MEMORANDUM 

DATE: July 7, 2010 

TO: Project file 

SUBJECT: Docket Entry for Draft Screening Risk Analysis for Mercury Cell 

Chlor-Alkali Plants 

 This memorandum introduces a draft screening risk analysis for the mercury cell chloralkali industry. The draft screening analysis was performed to gain a preliminary understanding 

of the potential risks from one form of mercury (divalent mercury) emitted from mercury cell 

chlor-alkali plants. The draft screening analysis did not consider risks from other forms of 

mercury and the quality of the data used in the analysis has not been determined. 

Because a risk analysis is not required in setting technology based MACT standards, EPA 

did not go forward with further risk analyses and peer review of the attached draft screening 

analysis. Moreover, because this was only a screening analysis, it did not address several 

properties of mercury that the Agency considers important in understanding risk from this 

particular pollutant. The analysis addressed only inhalation, and not ingestion as a pathway of 

exposure. Mercury accumulates both in the environment and in the body tissues of fish, animals, 

and people. Mercury crosses both the blood-brain barrier and the placental barrier, and as such 

presents an exceptionally high risk to women, nursing and pregnant mothers, and women who 

may become pregnant. The screening risk analysis did not consider that mercury has 

accumulated in the environment as a result of this industry, that a portion of elemental mercury is 

converted to the more toxic mercury compounds (such as methyl mercury), nor did it consider 

the current level of bioaccumulation within the population. More information on the health 

effects of mercury are presented in the preamble to the rule, and elsewhere in EPA’s mercury 

studies. 

In general, reducing the amount of mercury released to the air, water, and other media 

also reduces the resulting exposure, and subsequent environmental and human health effects. 

Therefore, while it is informative, the attached draft screening risk analysis is inadequate to 

represent all the risks that mercury presents from the mercury cell chlor-alkali source category. 

070810 Page 1 of 11
E Providing Environmental Technical Support Since 1989 C

/R Incorporated

501 Eastowne Drive, Suite 250 y Chapel Hill, North Carolina 27514 

Telephone: (919) 484-0222 y Fax: (919) 484-0122 

 

MEMORANDUM

DRAFT 

DATE: February 16, 2009 

SUBJECT: Screening Risk Analysis for Mercury Cell Chlor-Alkali Plants 

FROM: Phil Norwood, EC/R Incorporated 

 Darcie Smith, EC/R Incorporated 

TO: Dr. Donna Lee Jones, EPA/OAQPS/SPPD/MICG 

The purpose of this memo is to present the results of a screening risk analysis conducted 

for the five mercury cell chlor-alkali plants currently operating in the United States. These plants 

are Olin Corporation in Augusta, Georgia (Olin GA); Olin Corporation in Charleston, Tennessee 

(Olin TN); ERCO Worldwide in Port Edwards, Wisconsin (ERCO); PPG Industries in New 

Martinsville, West Virginia (PPG); and Ashta Chemicals in Ashtabula, Ohio (Ashta). The first 

section describes the data used for the analysis, followed by the results of the inhalation and 

multipathway screenings. 

Source Data 

 The required inputs for the risk analysis include emissions and release characteristics. 

Specifically, the release parameters needed for point sources are stack height, stack diameter, and 

exit velocity, along with the coordinates. For area sources, the release parameters needed are the 

release height and the x and y dimensions (i.e., the length and width of the rectangular shaped 

area source). The mercury emission sources at mercury cell chlor-alkali plants include the cell 

room, the hydrogen by-product vent stream, the end-box ventilation system, and the mercury 

thermal recovery unit vent. Every plant has a cell room, but not every plant has all three of the 

remaining sources. In addition to these mercury emission points, there are other points that emit 

chlorine, hydrochloric acid (HCl), and other HAP. 

Emissions Data 

 Air toxics emissions data were obtained from the 2006 Toxics Release Inventory (TRI) 

and the 2002 National Emissions Inventory (NEI). Specifically, mercury emissions were 

obtained from the TRI and HAP emissions and release characteristics were obtained from the 

NEI. Table 1 shows the mercury emissions in the 2006 TRI.

070810 Page 2 of 11
DRAFT – February 16, 2009 

2 

Table 1. Mercury Emissions from the 2006 TRI 

Mercury Emissions in pounds/yr (tons/yr) Plant Fugitive Point 

Ashta 0 (0) 2 (0.0010) 

ERCO 1,078 (0.54) 80 (0.040) 

Olin GA 493 (0.25) 86 (0.043) 

Olin TN 1,032 (0.52) 109 (0.054) 

PPG 172 (0.086) 134 (0.067) 

 All records at the five sites were retrieved from the 2002 NEI. These records included 

emission points characterized by Source Classification Codes (SCCs) that do not appear to be 

associated with mercury cell production processes. Appendix A contains a list of the SCCs at 

these five sites and identifies the ones that were considered to be part of the mercury cell plant. 

Table 2 summarizes the emissions determined to be from the mercury cell processes at each 

plant. Attachment B contains more detailed information from the NEI. 

Table 2. Mercury Cell Chlor-Alkali Plant HAP Emissions from the 2002 NEI 

Plant State HAP Emissions (tons/yr) 

1,3-dichloropropene 0.36 

Ashta OH chlorine 0.23 

mercury (elemental) 0.70 

chlorine 0.88 

hydrochloric acid 0.032 

lead compounds 0.000006 

mercury compounds 0.54 

ERCO WI 

carbon tetrachloride 0.45 

chlorine 0.066 

Olin GA hydrochloric acid 0.0075 

mercury (elemental) 0.37 

chlorine 0.33 

Olin TN hydrochloric acid 0.009 

mercury (elemental) 0.56 

mercury compounds 0.71 

methylene chloride 2.2 

chlorine 0.37 

chlorine 0.0075 

PPG WV 

hydrochloric acid 0.026 

 Since mercury is the primary HAP of interest, additional analysis of the mercury 

emissions was conducted. Table 3 compares the mercury emissions from the 2002 NEI and the 

2006 TRI. 

070810 Page 3 of 11
DRAFT – February 16, 2009 

3 

Table 3. Comparison of Mercury Emissions 

Mercury Emissions (tons/yr) 

Plant Fugitive Stack 

2002 NEI 2006 TRI 2002 NEI 2006 TRI 

Ashta 0.52 0 0.18 0.0010 

ERCO 0.53 0.54 0.014 0.040 

Olin GA 0.29 0.25 0.077 0.043 

Olin TN 0.52 0.52 0.043 0.054 

PPG 0.66 0.086 0.053 0.067 

 With one exception, fugitive mercury cell emissions had not been measured during the 

time periods for which these data were reported. The fugitive mercury emissions for Ashta 

(NEI), ERCO, and Olin TN appear to based on the historical assumption that the mercury 

emission rate for cell rooms at mercury cell chlor-alkali plants is 1,300 grams per day: 

(1300 g/day) x (1 lb/454 grams) x (1 ton/2000 pounds) x (365 days/yr) = 0.52 tons/year 

It appears that the fugitive estimate for Olin GA is based on the testing program (the one 

exception) conducted at that facility in 2000,1 which reported an average emission rate slightly 

below 500 grams/day. The basis for the PPG estimates is not clear, and the zero emissions rate 

from Ashta in the TRI is not realistic. 

 As part of their reconsideration efforts, EPA collected eight separate fugitive mercury 

emission data sets from three different mercury cell chlor-alkali plants in 2005 and 2006 to 

produce an estimate of fugitive mercury emissions from cell rooms. The time periods of data 

collection range from 6 weeks to over 30 weeks, all of which provided an opportunity to include 

a complete range of maintenance activities and operating conditions. Two of the data sets were 

generated via EPA-sponsored test programs and the others were collected from cell room 

mercury monitoring systems that were validated by EPA. The daily mercury emission rates 

extrapolated from these data sets ranged from around 20 to 1,300 g/day per facility. The average 

daily emission rates ranged from around 420 g/day to just under 500 g/day per facility, with the 

mean of these average values being slightly less than 450 g/day per facility. (73 FR 33266, 

June 11, 2008). 

 We believe that the results of this EPA program, which are consistent with the earlier 

EPA study at Olin GA, provide the best estimate of fugitive mercury emissions at a mercury cell 

plant. Therefore, for the purposes of this risk analysis, an annual mercury emission rate of 

0.2 tons/yr (500 grams/day) was used for all plants. 

 The stack mercury emissions from the 2006 TRI were used as reported, with the 

exception of Ashta, whose mercury emissions were more than an order of magnitude lower than 

all the other plants. Therefore, for Ashta, the average value of all the other plants, 0.051 tons/yr, 

 

1

 Kinsey, J., Characterization of Mercury Emissions at a Chlor-Alkali Plant. NRMRL-RTP-236a. U.S. 

Environmental Protection Agency, Research Triangle Park, NC. January 2002. 

070810 Page 4 of 11
DRAFT – February 16, 2009 

4 

was assumed for their stack mercury emission rate. For all the other (i.e., non mercury) HAP, 

the values in the 2002 NEI were used in the analysis. 

Release Characteristics 

 As can be seen in Attachment 2, the stack parameters for all points appear to be default 

values. For the point sources, those parameters were used. Even though there are likely multiple 

stacks at a mercury cell plant, all stack emissions were modeled from a single point source. 

 For the fugitive emission sources, these parameters are actually point source parameters 

intended to simulate a fugitive type sources. We do not believe that the parameters in the NEI are 

adequate to represent the release characteristics of a cell room. Cell rooms, the source of the 

fugitive mercury emissions, are large buildings typically vented through long rectangular ridge 

vents. While there is a flow from the vent, these ridge vents are covered by a cupula or other 

structure that does not allow the exiting air to exit vertically from the building. Therefore, the 

cell room was modeled as a long, elevated rectangular area source. 

 However, specific data were not readily available on every cell room. Therefore, a model 

cell room ventilator was used for all plants using the available data. The peak of the cell room at 

the Olin GA facility is 16 meters from ground level,2

 and this was used as the height of the 

fugitive source for every facility. The width of the roof ventilator at Olin GA, 34 feet,3

 was used 

as the width of the area source. The length of the ventilator at Olin GA was 62 meters. To 

determine the length of the cell room ventilators at the other facilities, we used GoogleEarth, 

identified the cell room, and measured the length of the building. Where the resolution was 

adequate and the ventilator could be identified, the length of the ventilator was measured. 

GoogleEarth was also used to identify the coordinates to use for the modeling. Table 4 provides 

the length and coordinates used for the analysis. While mercury point sources are typically 

adjacent to the cell room, the exact location was not known. Therefore, the point source was 

placed at the center of the cell room. 

Table 4. Ventilator Lengths and Emission Point Coordinates* 

Plant 

Length of 

Ventilator 

(meters) 

Coordinate of Southwest 

Corner of Ventilator 

(darcie – add units) 

Coordinate for Point 

Source 

(darcie – add units) 

Ashta 108 41.89309, -80.74831 41.89355, -80.748506 

ERCO 85 44.33708, -89.860151 44.33721, -89.859592 

Olin GA 62 33.345079, -81.950657 33.345144, -81.950434 

57 35.06031, -84.780723 Olin TN 65 35..06278, -84.780307 35.306448, -84.780442 

PPG 77 39.750019, -80.852332 39.750312, -80.852327 

* All ventilators were assumed to be at a height of 16 meters and have a width of 10.4 meters 

(34 feet). 

 

2 Kinsey, p. 15. 

3 Kinsey, p. 26. 

070810 Page 5 of 11
DRAFT – February 16, 2009 

5 

 At the PPG facility there were two other fugitive emission sources that did not emit 

mercury. These sources were modeled as point sources using the release characteristics in the 

NEI. 

Screening Risk Estimates 

Inhalation Risks 

 In order to estimate the inhalation risks from these mercury cell plants, the HEM3 model 

was used.4 Table 5 summarizes the results. As can be seen from the table, there is no plant with 

an estimated cancer risk approaching 1 in 1 million and no chronic hazard index (HI) 

approaching 1. Every plant has an acute HQ greater than 1 at the no effects (REL) level for 

mercury, but there was no HQ approaching 1 for any mild effects dose response value (AEGL1, 

ERGP, IDLH/10). More detail on these results is provided in Attachment C. 

Table 5. Screening Inhalation Risk Results

Max Chronic HI Max Acute HQ Plant Max Cancer Risk 

(in 1 million) Respiratory Neurological Mild Effects No Effects 

Ashta 0.04 0.03 0.02 0.01 10 

ERCO 0.4 0.3 0.04 0.07 10 

Olin GA * 0.002 0.009 0.0005 10 

Olin TN * 0.01 0.007 0.003 10 

PPG 0.01 0.03 0.03 0.4 30 

* No HAP with a URE was reported to be emitted from this facility. 

Multipathway Risks 

 The most significant mutipathway risks from mercury are due to divalent mercury. 

Divalent mercury emitted from a source may be deposited relatively quickly by wet and dry 

deposition processes, leading to a residence time of hours to months. In contrast, elemental 

mercury has an average residence time in the atmosphere of about one year and will be 

distributed fairly evenly in the troposphere. While the transformation of elemental mercury to 

divalent mercury can result in mercury deposition to land and water, this deposition can occur far 

from the source due to the slow rate of elemental uptake in cloud water. It has been suggested 

that this mechanism is important in a global sense for mercury pollution, while direct wet 

deposition of divalent mercury is the most important locally.5 Therefore, the multipathway risks 

in the area surrounding a mercury cell chlor-alkali plant would result from emissions of divalent 

mercury. In the 1997 Report to Congress, EPA assumed that 30 percent of mercury emissions 

from mercury cell plants was divalent.6

 However, a study conducted at the Olin GA plant 

 

4 http://www.epa.gov/ttn/fera/human_hem.html 5 U.S. Environmental Protection Agency. Mercury Study Report to Congress. Vol. 3. EPA-452/R-97-003. Office 

of Air Quality Planning and Standards. Office of Research and Development. 1997. 

6 Report to Congress, Vol. 3. 

070810 Page 6 of 11
DRAFT – February 16, 2009 

6 

accompanying the Kinsey study found that mercury cell room emissions only consisted of 

around 2 percent inorganic reactive gaseous mercury.7 

 As part of the Risk and Technology (RTR) program, EPA developed PB-HAP de minimis

thresholds in order to provide a screening-level check to see if the potential exists for 

multipathway risks.8

 To evaluate the potential for human health risks, reported emissions of PBHAPs are compared to de minimis emission thresholds established for the purposes of RTR 

multipathway risk assessment. Facilities whose emissions of a PB-HAP are below the de 

minimis threshold are not expected to pose significant human health risks. In other words, if PBHAP emissions at a facility do not exceed the de minimis level for that PB-HAP, EPA can be 

reasonably certain that the resulting exposures and associated risks are negligible. Facilities 

emitting PB-HAPs in amounts exceeding the de minimis level should be the focus of more 

refined multipathway exposure and risk analyses for RTR. The de minimis threshold for 

divalent mercury is 0.183 tons/year. Table 7 provides the potential divalent mercury estimates 

from each plant using both the 30 and 2 percent assumptions. 

Table 7. Estimation of Divalent Mercury Emissions 

Divalent Mercury Emissions (tons/yr) Plant Mercury Emissions 

(tons/yr) Assuming 30% Assuming 2% 

Ashta 0.25 7.6E-02 5.0E-03 

ERCO 0.24 7.3E-02 4.9E-03 

Olin GA 0.26 7.7E-02 5.1E-03 

Olin TN 0.27 8.0E-02 5.4E-03 

PPG 0.24 7.2E-02 4.8E-03 

 As can be seen from Table 7, the highest divalent mercury emission rate (0.08 tons/yr for 

Olin TN assuming 30 percent divalent mercury) is less than half the de minimis level. This 

suggests there is no need to conduct further multipathway analysis for this source category. 

However, in addition to the conclusion cited above regarding the emissions of reactive gaseous 

mercury, the Landis study also concluded that mercury cell chlor-alkali plants “were still found 

to present a significant impact on near field atmospheric mercury dry deposition. The mean 

estimated dry deposition of mercury within a 10km radius of the facility contributed the 

annual equivalent of 4.6 μgm

-2 (almost half of the total wet mercury deposition measured at a 

nearby MDN sampling site).” 

 

7 Landis, M., Keeler, G, Al-Wali, K., and Stevens, R. Divalent inorganic reactive gaseous mercury emissions from 

a mercury cell chlor-alkali plant and its impact on near-field atmospheric dry deposition. Atmospheric 

Environment 38 (2004). 613-622. 

8

 Memorandum. Burch, D., Cleland, J., Holder, C., Shapiro, A., and Turley, A. ICF International to Hollingsworth, 

T., Palma, T., Guinnup, D., EPA/OAQPS. Revised RTR PB-HAP De Minimis Levels and Updated Group 3 

Screening Results. January 30, 2009. 

070810 Page 7 of 11
DR

A-1 

APPENDIX A: SCCS AT MERCURY CHLOR-ALKALI PLANT SITES SCCs Attributed to the Mercury Cell Plant 30100802 Industrial Processes Chemical Manufacturing Chloro-alkali Production Liquefaction (Me30100805 Industrial Processes Chemical Manufacturing Chloro-alkali Production Air Blowing of M30100899 Industrial Processes Chemical Manufacturing Chloro-alkali Production Other Not Classif30107002 Industrial Processes Chemical Manufacturing Inorganic Chemical Manufacturing (General) Storage/Transfer 30187002 Industrial Processes Chemical Manufacturing Inorganic Chemical Storage (Fixed Roof Tanks) Hydrochloric AciOther SCCs at the Plant Sites Not Attributed to the Mercury Cell Plant 10200202 External Combustion Boilers Industrial Bituminous/Subbituminous Coal Pulverized Coal: 10200601 External Combustion Boilers Industrial Natural Gas > 100 Million Btu10200602 External Combustion Boilers Industrial Natural Gas 10-100 Million B10200603 External Combustion Boilers Industrial Natural Gas < 10 Million Btu/10201401 External Combustion Boilers Industrial CO Boiler Natural Gas 10200202 External Combustion Boilers Industrial Bituminous/Subbituminous Coal Pulverized Coal: 30130101 Industrial Processes Chemical Manufacturing Chlorobenzene Tail Gas Scrubbe30130107 Industrial Processes Chemical Manufacturing Chlorobenzene DCB Crystallizat30130180 Industrial Processes Chemical Manufacturing Chlorobenzene Fugitive Emission30130101 Industrial Processes Chemical Manufacturing Chlorobenzene Tail Gas Scrubbe30190004 Industrial Processes Chemical Manufacturing Fuel Fired Equipment Process Gas: Proc30190099 Industrial Processes Chemical Manufacturing Fuel Fired Equipment Specify in Comm40703602 Petroleum and Solvent Evaporation Organic Chemical Storage Fixed Roof Tanks - Aromatics Benzene: Workin40706008 Petroleum and Solvent Evaporation Organic Chemical Storage Fixed Roof Tanks - Halogenated Organics Chlorobenzene: W40706010 Petroleum and Solvent Evaporation Organic Chemical Storage Fixed Roof Tanks - Halogenated Organics o-Dichlorobenzen40706012 Petroleum and Solvent Evaporation Organic Chemical Storage Fixed Roof Tanks - Halogenated Organics p-Dichlorobenzen40899995 Petroleum and Solvent Evaporation Organic Chemical Transportation Specific Liquid Cars/Trucks: Loa40706012 Petroleum and Solvent Evaporation Organic Chemical Storage Fixed Roof Tanks - Halogenated Organics p-Dichlorobenzen40899995 Petroleum and Solvent Evaporation Organic Chemical Transportation Specific Liquid Cars/Trucks: Loa070810 
DR

C-1 

ATTACHMENT B. SUMMARY OF MERCURY CELL CHLOR-ALKALI PLANT NEI DATA 

NTI ID Name State SCC EmrelType* 

Stack 

Height 

(ft) 

Stack 

Diameter 

(ft) 

Stack 

Temperature 

(F) 

Stack 

Velocity 

(ft/sec) 

Stack 

Flow 

Rate 

(ft3/min) 

01 10 0.003 72 0.0003 0 

NEI10894 OLIN CORP TN 30100802 

02 58.19 3.516 234 31.8582 9.28171 01 10 0.003 72 0.0003 0 

30100805 

02 35 1 75 4.4 3.41667 

30100899 01 10 0.003 72 0.0003 0 30107002 02 91 4 120 55 83.33331 

NEI42444 

PPG INDUSTRIES INC 

WV 

30187002 01 10 0.003 72 0.0003 0 

01 10 0.003 72 0.0003 0 

30100802 

02 58.19 3.516 234 31.8582 9.28171 

NEI42973 

VULCAN MATERIALS CO PORT EDWARDS PLANT 

WI 

30100899 02 49 1 85 7.4272 5.83333 

01 10 0.003 72 0.0003 0 

NEIGAT$3892 OLIN CORP GA 30100802 

02 58.19 3.516 234 31.8582 9.28171 01 10 0.003 72 0.0003 0 

NEIOHT$5933 

ASHTA CHEMICALS INC 

OH 30100802 

02 58.19 3.516 234 31.8582 9.28171 

* EmrelType 01 = fugitive source, EmrelType02 = vertical stack source070810 
DR

C-1 

ATTACHMENT C. SUMMARY OF SCREENING-LEVEL RISK ESTIMATES Table C-1. Summary of Chronic Risks 

 ASHTA ERCO OLIN TN OLIN Cancer risk Max Cancer Risk (in 1 million) 0.04 0.4 0. 0  driver source cell room point source n/a n/a  driver HAP 1,3-dichloropropene carbon tetrachloride n/a n/a Noncancer Hazard Indices Max Respiratory HI 0.03 0.3 0.01 0.00 driver source cell room cell room point source point so driver HAP chlorine chlorine chlorine chloriMax Neurological HI 0.02 0.04 0.007 0.00 driver source cell room cell room cell room cell ro driver HAP mercury mercury mercury mercu

070810 
DR

C-2 

Table C-2. Summary of Acute Risks 

Acute Hazard Quotient (HQ) 

No Effects Level Mild Effects Level Serious Effects 

Plant/HAP rel aegl_1_1h aegl_1_8h erpg_1 aegl_2_1h aegl_2_8h ASHTA 1,3-dichloropropene Chlorine 0.07 0.01 0.01 0.01 0.00 0.01 mercury (elemental) 8 0.01 0.04 ERCO carbon tetrachloride 0.02 0.0001 0.0003 0.0001 0.00003 0.0001 chlorine 0.5 0.07 0.07 0.07 0.02 0.05 hydrochloric acid 0.0004 0.0003 0.0003 0.0003 0.0000 0.0001 lead compounds mercury (elemental) 13 0.01 0.07 OLIN GA Chlorine 0.003 0.0005 0.0005 0.0005 0.0001 0.0003 Hydrochloric acid 0.0003 0.0003 0.0003 0.0003 0.0000 0.0000 mercury (elemental) 11 0.01 0.06 OLIN TN Chlorine 0.02 0.003 0.003 0.003 0.0009 0.002 Hydrochloric acid 0.00003 0.00003 0.00003 0.00003 0.000002 0.000005 mercury (elemental) 12 0.01 0.07 PPG Chlorine 2 0.3 0.3 0.3 0.09 0.2 Hydrochloric acid 0.02 0.01 0.01 0.01 0.001 0.002 Mercury (elemental) 33 0.03 0.2 Methylene chloride 0.01 0.0003 0.0003 0.0001 0.001 

070810