwater plus any soil and/or air exposure does not guarantee compliance with overall groundwater compliance criteria. Compliance with statewide standards for protected groundwater is still required for any actual or potential (i.e., not precluded by institutional control) drinking-water use of groundwater from a protected groundwater source.

Target Organ Results: Chemicals for which no target organ has been presented in any of the four standard reference sources for target organs (see Table 2 of "Background" under "Help") and the Iowa Department of Public Health (DPH) has not assigned a target organ(s) have been assigned all target organs, until such time that specific target organs are identified. These chemicals include:

  • Chlorotoluene, p
  • Chromium VI
  • Isopropyl methylphosphonate
  • Nitrophenol, p
  • Phenmedipham
When non-cancer "Sum" values exceed 1.00 as result of such chemicals, but may not if such chemicals were not associated with all target organs; the DPH may be asked to make a determination of appropriate target organs for such chemicals. There may be other situations where the non-cancer sum exceeds 1.00 for only the "Other" target organ, but the hazard quotient for no single contaminant exceeds 1.00. The DPH may also be contacted in such situations to determine if further refinement of the "Other" target-organ category may result in compliance.