Southeast Idaho Phosphate Mining Resource Area - Agency for ...

occur primarily on public lands where a residential scenario cannot occur. Also, it should
be noted that no gardens, residential or otherwise, have been observed on any areas along
streams in the Resource Area (TtEMI 2002).
Public health implications
Among the above discussed contaminants of concern in the soil, arsenic is the
contaminant of concern with the highest cancer risk. The average concentration of arsenic
in the soil of the impacted area is about 19 times higher than its cancer risk evaluation
guide (CREG) (Appendix C, Table C-1). The CREG is the estimated concentration that
would be expected to cause no more than one additional excess cancer in one million
people exposed over a lifetime (365 days/year × 70 years). As discussed before, no
residences have been observed along any streams in the Resource Area. Even for people
living in the Resource Area 190 days per year for 70 years, the estimated highest cancer
risk is still below one estimated cancer for 100,000 persons exposed. Therefore, the
contaminants in the soil are highly unlikely to result in any appreciable increase in cancer
risk to hunters, anglers, or collectors in the Resource Area and residents around the
Resource Area.
For non-cancer health effects, the maximum concentrations of arsenic, cadmium,
chromium and vanadium are higher than the corresponding CVs for children (Appendix
C, Table C-1). However, the average concentrations are all below the CVs for children.
Even the maximum concentrations of the above contaminants are still several times lower
than the CVs for adults (Appendix C, Table C-1). Since there is little possibility of
children consuming the maximum levels of arsenic, cadmium, chromium, or vanadium in
the soil on a daily basis, the contaminants in the soil are unlikely to result in any adverse
non-cancer health effects to residents, including children, hunters, collectors, and anglers.
Both children and adults are more likely to be exposed to contaminants by ingesting soil
than by inhaling soil (Hawley 1985). However, for chemicals that have specific toxic
effects on the respiratory tract (such as chromium and beryllium), special consideration
must be given. EPA Region 9’s residential soil preliminary remediation goals (RS-PRGs)
take into account the ingestion, inhalation, and dermal absorption of contaminants in soil.
While the maximum concentration of chromium is higher than its RS-PRG (210
miligrams per kilogram, mg/kg, 1:6 ratio Cr VI: Cr III), the average concentration is
below the RS-PRG. As discussed above, there is little possibility of children consuming
the maximum levels of chromium in the soil on a daily basis due to no one residing in the
mining areas. Also, even the maximum concentration of beryllium in the soil is below its
RS-PRG (150 mg/kg). Therefore, beryllium and chromium in surface soil are unlikely to
result in any adverse health effects through ingestion, inhalation, and dermal contact.
In conclusion, ingestion of the contaminants, inhalation of the contaminants, and dermal
contact with the contaminants in the soil in the Resource Area are unlikely to result in
cancer or adverse non-cancer health effects for hunters, anglers, collectors, and residents,
including children, who live near or recreate in the Resource Area.
10