Preliminary Assessment and Site Investigation Results

Human Health Risk

The results of the manganese risk assessment are provided in the tables below. CS is the soil concentration, IR is the intake rake, CDI is the chronic daily intake, and HI is the Hazard Index.

Manganese – Human Health Risk Assessment
Scenario	Person	CS	IR	CDI (mg/kg*day)	HI
Recreational	Adult	50%	95%	0.000009	6.51E-05
Recreational	Adult	95%	95%	0.000018	0.000129
Recreational	Child	50%	95%	0.000039	0.000276
Recreational	Child	95%	95%	0.000077	0.000548
Worker	Adult	50%	50%	0.001139	0.008134
Worker	Adult	95%	95%	0.004519	0.032277

The results of the arsenic risk assessment are provided in the tables below.

Arsenic – Human Health Risk Assessment
Scenario	Person	CS	IR	CDI (mg/kg*day)	HI	Cancer Risk
Recreational	Adult	50%	95%	1.76E-08	0.000059	2.64E-08
Recreational	Adult	95%	95%	5.53E-08	0.000184	8.30E-08
Recreational	Child	50%	95%	7.46E-08	0.000249	1.12E-07
Recreational	Child	95%	95%	2.35E-08	0.000783	3.52E-07
Worker	Adult	50%	50%	2.20E-08	0.007329	3.30E-06
Worker	Adult	95%	95%	1.38E-08	0.046119	2.08E-05

Based on the hazard index and cancer risk results, it can be concluded that all the recreational scenarios fall within the acceptable range for human health risk as identified by the EPA. However, both worker scenarios pose a cancer risk as both values are greater than 10-6.

The data provided in tabels below show the adult lead model (ALM) outputs. Highlighted in the tables are the blood lead levels of adults as well as the 95th percentile blood lead level among fetuses of adult workers. At the end of each ALM output there is also the probability of exceeding the target blood lead level of 5 micrograms per deciliter for fetal blood lead levels.

The following table is the ALM output for a recreational adult exposed to the 50% exposure point concentration (EPC).

The following table is the ALM output for a recreational adult exposed to the 95% EPC.

The following table is the ALM output for a working adult exposed to the 50% EPC.

The following table is the ALM output for a working adult exposed to the 95% EPC.

The tablesbelow show the estimated blood lead level concentrations from the IEUBK model. Children exposed to lead concentrations at the 50% EPC on average have blood lead levels below the 5 micrograms per deciliter, suggesting they will be minimally effected by site contamination. Children exposed to lead concentrations at the 95% EPC all experienced blood lead levels exceeding the 5 micrograms per deciliter suggesting excess risk from lead at the site for children.

This table shows the IEUBK estimated blood lead levels among children for the 50% EPC.

Child Age Range (years)	Blood Pb (μg/dL)
0.5 - 1	3
1 - 2	2.6
2 - 3	2.3
3 - 4	2.2
4 - 5	2
5 - 6	1.9
6 - 7	1.8

This table shows the IEUBK estimated blood lead levels among children for the 95% EPC.

Child Age Range (years)	Blood Pb (μg/dL)
0.5 - 1	12.9
1 - 2	11.5
2 - 3	10.1
3 - 4	9.7
4 - 5	9.4
5 - 6	9.0
6 - 7	8.4

Conclusion

Overall, the site would produce the highest risk to human health during the remediation process as the workers would be consistently exposed to the contaminants; especially lead and arsenic. The recreational scenarios showed that for both children and adults, the exposure over the course of ten years does pose a human health risk at the 95% EPC. The ecological risk is more substantial, as most contaminants exceed all of the contaminant level standards for mammals, avian wildlife, and plants. Many of the endangered species in the area use central Arizona for migration, mating, and habitat throughout the changing seasons and weather. Signal Mill does not pose a significant risk to humans but will need further analysis to determine the extent of the harm it may bring to the wildlife found in the area.