-------
MIDLOTHIAN, TEXAS CUMULATIVE RISKj^SSESSHENT
Methodology and Result!
In summary, the assessment conducted on the Chaparral Steel focused on inorganic
constituents emitted from and associated wift the two EAF's. Tables 2.2.1 and 2.2,2 identify the
estimated emission rates that were applied to AFA and AFB, respectively. With the exception of
lead and zinc, emission estimates were developed baaed on the total participates emitted from AFA
and AFB and the concentration profile reported in the ICR. Emissions of lead and zinc were
developed by using stoichiometry to back-calculate metal emissions from the amount of metal
oxides reported and then compared to the estimated representative amount of total participates
reported.* Once developed, the emissions profile was multiplied by the estimated emission rates
presented in Tables 2.2.1 and 2.2.2. The emission rates presented in these tables were used as
inputs to the risk analyses. The rates were adjusted to reflect only PM,0 emissions in evaluating
direct inhalation risks. These adjustments were made by multiplying the emission rates by the
ratios of PM,0 to total particulates.
Even though the emission rates for all the constituents excluding zinc and lead were
developed based on analytical data reported for the steel industry as a whole, it is believed that,
with the exception of antimony, a reasonable level of uncertainty is associated with the emission
rates. Region 6 compared the contaminant concentrations in baghouse dust reported in the ICR
against those provided by CSC with a recent letter of December 20, 1995. With the exception of
antimony, the two sets of concentrations are reasonably similar. For example, the emissions profile
assumes that EAF dust contains 0.33% chrome. Actual data from CSC indicates that CSC EAF dust
contains 0.20 to 0.27% chrome. The emissions profile assumes that EAF dust contains 0.0033%
arsenic. Actual data from CSC indicates that CSC EAF dust contains 0.0040 to 0.0054% arsenic.
The emissions profile assumes cadmium to comprise 0.054% of EAF dust. CSC reports cadmium
concentrations ranging from 0.05% to 0.09% in its EAF baghouse dust. The CSC data did not
provide any information concerning actual concentrations of antimony, a relatively significant
fraction of contaminants in the ICR profile, in its December 1995 letter. Another significant
source of uncertainty is Ihe assumption that contaminant concentrations in fugitive emission from
the meltshop are similar to a concentration profile of baghouse dust. A more detailed discussion
of uncertainty is provided in Section 4.
* It should be noted that the fraction of lead developed using reported data are very similar to those estimated using
the emissions profile developed based on the KQ61 data. Specialty, the average fraction of fead back-calculated based on
reported emissions was I while the profile fraction (i.e., based on EAF ICR report data) was 2.4 for lead.
-------
MIDLOTHIAN. TEXAS CUMULATIVE RtSKASSESSMBSTT
Methodology &d Rente
Table 2.2.1 Arc Furnace A Emissions
•TBbtfPatkJatgt
Chw»t»m VI
ArcFumac*
"A"
EmKsion Point
7.2B-04
1.1&01
1.2B-02
7.2E-02
1.4E-03
L9E-01
4.1B45
3.1R02
2.4B+00
Arc Furnace
"A"
EniaMM Point:
MdtSbop
3.2E+01
L1B-03
1.7B-01
1.7E-02
1.11-01
2.2&03
3.2E4J1
6.11-05
4JE-02
3.6E+00
Estimated representative emission rates for lead and zinc were estimated based on reported metal oxide
emission rates, in the absence of such data, consttuent-specHic emission rates were estimated based on
actud amount of t0U particulates reported in Mn Emissions Inventory and the developed emission profile.
Thx*^ioutthisrepcrt,1r«terminotogx)£yBusedtodenotextirnes 10 raised to the power of 'in order
to make it easier to report a complex series of numbers. For example, 2,2i+01 stands for 2.2 x 10' or 22,
The o*»tal letter E tete the reader that the numerical value reported is the valye of the number preceding
tt»EmuNipied by the number 10 raised to the power succeeding the E. It is also important to remember
that numbers vvith positive * values are greater than numbers with negative "values. In the earlier example
22E+01 sands far the number 22. However, if the number had been reported as 2.2E4) I, then the true
value of the number would be 0.22,
-------
MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
Methodology and Results
Table 2.2.2 Arc Furnace B Emissions
Arc Furnace "B"
>B»
Arc Furnace "B"
Emission Point:
Me* Shop
Fugitives
Tout Puticalates
5.3B+01
3.2E+01
1.8E-03
1.1E-03
Anttaoay
1.7R01
2.9B-02
1.7B-02
1.8E-01
1.1&01
2.2E-03
4.6&4H
3.2B-01
1.0&04
6.1&OS
7.4E-02
4.5E-02
S.8E+00
3.6E+00
Estimated Representative emission rates far lead and zinc were estimated based on reported metal oxide
emission rates. In the absence of such data, constituent-specific emission rates were estimated based on
estimated representative amount of total particuiates reported and the developed emission profile.
-------
MIDLOTHIAN, TEXAS CUMULATIVE RISKASSESSMPJT
Methodology xrf Results
North Terns Cement Company (NTHC)
NTCC poduces approximately 900,000 tons per year of Portland cement through the use
of a wet production process that employs three kUns that may be fired with coal, natural gas,
petroleum coke, wood chips, oil, and tire derived fuel. Kiln exhaust gases pass through a four
stage electrostatic precipitator before being discharged to the atmosphere. Data used to estimate
emissions from NTCC were collected during a trial bum and compliance test Ihat were conducted
when NTCC also burned hazardous waste derived fuel while operating as an interim status facility,
NTCC has since abandoned its plans to burn hazardous waste derived fuel. The primary data
sources that were used in identifying emission sources, constituents of concern, and emission rates
included the following:
• Appendix I1LA to NFCC's Port B Permit Application entitled ^General Engineering
Report for North Texas Cement Company (1992):" provides an overview of the
facility's operations and identifies existing operating units.
* Certificate of Compliance Form 1 (CC-1) (August 1992): presents metal emission
rates for the kilns operating at maximum feed rate and flue gas flow obtained
during the BIF Trial Bum (June 1992).
• TACB MM &nissions Inventory Report from the Point Source Data Base (May 2,
1995): identifies emission point sources located at the facility. However, it does
not provide constituent-specific emission rates.
• Section II of a draft risk assessment protocol prepared by NTCC: presents
emission rates that NTCC believes are appropriate for use in conducting a
screening level risk assessment. The primary data source used in developing these
rates include the Texas Reg. I Test Condition H results, June 1992 BIF Trial Burn
(June 1992), and Material Safety Data Sheets (MSDSs) from Gibraltar Chemical
Resources.
» Texas Reg I Test Condition I (i.e., 36% WDF) and n (i.e., 60% WDF) results for
dioxins and furans.
• Texas Natural Resource Conservation Commission (TNRCQ memorandum (March
20, 1995): presented draft emission estimates proposed for use in conducting a
screening level risk assessment for the facility. Data from OAQ permit, Reg I
Texas Conditions I and n, and BIF Trial Burn/Certificate of Compliance are
10
-------
MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSBSMEhfT
compiled for all constituents identified in the April, 1994 version of the Screening
Guidance.
The constituents that were included in the assessment were identified based on the
preliminary list of constituents provided by the facility (i.e., an analyte list developed from the
Reg I and BIF trial burns during which coal and hazardous waste were being burned) and the
Screening Guidance. The constituents identified for inclusion in the indirect assessment include
those specified in the Screening Guidance. In addition to those constituents, zinc and nickel which
were identified as being constituents of concern for Chaparral Steel were included for NTCC.
Table 2.2.3 identifies the estimated representative rates that were applied in conducting
the screening level assessment for NTCC. These emission rates are totals for all three stacks. In
selecting estimated representative emission rates, attempts were made to identify emission rates
that would be representative of typical operating conditions and yet be conservative enough to
allow for operational upsets and account for the quality of the data. Therefore, all of the data
sources were reviewed and the data supplied by the facility was selected to be most representative
of these conditions. As discussed above, the primary data sources used by the facility in
developing these rates included the Texas Reg. I Test Condition D (60% WDF) results, June 1992
BEF Trial Bum (June 1992), and Material Safety Data Sheets (MSDSs) from Gibraltar Chemical
Resources. In the absence of data from these sources or a no detect (ND), the facility assumed
that the constituent emission rate was equal to % a "Typical Detection Limit."7 These emission
rates were replaced with rates estimated based on one half the method detection limit (MDL) when
these values were available and the data of sufficient quality. To ensure that the recommended
estimated rates were reasonable, these values were compared across other identified data sources.
Due to the lack of data on semi-volatile and volatile compounds, this comparison could only be
conducted for the metals and dioxin/furans.
1 Because test data were not available for PCB's, dinitrobenzene, and pentachloronrtrobenzene, these compounds were
assumed to have emission rates similar to Ihe other organic species not detected {i.e., S.4E-5).
11
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MIDLOTHIAN, TEXAS CUMULATIVE RJSK ASSESSMENT
Methodology and Rente
Table 2.2.3 NfTCC and TXI Estimated Emission Rates
I.6MHO
Anoofc
1.07B-S
Z.S5E-S
I.77B4
4.Z78-4
Mere*?
3*-"
I.26B-5
1.23&4
1.43B-4
ActtooiUik
Acrykwilnfc
5.4JE-5
IJ9B-2
1.I5B-6
4.WE-S
12
-------
MIDLOTHIAN. TEXAS CUMULATIVE REASSESSMENT
Methodology andHesulls
T58F-6
J.IDB-*
J.1WJ
1.2A&4
10HB-*
l:.T:ITiftilTiriintiplr
1,2*1
I.02E-6
13
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MIDLOTHIAN. TEXAS CUMULATIVE REASSESSMENT
Methodology and KeajUs
*•*•)
2.SJ&4
S.28E-6
S.4IB-5
I.ME4
I 56E-6
N.N«n»od^*
nu.iit.ni>.. JM
VlXIF^A
8-»B-6
Trfumc
7.MM
14
-------
MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
Methodology and Results
7-MB4
7.58B-IS
l.OI B-J
1.1064
Industries TXT
TXI produces approximately 1,200,000 tons per year of Portland cement through the use
of a wet production process that employs four kilns that may be fired with coal, natural gas,
petroleum coke, wood chips, fuel oil, and hazardous waste derived fuel. Kiln exhaust gases pass
through electrostatic precipitators before being discharged to the atmosphere. The primary data
sources that were used in identifying emission sources, constituents of concern, and emission rates
for TXI included the following:
* Texas Industries, Inc. Pan B Permit Application: presents results from test burns
conducted in August 1990 and April 1991.
* Texas Natural Resource Conservation Commission (TNRCC) memorandum (April
12, 1995): presents draft emission estimates for all constituents identified in the
April, 1994 version of the Screening Guidance. These emission rates were used
in conducting a screening level risk assessment for the facility.
» Pages I through 1-17 of the Texas Industries, Inc. Trial Bum Report (1992):
presents metal emission data obtained during the 1991 trial bum,
The constituent list that was used in the assessment is the same as the list specified for the
North Texas Cement Company. It was determined mat applying this 1st to TXI is appropriate due
to the similarities between the facilities' production processes and the fuel(e.g., coal, petroleum
coke, and waste derived fuel) that are utilized to meet the energy requirements of the Wins. As
15
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MIDLOTHIAN, TEXAS CUMULATIVE RISK ASSESSMBSfT
Methodology andReaJts
discussed above, the constituents on the list that were included in the indirect assessment included
those specified in the Screening Guidance. In addition to those constituents, zinc and nickel which
were identified as being constituents of concern for CSC, were included. In conducting the direct
assessment, all of the constituents evaluated under the indirect assessment as well as additional
volatile and semi-volatile constituents identified on the list were included.
Table 2.2.3 identifies the estimated emission rates that were used in conducting the
screening level assessment for TXI. These emission rates are totals for all four stacks. In
selecting estimated emission rates, attempts were made to identify rates that were representative
of typical operating conditions yet still be conservative enough to account for operational upsets
and the quality of the data. Since almost no facility specific data were available to estimate the
emission rates of many volatile and semi-volatile compounds from TXI, organic emission rates
were estimated by applying an adjustment factor to the lower limits of quantitation measured
during the trial bum for the North Teias Cement Company while burning coal and hazardous
waste. As seen in Table 2.2.4, the adjustment factor of approximately 1.15 was calculated as a
ratio of the TXI cumulative flow rates to the NTCC cumulative stack flow rates. The PCB
emission rate was extracted from the TNRCC memorandum cited in the source summary cited
above. This memo states the PCB emission rate was estimated based on a 99.999% ORE and the
maximum theoretical feed to the kilns.
Table 2.2.4 Ratio of Cumulative Stack Flow Rates
¥»aaty '
:•'•'' •:
;i?m
•:|W2<3
Number of
Stacks
4
3
Stack Average
VohwutricFlow :
R*teOKCfM> :
<':&##, • - .
a«2tmJbum) .',
'Wjm: ' :':
(K»z 1 teetf ) . •....- ,. <
Cumulative
VohuwtricRow
IUte(DSCTM> ,
239,600
209,100
Ratio
1.1 :
16
-------
MIDLOTHIAN. TEXAS CUHULATTVE RISK ASSESSMBNfT
Methodology and Reads
Holnam Texas L.P.
Holnam produces approximately 1,000,000 tons per year of Portland cement
through the use of a dry production process that employs a preheater/precalciner and one Mln that
may be fired with coal, natural gas, and tire derived fuel. Kiln exhaust gases pass through a fabric
filter baghouse before being discharged to the atmosphere. The primary data sources that were
used in identifying emission sources, constituents of concern, and emission rates included the
fallowing:
« Baxcrtnv Cement Company Application to Amend Texas Air Control Board Permit
8996 (1992)*: provides an overview of the facilities operations and presents
emission requested maximum allowable emission rates and emission rates obtained
from stack testing.
« Letter from Holnam Texas L.P. addressed to Mr. David Weeks EPA Region VI
(May 19, 1995): presents the emission rates that the facility believe are
appropriate for use in the screening level assessment.
The constituents that were included in the assessment were identified based on the list of
constituents provided by the facility and the Screening Guidance. The constituents identified for
inclusion in the indirect assessment include those specified in the Screening Guidance. In addition
to those constituents, zuic and nickel which were identified as being constituents of concern for
CSC, were included as emissions of concern for Holnam. All the constituents evaluated under
me indirect assessment were evaluted in the direct assessment as well as some additional volatile
and semi-volatile constituents for which information were available in the Boxcrow Permit
Amendment Application.
Table 2.2.5 identifies the estimated emission rates that were used in conducting the
screening level assessment. The primary data source used in developing these emission rates was
the Holnam Texas L.P. letter to Mr. David Weeks. The data presented in this letter were based
on data obtained during 1991 stack testing. This data was judged to be most appropriate because
it was collected while the facility was burning tire derived fuels and because detection limits were
stated when the results were below the detection limit.
* Holnam Texas L.P. bought the facility fronn Boxerow Cement Company.
17
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MIDLOTHIAN, TEXAS CUMULATIVE REASSESSMENT
Mcthodotew and Rente
Table 2.2.5 Holnam Texas L.F. Emission Rates
•**•*::..
2.0t>E-6
1.11B-5
Sitva
2.S4S-4
4.1 IF, I
I.40B-S
1.KUB4
1.10B4
1-10B-*
1.10E-4
MethyiawCkolonde
6.WE-J
18
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MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
NA - N.t Av^Ubfc. DM. vm «x .vukfcle k) e
• of th« coattnxioaot
For those compounds not detected during the testing, the letter recommends applying an
emission rale equal to one half the instrument detection limit (H>L). The IDL is defined in EPA
guidance as the lowest amount of a chemical that can be "seen" above the normal, random noise
of an analytical instrument. Region 6 modified this approach by revising the DDLs to approximate
method detection limits (MDL). The modification was accomplished by multiplying the stated
1A IDL by a fector of 10. MDLs are preferred over IDLs because MDLs account for error in the
sample preparation and recovery while IDLs only account for error in the instrument. Use of %
the MDL is more conservative than using V4 the IDL to estimate contaminant emissons.
To ensure that the emission rates presented in the letter were reasonable emission rates and
to identify any additional appropriate emission rates, these values were compared to the test data.
Based on this comparison, several changes were made to the emission rates proposed by Holnam.
1. Emission rates of mercury were proposed in Holnam's letter were increased to match those
reported in the test data. The mercury emission rate in the letter was reported as being
greater than the instruments detection limit at 2E-5 grams/second. However, the
"Summary of Results" from Homam's October 1991 Source Emissions Survey reports
mercury emisson rates at 3 JE-4 grams/second for Condition I (not using tire derived fuel)
and 2.5E-4 for Condition IV (using tire derived fuel). Thus, actual tests data estimate
emissions at an order of magnitude greater than suggested in Holnam's letter.
2. Emission rates for several of the metals that were not included in Holnam's letter were
estimated from other data sources. The letter did not report emission rates for the
chromium, nickel, thallium, and zinc. Therefore, stack emission data were extracted from
-------
MIDLOTHIAN. TEXAS CUMULATIVE REASSESSMENT
Methodology and Resite
the permit amendment application to serve as estimated representative emission rates for
these compounds.
Finally, the letter reports that PCB's were not analyzed for in the 1991 test. Therefore,
an emission rate equal to one half the IDL (i.e., 1. IE-OS g/sec) was assumed for PCBs. One-half
the IDL was assumed for PCBs rather than 1A the MDL because PCBs are not expected to be
present in the fuel in any quantity other than at trace levels.
2.3 Characteristics of Study Area
The area subject to this study is located approximately 30 miles south of the Dallas-Ft.
Worth metropolitan area. From TXI (see Map 1, p. 35), the study area extends 8 miles north to
Joe Pool Lake, 3 miles south, 3 miles east, and 6 miles west. The area is characterized by small
hills and valleys with elevations generally ranging from approximately 800 feet mean sea level
south of TXI to 500 feet mean sea level at Joe Pool Lake. Predominant wind direction is from
the south.
CSC and TXI are the two southern most facilities. CSC is located 0.7 miles southwest of
TXI. NTCC and Holnam are located approximately 4 and 5 miles northeast of TXI, respectively.
With the exception of the city of Midlothian (approximate population of 5100) which is
located approximately 3 miles northeast of TXI, the land use of the study area is predominately
agricultural with some industrial development. The area is home to several small cattle operations
and rural residential developments. Gardens were sighted at many homes in the area during
several site visits.
In addition to Joe Pool Lake (surface area approximately 7600 acres), the area also
contains two privately owned lakes known as Soil Conservation Service (SCS) Lakes 9 and 10
(combined surface area of approximately 84 acres). SCS Lakes 9 & 10 are located approximately
2 to 3 miles northwest and north, respectively, of the CSC/TXI complex very near residential
developments.
2.4 Scenarios and Pattiways
The four human scenarios that were considered in this screening level risk assessment are
the subsistence farmer, the adult and child resident, and the subsistence fisher. The individuals
included in each of these scenarios were assumed to be exposed to contaminates from the emission
20
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MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
~ ~~ Methodology and Resdto
sources via ingestion of above-ground vegetables, incidental ingestion of soil, consumption of
drinking water and direct inhalation of particles and vapors. These exposure scenarios differed
primarily in their consumption of certain foods. Specifically, only the subsistence farmer was
assumed to consume emtanrinated beef and milk, while only the subsistence fisher was assumed
to consume contaminated fish. Because the drinking water supplied to the area surrounding the
facilities comes from Joe Pool Lake, exposure via contaminated drinking water was considered
under all of the scenarios. Table 2.4,1 presents the consumption rates and contaminated fractions
of food applied for each of the scenarios.
Although differences in consumption are the primary difference between the scenarios,
other differences exits. As seen in Table 2.4,1, the ingestion rate of soil and above-ground
vegetables and the inhalation rate of air differ for the child and the adult scenarios. Exposure
duration is another difference. The adult resident and fisher are assumed to be exposed for 30
years, the subsistence former for 40 years, and the chOd exposed for 6 years. Attachment B lists
all the exposure parameters used in calculating risk! to the four human scenarios.
Table 2.4.1 Consumption Rates and Fraction Contaminated Used
in Exposure Scenarios
Contaminate* Food
' - ocM«dU '
RlK*
frtftiot
57
NA
NA
-MM-
NA
Milk (g FW/dny)
181
NA
NA
.-NA-'.
NA
NA
KA-;
60
NA
NA
19.7
19.7
19.7
14
0.2S
100
too
100
200
Drinkioa Water (liters/day)
1.4
1.4
1,4
0.5
Air
20
20
20
.......
Values reflect changes from the Scrserwg Guobnce document.
A drinkin| water consumption rate for adub of 1.4 L/rf was applied in this analysis. As pointed out in U .S. EPA 1990a,
this value may be more accurate for average consurrption than the 2L/d value based on a recent EPA document that
indicate that this rate may overestirrHte estimated representative rates. Furthermore, the 2L/d rate most litety represents
a 90th percentite value.
21
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MIDLOTHIAN, TEXAS CUMULATIVE REASSESSMENT,
Methodology and fteajKt
The watersheds and water bodies considered in the analysis were selected from
U.S.Geologie Survey (USGS) topographical maps and on information collected during a visit to
Midlothian. The selected water bodies and watersheds that were included in the analysis are those
that would be large enough to support fish and reflect the highest impact from the facilities. In
addition, one of the water bodies selected (i.e., Joe Pool Lake) was identified as the City of
Midlothian's primary drinking water source based on information from the Texas Department of
Health. As a result, Joe Pool Lake was modeled as the drinking water source. The topographic
maps were used in identifying the watersheds associated with each water body and in estimating
water body and watershed surface areas. Table 2,4.2 lists the surface areas and other surface
water parameters applied in the analysis.
The SCS Lake 9 & 10 watershed includes Cottonwood Creek and portions of the Newton
Branch of Soap Creek. The SCS Lake watershed is also a subsection of the Joe Pool Lake
watershed. Assuming that the SCS Lake watershed is sufficient to support subsistence fishing is
conservative because the true viability of the SCS Lake watershed to support subsistence fishing
is unknown.* Nevertheless, Region 6 assumed that these water bodies could potentially support
subsistence activity based on their size and their nearby proximity to residential development.
Furthermore, these water bodies are in an area that could be significantly impacted by the
facilities' emissions due to their near central location to the facilities being evaluated in the study.
Contaminants were assumed to be emitted from the four facilities at the emission rates
identified in Section 2.2, 24 hours/day, 7 days/week, 365 days/year. EPA's air dispersion model
ISCSDFT was employed to estimate the fate and transport of the contaminants to the surrounding
area. Soil was assumed to become contaminated by wet and dry deposition of particles and
vapors. Above-ground vegetation, for human and animal consumption, were assumed to become
contaminated via deposition of particles on plants, transfer of vapor phase contaminates, and
uptake through the roots. Beef and milk were assumed to be contaminated via ingestion of
contaminated forage (including hay), silage, grain, and soil. Fish and the drinking water source
were assumed to be contaminated by deposition directly onto the water body and through
contaminants transported to the water body via storm water. Additional modeling data are
presented in Attachment C. Example calculations are presented in Attachment D.
9 Both of the SCS lakes are privately owned. The property upon which SCS 10 (the northern most lake) is
located is posted "No Trespassing."
22
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Table 2.4.2 Surface Water Parameters
Swfttce Area
3.4 E+OS
Watershed Area
'
" 4,41*0?
Wstenhed
4.4E+05
Flow Rate
N/A
300
3.1E+07
3.6B+06
NA
Watershtd
300
odie« wft
wstoofaod «tt»» were eetiiMtod ftwn USOS quadnuieJe*,
u»e« cooducted by C*m(), Dresser,
Flownttaswere
Currert velocjti«i for lakw
Depth for the Joe Pool I^e wit b*i^<»infoim«tx>pu^ in ttaeTexM N«tar«^
"" --••'•••"••••••l-:-------- "•"''•""'•''•'^"•""•:™-''J--|^|^%^-|g|^^
23
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MIDLOTHIAN, TEXAS CUMULATIVE RISK ASSESSMENT
Mdhodoiofy and Retufts
2.5 Mr Dispersion Modeling
The results of the air dispersion modeling represent the initial fate and transport of
constituents in the environment. Vapor and particle air concentrations, wet and dry deposition
of particles, and wet deposition of vapors were modeled. The Screening Guidance recommends
the use of the ISCSTDFT (previously known as ISC-COMPDEP) to estimate the air
concentrations and deposition rates needed for the indirect exposure assessment. ISCSTDFT is
a draft version of the EPA's Industrial Source Complex Short Term Model (ISCST). It is a
Gaussian plume model that is applicable in simple, intermediate, and complex terrains, and it can
simulate both wet and dry deposition and plume depletion.
ISCSTDFT requires site-specific information on the facility emission sources in order to
estimate air concentrations and deposition rates. The facUity-specifie inputs that were applied in
conducting the air dispersion modeling were obtained from facility-specific information provided
by TNRCC, The facility-specific emission sources that were considered in this analysis were
discussed in Section 2.2.
The ISCSTDFT also requires a variety of meteorological data, which are available from
several different sources. The National Weather Service Station at Dallas/Fort Worth, Texas
provided the most appropriate surface data for the facility. Upper air data from Stephenville,
Texas was paired with the surface daa for air dispersion modeling. The National Weather Service
Station in Dallas/Ft. Worth is located approximately 35 miles north of Midlothian and
Stephenville is located approximately 90 miles southwest of the facilities. Five years of
meteorological data, for the year 1985 and 1987-1990, were obtained from EPA's SCRAM
bulletin board and were used to determine long-term average air dispersion and deposition
estimates. The precipitation type, precipitation amount, and station pressure are additional
meteorological data required by ISCSTDFT. These data were obtained from the Solar and
Meteorological Surface Observation Network (SAMSON) CD-ROM (NOAA, 1993).
The meteorological preprocessors PCRAMMET, DEPMET, and PMEROE are needed to
convert the meteorological data gathered from various sources into the format used by
ISCSTDFT. PCRAMMET pairs the surface data with the upper air data to create a
meteorological file that contains hourly wind speed, wind direction, atmospheric stability class,
temperature, and mixing height, PMERGE prepares a precipitation amount File for the modeling
of wet deposition, DEPMET creates a short term meteorological file from the outputs of
PMERGE and PCRAMMET and the precipitation type from hourly surface observations. The
preprocessor DEPMET also requires additional inputs based on site-specific land use data, and
these inputs are listed in Table 2.5.1. DEPMET inputs were derived from recommendations from
the ISCSTDFT User's Guide (US EPA, 1994d) based on the site-specific land use data. Land use
24
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MIDLOTHIAN. TEXAS CUMULATIVE REASSESSMENT
Methodology and Results
information for the facility was determined based on information from the U.S. EPA Region VI
and the TNRCC and assessed tough topographic maps.
The ISCSTDFT model was run using "default" model options specified in the Guideline
on Air Quality Models. These options include the use of stack-tip downwash, buoyancy-induced
dispersion, final plume rise, a routine for processing averages when calm winds occur, default
values for wind profile exponents and for the vertical potential temperature gradient, and the use
of upper bound estimates for super-squat buildings (U.S. EPA, 1994d).
Additional ISCSTDFT modeling options that can be important in characterizing plume
dispersion are the terrain option and the building downwash algorithms. The terrain option was
not used in conducting the air modeling. However, the building downwash option was used for
all sources of emission except for fugitives from CSC.
Table 2.5.1 Air Modeling Inputs Used in ISCSTDFT Modeling
Dallas, Fort Worth/StephenvilJe
6.7 meters
DEPMgTPrtprowatorlmiBte
Land use wiuila 5 km
rural
0.2
Dtybccacat beigtot to)
1.0
1JPP&
0.2
0.8
0.15
b « fW/in1!
Because facility-specific particle size distribution and the associated scavenging coefficients
were not available, the distributions specified in EPA's Compilation of Air Pollutant Emission
Factors (AP-42) were obtained from the Air-CHIEFS Bulletin Board on the U.S. EPA Office of
Air Quality Planning and Standards' (OAQPS1) Technology Transfer Network (TTN).
Specifically, the wet process cement kiln particle size distribution, as seen in Table 2,5.2, was
applied to both TXI and NTCC because these facilities manufacture portland cement by utilizing
wet production processes. However, the dry process cement kiln particle size distribution, as seen
in Table 2.5.3, was applied for Holnam. Tables 2.5.4 and 2.5.5 present the particle size
25
-------
MIDLOTHIAN, TEXAS CUMULATIVE RiSKASSESSHB^JT
Methodology and Kesifa
distributions applied to CSC, As seen from these tables, two distributions were applied to CSC.
The controlled electric are furnace (EAF) distribution, was applied to the baghouse emissions
while the uncontrolled EAF distribution was applied to the fugitive emissions. The scavenging
coefficients associated with the particle size distribution were obtained from Jindal and Heinhold
(1991). Liquid and frozen scavenging coefficients were set equal to each other as performed in
past studies (PEI, 1986), For CSC, gases were assumed to behave as extremely small particles
in the air dispersion modeling. The value of 1.7E-4 (h/mm-s) for the gas scavenging coefficient
was also taken from Jindal and Heinhold (1991).
As specified in the Screening Guidance, the initial air dispersion modeling was conducted
over a polar array of ceceptors, along 16 radials spaced at varying distances out to 10 kilometers.
With the origin of the 10-Mlometer radius placed at a point centrally located between the four
facilities, attempts were made to identify the points of maximum combined deposition and air
concentration, the closest residence, and the subsistence fanner using this radial array of receptors.
However, the methodology specified in the Screening Guidance is intended for use with one
facility located at the origin. As a consequence, the receptor spacing near the location of the four
modeled facilities was too great (i.e.,not sufficiently refined) to determine accurately the points
of maximum combined deposition and air concentration. Consequently, modeling with ISCSTDFT
was repeated using a Cartesian coordinate grid with receptors spaced 500 meters apart out to 10
kilometers from the origin. In addition, the modeling was conducted using a unit emission rate
of 1 gram/^cond from each source type located at each facility. The results of the air modeling
for each receptor location of concern are presented in Tables 2,5.6 through 2.5.12.
The air modeling results were converted to chemical-specific air concentrations and
deposition rates to identify the points of maximum concentration and deposition. This conversion
accounted for chemical-specific emission rates (Q) and the partitioning of chemicals between the
vapor and particle phases. All vapor phase air model outputs were multiplied by the fraction of
emissions in the vapor phase under ambient conditions (fv) and the emission rate, Q. All particle-
bound air model outputs were multiplied by the fraction of emissions in the particle phase (1-fV)
and the emission rate, Q, The fraction of emissions in the vapor phase is chemical-specific and
is contained in Attachment C, which lists the properties of the constituents considered in this risk
analysis.
26
-------
Table 2.5.2 TXI and NTCC Modeling Particle Information
.
•^p^Pf _(*F^5fl^^?W^?w
0.64
1.0
O.TE-4
0.7E-4
0.19
0.158^*
1.0
0.7B4
0.7B-4
0.02
0.00835^;-.
1.0
i:i
0.06
1.0
0.7E4
0.7B4
0.7B4
0.7E-4
0.07
1.0
0.7B4
0.7B4
0.02
1.0
0.7E4
0.7E4
27
-------
Table 2.5.3 Holiuun Modeling Particle Information (AP-42 Dry Process)
Table 2.5.4 Chaparral EAF (Stack) ModeUng Particle Information
for Process Emissions
'
0.74
Dearfty
<»tWVie»t
•^^MtnmL .H
4E-5
0.02
5E-5
0.04
6.62E-4
6.62E-4
28
-------
MIDLOTHIAN, TEXAS CUMULATIVE RISK ASSESSMENT
and Results
Table 2.5.5 Chaparral Modeling Particle Information tor Fugitive Emissions
fltaaeter (jun)
..
dWrlfaifloa
(teftrflxifloo
fwBqaW
cMfltcteal
r«r frozen
0.08
0.30
.«»&•
4.0B-5
0.15
4.0E-5
0.2
8E-S
0.1
2.7E-4
0.05
5.0&4
.as*.
0.03
&005
6.62E-4
004
6.62E-4
29
-------
Table 2.5.6 Results of Air Modeling: CSC Fugitive Emissions
MODEL
PA1T1CUE
.
Mm*
-J5SO, -6540
-1500, -6500
4.4
4.3
0.11
2.7
0.10
RECEPTOR 11
805, 2940
1000, 3000
0,02
0.01
0.71
0.01
-3013, -»51
-MOO, -3000
61
J9
2,3
1.3
-JOOO, -1000
0.24
0,19
Table 2.5.7 Results of Air Modeling: CSC Baghouse A
ACTUAL
COORD.
''''
~ MODEL
COORD.
' COMBINES
fARTtCLE .
.
FAJtnOUE
" M3PK "
mmm.
cone.
• MET
-1550, -6540
-1SOO, -6SOO
0.06
0.06
0.002
0.0(13
0.002
S05, 2940
1000,3000
0.001
0.016
0.0»
2.9E-4
-3013, -2951
-3000, -3000
2.2
2.2
0.026
2.56
0,019
RECEMORO
-2775, -1147
-3000, -1000
0.32
0.32
0.003
0.375
0.004
30
-------
Table 2.5.8 Results of Air Modeling! CSC Baghouse B
COORD,
MODEL
COORB.
COMBINED
PARTKXE
. -MBT ••••'•"
PASTICLE
''
-CG8SC,
'maim
-1SSO. -SS40
-1500, -*$00
0.003
0.032
0.002
0.033
0,003
105, 2940
1000,3000
0.012
o.oot
UE-5
0.011
2.SE4
RSCBPTORCl
-3013, -2951
-3000, -3000
0.055
0.034
0.022
0.024
0,002
RECEPTOIta
-2775, -1147
•3000, -1000
0.07»
0.003
0,063
0,004
Table 2.5.9 Results of Air Modeling: CSC Bagbouse C
"ACttfiMK
coopi.-
COMWNEO
'Wimcui'
::»E«Jil X
f ARTICLE .
AIR
-1J50, -6540
-1500, -6500
0.031
0.021
0.002
0.029
0,003
RECCfTOlBl
MB, 2MO
1000,3000
0.012
0.012
2.3E4
0.016
3.I&4
RECETTORC1
-3013, -29S1
-3000, -3000
0.062
0.049
0.013
0.035
0.015
.2775, -1147
-3000, -1000
0.078
0.076
0.003
0.063
0.003
31
-------
Table 2.5,10 Results of Air Modeling: NTCC
COOM.
MODEL
'
RECEPTOR AI
-1550, -6540
-1500, -6500
0.013
0.012
0,001
0.023
0,001
805, 2940
1000, 3000
0.021
0.018
0.003
0.017
0.003
MECEPTORCl
-JOB, -295 1
-3000, -3000
0.005
0.005
0.001
0,001
0.001
-2775, -1147
-JOOO, -1000
0.005
0,004
0.001
0006
D.001
Table 2.5.11 Results of Air Modeling: TXI
UM;ATION
;tec»TO*t.M '.': .
WfcfcpMtM :
••XSCWrtWtW
1UECCPTOBC3 •
ACTUAL '••• :
cooitfl. • • ;
-1550, 4540
805, 2940
-3013, -29J1
-ITOj -1147
' MODEL :
C008B. :
4500, -6500
1000,3000
-3000, -3000
-3000, -1000
:: -iOCWIWSHp-
fAMTKU; •
•:':»«!*r
u, . (tet^Vrt .'
0.051
0.009
0.111
0.012
DRV: -
. PAJtncLt; ., -
OEPO, • :.
(xert.'-yr) . ^.- ^
0.047
0.009
0.001
0.008
>'•••''• '"':':Wtf-y '
-•".^iiii: ;".
'•• •-' • ' •-. '.PWOi, ;
iMcM'-srt -!
0.004
4.4E-4
0.010
0.004
:' ':- :-Mik-:-- ~*
: .••mm •..-:.•
;. \lifar;..;--;--
•••• fw-MC/Mrt ~ ':
0,067
0.013
0.004
0.013
;• " -Itt* ;.
v .. VAPOR
: ' IWK>.
• twcita'-m '
0.004
4.0E-4
0.008
0.003
32
-------
Table 2.5.12 Results of Air Modeling: Holnam
COORD.
' MODEL
-1550, -6540
-1500, -6500
0.004
0.003
Z.I&4
0.005
2.I&4
RECETtORBt
SOS, 2940
MXW, 3000
0.006
0-OOt
0.005
0.003
0.003
-3011, -2951
-3000, -3000
0.001
0.001
S.OE4
0.001
4.SB4
RECEPTOR O
-2775, -1147
-3000, -1000
0.001
0.001
0.001
0.001
0.001
Table 2.5.13 Site-Specific Receptors Locations
3. 4 km Sooth of TXI
1.1 km SouOwut of NTCC
0.5 km Ninth of Ch»p»rr»l
Al
3.4 km South of TX1
1 . 1 km Smitten of NTCC
0.5 km North of Chaparral
Site-ipttto w»lmi«li u§«d tor fijfcingerticHi bj 0fe
B*iod on location of the residents
SCS Lakes 9 & 10
Joe Pool Lake
Joe Pbo) L*kc
33
-------
MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
Methodology xtd Results
Map I identifies the points of maximum air concentration and combined deposition based
on estimated constituent-specific emission rates. As seen from this map, there were three points
of maximum air concentration and three points of maximum deposition identified. For each
compound, these points were typically located in close proximity to the facility emitting the
compound at the highest rate. Maps 2 and 3 graphically present the maximum combined
deposition for bis(2-ethylhexyl) phthalate and maximum combined deposition for TCDD.
Map 1 also shows the general location of each site specific receptor evaluated in the study.
In the original draft of the report, risks at the maximum locations were estimated and
reported. However, based on comments from several reviewers, Region 6 did not report risk at
the maximum receptor locations in this final version of the report. Reporting risk at the maximum
receptor locations was judged to be overly conservative because such an analysis would have
required Region 6 to assume that maximum deposition and air concentrations occur at the same
location. Such a phenomenon is not indicative of the model and would result in overly
conservative estimates of risk in some instances.
Rather than estimate theoretical worst case risk, Region 6 obtained information regarding
the location of several potential resident and farm locations likely to be most impacted by the
facilities.10 This information was obtained during several site visits that were conducted during
the summer of 1995. As seen from Table 2.5.13, three site-specific residents/subsistence fishers
and subsistence farmers were identified and modeled in the analysis. Multiple receptors were
considered in order to ensure that the maximum media concentrations of each pollutant were
considered because the overall risks for each pathway could vary according to which contaminant
was deposited at the highest rate or was present at the highest ambient air location. Resident A1
and subsistence farmer Al, resident Bl and subsistence farmer B2, and resident Cl and
subsistence fanner C3 are the receptors located closest to the points of maximum combined
deposition A, B, and C, respectively. The exposed individuals assumed to live at residence Al,
Bl, and Cl included the adult and child resident and the subsistence fisher. The difference
between the adult resident and subsistence fisher was that the fisher was additionally exposed
through the consumption of contaminated fish.
10 It should be noted that these locations do not necessarily refect actual residences and farms based on
interviews etc., but rather reflect a reasonably conservative analysis of activities as seen from driving in and about the study
area. For example, residential locations typically correspond to locations of houses or similar residential-type structures.
Farms were estimated based on the presence of livestock or bam type structures in the area of interest,
34
-------
Map 1:
Points of Maximum Combined Deposition and
Air Concentration
Points of Maximum
Combined Deposition
TCDD, 2, 4 -and 2, 6-dimtrotolucne
hexachlorobenzeoc, PCNB,
pentachlorophcool,
9 B For all other organic compounds
• C For ill other metals
Points of Maximum Air
Concentration
* D TCDD, 2, 4 -and 2, 6-dimtzotokiene
PCNB,
pentachloroptienol.
thallium, and beryllium
£ For all other organic compounds
F For all other Metals
Approiimaie ftopcrty
Boundaries
Local Roads
Primary Roads and
Highways
Hydrography
Railroads
Facility Emission Points
-------
Map 2:
Combined Deposition Contours
for Bis(2-ethylhexyl)PhthaIate
— Combined Deposition Contours
for Bis(2-ethylhexyi)PhthaIate
Base Contour 1.1E-6 g/n^/yr
Contour Interval 1E-6 pm/yr
Points of Maximum
Combined Deposition
A TCDD, 2, 4 -and 2, 6-dinitrotoluene,
hexachlorobenzene, PCNB,
pentachlorophenol,
thallium and beryllium
B For all other organic compounds
C For all metals
Points of Maximum Air
Concentration
D TCDD, 2, 4 -and 2, 6-dinitrotoluene
hexachlorobenzene, PCNB,
pentachlorophenol,
thallium, and beryllium
E For all other organic compounds
F For all Metals
Facility Emission Points
Origin
Approximate Property
Boundaries
Hydrography
Approximate Scale:
1 Inch = 1.42 Miles
RTI
-------
Map 3:
Combined Deposition Contours
tor TCDD
— • TCDD Combined Deposition
Contours
Base Contour JE-9 g/m2/yr
Contour Interval JE-9 g/m/yr
Points of Maximum
Combined Deposition
* A TCDD, 2, 4 -and 2, 6-dinitrotoluene
hexachtorobenzene, PCNB,
pentachlorophenol,
thaUium and beryllium
* B For all other organic compounds
* C For all metals
Points of Maximum Air
Concentration
* D TCDD, 2, 4 -and 2, 6-dinitrotoiuene
and hexachlorobenzene, PCNB,
pentachlwrphenol,
thallium, and beryllium
* £ For all other organic compounds
• F For all Metals
* Facility Emission Points
* Origin
Approximate Property
Boundaries
Hydrography
Approximate Scale: /IM>I
1 Inch = 1.42 Miles /ICI1
-------
MIDLOTHIAN. TEXAS CUMULATIVE REASSESSMENT
Methodology and Results
2.6 Deviaik3re(hDmttieSo«eningGuitJanoeMe(hodoIog>f
This section summarizes instances where the methodology used in this risk assessment
deviated torn that contained in the Screening Guidance document. These instances included the
estimation of soil concentration due to deposition, the development of the default watershed
parameters, the use of chemical specific fete and transport parameters, and the modification of
exposure parameters for the child.
The most significant deviation from the Screening Guidance methodology occurred in the
calculation of soil concentration due to deposition of contaminants. The Screening Guidance gives
the following equation which is used to calculate an average contaminate soil concentration for
the scenario exposure duration:
Ds • Tc -Sc.
Te
ks
Equation 1
where
Sc = average soil concentration over exposure duration (mg/Kg)
Scrc = soil concentration at time Tc (mg/Kg)
Ds = deposition term (per unit time)
ks = overall soil loss constant (per unit time)
Tc = time period of combustion (year)
Tt = time at the beginning of exposure duration (year)
T2 = time at the end of exposure duration (year).
Equation 1 is appropriate for carcinogenic chemicals where the risk is averaged over the
lifetime of an individual. Since the hazard quotient associated with chemicals not known to cause
cancer chemicals is based on a reference dose and not on a lifetime exposure, the highest annual
average soil concentration occurring within the exposure duration period is more appropriate. The
maximum annual average soil concentration would occur at the end of the time period of
combustion (which is assumed to be 30 years for this analysis) and is estimated by the following
equation:
38
-------
MIDLOTHIAN, TEXAS CUMULATIVE RISK ASSESSMENT
m.
fa
A comparison of the two soil equations showed that the maximum annual average soil
concentration can be up to two times as great as the soil concentration averaged over the entire
exposure duration, depending on the type of chemical. Using Equation 1- the soil concentration
averaged over the exposure duration - as directed in the Screening Guidance, would result in an
underestimation of the risk for chemicals not known to cause cancer chemicals. Therefore, in this
analysis, the soil concentrations for chemicals not known to cause cancer chemicals were
calculated using Equation 2.
Equation 1 is not applicable for cases where the exposure duration (Tj) is less than time
period of combustion (TJ. In such instances, the average concentration calculated from this
equation can result in a negative soil concentration for some chemicals. Since the exposure
duration for the child scenario was assumed to be 6 years, this equation could not be used.
Instead, another soil equation was used to calculate the average soil concentration of carcinogenic
chemicals for the child scenario. The equation is as follows:
7r- Ds
&,=
ks 1 ks
for Tl < Tc
Equation 3
where
Sc, = soil concentration over period in which exposure occurs (mg/Kg).
The T, in Equation 3 represents the beginning of the exposure duration and was assumed to occur
at year 24 for the child. Thus, the child would be exposed over the time period having the highest
average soil concentration. The above equation for the child is used only for carcinogens. As
with the adult scenarios, soil concentration of chemicals not known to cause cancer chemicals was
based on the maximum soil concentration (Equation 2) over the time period of exposure.
Some of the chemical inputs specified in the Screening Guidance have been updated and
revised since the draft document was prepared in December 1994. Most notably, the fraction of
mercury assumed to be in vapor is now modeled as 0.85 and not as 1 as specified in the Screening
39
-------
MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
Methodology-and'Results
Guidance. The revised vapor/particle partitioning for mercury is assumed, and it differs from that
specified in the Mercury Study Report to Congress (U.S. EPA 1994b). The reason for this
difference is attributable to where partitioning is assumed to occur. The Report to Congress
presents the partitioning of mercury at the stack and the fraction of vapor as it would exist in stack
emissions. As specified in the Addendum (U.S. EPA, 1993) and applied in this analysis, the
vapor/particle partitioning is calculated at the receptor location (i.e., the watershed, the plant, the
cow, etc.). The partitioning at the receptor location (i.e. at cooler, ambient temperatures) is
expected to differ from the stack emissions (U.S. EPA, 1994b).
Another change incorporated into this report is the air to plant biotransfer factor (Bv) for
PAHs and phthalates. The Bvs specified in this report are either based on measured data or (where
measured data were available) on a modified equation. The modification reduces the Bv by a
factor of 40 and is consistent with recommendations in the Dioxin document" (U.S. EPA 1994a).
A complete list of the chemical date is contained in Attachment C, These data are consistent with
both the most recent Dioxin document (U.S. EPA I994a) and, with the exception of the vapor
fraction for mercury, the Mercury Report to Congress (U.S. EPA, 1994b),
The beef and milk biotransfer factors for cadmium and mercury have also been changed
since the December version of the Screening Guidance document. The revised biotransfer factors
are used to calculate risks from beef or milk on a dry weight basis. The consumption rates
currently used for beef and milk had to be adjusted to a dry weight to account for these new
factors. The conversion factors are 0.4 and 0.1 for beef and milk, respectively (Memorandum,
US EPA/ORD 1994).
Some of the exposure parameters for the child scenarios were also changed. Specifically,
the consumption rate of above-ground vegetables and the inhalation rate have been revised.
Values for these parameters provided in the Screening Guidance document were estimated by
applying a body weight adjustment fector to the adults consumption and inhalation rates. Finally,
the consumption rate of vegetables that was used in this analysis was revised from the Screening
Guidance to be consistent with the Mercury Report to Congress, which recommends a value based
on the dietary habits of children.
1' The Dioxin document (U .S, EPA, 1994a) recommends reducing Bvs by 40 for dio»n and diown-Iike
compounds. The PAHs and phthalates behave similarly to dbxins in the environment (t.e,, they are lipophilic) and the
adjustment makes the calculated values similar to the values measured for a setect group of lipophiltc compounds in Hites
(1994).
40
-------
MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
Mettxxfolosy 3nd Results
3. RESULTS
rphe results of the theoretical risk assessment are presented in this section, Some general
J. background information about risk assessment is presented followed by the specific
results for each receptor location and each pathway for both theoretical carcinogenic and
theoretical potential non-cancer effects. An overall summary of the results is pesented in
Section 3.3. All results are presented in tabular format in Attachment A.
3.1 Background
The national risk, or probability, that an individual may develop some form of cancer from
everyday sources, over a 70-year life span, is estimated at three in ten. Activities such as too
much exposure to sun, occupational exposures, or dietary or smoking habits contribute to this high
risk. The three in ten probability is considered the "natural incidence" of cancer in the United
States.
In the Superfund program, EPA established an excess acceptable lifetime cancer risk range
from one in ten thousand to one in one million. This range may be expressed as 1 x 10"4 to
1 x 10* (expressed throughout mis report as 1E-4 to IE-*). For example, a risk of 1 x 10"* means
that 1 person out of one million could develop cancer as a result of a lifetime exposure to a
emissions from the four facilities studied in this assessment. In the Superfund program, EPA must
consider the need to conduct remedial action at a site if the risk exceeds 1 x 10"* and EPA usually
requires remedial action at locations where excess cancer risks are greater than 1 x 10"* (1 excess
cancer case in ten thousand people could potentially occur).
The level of concern for non-carcinogenic contaminants is determined by calculating a
Hazard Quotient (HQ) or Hazard Index (HI). An HI is the sum of the HQs for several chemicals
that affect the same target organ. If the HQ or HI equals or exceeds one, there may be concern
for potential exposure to site contaminants. EPA typically considers the need for taking a
remedial action at locations where the HQ or HI values equal or are slightly greater than 1.0 for
human populations who may reasonably be expected to be exposed. EPA usually requires
remedial action at locations where HQ or HI values significantly exceed one.
41
-------
MIDLOTHIAN, TEX*S CUMULATIVE REASSESSMENT
Metftodotegy and Results
3.2 Resute by Receptor Location
The greatest estimated theoretical risk is 1E-4 for a subsistence fisherman that resides at
either Point Bl or Cl and who fishes SCS Lakes 9 and 10. Theoretical hazard quotients equal to
or slightly greater than one were estimated for all of the receptors at all three locations.
The presentation is divided into two sections; theoretical cancer risk and potential for
theoretical noncancer health effects. These sections are further subdivided by receptor location.
3.2.1 Theoretical Cancer Risks Estimates
Point Al
Theoretical cancer risks for each pathway and each receptor are summarized in Table
3.2.1.1.
Table 3.2.1.1 Point Al Cancer Risk Results
•' '. '''$tifcKl£il&
>'• :;:||^gfJ$Hr "•
-:''.- • -. , -,::
Adnh Resident
ChiW Resident
Farmer
Fisherman
SCS Lake
Fisherman
Joe Pool LaJc&
'<• • INDIRECT '•••
i - :-::f*liftWfcy :•:;. .;:;
;•• . '", •; .._ _•_ _.;: ,: ._V
3B-7
71-7
4B-S
8E-5
2E-S
DRINKING :
;yx'::'Wlfr«r-- . ;
&*•;.; fJKWitm-:- - ;
6E-6
2B-6
7E-6
6E-6
6B-6
JNHALATN ;
:,: ;:P*tlWf^if. ;;
1E-6
«B-7
1E-6
1B-6
1E-6
•MJ-TAt '
7E-6
3E-6
5E-5
9E-5
3E-5
The risks associated with the adult resident are driven by the drinking water and inhalation
pathways. The primary contaminants contributing to this risk are arsenic for the drinking water
pathway and cadmium for the inhalation pathway.
Two-thirds of the risks associated with the child resident are provided by the drinking
water pathway with the indirect and inhalation pathways providing the additional third of the risk.
42
-------
MIDLQTHiAN. TEXAS CUMULATIVE RISKASSESSHEhfT
Methodology and Rente
The primary contaminants contributing to the drinking water and inhalation risk are arsenic and
cadmium, respectively. Dioxin, benzo(a)pyrene equivalents (BAP), and arsenic combine to make
up the remainder of the indirect pathway risk.
The risks associated with the subsistence fanner are driven by the indirect pathway.
Dioxin, BAP, and arsenic combine with bis-2-(ethylhexyI)phthalate (DEHP) to cause risk via the
indirect pathway risk. The remaining 20% of the risk are provided by the drinking water and
inhalation pathways with arsenic and cadmium, respectively, driving the risk.
The risks associated with the subsistence fishermen are driven by the indirect pathway.
Arsenic is the predominate contaminant driving this risk with some contribution from dioxin and
BAP. The remaining risk from the drinking water and inhalation pathways are again associated
with arsenic and cadmium.
Point fll
Cancer risk for each pathway and each receptor are summarized in Table 3.2.1.2.
Table 3.2.1.2 Point Bl Cancer Risks Results
••....;,-..'' - - . : : .\:";T«MJ63.1O •...••. •• ': . \
•':' RECEPTOK '• ,
AduU Resident
Child Resident
Firmer
Fisherman
SCSUlce
Fiahentum
Joe Pool Lake
" "•••^i&^f- '
, • •ynaftfjiitif'
6E 8
1E-7
1E-5
8E-5
2B-5
' DRTNKING . .;
-WATEB-> • ,•
: ,• •- .ePMWWAt-,- . ,
6E-6
2E-6
7B-6
6E-6
6E-6
-' . INHALATO
IMrtiWWHF
> • . ' ' • ' . . .'. . ' ,",•
2E-S
9E-6
2E-5
2E-5
2B-5
I ' imai. •
3E-S
1E-5
4E-5
lE-»
5E-5
The inhalation pathway dominates the adult resident risk at this location. The primary
contaminant driving the inhalation risk is hexavalent chromium. Arsenic dominates the drinking
43
-------
MIDLOTHIAN. TEXAS CUMULATIVE RSK ASSESSMENT
Methodology-and Rcstjtx
water risk. The indirect pathway does not significantly contribute to the overall risk to adult
residents at receptor location Bl, The child resident risk is also due primarily to the inhalation
and drinking water pathway for similar reasons.
The risks to the subsistence farmer are controlled equally by the inhalation pathway and
a combination of the indirect and drinking water pathways. Chrome VI drives the inhalation
pathway risk and arsenic dominates the drinking water pathway. Dioxin, BAP, DEHP, and
arsenic make up most of the indirect pathway risk.
The risks to the subsistence fisherman vary depending upon which water body is used to
support subsistence activities. If the SCS lakes are the primary source of fishing, the indirect
pathway drives the risk. Arsenic is primary contributor to the SCS Lake indirect pathway risks
with additional contributions by dioxin, BAP, DEHP, and beryllium. If Joe Pool Lake is fishing
source, then overall risk are controlled equally by the indirect and inhalation pathways with some
contribution by the drinking water pathway. The drinking water and inhalation risks are attributed
to arsenic and chrome VI, respectively, while the indirect pathway risk is driven by a combination
of dioxin, BAP, DEHP, and PCBs.
Point CA"
Cancer risk for each pathway and each receptor are summarized in Table 3.2,1.3.
12 Indirect pathway risks attributed to the subsistence farmer are actually calculated at point 7,640 feet north of
Point Cl, at Point C3. Subsistence farming activity was not present in the area of point Cl (which is almost directly across
Highway 67 from CSQ.
44
-------
MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
Methodology arxfRi
Table 3,2.1.3 Point Cl Cancer Risk Results
* . ":".'.. :>TiHtt*JUi-I3' , .
.• ;, - - ...._....
?; •meynm
Adutt Resident
CIliM Resident
Fumer
Fishermaj)
SCSLake
Fiiherman
Joe Pool Lake
;• jwwiieT:-;-
K :?*ffl9^^x. ••••
11-6
IE-6
4E-S
9E-S
2E-5
: DRINKING :
•<, :, ::::<*§****;
'^WijJMflW^..-- -
6E-6
2B-6
7B-
-------
MIDLOTHIAN, TEXAS CUMULATIVE RISK^fiSESSMEhfT
Methodology md Results
3.2.2
The contaminants estimated to have the most significant potential for non-cancer health
effects are arsenic, cadmium, chromium, mercury, and zinc. The results of the non-cancer health
effects evaluation are presented for each receptor location below.
Point AI
Table 3.2.2.1 Point Al Non-Cancer Effects Results
1- -••-••••••••••••••••••
:' '' ' '. ' • . . :•-.':.:-
•'•:'•-'.' ': " •. : ; : ,'::::- -:
Adult Retideot •}
Cfcild R«id«SJ*
-RsSifctrf : :":
^-iSS''.'::
fl^ilpistiate-::--
i: •..:• ,:-A. ....::: :.;:
0.03
0.05
0.05
0.4
0.05
',-.,-,,..„ .***,., •-,,,.
0.3
0.7
0.4
1
0.5
ASLB3J.2.1
.. .. f^vt
0.004
0.006
0005
0,01
0.004
H« .. ......
0
0.004
0
1
I
S3,
3
6
3
3
3
to.
0.1
0.2
0.1
0.4
0.1
The analysis shows mat the hazard quotient (HQ) for antimony is greater than the
threshold value of one. An HQ greater than or equal to one indicates that there is a potential for
noncancer health effects from antimony. However, readers are reminded that an HQ equal to or
exceeding the threshold no way indicates that non-cancer health effects can or will occur, only that
a potential for non-cancer effects exist based on a specific set of model and exposure assumptions.
The most significant contribution to antimony exposure is through the drinking water pathway.
Because the HQ for antimony was greater than one, Region 6 expanded its study to include an
analysis of existing antimony concentrations in Joe Pool Lake and the Midlothian water supply.
Although very little data were available, water analysis report prepared by the Texas Water
Commission in 1993 was located which reports concentrations of antimony in the Midlothian
water supply at less than the 0.002 milligrams per liter (mg/1) detection limit. The HQ associated
with % this detection limit (0.001 mg/1) and the exposure parameters previously specified in
Table 2.4.1 and Attachment B, is 0.05. Thus, the most recent site data available to Region 6
show no significant potential for adverse health effects from antimony.
46
-------
MIDLOTHIAN. TEXAS CUMULATIVE RISK ASSESSMENT
~ Methodology and Results
The HQs for mercury are estimated to be at the threshold level of 1 for both fish sources
and cadmium is predicted at the threshold level of one for the fisherman that uses the SCS Lakes
as a primary source of fish. The HQ for mercury needs to be reviewed with extreme caution,
however, as recent discussions within EPA have indicated that quantitative risk assessment results
for mercury are not confident enough for purposes of rendering regulatory decisions. Indeed, the
quantitative portions of the risk assessment for mercury included in the original version of the
hazardous waste combustion rule were withdrawn in favor of a more qualitative approach. This
change was instituted as a result of concerns within EPA regarding the risk assessment
methodology's application to mercury.
The potential for non-cancer health effects from cadmium should also be viewed within
the appropriate context. Readers are cautioned to remember that the SCS Lake subsistence fisher
scenario is the most uncertain of the two subsistence fishing scenarios and the relatively significant
uncertainties associated with the emission estimates for CSC, the predominate source of cadmium
emissions in this study.
Point Bl
Table 3.2,2.2 Point Bl Non-Cancer Effect Results
Adult Mcridot
Ckild Hesideot
1 ' ;?**r**.
::: MiherBua :
W^ersbed ••-
Joe faol L*ke '::
WaUrahed
:;>;0:14ip •*,?;>
0.03
0.05
0.04
0.4
0.05
^•:?:^.:*^
0.3
0.6
0.3
1
0.5
s^£&vM;!;~
0.004
0.008
0.01
0.5
0.004
,_,._..-_ •• • • : _ :_
•:^m^::ll
0
0.002
0
1
1
;:;-:v:-Ai::KSH
3
6
3
3
3
Sl^rt/2
O.I
0.2
0.1
0.4
0.1
The results of the study again indicate that the hazard quotient for antimony is greater than
the threshold value of one. The most significant contribution to antimony exposure is through the
drinking water pathway. Because the HQ for antimony is greater than one, Region 6 expanded
its study to include an analysis of existing antimony concentrations in Joe Pool Lake and the
Midlothian water supply. A water analysis report prepared by the Texas Water Commission in
47
-------
MIDLOTHIAN, TEXAS CUMULATIVE RISKASSESSNENTL
Methodology and Results
1993 reports concentrations of antimony in the Midlothian water supply as less than 0.002
milligrams per liter (mg/1). The HQ associated with, 0.001 mg/1 and the previously specified
exposure parameters is 0,05. Thus, the most recent site data available to Region 6 show no
significant potential for non-cancer health effects from antimony.
Similar to receptor Point Al, the HQs for mercury are estimated to be at the threshold
level of 1 for both subsistence fisherman pathways, and cadmium is predicted at the threshold
level for the fisherman that uses the SCS iakes as a primary source of fish. The HQ for mercury
needs to be reviewed with extreme caution, however, as recent discussions within EPA have
indicated that quantitative risk assessment results for mercury are not confident enough for
purposes of rendering regulatory decisions.
As noted in the discussion regarding Point Al, the potential for non-cancer health effects
from cadmium should also be viewed within the appropriate context. Readers are cautioned to
remember that the SCS Lake subsistence fisherman scenario is the most uncertain of the two
subsistence fishing scenarios, and the relatively significant uncertainties associated with the
emission estimates for CSC, the predominatE source of cadmium emissions in this study.
Point Cl
Table 3.2.2.3 Point Cl Non-Cancer Effects Results
•;. ... . : .-. ' .- -. .:' .
!:'U**»i*m:
Child Rorideot ;
-•'- ' ' . .:• • ' "•
;: scsi^k* '••
:; ' Fltberaua •
: J« Pwd I^k« ,
•• Witanhcd ' -
'-. : .• :*»•• -• :- .-:':•
0.03
0.05
O.I
0.4
0.06
:? . «,;• • .,.,
0.3
0.7
0.5
1
0.8
- fVVTrf,:.,-
0.004
0.006
0.008
0.01
0.005
-:•' -'.' ' ' . •-•,:••- • ••
'; 'i '.- ::«b-:>.''.: ••-•
0
0.004
0
1
I
&&•••:• -- -
3
I,
4
3
3
..;,.,%,, - ,;
0.1
0.2
0.2
0.5
0.2
The results for receptor Point Cl are similar to the results for Points Al and Bl. The
discussion of the results is the same and is not repeated here.
-------
MIDLOTHIAN, TEXAS CUMULATIVE RISKASSESSNENTL
Methodology and Results
1993 reports concentrations of antimony in the Midlothian water supply as less than 0.002
milligrams per liter (mg/1). The HQ associated with, 0.001 mg/1 and the previously specified
exposure parameters is 0,05. Thus, the most recent site data available to Region 6 show no
significant potential for non-cancer health effects from antimony.
Similar to receptor Point Al, the HQs for mercury are estimated to be at the threshold
level of 1 for both subsistence fisherman pathways, and cadmium is predicted at the threshold
level for the fisherman that uses the SCS iakes as a primary source of fish. The HQ for mercury
needs to be reviewed with extreme caution, however, as recent discussions within EPA have
indicated that quantitative risk assessment results for mercury are not confident enough for
purposes of rendering regulatory decisions.
As noted in the discussion regarding Point Al, the potential for non-cancer health effects
from cadmium should also be viewed within the appropriate context. Readers are cautioned to
remember that the SCS Lake subsistence fisherman scenario is the most uncertain of the two
subsistence fishing scenarios, and the relatively significant uncertainties associated with the
emission estimates for CSC, the predominatE source of cadmium emissions in this study.
Point Cl
Table 3.2.2.3 Point Cl Non-Cancer Effects Results
•;. ... . : .-. ' .- -. .:' .
!:'U**»i*m:
Child Rorideot ;
-•'- ' ' . .:• • ' "•
;: scsi^k* '••
:; ' Fltberaua •
: J« Pwd I^k« ,
•• Witanhcd ' -
'-. : .• :*»•• -• :- .-:':•
0.03
0.05
O.I
0.4
0.06
:? . «,;• • .,.,
0.3
0.7
0.5
1
0.8
- fVVTrf,:.,-
0.004
0.006
0.008
0.01
0.005
-:•' -'.' ' ' . •-•,:••- • ••
'; 'i '.- ::«b-:>.''.: ••-•
0
0.004
0
1
I
&&•••:• -- -
3
I,
4
3
3
..;,.,%,, - ,;
0.1
0.2
0.2
0.5
0.2
The results for receptor Point Cl are similar to the results for Points Al and Bl. The
discussion of the results is the same and is not repeated here.
-------
MIDLOTHIAN. TEXAS CUMULATIVE REASSESSMENT
Met}xxiolo®> and Results
Because health benchmarks for lead were not available, exposure estimates are not
presented for lead. Instead, lead concentrations in the air and sou were estimated and compared
to standard threshold type values EPA uses to in other programs such as Superfund and the Clean
Air programs. The results are shown in Table 3.2.2.4.
Lead concentrations in soil were compared to EPA Superfund's threshold level of
400 ppm for lead at Superfund sites. Further study is necessary to determine the potential health
effects of lead if concentrations are found to be present above the threshold level. As seen from
this table, the modeled concentrations of lead in soil are approximately five to ten times greater
than the threshold level. However, results of analysis from soil samples collected at the site show
that the model over predicts concentrations of lead in soil. According to TNRCC and recent
unvalidated sampling by CSC, actual soil concentrations of lead north of CSC typically range
from 7.95 to 141 mg/kg.
Lead concentration in air was compared with National Ambient Air Quality Standard for
lead of 1.5 ^ig/m3 and is also presented in Table 3.2.2.4. The model does not predict lead
concentrations above the NAAQS of 1.5 jig/m1. Air monitoring for lead conducted by TNRCC
also failed to show concentrations of lead in air above the NAQQS.
49
-------
MIDLOTHIAN, TEXAS CUMULATIVE MSK ASSESSMENT
MethodokyyndKesuhs
Table 3.2.2.4 Lead Concentrations in Air and Soil
Exposure Scenario
B*do of Lead
-it
. Soil to 400
Subsistence fanner
IE + 3
2.4
Ardutt midcot
2E + 3
6.0
Child res ideal
2B + 3
6,0
Subiisteoce fiiheniMui
2B + 3
6.0
Estimated
RatfoofLead
" ': ta Air to
Subsistence fanner
2E-1
.11
Adult Incident
4B-1
,28
Child ratideot
41 -1
.28
Subsistence fiihwiMi)
4B-1
.28
33 Overall Surrwnary of Resute
The risk assessment estimates theoretical cancer risk and the potential for theoretical non-
cancer health effects from 30 years (beginning today) of emissions, associated with CSC, NTCC,
TXI, and Holnam. No cancer risk above regulatory levels of concern were identified. Theoretical
and conservative modeling estimates that several receptors nave the potential for non-cancer health
effects. However, as explained in more detail in the Section 5, actual site data shows that the
models over predicts media concentrations of the principle contaminants driving the potential for
theoretical non-cancer health effects; antimony and cadmium.
The most significant theoretical cancer risk is attributed to the ingesm'on of fish caught from
SCS Lakes 9&10. Arsenic contributes up to 80% of the risk from this pathway. The next
pathways that result in the greatest risk are subsistence fanning, and subsistence fishing in Joe
Pool Lake. A combination of organic contaminants such as dioxin, BAP and DEHP drive the
subsistence farming risk while arsenic again dominates the subsistence fishing risk.
50
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________.^ MIDLOTHIAN. TEXftS CUMULATIVE RISK ASSESSMENT
" Methodology and teute
The thf»retical modeling shows a potential for non-cancer effects from exposure to
antimony in drinking water, and cadmium and mercury through the ingestion of fish from SCS
Lakes 9 & 10. The HQ for antimony is estimated to be three for adults and six for children at
every receptor location. The HQ for cadmium equals one for the subsistence fisherman that
fishes SCS Lakes 9 & 10 and the mercury HQ equals one for the subsistence fisherman that fishes
both SCS Lakes 9&10 and Joe Pool Lake.
The chronic oral reference dose for antimony (0.0004 mg/kg/day) contains an uncertainty
of factor of 1,000. An uncertainty factor of 1000 means that the critical amount of antimony
found in laboratory studies to cause potential non-cancer health effects was multiplied by 1000 to
account for uncertainties in the studies before that value was used in this study to estimate the
potential for non-cancer health effects. Critical health effects from studies upon which the
reference dose is based include a decrease in median life span, a decrease in nonfasting Wood
glucose levels, altered cholesterol levels, and a decrease in the mean heart weight of males. The
following tables present the overall results of the risk assessment process.
The chronic reference dose for cadmium (0.001 mg/kg/day for food and 0.0005 mg/kg/day
for water) contains an uncertainty factor of 10. Critical health effects attributed to cadmium
include anemia and pulmonary disease, edema, pneumonitis, possible effects on the endocrine
system, defects in sensory function, and bone damage.
Citizens in the local area also requested that Region 6 consider risk to infants from dioxin
via the breast milk pathway and risk from a tire fire that occurred in December, 1995, at a tire
shredding facility located in the study area. To address the risk via the breastmilk pathway,
Region 6 used the Scnening Guidance methodology to estimate an infant's daily intake of dioxin
if the mother were a resident, subsistence farmer, or subsistence fisher. These estimated intakes
were then compared to the average adult background exposure to dioxin of 0,5 picogram (pg) per
kilogram (kg) per day. Based on the modeled values, an infant's estimated daily intake of dioxin
is 0.01 pg/kg/day if the mother is m resident residing at location Cl, 0.45 pg/kg/day if the mother
is a subsistence fanner, and 0.38 pg/kg/day if the mother is a subsistence fisher. All of these
intakes are less than the comparison value of 0.5 pg/kg/day.
Region 6 considered including the effects of the December tire fire in this assessment, but
was unable to complete the evaluation because of a lack of data concerning the actual emission
rates of ccmtaminants during the tire fire and the uncertainties associated with using a methodology
based on long-term chronic exposures to estimate the effects from a short-term event.
Finally, Region 6 conducted a qualitative analysis of the combined effects of windblown
cement kiln dust (CKD) emissions and the contaminant emissions specified in this study. This
51
-------
MIDLOTHIAN, TEXAS CUMULATIVE REASSESSMENT
rtfetfroefafcgy and Results
qualitative analysis was conducted by comparing "best estimates* of high end baseline risks
outlined in EPA's Report to Congress on Cement KHa Dust with the maximum theoretical risk
estimates presented in this report. A quantitative analysis cannot be performed because the
exposure assumptions and fate and transport methodologies used in the two studies contain some
differences, However, the comparison does provide a general feel for the overall contribution of
CKD emissions to the theoretical risk estimated for the area.
As discussed above, the most significant cancer risk identified in the study was to a
subsistence fisherman at a level of 1E-4. Pathways contributing to this risk include ingestion of
fish, ingestion of drinking water, incidental ingestion of soil, ingestion of vegetables, and
inhalation. The CKD Report to Congress provides a 'best estimate" of high end baseline risk
from the ingestion of fish contaminated by CKD at 4E-6. Risk from ingestion of surface water
contaminated by CKD emissions are estimated at 1E-8. Risk from the ingestion of soil
contaminated by CKD are estimated at 1E-7. Risk from ingestion of vegetables is estimated at
2E-6 and risk from inhalation is estimated at 2E-12. All of these risks added together do not
materially affect the most significant estimate contained in this report of 1E-4. Thus, the
uncertainty associated with the failure to treat risk from the emissions of CKD in a quantitative
fashion does not appear to be significant.
52
-------
MIDLOTHIAN, TEXAS CUMULATIVE RISKASSSSMENT
Methodology and'Results
Table 3.3.1 Overall Direct and Indirect Cancer Risk
Across All Carcinogenic Chemicals
:;i- . ' -•• <
MilJ^iilifc^M,;-^..., 'I
ChUR^idnt ...'.-.. J
SJ*tet«»tt Faker
,:;- • • • • : • •.'"
..• - •'.-'"'.'•'
§»*»*«*» Far-cr ;;
Adak Ratio* .::,,, ,^
CVtaUtM** .,.;.^,v-.-.'
SHhate«<»yi«hi*-n '
S«bdsteB« Faraw
A^K RcsidMt .
OflW fiMMwH -•
Subsistence Flshtrman
^i^jt^K^^inplir
Theontieal
BWkfi
Point! Al
7B-6
3B-6
scs
Liken
94; 10
9E-5
;. J«> '
:::lleol;-'
•"•ia**;
•k.;P^:- \
SE-S
Points Bl
3E-5
1B-S
SCS
Lakes
9& 10
1B4
Joe I
fw*
...tri»-'
:; ;,5BiS?"
4B-5
fob** Cl
4E-S
2E-5
SCS
JUkes
9& 10
1B-4
Jw -:
• F«8:- •
' L»k»
: ^6B-5-:
6E-5
53
-------
MIDLOTHIAN, TEXAS CUMULATIVE REASSESSMENT
Afeftoobfcsy anrf/teute
4. LIMrTATIONS
pT
-------
^ MIDLOTHIAN, TEXAS CUMULATIVE RISK ASSESSMENT
Methodology and Results
given the availability of accurate data, fa feet, one of the outside reviewers noted that emission
rates for dioxin were consistent with EPA's experience in preparing the Estimating Exposure to
Dioxin-Uke Compounds (draft) report.
Another significant source of uncertainty in the overall Ike^process is the use of emission
rates for CSC that were based on the assumption that baghouse and fugitive emissions contained
concentrations of contaminants similar to those found in steel mill baghouse dust. Although
contaminant concentrations emitted to the atmosphere from the baghouses are unlikely to contain
concentrations greater than those found in the dust, the fugitive emissions could contain higher
concentrations than those found in the baghouse dust since are emissions that have not yet been
treated. In addition, the volume fugitive emissions could be more or less than assumed in this
study because CSC's actual fugitive emissons have not been measured. Hence the uncertainty in
the emission estimates for CSC are significant.
One area of uncertainty that has been addressed since the review of the draft report by
outside experts is the uncertainty associated with assumed baghouse dust emissions profile. As
discussed at length in Section 2.2, the emissions profile sets forth concentrations of contaminants
that are very similar to CSC actual baghouse dust data with the exception of antimony and
hexavalent chromium.
The lack of any method to check to the viability of antimony and hexavalent chromium
emissions is significant because both of these contaminants contribute to the overall cancer risks
and non-cancer effects estimates. Antimony emissions were based solely on the baghouse dust
profile contained in the ICR, The ICR is based upon data from both stainless and non-stainless
steel mill facilities. CSC reportedly operates a non-stainless steel mill. Hexavalent chromium
emissions were estimated by assuming that the hexavalent chromium emissions constituted only
two percent of total chromium emissions. This assumption of two percent is based on a table
include in the Agency for Toxic Substances and Disease Registry's Toxicological Profile for
Chromium. The actual amounts of antimony and hexavalent chromium emitted by CSC are
unknown.
4.2 Parameter Uncertainty
Another area of uncertainty includes the use of standard EPA default values in the analysis.
These include inhalation and consumption rates, body weight, and exposure duration and
frequency, which are standard default values used in most EPA risk assessments. These
parameters often assume that the exposed population is homogenous, when in estimated
representative variations exist among the population. Using a single point estimate for these
55
-------
MIDLOTHIAN, TEXAS CUMULATIVE RISKASSESSMBSfL
variables instead of a joint probability distribution ignores a variability that may influence the
results by up to a factor of two or three.
Other parameters that are subject to uncertainty are used to estimate the chemical
concentration in the media and locations of interests. The meteorological data from the
Dallas/Fort Worth National Weather Station provided an approximation of the meteorological
conditions at the site as no site-specific data of sufficient quality were available. Different
meteorologie conditions can influence the risk results by up to an order of magnitude given the
same facility characteristics and surrounding land uses.
Another area of uncertainty is the use of EPA verified cancer slope factors, Reference
Doses and Reference Concentration. These health benchmarks are used as single point estimates
throughout the analysis. These benchmarks have both uncertainty and variability associated with
them. However, the EPA has developed a process for setting verified health benchmark values
to be used in all EPA risk assessments. With the exception of the dioxin and BaP toxicity
equivalency methodology all health benchmarks used in this analysis are verified through the
EPA's work groups and available on the EPA's Integrated Risk Information System.
4.3 Limitations of ISCSTDFT /Mr Modeling
The indirect exposure model used in this analysis is EPA's current methodology for
addressing a variety of exposure pathways important for chemicals that bioaecumulate and persist
in the environment. Implementation of this methodology requires air dispersion modeling results
for wet and dry depositions and air concentrations of particles and vapors in a variety of settings.
ISCSTDFT is the only air dispersion and deposition model currently available to provide such
estimates from combustion sources located in both complex and non-complex terrains.
ISCSTDFT was released as a draft and has not been widely applied in the present form.
4.4 Uncertainty /associated with Scenarios
The exposure scenarios included in this screening level assessment include an adult and
child resident, a subsistence fisher and a subsistence farmer. Although a distribution of the
characteristics (e.g., consumption rates) of each type of receptor are reasonably well
characterized, population distributions for the modeled behaviors and activities have not been
adequately studied. For example, little is known about the fraction of the general population that
consists of subsistence farmers and fishers. Without population distributions for these receptors,
the number of people likely to be exposed to contaminated media cannot be determined and,
56
-------
HIDtOTTHiAN. TEXflS CUMULATIVE REASSESSMENT
therefore, the appropriateness of the receptors cannot be evaluated from the standpoint of
population risk.
5. CONCLUSIONS
'T'he results of this conservative screening level risk assessment are:
1, available site data show that Acre are no cancer risks or the potential for
non-cancer health effects above regulatory levels of concern even though
conservative, theoretical models estimate, exposures equal to or slightly
above threshold levels for potential non-cancer effects; and
2, ihe predominate source of the theoretical exposures above threshold levels
is CSC, not the cement companies.
Region 6 arrives at the first conclusion for two reasons. First, the models and exposure
scenarios upon which the estimates of risks and potential non-cancer health effects are theorized
to occur are, in our judgement, conservative. The experts who reviewed this report also
commented at length on the conservatism associated with the risk assessment. Because the risk
assessment is conservative, actual risks and exposures are likely to be less than the estimated risk
and exposures. Given this conservatism and the fact that the theoretical exposures of concern for
antimony, cadmium, and mercury are in the "grey" or "borderline" range (equal to or barely over
the threshold), Region 6 cannot presently justify the necessity for immediate regulatory action.
Secondly, actual measured concentrations of those contaminants that result in exposures
above threshold values appear to be present in media at concentrations less than modeled
concentrations. Actual exposure to antimony (the contaminant with the greatest exposure) in the
Midlothian drinking water supply system equals 0.05 (see Section 3.2) rather than 3 as presented
in Section 3.2. Secondly, actual measured concentrations in soil of two of the contaminants for
which exposures are above threshold levels (antimony and cadmium) are less than modeled
concentrations in me area north of CSC close to receptor locations Cl and C3. The measured and
modeled concentrations are compared in Table 5.1 below along with background data. The fact
that the measured concentrations are less than the modeled concentrations is particularly interesting
given that CSC has been operating since 1975 (20 years to date) and TXI has been burning waste
derived fuel since 1987 (9 years to date) and the risk assessment considers emissions for 30 years.
57
-------
MIDLOTHIAN, TB• •::• -:• JCOlte.* • - '
?V;;ft*tf«a.: .-...;
6,3
11-50
038
* ^ME»SWiiiP'/v":
i:: (MGfflKS .;
<• •• : •" \
o
< 0.095 - 3.6
<1.0
LOCAL BCKG«N»
:-;--rftiJSBfij--
-------
MIDLOTHIAN. TEXflS CUMULATIVE RtSKASSESSMENfT
Methodology and Results
Table 5.2 Comparison of Unit Deposition Hates and Air Concentrations
'•• ' • miXKFOf- •:.
'•'-- .- - '-
CSC Fujfitivci
CSCBtghoiweA
CSC BagfamiM B
CSC BaghouiM C
NTCC
TXI
Holnam
UNITCOMaiNKD
: •"'VDHFOiU ' '; . •-'
U/.'-tr) wrli/«t
30.8
0.320
0.080
0.078
0.005
0.012
0.001
UNIT AIR CONC. !
;:to|^::|^*aft*/
. -. .. ..-....-: r
18
0.37
0.06
0.063
0.006
0.013
0.001
As noted in Table 5.2 above, the deposition rate of contaminants from CSC are at least an
Older of magnitude greater than the contaminant deposition rate associated with Che cement kilns,
CSC's fugitive emissions overwhelm all other deposition rates by two to three orders of magnitude
while Holnam'i and NTCC's deposition rates at this location are almost negligible. TXI's
depostion rate at at this location is greater than Holnam's and NTCC's, yet still significantly less
than CSC's deposition rates.
Likewise, the unit air concentrations associated with emissions from CSC are at least 100
times greater than those associated with NTCC and Holnam. The effect of CSC's baghouse
emissions on contaminant air concentrations at this location is six time the effect of TXI, the next
most significant source. The effect of CSC's fugitive emissions is 1000 times the effect TXI's
emissions.
A comparison of the emission rates between the four facilities in Table 5,3 again shows
that CSC's emissions of antimony and cadmium dominate that of the other facilities, CSC's
estimated emissions of antimony are 186 times that of TXI and CSC's emissions of cadmium are
almost five times that of TXI. Thus, it is clear that the majority of the potential for theoretical
noncancer health effects associated with antimony and cadmium result from CSC, not the cement
manufacturing facilities.
59
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MIDLOTHIAN, TEXAS CUMULATIVE RISKASSESSMEhfL
Table 5.3 Comparison of Emission Rates
Oupaml
Eitimitcd
nsoitit
d/sec)
xn
EstinMlcd
KepmtntlHre
(l/MC)
2.971-02
1.60B-04
NA
Anorit
I.B9E-04
2.13E-W
NA
4.CBM3
8.82B-04
NA
1.17&06
2.08B-0*
3.021-OJ
650E-04
CtnaniumVl
3.78E-0*
16S&M
9.SOB-09
5.85B-02
1. 431-02
S.OOE-05
Mewirj
1.06E-OS
3.01E-04
MS**:
7.68E-03
3.01E-04
3,1^-04
Sttver
NA
S.33B-05
NA
NA
1.16E-03
5.04E-04
Zinc
5.96E-01
5.43E-06
2.69E-03
8.82E-004
60
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MIDLOTHIAN, TEX^VS CUMULATIVE RISKASSESSHENT
Methodology and Results
REFERENCES
General Information
4 USGS quadrangle maps (Cedar Hill, Britton, Venus, Midlothian).
Camp, Dresser, and McKee. 1989, Woter&etl Management Stuety: Lake Michie and Litlle River
Reservoir Watersheds. Prepared for the County of Durham, NC.
Document entitled Location of Known Commercial Animal Operations in the Midlothian Area,
Draft table entitled Emissions Estimates. This table was prepared by the TNRCC and describes
the rationale behind their selection of emission rates that are different from the rates recommended
by TNRCC permit engkeers in memorandums dated March 20 and April 12, 1995 (see list of
items for NTCC and TXI below).
Dravo Corporation. 1976. Managing and Disposing of Residues from Environmental Control
Facilities in the Steel Industry. Prepared for the U.S. EPA Office of Research and Development.
Contract Number R-803619.
Geological Survey Planimetric Map, Cleburne, Texas
Geological Survey Planimetric Map, Corsicana, Texas
Geological Survey Planimetric Map, Dallas, Texas
Geological Survey Planimetric Map, Ft. Worth, Texas
Geraghty, JJ, D.W. Miller, F. Van Der Leeden, and F.L. Troise. 1973. Water Atlas of the
United States. Water Information Center, Inc., NY.
Kites, R.A., and S.L. Simonich. 1994. Vegetation - Atmosphere Partitioning of Polycyclic
Aromatic Hydrocarbons. Env. Sri, Tech. Vol. 28 No.5.
Jindal, M. and D. Reinhold. 1991. Development of Particulale Scavenging Coefficients to Model
Wet Deposition from Industrial Combustion Sources. Paper 91-59.7. Annual Meeting -
Exhibition of Air and Waste Management Association, Vancouver, BC. June 16-21, 1991.
61
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MIDLOTHIAN, TEXAS CUMULATIVE RISK ASSESSMENT
Methodology m*t Refute
Memorandum, from U.S. EPA\ORD, to Addressees, January 20, 1995,
PEI Associates, Inc. 1986. Air Quality Modeling Analysis of Municipal Wasie Combustors.
Prepared for the U.S. Environmental Protection Agency, Monitoring and Data Analysis Division,
Research Triangle Park, NC.
Real Estate List (computer printout) for the Midlothian ISO, dated April 25, 1995. This report
was developed by the Ellis County Appraisal District and specifies property owners in the area
that have proven that their property is used for agricultural or ranching purposes. Code "D1" is
a ranch and code "D3" is a farm.
Research Triangle Institute. 1993, Detailed Summary of Information Collection Request
Responses for Electric Arc Furnace (BAF) NESHAP. Prepared for U.S. EPA Office of Air
Quality Planning and Standards.
Texas Department of Health, Division of Milk and Dairy Products, Establishment Report dated
April 24, 1995,
TNRCC draft report section entitled Selection of Receptors for 7X7 dated April 4, 1995.
TNRCC, 1995. Critical Evaluation of the Potential Empact of Emissions from Midlothian
Industries: A Summary Report. Office of Air Quality/Toxicology and Risk Assessment Section.
Austin, TX.
U.S. EPA, 1989. Risk Assessment Guidance for Superfimd. Office of Emergency and Remedial
Response. Washington, DC. EPA/540/1-89/002.
U.S. EPA. 1990. Exposure Factors Handbook, Office of Health and Environmental Assessment,
Exposure Assessment Group. Washington, D.C, March.
U.S. EPA. 1990a. Methodology for Assessing Health Risks Associated with Indirect Exposure
to Combustion Emissions. Interim Final. Office of health and Environmental Assessment/Office
of Research and Development. EPA/600/6-90/003.
U.S. EPA, 1994. Guidance for Performing Screening Level Risk Analysis at Combustion
Facilities Burning Hazardous Waste. Office of Emergency and Remedial Response/Office of
Solid Waste, Washington, DC.
62
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MIDLOTHIAN. TEXAS CUHUATIVE RISK ASSESSMENT
Mefaxtakigy and Results
U.S. EPA. 1994a. Estimating Exposure to Dioxim-tike Compounds. Review Draft. Office of
Research and Development. Washington D.C. June. EPA/6QO/6-88/OG55C.
U.S. EPA. 1994b. Mercury Study Report to Congress, Office of Air Quality Planning and
Standards and Office of Research and Development, Research Triangle Park, NC and
Washington, DC.
U.S. EPA. 1994d. User's Guide for the Industrial Source Complex Dispersion Models. Office
of Air Quality Planning and Standards, RTF, NC. Draft.
U.S. Department of Commerce. 1992. International Station Meteorological Climate Summary
CD ROM.
Vin der Leeden, F., F.L. Troise, and O.K. Todd. 1990, The Water Encyclopedia. Lewis
Publishers, Chelsea, MI.
Chaparral Steel
Dispersion Modeling of Emissions Jmm Large Section Mill Reheat Furnace (prepared by Forsite
Corporation for Chaparral Steel) dated November 1989.
Letter and enclosures from Chaparral Steel Company to Region 6 dated May 8, 1995, responding
to the Region's request for information about the emission of contaminants from Chaparral's
facility.
Unsolicited letter and enclosures from Chaparral Steel Company to Region 6 dated December 20,
1995. Enclosure entitled Ambient Monitoring Program contains concentrations of contaminants
in Chaparral's baghouse dust.
Unsolicited letter and enclosures from Chaparral Steel Company to Region 6 dated January 16,
19%. Enclosure entitled Analytical Results - Off-Site Investigation contains results of the analysis
of soil samples collected from the area immediately north of Chaparral Steel Company.
New/Modified Source Technical Review (prepared by TNRCC) dated May 22, 1992.
TAGS Mini Emissions Inventory Report (for Chaparral) from the Point Source Database dated May
2, 1995.
63
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MIDLOTHIAN, TEXAS CUMULATIVE R»9C ASSESSMENT
Texas Natural Resource Conservation Commission (TN1CC) Air Permit dated February 22,
1994.
Holnam Texas, L.P.
A letter from Holnam to TNRCC regarding the previous letter regarding dioxin emissions
submitted by its consultant Trinity. The letter corrects the emission rales identified in the Trinity
letter to account for sample dilution.
Letter from Holnam Texas, L.P. to Region 6 dated May 19, 1995, in response to Region 6's
request for information regarding emission rates.
Letter summarizing dioxin data from Trinity Consultants to TNRCC dated November 12, 1993.
Selected portions of Holnam's (known as BoxCrow Cement Co. at the time) application to amend
their air permit dated November 1992 prepared by Trinity Consultants.
TACB Mini Emissions Inventory Report (for Holnam) from the Point Source Database dated May
2, 1995.
TNRCC Air Permit for Holnam - Maximum Allowable Emission Rates. Permit number 8996 and
PSD-TX-454M1. September 26, 1994.
TNRCC Air Permit for Holnam - Special Provisions. Permit number 8996 and PSD-TX-454M2.
Apriil26, 1994.
North Texas Cement Company (NTCQ
Appendix ffl.A,, RCRA Part B Permit Application entitled General Engineering Report for North
Texas Cement Company,
Copies of Tables 21-24 summarizing results of dioxin testing conducted November 7-9, 1991.
Draft Table 2.2 dated May 2, 1995, entitled NTCC Emission Estimates Used in the Final Risk
Assessment. (This will eventually be used in TNRCC1 s risk assessment report. However, be
advised that Industry states that table contains an error with regard to emissions rates for As, Be,
Hg and Cr. TNRCC developed the emission rates based on permits limits in Ib/hr but incorrectly
64
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MIDLOTHIAN. TEXAS CUMULATIVE FUSKASSESSHEhfT
Me&odology and HesiMs
adjusted data to gram/sec).
Excerpt from a BIF test report entitled Semivolotite/PAH Data, June 1992 BIF Test. Excerpt
includes test data from Test 2, Runs 1-3. Analyses were conducted July 19, 1992.
Excerpt from the NTCC Trial Burn Report that provides information about contaminant
concentrations in NTCC's CKD,
Pages H-l through D-12 of a risk assessment protocol prepared by NTCC. This information was
provided to EPA during a meeting on May 8, 1995 with Bill Wilson of NTCC. The emission
rates identified in Table II-1 are the rates NTCC believes should be used to support the risk
assessment.
TACBMini Bntoloni Inventory Report (for NTCC) from the Point Source Database dated May
2, 1995.
TNMCC memorandum dated March 20, 1995 from Michael Koenig to Lucy Fraiser regarding
emission estimates for TNRCC's NTCC risk assessment.
TNRCC's, 1995. North Terns Cement Company (NTCC) Modeling Approach to Risk Assessment
Screening Analysis, April 21, 1995.
Texas Industries, Inc. (TXI)
Copy of draft Table 2.2 dated May 2, 1995, entitled TXI Emission Estimates Used in the Final
Risk Assessment, (This table will eventually be used in TNRCC's risk assessment report.)
Copy of TNRCC's draft Texas Industries, Inc. (TXI) Modeling Approach to Risk Assessment
Screening Analysis dated April 24, 1995.
Copy of TXTs draft Protocol for a Comprehensive Risk Assessment for the Texas Industries
Facility, Midlothian, Texas dated July 15, 1994.
Copy of draft memorandum from Paul DeCiutiis to Lucy Fraiser, dated April 12, 1995, regarding
emission estimates for TNRCC's TXI risk assessment.
65
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MIDLOTHIAN, TEXAS CUMULATIVE REASSESSMENT
MelhodolograndResules
Copy of selected portions of Part B Permit Application {Section 5.0 [contains modeling and stack
parameter/test data information]).
Copy of selected portions of Trial Burn Report (Volume 1, Chapter 1).
Copy of Adjacent Landowners Map identified as Figure LG. 1. The source of this information
is unknown.
Excerpt from the TXI Trial Bum Report that provides information about contaminant
concentrations in TXTs CKD.
Section 1 of Part B Permit Application. Contains facility background and land use information.
TNRCC Air Permit for TXI - Special Conditons. Permit Number 1360A. February 28, 1995,
TNRCC air Permit for TXT - Emission Sources - Maximum Allowable Emission Rates, Permit
Number 1360A. June 6, 1994,
66
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