Appendix 7

Acute Impacts Refined Analysis Figures
1

Refined Acute Modeling Approach

Initial acute screening risk calculations were performed with the HEM3 model

using the maximum hourly emissions estimates described in the memorandum 

Methodology for Estimation of Maximum Hourly Emissions for Ferroalloy Sources, 

which can be found in Appendix 1 to this report. HEM3 estimates acute (1-hour) impacts 

at both polar and census block receptors. It is assumed for this short period of time that 

an exposed individual could be located at any off-site location. The lack of readily 

available detailed property boundary information for many of the facilities evaluated 

made it difficult to determine whether receptors were on- or off-site. In the absence of 

such information, the first ring of polar receptors was placed 100 meters from the plant 

center for many facilities. However, these polar rings often transected on-site locations, 

restricting public access to exposures at these levels and thereby overestimating 

exposures.

The screening approach used by HEM3 to estimate maximum 1-hour exposures 

also likely overestimates exposures. To estimate maximum 1-hour concentrations at each 

receptor, HEM3 sums the maximum concentrations attributed to each source, regardless 

of whether those maximum concentrations occurred during the same hour. In other 

words, HEM3 assumes that the maximum impact from each source at each receptor 

occurs at the same time. In actuality, maximum impacts from different sources may occur 

at different times.

This appendix addresses refinements to determine the maximum offsite values by

plotting the HEM3 polar grid results on aerial photographs of the facilities for those 

facilities and pollutants that exceeded short-term health benchmarks. These photographs 

were examined to determine off-site locations that may be accessible to the public (e.g.,

roadways and public buildings.). The attached figures present the estimated property 

lines of the facilities and the estimated hazard quotient values (the modeled 1-hour 

concentration of a pollutant divided by its short-term health benchmark) at the polar 

receptors near the facilities. Table 1 provides the resulting change in acute risks taking 

into account these off-site locations for the baseline modeling scenario. There were no 

hazard quotients greater than 1 in the post-control modeling scenario.

Table 1. Refined Acute Risks Due to Off-site Receptors – Baseline Modeling 

Scenario

Facility NEI ID Pollutant Criteria

Original 

Acute 

Hazard 

Quotient

Off-site 

Hazard 

Quotient

54053NEIWV053FELMAN Nickel compounds REL 40 10

54053NEIWV053FELMAN Arsenic compounds REL 40 9

39167NEI11660 Arsenic compounds REL 4 2
Ferroalloys Facilities
Figure 1 – Estimated Eramet Fenceline
Figure 2 – Estimated Felman Fenceline
Ferroalloys Facilities –

Baseline Modeling Scenario
Figure 3 – NEIWV053FELMAN Acute Nickel HQ (REL)
Figure 4 – NEIWV053FELMAN Acute Arsenic HQ (REL)
Figure 7 – NEI11660 Acute Arsenic HQ (REL)
Ferroalloys Facilities –

Post-Control Modeling 

Scenario
Figure 10 – NEWV053FELMAN Acute Nickel HQ (REL)
Figure 11 – NEIWV053FELMAN Acute Arsenic HQ (REL)