Appendix 9

Technical Support Document: Human Health Multipathway Residual 

Risk Screening Assessment for the Primary Aluminum Reduction 

Source Category
Technical Support Document: Human Health Multipathway Residual 

Risk Screening Assessment for the Primary Aluminum Production 

Source Category 

DRAFT 

July 10, 2014 

Prepared For: 

U.S. Environmental Protection Agency 

Office of Air Quality Planning and Standards 

Research Triangle Park, NC 27711 

Under Contract No. EP-12-010, Work Assignment 2-20 

Prepared By: 

ICF International 

2635 Meridian Pkwy. 

Suite 200 

Durham, NC 27713 
[This page intentionally left blank.]
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft iii July 2014 

CONTENTS

Tables .......................................................................................................................................... iii

Figures ......................................................................................................................................... iii

1. Introduction ........................................................................................................................... 1

2. Tier 1 Emission Screening Assessment ............................................................................... 2

2.1 Tier 1 Emission Screening Results for this Source Category ...................................... 3

3. Tier 2 Emission Screening Assessment ............................................................................... 3

3.1 Adjustment Factors Applied to Tier 1 Screening Values ............................................. 4

3.2 Calculating Refined Tier 2 Fisher Screening Values ................................................... 5

3.3 Finalizing Tier 2 Farmer Screening Values ................................................................. 6

3.4 Tier 2 Screening Results for this Source Category ..................................................... 6

4. Tier 3 Emission Screening Assessment ............................................................................... 9

4.1 Lake Assessment ........................................................................................................ 9

4.2 Tier 3 Lake Assessments Results for this Source Category ..................................... 11

4.3 Plume-rise Assessment ............................................................................................. 14

4.4 Tier 3 Plume-rise Assessment Results for this Source Category .............................. 14

5. Comparison to Tier 1 Screening Results for this Source Category .................................... 16

6. References ......................................................................................................................... 18

TABLES 

Table 2-1. Tier 1 Emission Screening Results for this Source Category ...................................... 3

Table 3-1. Tier 2 Screening Results for this Source Category ...................................................... 8

Table 4-1. Results of Tier 3 Lake Assessments in this Source Category ................................... 11

Table 4-2. Results of Tier 3 Plume-rise Assessments in this Source Category .......................... 15

Table 4-3. Tier 3 SVs Before and After Additional Lake and Plume-rise 

Assessments in this Source Category .................................................................. 16

Table 5-1. Comparison of Tier 1 and Tier 3 Screening Results for this Source 

Category ............................................................................................................... 18

FIGURES 

Figure 4-1. Example of Lake Removed from Screening—Likely Covered in Algae 

or Thick Plant Matter ............................................................................................ 10

Figure 4-2. Example of Lake Removed from Screening—Likely an Industrial Lake ................... 10

Figure 4-3. Lakes Assessed for Cadmium Emissions at NEIWA19906 ...................................... 13
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft iv July 2014 

Figure 4-4. Lakes Assessed for PAH and Dioxin Emissions at NEI46970 ................................. 13
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 1 July 2014 

1. Introduction 

This report provides a discussion on a screening-level assessment of human health risks, via 

the ingestion pathway, from exposure to persistent and bioaccumulative hazardous air 

pollutants (PB-HAPs) emitted to the air from primary aluminum production facilities. While this 

report contains a discussion on some of the screening methods, a more detailed discussion on 

the development, methods, and implementation of the screening assessment can be found in 

Appendix 5 of the Risk Report.1 Where appropriate, this discussion provides references to 

particular sections of Appendix 5 to the Risk Report, where further details on the subject matter 

can be found. 

Cadmium, dioxins, mercury, and polycyclic aromatic hydrocarbons (PAHs) were the evaluated 

PB-HAP groups,2 selected from a larger list of PB-HAPs based in part on ranking their toxicityweighted air emissions across all source categories. The evaluated exposure scenarios were a 

fisher scenario (i.e., consumption of fish from a lake) and a farmer scenario (i.e., consumption of 

farm food chain [FFC] media such as animal products, fruits and vegetables, and incidental 

ingestion of soil). EPA evaluates the two scenarios together (i.e., the sum of fisher and farmer 

exposures and risks) in the first tier of the assessment, and EPA evaluates them separately in 

the second and third tiers. EPA designed the screening scenarios to be health-protective in 

estimating exposures and risks. Specifically, they are intended to avoid underestimating 

ingestion exposure and risk due to the air emissions of these PB-HAPs from facilities nationwide 

evaluated in the Risk and Technology Review (RTR) program. 

EPA uses the TRIM.FaTE3 model to evaluate the environmental transport, transfer, and fate of 

PB-HAP air emissions. The MIRC4 program then calculates FFC chemical uptake along with 

human exposure, human health cancer risks, and human health non-cancer hazard quotients 

(HQs) resulting from ingestion of fish and FFC media. For screening assessments of 

multipathway risk across the RTR program, EPA used these models with fate and transport 

parameter values, idealized spatial layouts, and generalized meteorology that overall create 

ingestion exposure situations that are unlikely to be exceeded at any actual facility evaluated in 

the RTR program. ICF (hereafter “we”) conducted these model runs to identify threshold 

emission rates (hereafter “thresholds”) that correspond to levels of concern for cancer risks and 

HQs. The levels of concern are incremental, lifetime, human cancer risks of 1-in-one million (for 

PAHs and dioxins) and chronic, non-cancer HQs of 1 (for cadmium and mercury). 

For the iterative (“tiered”) screening-level ingestion assessment described in this report, we 

assessed the potential for ingestion risks above levels of concern in the primary aluminum 

production source category by comparing PB-HAP emissions from facilities within the source 

category to the thresholds. We use the term “screening values” (SVs) to refer to the ratio of a 

facility’s emissions of a PB-HAP to that PB-HAP’s threshold. When rounded to one significant 

 

1Appendix 5 to the Risk Report is the Technical Support Document for the TRIM-Based Multipathway Tiered 

Screening Methodology for RTR. 

2The phrase “PB-HAP group” is used to distinguish the individual PB-HAP chemicals and congeners from the overall 

family (grouping) of those chemicals. For example, EPA’s ingestion risk methods in its Risk and Technology Review 

(RTR) program evaluate emissions of 17 individual congeners of chlorinated dibenzo-p-dioxins and chlorinated 

dibenzofurans in the “dioxin” PB-HAP group. 

3TRIM.FaTE is the Fate, Transport, and Ecological Exposure module of the Total Risk Integrated Methodology 

modeling system. Additional TRIM.FaTE information can be found at: http://www2.epa.gov/fera/total-risk-integratedmethodology-trim-trimfate. 

4MIRC is the Multimedia Ingestion Risk Calculator. 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 2 July 2014 

figure, an SV of 1 or lower indicates that the emissions did not exceed the threshold and are 

unlikely to pose health risks above levels of concern (i.e., the emissions “screened out”). An SV 

of 2 or higher indicates that the emissions exceeded the threshold and potentially pose health 

risks above levels of concern. 

The primary aluminum production source category contains 13 facilities. As described in this 

report, each facility emitted PAHs and dioxins at levels exceeding Tier 1 thresholds, and 10 of 

the facilities also emitted cadmium and/or mercury at levels exceeding Tier 1 thresholds. In the 

Tier 2 screening, emissions of cadmium exceeded the fisher threshold at one facility 

(NEIWA19906), and emissions of mercury exceeded the fisher threshold at one facility 

(NEI41217). The cadmium emissions at NEIWA19906 and mercury emissions at NEI41217 

screened out in Tier 3, which included additional assessments of its emissions and 

corresponding meteorology and/or lake data. The highest fisher and farmer SVs for PAH 

emissions, and highest farmer SV for dioxin emissions, correspond to one facility (NEI46970); 

these emissions did not screen out in Tier 3. 

In Sections 2, 3, and 4, we briefly describe the Tiers 1, 2, and 3 screening methods and discuss 

the results of those screening assessments. We provide in Section 5 a summary comparison of 

the Tier 1 screening results with the screening results after the Tiers 2 and 3 assessments. 

2. Tier 1 Emission Screening Assessment 

The thresholds developed for Tier 1 are intended to apply to any U.S. facility; that is, EPA 

designed them to be applicable to every facility regardless of the facility’s characteristics and 

surrounding environment and the population exposed in its vicinity. The approach to develop the 

thresholds5 assumes ingestion exposure situations that are unlikely to be exceeded at any 

actual facility evaluated in the RTR program. This health-protectiveness is achieved by several 

methods, including (but not limited to): (1) an idealized spatial layout where the evaluated lake 

and farming area are within 2 to 3 km of the emission source and, thus, receive high levels of 

direct deposition; (2) a watershed design where the lake receives substantial indirect chemical 

deposition through large magnitudes of runoff and erosion; (3) a meteorology scenario that 

enhances air concentrations and chemical deposition; and, (4) relatively high ingestion rates 

representing subsistence-level consumption of fish and FFC media. 

Each evaluated PB-HAP group has a single Tier 1 threshold, as shown in Table 2-1 (column e). 

For Tier 1, EPA normalizes the emissions of all dioxin congeners to 2,3,7,8-tetrachlorodibenzop-dioxin-equivalent emissions, and EPA normalizes the emissions of all PAH congeners to 

benzo(a)pyrene-equivalent emissions.6 These normalization factors (i.e., exposure equivalency 

factors [EEFs]) are based on oral toxicity factors and factors related to the congeners’ 

environmental fate and transport characteristics as analyzed in the TRIM.FaTE model.7 For 

mercury, EPA established the threshold for emissions of divalent mercury, although the 

threshold is based on hazards associated with ingestion of methyl mercury from contaminated 

fish (with relatively minimal contribution from ingestion of divalent mercury from FFC media).8 

 

5See Appendix 5 of the Risk Report (Sections 1 and 2) for additional information. 

6We sometimes use 2,3,7,8-TCDD and BaP this report as shorthand terms for 2,3,7,8-tetrachlorodibenzo-p-dioxin 

and benzo(a)pyrene, respectively. 

7See Appendix 5 to the Risk Report (Section 2.2.7) for additional information on Tier 1 screening methods. 

8TRIM models mercury transformation in the environment, and exposure in the screening scenario associated with 

ingestion of fish contaminated with methyl mercury (related to emissions of divalent mercury and transformation to 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 3 July 2014 

2.1 Tier 1 Emission Screening Results for this Source Category 

As shown in Table 2-1, emissions of mercury exceeded the threshold at nine facilities, and the 

highest SV was 10 (at NEIKY0912109100004, a Century Aluminum of Kentucky facility in 

Hawesville, KY). Emissions of cadmium exceeded the threshold at six facilities, and the highest 

SV was 30 (at NEIWA19906, an Alcoa facility in Ferndale, WA). NEI46970 (a Reynolds Metals 

facility in Massena, NY) had the highest SV for PAHs (SV = 2,000) and dioxins (SV = 200), 

though all facilities exceeded the thresholds for PAHs and dioxins. 

When PAH and dioxin SVs were summed together per facility (i.e., calculating the total 

PAH+dioxin screening-level potential cancer risk), the highest total “cancer SV” was 2,000 and 

all total “cancer SVs” were 20 or higher. 

Table 2-1. Tier 1 Emission Screening Results for this Source Category 

PB-HAP 

Group 

(a) 

Num. Facil. 

Exceeding 

Threshold 

(b) 

Highest 

SV 

[(d)/(e)]

(c) 

Facil. with Highest SV 

(d) 

Emiss. at 

Facil. with 

Highest 

SV (TPY)a

(e)

Emiss. 

Screening 

Thresh. 

(TPY) 

Mercuryb 

(non-cancer)

9 10 NEIKY0912109100004 

(Century Aluminum of Kentucky LLC; 

Hawesville, KY) 

3.21E-03 3.16E-04 

Cadmium 

(non-cancer) 

6 30 NEIWA19906 

(Alcoa Primary Metals Intalco Works; 

Ferndale, WA) 

3.46E-01 1.18E-02 

PAHs as BaP 

(cancer) 

13 2,000 NEI46970 

(Reynolds Metals, St. Lawrence Reduction Plant; 

Massena, NY) 

4.54 2.58E-03 

Dioxins as 2,3,7,8-

TCDD 

(cancer) 

13 200 NEI46970 

(Reynolds Metals, St. Lawrence Reduction Plant; 

Massena, NY) 

6.24E-07 2.81E-09 

Notes: TPY = tons per year. SVs rounded to one significant figure. Cell shadings indicate records corresponding to SVs of 2 or 

higher (i.e., the emissions exceeded the threshold). a

We normalized PAH and dioxin emissions in this column to BaP and 2,3,7,8-TCDD, respectively, for oral toxicity and Tier 1 

modeled environmental fate and transport. 

b

The emission screening threshold for mercury applies to emissions of divalent mercury, although EPA derived it based on hazards

associated with ingestion of fish contaminated with methyl mercury (i.e., emissions of divalent mercury, which transforms to methyl 

mercury within the environment, accumulates in fish tissue, and is consumed by the fisher). The contribution from hazards 

associated ingestion of divalent mercury from contaminated FFC or fish media is relatively minimal.

3. Tier 2 Emission Screening Assessment 

The generic site characteristics used in Tier 1 can differ from those actually present at many 

facilities. In Tier 2, EPA takes into account some site-specific characteristics—specifically, 

meteorological conditions and locations of potentially fishable lakes—to apply adjustments to 

the Tier 1 SVs, creating Tier 2 SVs.9 

For a facility undergoing Tier 2 screening, EPA partitions the 50-km area around the facility into 

eight “wedges” or “octants” centered on the facility and compartmentalizing areas north of the 

facility, northeast, east, and so on. As described in Section 3.1, the lake locations and some 

 methyl mercury) results in much larger hazards than exposure associated with ingestion of fish or FFC contaminated 

with divalent mercury. (See Section 2.2 and 2.5.3 in Appendix 5 to the Risk Report.) 

9See Appendix 5 to the Risk Report (Sections 1.2 and 3) for additional information on Tier 2 screening methods. 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 4 July 2014 

meteorological conditions related to a facility can vary by octant in Tier 2. Though the distance 

from facility to modeled farm remains fixed for each octant, EPA adjusts the location of the 

modeled lake based on actual lake locations. This affects chemical concentrations in some FFC 

media due to modeled erosion and runoff patterns that are directed mostly toward the lake. 

Therefore, for every relevant PB-HAP emitted by a facility, EPA calculates the fisher SV of each 

lake, using the distance from facility to lake and the meteorology conditions of the octant the 

lake is in; and, since lake location can affect the farm SV, EPA calculates a corresponding 

farmer SV for each lake scenario. 

Based on the Tier 2 SVs and other considerations with respect to the source category being 

assessed, EPA might conduct a Tier 3 assessment on some facilities, leading to adjustments to 

the Tier 2 SVs for those facilities. The results we present in Section 3.4 are prior to this Tier 3 

assessment; we discuss the Tier 3 assessment and its effects on SVs in Section 4. 

3.1 Adjustment Factors Applied to Tier 1 Screening Values 

In developing the adjustment factors used in Tier 2, we conducted hundreds of TRIM.FaTE and 

MIRC model runs corresponding to ranges of meteorological characteristics expected to be 

found at most U.S. locations, and corresponding to lake locations ranging from 2 km to 40 km 

away from the facility. As in Tier 1, the model runs provided emission rates corresponding to risk 

and hazard levels of concern. Because each modeled scenario has different environmental fate 

and transport characteristics, each scenario also has different EEFs to relate PAH and dioxin 

congeners to BaP and 2,3,7,8-TCDD, respectively. Unlike in Tier 1, EPA calculates EEFs and 

thresholds separately in Tier 2 for the fisher and farmer scenarios. The Tier 2 adjustment factors 

are the ratios of the Tier 2 EEFs and thresholds to those of Tier 1. EPA applies the Tier 2 

adjustment factors to Tier 1 SVs in order to calculate Tier 2 fisher SVs and Tier 2 farmer SVs. 

We discuss below an additional adjustment factor based on wind direction. 

In order to match an assessed facility in Tier 2 with its appropriate meteorology- and lakerelated Tier 2 adjustment factors, EPA matches the facility with the same meteorology station to 

which it is matched in the RTR inhalation risk assessment (i.e., typically the closest station), and 

EPA also identifies qualifying lakes around the facility. Some of a facility’s meteorology patterns 

vary by octant, and qualifying lakes (discussed below) can be scattered around multiple octants 

and at multiple distances from the facility. Therefore, for each lake in each octant around a 

facility, EPA matches its combination of meteorology data and lake distance to its appropriate 

scenario in the Tier 2 model runs and, thus, to the appropriate Tier 2 adjustment factors. 

EPA bases the meteorology data used in Tier 2 on the same dataset used in RTR inhalation risk 

assessments, consisting of more than 800 meteorology stations nationwide. We processed 

hourly data from the meteorology stations to derive typical or total station-specific values of wind 

speed, wind direction, mixing height, and precipitation. For each station, we then matched the 

combination of these values with the most representative meteorological scenario used in the 

Tier 2 model runs. The matching method is health-protective (i.e., wind speeds and mixing 

heights match to their closest, smaller value in the Tier 2 model runs, and a precipitation value 

to its closest, larger value). We also calculated the frequency of winds blowing toward each of 

the octants around each station. EPA compares the frequency of winds blowing into an octant to 

the frequency used in Tier 1, creating a Tier 2 wind frequency adjustment factor. 
Human Health Multipathway Residual Risk Screening Assessment for the 

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Draft 5 July 2014 

EPA analyzes all qualifying lakes within 50 km of the facility. A qualifying lake (1) is at least 25 

acres in surface area but no larger than 100,000 acres;10 (2) is classified by USGS as a lake or 

reservoir but not used for disposal, treatment, or evaporator purposes; (3) does not have a 

name suggesting it is not intended for public use (e.g., “Gavin Fly Ash Impoundment”); and, (4) 

has not been removed in previous source category assessments based on these and other 

inspection methods. EPA assigns each lake to its respective octant around the assessed facility 

and to the closest lake distance value used in the Tier 2 model runs, where the matching 

method is health-protective (i.e., a lake’s distance matches to its closest, smaller value in the 

Tier 2 model runs). In cases where there are no qualifying lakes around the facility, there is no 

exposure or risk to the fisher. 

The Tier 2 fisher and farmer SVs calculated at this point in the assessment are “initial SVs”; this 

is because subsequent steps in Tier 2 refine the fisher SVs (see Section 3.2) and select one of 

the potentially many farmer SVs (see Section 3.3). 

3.2 Calculating Refined Tier 2 Fisher Screening Values 

The subsistence fisher in Tier 1 consumes fish from one lake at the subsistence ingestion rates, 

regardless of the lake’s ability to support a fish population that allows for that level of 

consumption across many years. In Tier 2, EPA considers the lake’s capacity to accommodate 

the assumed fish ingestion rates. For any particular lake, the fisher in Tier 2 catches and 

consumes fish from that lake at an amount proportional to the area of the lake, which serves as 

an approximation of the lake’s biological productivity.11 In order to consume fish at the ingestion 

rate used in Tier 2, the fisher might need to fish multiple lakes (and be exposed to several 

different chemical concentration levels in fish). 

The initial Tier 2 fisher SVs and the Tier 1 fisher SVs use a fixed set of fish ingestion rates 

covering a range of ages. The highest fish ingestion rate among the age groups is 373 g fish/d 

for adults, which for simplicity EPA uses to estimate a lake’s capacity to support subsistence 

fishing. Smaller lakes are unlikely to support this level of fish consumption over time (i.e., the 

lake would be “fished out”), although the fisher could catch and consume that amount of fish 

collectively from multiple small lakes. In Tier 2, EPA assumes that a fisher can catch and 

consume no more than 1 g fish/d/acre lake without impacting the lake’s long-term sustainability. 

In order to reach the assumed ingestion rate, EPA assumes that the fisher catches and 

consumes fish from one or more lakes until he is able to fish a total of 373 acres of lake and 

consume a total of 373 g fish/d (i.e., the screening scenario adult fish ingestion rate) or until 

there are no more qualifying lakes to fish to reach 373 total acres. 

EPA uses the initial Tier 2 fisher SVs calculated for all qualifying lakes around a facility, along 

with the acreage values of those lakes, to identify which lake(s) the fisher catches and 

consumes fish from and the amount of fish caught from each lake. Using this information, EPA 

refines the Tier 2 fisher SV based on a scenario assuming consumption of fish from multiple 

lakes. EPA conducts the steps below for each PB-HAP group emitted by a facility. 

 

10Discussed further in Appendix 5 (Section 3 and Attachment E) to the Risk Report. 

11See Appendix 5 to the Risk Report (Section 3 and Attachment E) for additional information on potential lake 

productivity. 
Human Health Multipathway Residual Risk Screening Assessment for the 

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1. Identify the lake with the highest chemical concentration in fish12 for a given PB-HAP group, 

according to the initial Tier 2 fisher SVs. 

2. If the lake with the highest concentration is at least 373 acres in area, then the fisher 

consumes fish from only that lake, at the subsistence-level ingestion rates (the adult rate 

being 373 g fish/d). That is, the refined Tier 2 fisher SV equals the initial Tier 2 fisher SV. 

3. If the lake with the highest concentration is smaller than 373 acres, then the fisher catches 

only the amount of fish consistent with the assumption of 1 g fish/d/acre lake. That is, 

multiply the initial Tier 2 fisher SV for that lake by [its acreage]÷[373 acres]; put another way, 

multiply the SV by [the daily mass of fish consumed from the lake]÷[373 g fish/d]. Apply the 

following logic to subsequent lakes. 

a. The fisher catches and consumes fish from one or more additional lakes, in order 

of highest to lowest concentration. If multiple lakes have the same concentration, 

then he fishes them in order of largest to smallest acreage. He stops fishing 

when he fishes lakes totaling 373 acres or when there are no more qualifying 

lakes to fish to reach 373 total acres. Scale each additional lake’s initial Tier 2 

fisher SV by acreage (i.e., by fish consumption rate) in the same way as the first 

fished lake (see above). 

b. If the cumulative area of all qualifying lakes is smaller than 373 acres (i.e., if all 

lakes together cannot support a 373 g fish/d adult ingestion rate, assuming 1 g 

fish/d/acre lake), then the fisher does not consume the full 373 g fish/d. 

c. If the cumulative area of all qualifying lakes is larger than 373 acres, the fisher 

consumes only the amount of fish from the final lake necessary to reach 373 g 

fish/day. That is, scale the initial Tier 2 fisher SV for that lake by [the remaining 

acreage necessary to reach 373 acres, after fishing the prior lake(s)]÷[373 

acres]. 

d. The refined Tier 2 fisher SV (reflecting the refined fisher methods) is the sum of 

the adjusted Tier 2 fisher SVs of all fished lakes as calculated above. 

3.3 Finalizing Tier 2 Farmer Screening Values 

For a given PB-HAP group emitted by a facility, EPA identifies the highest Tier 2 farmer SV from 

all the relevant meteorology and lake-distance scenarios. This helps to avoid underestimating 

exposure and risk. 

3.4 Tier 2 Screening Results for this Source Category 

In this section, we discuss the Tier 2 screening results. The results in this section use the 

refined Tier 2 fisher SVs (discussed in Section 3.2) and the highest Tier 2 farmer SVs 

(discussed in Section 3.3). 

As shown in Table 3-1, emissions of mercury and cadmium screened out for the farmer, though 

the mercury fisher SV was 2 at NEI41217 (an Alumax of South Carolina facility in Goose Creek, 

SC) and the cadmium fisher SV was 2 at NEIWA19906. EPA assessed these emissions at 

NEI41217 and NEIWA19906 in Tier 3, as discussed in Section 4. Emissions of PAHs exceeded 

 

12In the screening assessments, for a given ingestion rate, SVs are directly and proportionally related to chemical 

concentrations in the exposure media. For simplicity and to more clearly relate the potential health impacts of 

consuming a lake’s fish to the chemical concentrations in those fish, EPA discusses fish concentrations in describing 

the methods of calculating the refined Tier 2 angler SVs. 
Human Health Multipathway Residual Risk Screening Assessment for the 

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Draft 7 July 2014 

the fisher or farmer threshold at 11 facilities, with emissions at NEI46970 corresponding to the 

highest SVs (SV = 60 for fisher, SV = 100 for farmer). Emissions of dioxins exceeded the 

thresholds at 12 facilities, with the highest fisher SV of 40 corresponding to NEI32661 (Alcoa 

facility in Newburgh, IN) and the highest farmer SV of 20 corresponding to NEI46970. EPA 

assessed PAH and dioxin emissions at NEI46970 in Tier 3, as discussed in Section 4. 

When PAH and dioxin SVs were summed together (i.e., calculating the total PAH+dioxin 

screening-level potential cancer risk), the highest total “cancer SVs” were 2 or higher for the 

fisher at all 13 facilities and for the farmer at 12 facilities (not shown in table). 
Human Health Multipathway Residual Risk Screening Assessment for the 

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Draft 8 

Table 3-1. Tier 2 Screening Results for this Source Category 

PB-HAP 

Group 

Num. Facil. 

Exceeding 

Fisher 

Threshold 

Num. Facil. 

Exceeding 

Farmer 

Threshold 

Num. Facil. Exceeding 

Threshold, 

Either Fisher or Farmer, 

Both Fisher and Farmer 

Highest 

Fisher SV 

Highest 

Farmer SV 

Facil. with Highes

Fisher SV 

Mercurya (non-cancer)

1 0 1 

0 

2 0.0008 NEI41217 

(Alumax of South CaroliGoose Creek, SC)

Cadmium (non-cancer) 

1 0 1 

0 

2 0.4 NEIWA19906 

(Alcoa Primary Metals Intalco Works; Ferndale, WA)

PAHs as BaP (cancer) 

10 9 11 

8 

60 100 NEI46970 

(Reynolds Metals, St. Lawrence Reduction PlaMassena, NY)

Dioxins as 2,3,7,8-TCDD (cancer) 

12 12 12 

12 

40 20 NEI32661 

(Alcoa Inc. – Warrick Operations; Newburgh, IN)

Notes: TPY = tons per year. SVs rounded to one significant figure. Cell shadings indicate records corresponding to SVs of 2 or higher (i.e., the emissions e

Emissions and screening thresholds not shown for space purposes. Notes: N/E = not emitted. TPY = tons per year. SVs rounded to one significant figure. 

corresponding to SVs of 2 or higher (i.e., the emissions exceeded the threshold). Emissions and screening thresholds not shown for space purposes. aThe emission screening threshold for mercury applies to emissions of divalent mercury, although EPA derived it based on hazards associated with ingest

methyl mercury (i.e., emissions of divalent mercury, which transforms to methyl mercury within the environment, accumulates in fish tissue, and is consum

contribution from hazards associated ingestion of divalent mercury from contaminated FFC or fish media is relatively minimal.
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 9 July 2014 

4. Tier 3 Emission Screening Assessment 

Based on the Tier 2 SVs and other considerations with respect to the source category being 

assessed, EPA may conduct Tier 3 assessments on some facilities. We discuss in this section 

the Tier 3 assessment conducted for NEI41217 (whose Tier 2 mercury SV was 2 for the fisher), 

NEIWA19906 (whose Tier 2 cadmium SV was 2 for the fisher), and NEI46970 (whose Tier 2 

PAH SVs were 60 and 100 for the fisher and farmer, respectively, and whose Tier 2 dioxin SVs 

were 10 and 20 for fisher and farmer, respectively). 

4.1 Lake Assessment 

Other than verifying a facility’s emission rates, one of the simplest assessments EPA can 

conduct (beyond the Tier 2 methods) is assessing the existence, the potential purpose, the 

accessibility and fishability, and the suitability of lakes for the models and methods used in Tier 

2. The full USGS dataset of lakes and reservoirs nationwide that EPA uses in Tier 2 does not 

contain information on lake accessibility or fishability. In addition, it occasionally identifies a lake 

that no longer exists (e.g., it has evaporated or been drained) or it uses a classification that 

might not accurately reflect the lake’s purpose or type. EPA uses aerial and street-view imagery 

and internet searches to quickly ascertain if an assessed lake actually exists, if it is probably not 

fished (e.g., appears swampy or covered in algae), if it is likely used for industrial or waste 

disposal/treatment purposes, and/or if it is adjacent to or connected to a river or saltwater body 

(estuaries, rivers, and saltwater areas are not ideal for the assessment models and methods). 

For example, the blue outline in Figure 4-1 identifies a lake from the USGS dataset that 

originally qualified for Tier 2 based on the information provided in that dataset, but aerial 

imagery shows it is likely covered in algae or other thick plant matter. Similarly, the outline in 

Figure 4-2 identifies a lake that originally qualified, but aerial imagery shows that it is directly 

adjacent to an industrial facility and likely used only for on-site industrial purposes. 

For facilities undergoing the lake assessment portion of Tier 3 screening, EPA evaluates all 

lakes from which the fish catches and consumes fish according to the refined Tier 2 fisher 

methods discussed in Section 3.2. EPA permanently removes, from the screening assessment, 

all lakes meeting the criteria discussed in the previous paragraphs, so that they are no longer 

used in any screening assessment. If EPA removes a lake from the facility’s assessment, it 

might be necessary for the hypothetical fisher to catch and consume fish from additional lake(s) 

in order to fish a total of 373 acres. In this case, EPA evaluates additional lakes that were not 

fished, using the methods discussed in Section 3.2, in descending order of initial Tier 2 fisher 

SV and lake area. 

If EPA removes any lakes from the screening, EPA conducts the screening again (using the Tier 

2 methods) with the revised lake dataset. Although EPA conducts this additional lake 

assessment based on the Tier 2 SVs of a particular set of facilities, lakes removed during that 

assessment could affect the SVs of other facilities in the source category beyond that original 

set. This can happen if an assessed facility is within 50 km of another assessed facility, whereby 

removing a lake could affect the SVs of both facilities. EPA does not sum SVs across facilities. 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 10 July 2014 

Figure 4-1. Example of Lake Removed from Screening—Likely 

Covered in Algae or Thick Plant Matter 

Note: Aerial imagery from ESRI World Imagery (2014). 

 

 Figure 4-2. Example of Lake Removed from Screening—Likely an 

Industrial Lake 

Note: Aerial imagery from ESRI World Imagery (2014). 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 11 July 2014 

4.2 Tier 3 Lake Assessments Results for this Source Category 

The information in Table 4-1 is related to the lakes evaluated in the Tier 3 screening of cadmium 

emissions from NEIWA19906 and dioxin and PAH emissions from NEI46970. EPA did not 

assess lakes in Tier 3 for NEI41217 because there were more than 70 lakes within 50 km of the 

facility that qualified for Tier 2 screening; while a Tier 3 lake assessment might have disqualified 

some of the lakes, it was still likely that the fisher would catch and consume 373 g fish/day 

cumulatively from the remaining lakes. As such, it was more efficient to perform a plume-rise 

assessment on NEI41217 prior to any potential lake assessment, as discussed in Section 4.4. 

The table includes several lakes we removed during the assessment (see gray shaded rows). 

For lakes remaining in the screening after the lake assessment, the table contains information 

on how much of the subsistence fisher’s daily fish consumption came from each lake, and how 

much of the corresponding fisher SV was attributable to each lake. For NEIWA19906, lakes 

labeled RMV-3, RMV-4, and RMV-5 were on islands and EPA concluded that it was unlikely for 

a fisher to boat to lakes on multiple islands in one day. These island lakes were not permanently 

removed from future assessments, as they technically still qualify for screening assessments. 

Table 4-1. Results of Tier 3 Lake Assessments in this Source Category 

Facil. NEI ID 

PB-HAP 

Group 

Lake 

Name 

Lake 

Area 

(acres) 

Selection 

Order 

Percent 

of 

Ingested 

Fish 

Coming 

From 

This 

Lake 

Percent 

of Tier 3 

Fisher SV 

Attributed 

To This 

Lake 

Reason for 

Removal 

NEIWA19906 

 

 

 

 

 

 

Cadmium 

 

 

 

 

 

 

Lake 

Terrell 

316 1 85% 87% -- 

Wiser Lake 91 2 15% 13% -- 

Tennant 

Lake 

44 RMV-1 -- -- Appears 

contaminated with 

algae or thick plant 

matter 

Barrett 

Lake 

42 RMV-2 -- -- Appears to be a tiny 

creek 

Horseshoe 

Lakea

69 RMV-3 -- -- On an island, 

unlikely that fisher 

would boat to lakes 

on multiple islands 

in one day 

Spencer 

Lakea

67 RMV-4 -- -- On an island, 

unlikely that fisher 

would boat to lakes 

on multiple islands 

in one day 

Name Not 

Provideda

35 RMV-5 -- -- On an island, 

unlikely that fisher 

would boat to lakes 

on multiple islands 

in one day 

NEI46970 

 

 

 

 

Dioxin 

 

 

 

St. Moses 116 1 31% 76% -- 

Allen Falls 

Reservoir 

77 2 21% 9% -- 

Lake Titus 410 3 48% 15% -- 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 12 July 2014 

Facil. NEI ID 

PB-HAP 

Group 

Lake 

Name 

Lake 

Area 

(acres) 

Selection 

Order 

Percent 

of 

Ingested 

Fish 

Coming 

From 

This 

Lake 

Percent 

of Tier 3 

Fisher SV 

Attributed 

To This 

Lake 

Reason for 

Removal 

 

 

 

Name Not 

Provided 

109 RMV-1 -- -- Appears to be creek 

that sometimes 

swells (hasn't looked 

like a lake since the 

1990s) 

PAH 

 

 

 

St. Moses 116 1 31% 80% -- 

Allen Falls 

Reservoir 

77 2 21% 8% -- 

Lake Titus 410 3 48% 13% -- 

Name Not 

Provided 

109 RMV-1 -- -- Appears to be creek 

that sometimes 

swells (hasn't looked 

like a lake since the 

1990s) 

Notes: 

The lakes shown in this table, and their corresponding selection order and percentages of ingestion and SV, are related only to the 

indicated facilities and PB-HAP group emissions. For other PB-HAP groups emitted by these facilities, the fisher might fish a 

different set of lakes and/or with a different selection order. 

“RMV” indicates that we removed the lake during Tier 3. The number beside the “RMV” designation was for map labeling purposes 

(see the figure in this subsection). The percentages of ingestion and SV reflect the assessment after we removed this lake. a

These island lakes were not permanently removed from future assessments, as they technically still qualify for screening 

assessments. 

Figure 4-3 and Figure 4-4 are aerial images delineating the NEIWA19906 and NEI46970 lakes, 

respectively, in Table 4-1. The labels of the lakes in the map correspond to the data in the 

“Selection Order” column of the table. Lakes labeled in the map with negative numbers (e.g., -1, 

-2, and so on) are qualifying lakes that the fisher did not fish because the fish ingestion rate was 

already met by fishing the first set of lakes (i.e., by fishing those labeled 1, 2, and so on). The 

maps are focused on the fished and removed lakes, so they might not show all unfished lakes. 

As discussed in Section 3.4, NEIWA19906’s cadmium emissions exceeded the Tier 2 fisher 

threshold by approximately a factor of 2. Removing five lakes from this facility’s screening did 

not effectively decrease its fisher SV. NEI46970’s PAH emissions exceeded the Tier 2 fisher 

and farmer thresholds respectively by approximate factors of 60 and 100, and NEI46970’s 

dioxin emissions exceeded the Tier 2 fisher and farmer thresholds respectively by approximate 

factors of 10 and 20. Removing one lake from this facility’s screening did not effectively 

decrease its PAH and dioxin SVs. As discussed in Sections 4.3 and 4.4, we conducted a plumerise assessment on these emissions and on mercury emissions from NEI41217. 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 13 July 2014 

 Figure 4-3. Lakes Assessed for Cadmium Emissions at 

NEIWA19906 

Notes: Aerial imagery from ESRI (2014). Lake labels correspond to the “Selection 

Order” column in Table 4-1. The “lake” shown in Figure 4-1 corresponds to “RMV-1” 

here. Lake labels using negative numbers are not shown in Table 4-1—those are 

qualifying lakes that the fisher did not fish because the fished lakes altogether met the 

fish ingestion rate. Not all of the unfished lakes are shown. 

Figure 4-4. Lakes Assessed for PAH and Dioxin Emissions 

at NEI46970 

Notes: Aerial imagery from ESRI (2014). Lake labels correspond to the “Selection 

Order” column in Table 4-1. Lake labels using negative numbers are not shown in 

Table 4-1—those are qualifying lakes that the fisher did not fish because the fished 

lakes altogether met the fish ingestion rate. 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 14 July 2014 

4.3 Plume-rise Assessment 

In Tiers 1 and 2, all chemicals are emitted inside the mixing layer and are available for groundlevel exposure. In reality, the physical height of an emission source, in combination with the 

temperature and velocity of the chemical plume as it leaves the source, can cause some of the 

chemical plume to reach areas above the mixing layer. In TRIM.FaTE modeling, the chemical 

mass deposited above the mixing layer (i.e., the model’s upper-air layer) is unavailable for 

ground-level exposure (i.e., the upper-air layer functions as a chemical sink). Many emission 

sources in RTR are physically taller than the mixing height during some hours, and hot exit gas 

temperatures (i.e., buoyancy) and/or high exit gas velocities (i.e., momentum) can further 

elevate the chemical plume. 

EPA uses methods summarized by Seinfeld and Pandis (1998) to estimate how often a facility’s 

emissions reach the upper-air sink, which decreases availability for ground-level exposure. The 

methods to estimate the amount of chemical lost to the upper-air sink require use of the facility’s 

corresponding meteorology data (e.g., air temperature and vertical temperature gradient, wind 

speed, and atmospheric stability), the mass of the PB-HAP emitted from each source, the 

physical characteristics of the sources (i.e., release height, inside diameter at the release point, 

and exit gas temperature and velocity), and an estimate of the size of the facility. 

For each relevant emission source, EPA estimates the hourly effective release height (i.e., sum 

of actual release height and plume rise) and compares it to the hourly mixing height to 

determine the mass of chemical remaining in the mixing layer. EPA compares the mass of 

chemical remaining in the mixing layer, summed across the sources, to the total emitted mass 

of the chemical. This results in an adjustment factor expressing the fraction of emissions 

remaining in the mixing layer after accounting for release height and plume rise. EPA applies 

this final plume-rise adjustment factor to the Tier 2 SVs. 

4.4 Tier 3 Plume-rise Assessment Results for this Source Category 

The Tier 3 lake assessment did not effectively lower the fisher SVs for cadmium emissions from 

NEIWA19906 or for PAH and dioxin emissions from NEI46970 (see Section 4.2). We conducted 

a plume-rise assessment on these emissions. We also conducted a plume-rise assessment on 

mercury emissions from NEI41217, which exceeded the Tier 2 fisher threshold by a factor of 2 

and which had more than 70 lakes, making a Tier 3 plume rise assessment a more efficient than 

a Tier 3 lake assessment. Table 4-2 contains information on these emissions and the physical 

characteristics of each unique emission source, along with the fraction of emitted chemical from 

each source that remained in the mixing layer (i.e., is not deposited into the upper-air sink). For 

these purposes, we define a unique emission source as having a unique combination of 

physical characteristics (i.e., height, diameter, temperature, and velocity), though in some cases 

we grouped together sources with roughly similar physical characteristics. We show in the last 

column the total fraction of emissions from all sources together that remained in the mixing 

layer. We calculated this value by weighting the value in the previous column (fraction remaining 

in the mixing layer, by source) by the fraction of mercury emissions coming from each source 

(i.e., the third column), and summing those weighted values. To account for these plume-rise 

data, we scaled the Tier 2 SVs by the fractions shown in the last column. 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 15 July 2014 

Table 4-2. Results of Tier 3 Plume-rise Assessments in this Source Category 

Facil. NEI ID 

Source 

Num. 

Fraction 

of 

Emiss. 

From 

This 

Sourcea

Physical Characteristics of Emiss. 

Source 

Fraction of 

Emiss. 

Remaining in 

Mixing Layer 

Height 

(m) 

Exit 

Gas 

Temp. 

(K) 

Inside 

Diameter 

(m) 

Exit Gas 

Vel. 

(m/s) 

By 

Source 

Facility 

Total 

NEIWA19906 (Cadmium 

emissions) 

1 0.97 16.5 289 4.2 4.0 0.67 0.67

2 0.03 25.6 370 6.1 15.9 0.52 

NEI41217 (Mercury 

emissions) 

1 0.70 22.5 295 0.0009 0.000009 0.99 0.94

2 0.21 61.0 353 3.2 23.5 0.80 

3 0.09 61.3 353 1.4 26.4 0.84 

4 0.01 48.5 322 1.1 19.5 0.90 

NEI46970 (Dioxin 

emissions) 

1 0.94 14.9 303 0.0009 0.00009 1.00 0.99

2 0.06 44.5 305 7.5 11.3 0.77 

NEI46970 (PAH 

emissions) 

1 0.98 14.9 303 0.0009 0.00009 1.00 0.99

2 0.02 44.5 305 7.5 11.3 0.77 

a

We normalized PAH and dioxin emissions to BaP and 2,3,7,8-TCDD, respectively, for oral toxicity and Tier 2 modeled 

environmental fate and transport.

Table 4-3 contains the previously calculated Tier 2 SVs for the emissions screened in Tier 3 

(reflecting the assessment described in Section 3), along with the SVs after the Tier 3 lake and 

plume-rise assessments. For cadmium emissions from NEIWA19906, while the Tier 3 lake 

assessments alone did not effectively decrease the SVs, the combined effect of the lake and 

plume-rise assessments was a decrease in the fisher and farmer SVs from 2 to 1 and from 0.4 

to 0.3, respectively. The Tier 3 plume-rise assessment decreased the mercury fisher SV at 

NEI41217 from 2 to 1. The combined lake and plume-rise assessments did not effectively lower 

dioxin and PAH SVs related to NEI46970. 

Because these cadmium and mercury emission screened out in Tier 3, and because the PAH 

and dioxin SVs for the fisher were below 100, we did not conduct any other Tier 3 screening 

assessments. The farmer SV of 100 for PAH emissions from NEI46970 is of less concern 

because of the assumptions made about the farmer scenario in the screening assessments. 

The screening evaluates hypothetical farm areas at a fixed distance in all compass directions 

around the facility. EPA does not validate these modeled farm locations nor the types and 

amounts of crops grown and livestock raised. EPA assumes the farms are there and that they 

produce all the assessed foodstuffs in the amounts necessary for the evaluated subsistence 

ingestion rates. 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 16 July 2014 

Table 4-3. Tier 3 SVs Before and After Additional Lake and Plume-rise Assessments in 

this Source Category 

Facil. NEI ID 

Facil. 

Name 

Facil. 

City 

Facil. 

State 

SVsa

Before Tier 3 

Assessments 

After Tier 3 Lake 

Assessments 

After Tier 3

Lake AND 

Plume-rise 

Assessments 

Fisher Farmer Fisher Farmer Fisher Farmer

NEIWA19906 

(Cadmium 

emissions) 

Alcoa 

Primary 

Metal 

Intalco 

Works 

Ferndale WA 2 0.4 2 0.4 1 0.3

NEI41217 

(Mercury 

emissions) 

Alumax of 

South 

Carolina 

Goose 

Creek 

SC 2 0.0003 (Assessment 

not 

performed) 

(Assessment 

not 

performed) 

1 0.0003

NEI46970 

(Dioxin 

emissions) 

Reynolds 

Metals, St. 

Lawrence 

Reduction 

Plant 

Massena NY 10 20 10 20 10 20

NEI46970 

(PAH 

emissions) 

Reynolds 

Metals, St. 

Lawrence 

Reduction 

Plant 

Massena NY 60 100 60 100 60 100

a

SVs rounded to one significant figure. Cell shadings indicate SVs of 2 or higher (i.e., the emissions exceeded the threshold).

5. Comparison to Tier 1 Screening Results for this Source Category 

In Table 5-1, we present a high-level comparison between the Tier 1 SVs and Tier 3 SVs. The 

Tier 3 SVs reflect the Tier 3 screening of some emissions from three facilities; otherwise, the 

Tier 3 SVs are unchanged from the Tier 2 screening. The remainder of this section provides an 

overview of the results for each of the four PB-HAPs. 

 Mercury: 

– Emissions at nine facilities exceeded the Tier 1 threshold but screened out in Tier 3. 

– The highest Tier 3 fisher and farmer SVs were respectively approximately 10 times 

and 12,500 times lower than the highest Tier 1 SV (which combined fish- and FFCrelated exposure). 

– When the highest Tier 3 fisher SV was combined with the highest Tier 3 farmer SV (to 

directly compare to the highest Tier 1 SV), the combined Tier 3 SV was approximately 

10 times lower (not shown in the table). This is because nearly all mercury exposure 

occurs through fish ingestion. 

 Cadmium: 

– Emissions at six facilities exceeded the Tier 1 threshold but screened out in Tier 3. 

– The highest Tier 3 fisher and farmer SVs were respectively approximately 30 times 

and 100 times lower than the highest Tier 1 SV (which combined fish- and FFCrelated exposure). 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 17 July 2014 

– When the highest Tier 3 fisher SV was combined with the highest Tier 3 farmer SV (to 

directly compare to the highest Tier 1 SV), the combined Tier 3 SV was approximately 

20 times lower than the Tier 1 SV (not shown in the table). This is because nearly all 

cadmium exposure occurs through fish ingestion. 

 PAHs: 

– Emissions at all 13 facilities exceeded the Tier 1 threshold, but three screened out for 

the Tier 3 fisher and four screened out for the Tier 3 farmer. 

– The highest Tier 3 fisher and farmer SVs were respectively approximately 30 times 

and 20 times lower than the highest Tier 1 SV (which combined fish- and FFC-related 

exposure). 

– When the highest Tier 3 fisher SV was combined with the highest Tier 3 farmer SV (to 

directly compare to the highest Tier 1 SV), the combined Tier 3 SV was approximately 

10 times lower than the highest Tier 1 SV (not shown in the table). 

 Dioxins: 

– Emissions at all 13 facilities exceeded the Tier 1 threshold, but one screened out for 

the Tier 3 fisher and one screened out for the Tier 3 farmer. 

– The highest Tier 3 fisher and farmer SVs were respectively approximately five times 

and 10 times lower than the highest Tier 1 SV (which combined fish- and FFC-related 

exposure). 

– When the highest Tier 3 fisher SV was combined with the highest Tier 3 farmer SV (to 

directly compare to the highest Tier 1 SV), the combined Tier 3 SV was approximately 

three times lower than the highest Tier 1 SV (not shown in the table). 

 PAHs + Dioxins: 

– The facility-level sum of PAH and dioxin SVs was 20 or higher at all 13 facilities in 

Tier 1 (with 12 facilities at 100 or higher), 5 or higher at all 13 facilities for the Tier 3 

fisher (all lower than 100), and 5 or higher at 12 facilities for the Tier 3 farmer (one 

100 or higher). This is not shown in the table. 
Human Health Multipathway Residual Risk Screening Assessment for the 

Primary Aluminum Production Source Category 

Draft 18 July 2014 

Table 5-1. Comparison of Tier 1 and Tier 3 Screening Results for this Source 

Category 

PB-HAP 

Group 

Num. Facil. Exceeding Threshold Highest SV 

Tier 1, Combined 

Fisher and Farmer 

Tier 3, 

Fisher

Tier 3, 

Farmer

Tier 1, Combined 

Fisher and Farmer 

Tier 3, 

Fisher

Tier 3, 

Farmer

Mercurya 

(non-cancer)

9 0 0 10 1 0.0008 

Cadmium 

(non-cancer) 

6 0 0 30 1 0.3 

PAHs as BaP 

(cancer) 

13 10 9 2,000 60 100 

Dioxins as 2,3,7,8-TCDD 

(cancer) 

13 12 12 200 40 20 

Notes: N/E = not emitted. SVs rounded to one significant figure. Cell shadings indicate records corresponding to SVs of 2 or higher 

(i.e., the emissions exceeded the Tier 1 threshold). Emissions and screening thresholds not shown for space purposes. a

The emission screening threshold for mercury applies to emissions of divalent mercury, although EPA derived it based on hazards

associated with ingestion of fish contaminated with methyl mercury (i.e., emissions of divalent mercury, which transforms to methyl 

mercury within the environment, accumulates in fish tissue, and is consumed by the fisher). The contribution from hazards 

associated ingestion of divalent mercury from contaminated FFC or fish media is relatively minimal.

6. References 

ESRI (Environmental Systems Research Institute). 2014. World Imagery. Accessed July 9, 

2014. Available at: 

http://www.arcgis.com/home/item.html?id=10df2279f9684e4a9f6a7f08febac2a9. 

Seinfeld, J.H., and S.N. Pandis. 1998. Atmospheric Chemistry and Physics: From Air Pollution 

to Climate Change, Wiley-Interscience, New York, pp. 931–933.