A RISK ASSESSMENT OF
THE USE AND REUSE OF NORM-
CONTAMINATED WASTE
Prepared by
Rogers & Associates Engineering Corporation
P.O. Box 330
Salt Lake City, Utah 84110-0330
(801) 263-1600
under contract with
Sandy Cohen & Associates, Inc.
1311 Dolley Madison Blvd., Rte. 123
McLean, VA 22101
Contract No. 68-D90-170
Work Assignment 2-28
Prepared for
U. S. Environmental Protection Agency
Office of Radiation Programs
Washington, D.C. 20460
William E. Russo
Work Assignment Manager
September 1992

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Table of Contents
Executive Summary	ES-1
Figures	 v
Tables 	 vii
1.	Introduction 	 1-1
2.	NORM in Production Wastes 	2-1
2.1	Oil and Gas Production Wastes	2-1
2.1.1	Oil and Gas Scale and Sludge Production Rates	2-2
2.1.2	Radionuclide Concentrations	2-4
2.2	Phosphogypsum 	2-11
2.2.1	Production Process 	 2-11
2.2.2	Physical and Radiological Properties	2-14
3.	Scenarios and Exposure Pathways for Reuse	3-1
3.1	Oil and Gas Production Equipment	3-1
3.1.1	General Unrestricted Release 	3-1
3.1.2	Reprocessing of Scrap Steel	3-3
3.1.2.1	Pipe Cleaning 	3-5
3.1.2.2	Storage Yard	3-7
3.1.2.3	Transportation	3-7
3.1.2.4	Smelting NORM-Contaminated Materials ... 3-8
3.1.2.5	Steel Mill and Scrap Yard Alarm Systems . . 3-15
3.2	Phosphogypsum 	 3-17
3.2.1	Phosphogypsum in Agriculture		3-17
3.2.2	Phosphogypsum in Road Construction	3-18
3.2.3	Phosphogypsum in Research and Development		3-19
3.2.4	Filter Pan Cleaning		3-19
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Table of Contents (Continued)
4.	Risk Assessment Methodology 	4-1
4.1	Computer Models	4-1
4.1.1	The PATHRAE Dose Assessment Model	4-3
4.1.2	The PRESTO-EPA-PILCPG Computer Code	4-3
4.1.3	The COMPLY Computer Code	4-4
4.1.4	The MICROSHIELD Computer Code	4-4
4.1.5	The VARSKIN Computer Code	4-5
4.2	Exposure Scenarios	4-5
4.2.1	Oil and Gas	4-5
4.2.1.1	Equipment Released to Schools 	4-6
4.2.1.2	Unrestricted Residential ReUse 	4-11
4.2.1.3	Pipe Cleaning	4-13
4.2.1.4	Storage of Contaminated Equipment	4-15
4.2.1.5	Transportation of Contaminated Equipment	4-22
4.2.1.6	Steel Mill and Scrap Yard Alarm Systems	4-22
4.2.1.7	Recycled to Smelter	4-25
4.2.2	Phosphogypsum 	4-29
4.2.2.1	Phosphogypsum in Agriculture	4-29
4.2.2.2	Phosphogypsum in Road Construction 	4-38
4.2.2.3	Phosphogypsum in Research and Development
Activities	4-41
4.2.2.4	Cleaning of Stainless Steel Filter Pans 	4-41
5.	Risk Assessment Results 	5-1
5.1	Oil and Gas Production 	5-1
5.1.1	Maximum Individual Exposures 	5-1
5.1.2	NORM Transportation	5-7
5.2	Phosphogypsum 	5-11
5.2.1	Phosphogypsum in Agriculture	 5-11
5.2.2	Phosphogypsum in Road Construction	5-14
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Table of Contents (Continued)
5.2.3	Phosphogypsum in Research and Development Activities 	5-14
5.2.4	Cleaning of Stainless Steel Filter Pans	5-19
6. Conclusions 	6-1
References 	R-l
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Figures
2-1 Principal nuclides, decay modes, and mobilities of the Uranium-238 and
Thorium-232 decay chains 	2-3
2-2 Median of differences of external gamma readings over local background for
NORM-contaminated gas production equipment (API89)	2-6
2-3	Median of differences of external gamma readings over local background for
NORM-contaminated oil production equipment (API89)	2-7
3-1	Steel reprocessing technology	3-4
3-2	Schematic diagram of a smelting furnace	3-9
4-1	Exposure pathways from a jungle-gym contaminated with NORM	4-7
4-2 Exposure pathways from the use of NORM-contaminated scrap steel
in a welding shop 	4-8
4-3 Exposure pathways from the unrestricted use of NORM-contaminated
equivalent in residential applications 	4-12
4-4 Exposure pathways from the mechanical cleaning of NORM
contaminated tubing and pipe	4-16
4-5 Exposure pathways from the hydrolaser cleaning of NORM
contaminated tubing and pipe	4-17
4-6 Exposure pathways from the storage of NORM-contaminated tubing	4-20
4-7 Exposure pathways from the transport of NORM-contaminated
material 	4-23
4-8 Exposure pathways from the smelting of NORM-contaminated scrap
steel	4-27
4-9 Exposure pathways from the agricultural use of phosphogypsum	4-32
4-10 Scenarios involving the use of phosphogypsum in road construction 	4-39
4-11 Exposure pathway from research activities using phosphogypsum	4-42
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Figures (Continued)
5-1 Alarm exposures from NORM-contaminated trailers for varying
loading schemes 	5-8
5-2 Variations in alarm exposures with respect to NORM-contaminated
equipment group position in load	5-9
5-3 Alarm exposures for uniformly distributed loads of NORM
contaminated equipment vs. radium concentration of the NORM	5-10
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Tables
1-1	Application of 10 CFR 50 and 40 CFR 141 to NORM-contaminated
equipment reuse 	1-2
2-1	Median and 90 percentile gamma radiation levels and NORM
concentrations based on (API89) survey data 	2-8
2-2 Median and 90 percentile radium concentrations in NORM scale (RAE92)
(using measurement data exceeding 15 pCi/g equivalent)	2-10
2-3 Median and 90 percentile radionuclide concentrations in gas and oil
production NORM scale (RAE92)	2-12
2-4 Median NORM-contaminated equipment volumes for a ten well
facility (EPA91, RAE91b) 	2-13
2-5	Phosphogypsum median and 90 percentile radionuclide concentrations	2-15
2-6	Phosphate scale median and 90 percentile radionuclide concentrations	2-17
3-1	Exposure scenarios for evaluation 	3-2
3-2	Surface decontamination technology alternatives (CHA91)	3-6
3-3 Properties of critical compounds in the smelting of NORM
contaminated steel	3-11
3-4	Alarm screening settings for contaminant detection at steel mills,
scrap yards, and landfills 	3-16
4-1	Dose and risk conversion factors	4-2
4-2	Input parameters for school scenarios	4-9
4-3	Residential reuse input parameters	4-14
4-4	Input parameters for the mechanical abrasive pipe cleaner scenario	4-18
4-5	Input parameters for the hydroblaster cleaning scenario 	4-19
4-6	Storage yard exposure scenario input parameters	4-21
vii

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Tables (Continued)
4-7	Transportation scenario input parameters 	4-24
4-8	Alarm scenario input parameters	4-26
4-9	Smelting input parameters 	4-28
4-10	Site-specific input parameters for phosphogypsum risk assessments	4-30
4-11	Phosphogypsum use parameters for agricultural scenarios	4-33
4-12	Ra-226 soil concentration calculation parameters	4-36
4-13	Ra-226 soil concentrations 	4-37
4-14	Stainless steel filter pan cleaning scenario input parameters 	4-44
5-1	Risk assessment results for unrestricted release scenarios with
median NORM concentrations	5-2
5-2 Risk assessment results for unrestricted release scenarios with 90
percentile NORM concentrations	5-3
5-3 Risk assessment results for the contaminated oil production
equipment reprocessing scenarios for median NORM concentrations	5-4
5-4 Risk assessment results for the contaminated oil production equipment
reprocessing scenarios for 90 percentile NORM concentrations	5-5
5-5 Risk assessment results for agricultural scenarios involving median
phosphogypsum concentrations	5-12
5-6 Risk assessment results for agricultural scenarios involving 90 percentile
phosphogypsum concentrations	5-13
5-7 Risk assessment results for road construction scenarios involving
median phosphogypsum concentrations 	5-15
5-8 Risk assessment results for road construction scenarios involving 90
percentile phosphogypsum concentrations	 5-16
viii

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Tables (Continued)
5-9 Risk assessment results for the research and development scenario
involving median phosphogypsum concentrations 	5-17
5-10 Risk assessment results for the research and development scenario
involving 90 percentile phosphogypsum concentrations 	5-18
5-11 Risk assessment results for the stainless steel filter pan cleaner
scenarios 	5-20
ix

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Executive Summary
The Environmental Protection Agency (EPA) has had a continuing interest in addressing potential
including emissions from several NORM sources such as elemental phosphorus plants and the
disposal of phosphogypsum, and guidance on the disposal of drinking water treatment residues.
The EPA, in May 1991, released a draft risk assessment characterizing generation and disposal
practices of wastes which contain diffuse levels of NORM (EPA91).
In order to minimize wastes, alternative uses of NORM-contaminated oil production equipment
and phosphogypsum arc currently being developed and practiced. An investigation into the
recycling and reuse of these materials is needed to evaluate risks and exposures to the public.
The overall objective of this report is to present a risk assessment of the products associated with
reprocessing and reuse of NORM-contaminated oil production equipment and phosphogypsum.
Current reuse and recycling practices are summarized along with any associated requirements and
regulation for transportation and reuse of NORM-contaminated material.
The oil and gas production industry produces approximately 700,000 m3 of waste (sludge, scale,
and equipment) annually (EPA91). It is estimated that ten to thirty percent of this waste contains
naturally-occurring radioactive material (NORM) (EPA91). The production of oil and gas can
concentrate the NORM. NORM waste from oil and gas production contains about 10 to
100,000 pCi of radium per gram of waste (EPA91). A median value of 360 pCi (API89) radium
per gram of scale is used in the risk assessment. Lower radium concentrations (50 pCi/g) occur
in sludges from oil and gas production, but neither sludge nor the equipment containing sludge
are reused (API89).
The yearly phosphogypsum production has averaged nearly 40 million MT since 1984 (EPA91).
The total phosphate waste volume generated in the U.S. from 1910 to 1981 has been estimated
at 7.7 billion MT (EPA91). An average of eight percent of the mined phosphate rock
radiation exposures from the use and management ofjNaturally Occurring Radioactive Materials
Draft standards and recently promulgated regulations address several areas of concern,
ES-1

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(approximately 3.2 million MT) are processed annually in thermal plants for the production of
elemental phosphorous (EPA91). Since the thermal process yields about 0.07 MT (EPA91) of
elemental phosphorous per MT of phosphate rock, approximately 3.0 million MT of slag are
generated yearly by U.S. thermal plants. The annual average slag generation rate is estimated
to be 600 thousand MT per plant.
Alternative uses of NORM-contaminated oil and gas production equipment and phosphogypsum
reviewed in this document are based on actual practices. Before the accumulation of NORM in
oil and elemental phosphorous production equipment was fully recognized, contaminated
equipment, such as tubing, was occasionally released to the public for alternative uses (FUE92).
The uses included: load-supporting beams in house construction, plumbing for culinary water,
fencing material, for playground equipment in school yards, awning supports, and practice
welding material in classrooms (FUE92).
Since its discovery, greater precautions have been taken to evaluate and remove NORM
contamination from used oil and phosphate-production equipment before its release for reuse
(ZAL92). Loads of scrap metal being transported are often surveyed for hidden radioactive
sources and for NORM (MIN92, BER92). Piping and equipment are generally cleaned before
release or before being sent to a smelter. Additionally, pollution control devices such as filters
and bubblers are emplaced in the smelter stacks to reduce airborne emissions (ROW92).
Selection among these alternatives depends in part on the quantity of NORM remaining in the
equipment.
Alternatives for the use of phosphogypsum have included use as a soil conditioner for agriculture,
as a base for secondary road construction, as a concrete additive, and in research and
development activities (RAE92). Recent revisions to the NESHAP for phosphogypsum reuse
limit the average radium-226 concentration in phosphogypsum for agricultural use to no greater
than 10 pCi/g. Additionally, the use of phosphogypsum in research and development is
permitted. However, no facility may purchase or process more than 700 pounds of
ES-2

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phosphogypsum. Other uses of phosphogypsum are now prohibited without prior EPA approval
(FR92).
Risks resulting from exposures in the various scenarios are estimated. The PATHRAE
methodology is used to determine the risks of human exposure to various contaminant pathways.
The MICROSHTEI.D code is used to determine direct gamma exposure rates for scenarios too
complex for the PATHRAE methodology. PRESTO-PILCPG is used to determine exposures
from atmospheric resuspension pathways. COMPLY is utilized to determine exposures from
stack releases. VARSKIN is used to determine acute dermal exposures from direct contact with
NORM scale.
Risks resulting from the reuse and recycling of NORM are found to be significant in several
cases. For the scenarios involving past practices of unrestricted general release, overall risks
range from 1.7E-08 for a teacher supervising a playground to 1.2E-05 for a child playing on a
NORM-contaminated jungle gym (for median NORM concentrations). In the scenarios where
NORM-contaminated equipment is reprocessed, risks are comparable where the amount of scale
transported via the dominant exposure pathways and exposure times are larger (9.0E-09 for a
truck driver and 2.0E-04 for a smelter yard worker where no special NORM capturing slag agents
are added).
The risks from the use of phosphogypsum are significantly affected by inhalation of radon. Risk
to the fanner of land where phosphogypsum was used as fertilizer is 6.8E-06 (with 3.1E-06
resulting from radon inhalation). Risk to the reclaimer of land where phosphogypsum was used
as an additive to concrete for road construction is 1.4E-04 with 8.1E-05 resulting from radon
inhalation.
The risk assessments are calculated to provide insight into the potential health impacts associated
with the reuse and recycling of NORM wastes; to determine whether a more vigorous analysis
or more detailed characterization is justified; and to help evaluate the need for future regulatory
action.
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1. Introduction
Natural radioactivity occurring at trace concentrations in oil and gas formations, ore bodies, and
water supplies can accumulate during production or purification. Since the radioactivity is
generally low and of natural origin, its accumulation and significance were not noted and studied
until recently (MAR87). This report presents analyses of the radiological impacts from the reuse
of equipment containing naturally-occurring radioactive materials (NORM) from oil and gas
production facilities and from phosphate fertilizer production plants. Additional concerns result
from past general reuses of NORM-contaminated equipment and wastes without knowledge of
their NORM concentrations.
NORM concentrations in oil and gas production equipment and phosphogypsum vary from
background levels to levels exceeding 100,000 pCi/g (EPA91), suggesting a similarly broad range
of risks from alternative uses for the contaminated equipment When elevated occurrences are
found, the equipment use should be handled in a way that protects against significant radiation
exposure. Although detailed regulations restrict the uses of radioactive materials regulated under
the atomic energy act (10 CFR 61, 40 CFR 192), there is no specific federal guidance on the
reuse of wastes and contaminated equipment containing NORM with elevated radionuclide
concentrations. Due to the lack of specific federal guidance, NRC Regulatory Guide 1.86,
providing direction for implementation of the requirements of 10 CFR 50, is often applied for
guidance in NORM-contaminated equipment release and reuse.
Specifically, 10 CFR 50 presents requirements for termination of an operating license for a
nuclear reactor, including decontamination of the facility and equipment. Residual radioactive
contamination levels are specified for release of areas, equipment, and materials for unrestricted
reuse. These levels are expressed as dpm per 100 cm2 area. If contaminated tubing and pipes
are to be used for culinary water plumbing, then the national primary drinking water regulations
and maximum allowable radionuclide water concentrations specified in 40 CFR 141 are also
applicable. Table 1-1 presents a summary of the applicable regulation from 10 CFR 50 and
40 CFR 141.
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Table 1-1. Application of 10 CFR 50 and 40 CFR 141 to NORM
contaminated equipment reuse.
Citation & Title
Limit
10 CFR 50, Domestic Licensing of
Production and Utilization
Facilities/NRC Regulatory Guide 1.86
40 CFR 141, National Primary
Drinking Water Regulations
Avg: 100 dpm/100 cm2 a
Max: 300 dpm/100 cm2
Pb-210	4 mrem/y
Ra-226	20 pCi/1
Ra-228	20 pCi/1
Po-210	15 pCi/1
Th-228	15 pCiyl
Limit applies to overall exposure reading from NORM (approx. 45 pCi/100 cm ).
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The Part N subcommittee of the National Conference of Radiation Control Program Directors has
been working since 1983 to develop model state regulations (Part N of suggested State
Regulations for control of Radiation) for the control of NORM (CPD87). These model
regulations are intended to help individual states develop regulations in a uniform way such that
the regulations are consistent from state to state and with Federal regulations.
The NORM Ad Hoc Committee, consisting of representatives from the Environmental Protection
Agency Alabama, Arkansas, Louisiana, Mississippi, Oklahoma and Texas, met June of 1990 and
informally adopted interim guidance on the release of NORM-contaminated equipment It is
recommended that equipment contaminated below SO pR/hr should be released for general reuse.
Additionally, equipment contaminated above 50 pR/hr should be cleaned to levels below 50 pR/hr
before release (AHC90). It should be noted that the Environmental Protection Agency does not
agree with these proposed standards (EPA92a). Additionally, both Mississippi and Texas have
since proposed different regulations.
Louisiana is the only state at this writing that has regulations specifically concerning NORM and
NORM-contaminated equipment The State of Louisiana licenses the operators of cleaning and
refurbishing shops which handle oil production equipment NORM-contaminated scale is now
regulated to protect the cleaning operators and the general public. Transfer of oil production
equipment and land must be preceded by a release survey to insure that NORM is not released
to the general public for unrestricted use.
Other states are applying broad ionizing radiation regulations to NORM guidance. The State
of Michigan, in Rule 2410, restricts any employer from possessing, using, or transferring sources
of ionizing radiation in such a manner as to cause any individual in a restricted area to receive
in any period of one calendar quarter a whole body dose in excess 1.25 rem. Additionally, Rule
2410 restricts airborne contaminants (R2410).
The U.S. Department of Transportation (DOT) also does not specifically regulate NORM, but it
does regulate the transportation of radioactive material. The DOT regulations, applicable to the
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transport of low-level radioactive waste, arc found in Title 49 of the U.S. Code of Federal
Regulations Parts 171, 172, 173, and 177. Paragraph 173.403(y) specifically defines regulated
radioactive material as "any material having a specific activity greater than 0.002 microcuries
per gram" (49 CFR 173). Since the radionuclides of the Ra-226 decay chain are the principal
elements in NORM, the applicability of the 49 CFR 173 limit can be determined as follows:
CRa-226 " 3 CRa-228
where
CRa-226 = concentration of Ra-226 in scale (pCi/g)
CRa-228 = concentration of Ra-228 in scale (pCi/g)
Applying this relationship and the five principal nuclides (including daughters) being considered
(see Table 2-3) gives:
3 CRa-226 + 2	= 2,000 pCi/g	(1*2)
Solving equations 1-1 and 1-2 simultaneously gives a limiting total radium (Ra-226 and Ra-228)
of 726 pCi/g. NORM-contaminated equipment with total radium concentrations greater than this
limit are then required to follow DOT regulations for the transportation of low-level radioactive
waste before being shipped. Additionally, paragraph 173.441(b3) restricts radiation levels at any
point 2 meters from the outer lateral surfaces of a transport vehicle to a maximum of 10 mR/hr
(49 CFR 173).
This report analyzes the risks associated with the reuse and handling of oil and gas production
equipment and phosphate scale equipment contaminated with NORM (cleaned or undisturbed)
and phosphogypsum. Reuse alternatives analyzed include: 1) storage of equipment on site;
2) use of phosphogypsum as a soil conditioner, a road construction base, and as a concrete
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additive; 3) unrestricted release of contaminated equipment to the general public; and 4) smelting
of equipment for the fabrication of new products. The exposures from both median and 90
percentile NORM concentrations are evaluated separately to better estimate their range. For the
reuse alternatives, radiation exposures aie considered from radon gas inhalation, external
gamma-ray exposure, contaminant ingestion and dust inhalation. Scenarios analyzed are based
on current industrial methods and actual practices where possible. Using the NORM
concentrations and the risk involved in each exposure pathway an evaluation can be made as to
the risks from reuse practices.
Risks from exposures during cleaning and reprocessing of contaminated oil and gas production
and phosphate ore equipment are also analyzed. Exposure pathways during cleaning and
recycling of NORM-contaminated equipment are identified from point of generation to the final
release of the recycled product Potential worker risks and radionuclide concentrations and
dilutions are evaluated for each process. Additionally, alternative cleaning methods and exposure
reduction procedures currently being utilized in the steel industry are reviewed.
As a safeguard against unknowingly receiving radioactive sources and other materials, many steel
mills and scrap yards are installing alarmed detection systems (ZAL92). Some of these alarm
systems are being tripped by NORM-contaminated equipment being received for reprocessing
(ZAL92). Minimum detectable NORM concentrations, loading distributions and volumes are
analyzed as part of this risk assessment Additionally, these limiting concentrations and volumes
are compared with applicable DOT regulations.
This report presents a waste and use characterization and risk assessment for NORM generated
in oil and gas production and fertilizer production. The general methodology presented here can
be used to evaluate similar scenarios and situations. Chapter 2 presents an overview of the
industry, the characterization of physical and radiological properties of the waste and the waste
generation rates. Chapter 3 presents the reuse practices which determine the pathways of
exposure. Additionally, current radiation detection methods and alarm settings are presented.
The risk assessment methods, presented in Chapter 4, document the exposure scenarios.
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Chapter 5 gives the results of the risk assessments. The risk assessments are calculated to
provide insight into the potential health impacts associated with the reuse and recycling of
NORM waste; to determine whether a more vigorous analysis or more detailed characterization
is justified; and to help evaluate the need for future regulatory action. Chapter 6 provides a
summary and conclusions.
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2. NORM in Production Wastes
This chapter discusses the production of NORM wastes in the oil, gas and phosphate industries.
The wastes are characterized and median and high radionuclide concentrations are estimated.
Source terms used in the risk assessments of Chapter 4 and 5 are presented and justified.
2.1 OIL AND GAS PRODUCTION WASTES
Both uranium and thorium and their decay products are known to be present in varying
concentrations in underground geological formations from which oil and gas are produced
(BEL60, JOH73, PIE55). The presence of these naturally occurring radionuclides in petroleum
reservoirs has been recognized since the early 1930's and has been used as one of the methods
for finding hydrocarbons beneath the earth's surface (MAR87). Uranium and thorium are
insoluble and, as oil and gas are brought to the surface, they remain mostly in place in the
underground reservoir (EPA91). However, radium and the radium daughters are slightly soluble,
and under some conditions may become mobilized by the liquid phases in the formation
(EPA91). When brought to the surface with liquid production streams, radium and its daughters
may remain dissolved at dilute levels, or they may precipitate because of chemical changes and
reduced pressure and temperature (EPA91). Since radium concentrations in the original
formation are highly variable, the concentrations that precipitate out on the surfaces of oil and
gas production and processing equipment are also variable and may exhibit elevated radioactivity
levels. Scales and sludges that accumulate in surface equipment may vary from background
levels of NORM (~1 pCi/g) to elevated levels as high as hundreds of thousands of picocuries per
gram depending on the radioactivity and chemistry of the geologic formation from which oil and
gas are produced and on the characteristics of the production process (EPA91, RAE92).
The initial production of oil and gas from a reservoir is usually dry (EPA91). However, as the
natural pressure within the petroleum bearing formation falls, groundwater present in the reservoir
will also be brought to the surface with the oil and gas. This formation water contains dissolved
mineral salts, a very small proportion of which may be radioactive because of the presence of
2-1

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uranium and thorium and their decay products in the underground formation. Thus, the amount
of surface NORM material from a producing field generally increases with the increases in the
amount of water pumped from the formation (EPA91).
Deposits in production equipment are generally in the form of scale, loose material, and oily
sludge. The scale in these chemical matrices is very hard and relatively insoluble. It may vary
in thickness from a few millimeters to more than 3 cm (RAE92). Some accumulations have been
known to completely block the flow in pipes as large as 4 inches in diameter (EPA91).
The NORM accumulated in production equipment scales typically contains radium coprecipitated
in barium sulfate (BaSO^ (EPA91). Sludges are dominated by silicates or carbonates, but also
incorporate trace radium by coprecipitation. Ra-226 is generally present in scales and sludges
in higher concentrations than Ra-228 (EPA91). The nominal activity ratio appears to be about
three times as much Ra-226 as Ra-228 (EPA91). Typically, Ra-226 is in equilibrium with its
decay products, but Ra-228 is not in equilibrium with its decay products. Reduced concentrations
of Ra-228 daughters are due to the occurrence in the thorium series decay chain of two radium
nuclides (Ra-228 and Ra-224) separated by Th-228 with a 1.9-year half-life. Thus radium
mobilized from the formation initially becomes depleted in Ra-224 (half-life = 3.6 days) until
more is generated by Ra-228 decay through Th-228 (Figure 2-1). For the sake of simplicity, the
term radium is used in this report to refer to the combination of Ra-226 and Ra-228.
2.1.1	Oil and Gas Scale and Sludge Production Rates
The volume of NORM scale and sludge that is produced annually is uncertain, but recent
estimates suggest that as many as one-third of domestic oil and gas wells may produce some
radium-contaminated scale (MCA88, EPA91). The geological location of the oil reserve and the
type of production operation strongly influences the prevalence of NORM accumulations. A
review of surveys conducted in 13 of the major oil producing states revealed that the number of
facilities reporting NORM in production wells ranged from 90 percent in Mississippi to none or
only a few in Colorado, South Dakota, and Wyoming (MCA88). However, 20 to 100 percent
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238
u
4.5 bll v

a

i
234
Th
24 d
1/
234 Pa
lim
/
234
u
240,000 y

a
Thorium Daughters,
Deposited At
Radon Decay Sites
^Th
ttftZiTl
226 Ra

iz
222 Rn
3.8 d

a

'
218 po
3.1 m

a
214
Pb
27m
Mostly Immobile, Remaining In
Underground Formations
Partially Mobilized, Occasionally
Accumulating In Scales and Sludges
Mobile Gas, 5%-22% Emanated From
Scales and Sludges, Soluble In
Petroleum Liquids
/
214 Bi
20 m
/
214 p0
160|i
sac

a
210
Pb
»y
1/
P
210
Bi
"5ira"
/
210 |

1 140 d |

a
1206
Pb]

Uranium-238 Decay Series
232
Th
14 bll V

a


228
Ra
5.8 y
228

Ac
f.
6.2 n
Thorium Daughters,
Deposited At
Radon Decay Sites
228 Th
l.fly
224
Ra
3.7 d
220 Rn
wr
216
Po
0.15 »
a
Mostly Immobile, Remaining In
Underground Formations
Partially Mobilized, Occasionally
Accumulating In Scales and Sludges
Mobile Gas, 5%-22% Emanated From
Scales and Sludges, Soluble In
Petroleum Liquids
212
Pb
ITTT

212
Bi
61 ni7 m

a
208
Tl
3.1 m
212
Po
0.30US


210
Bi
5.0 d
Thorium-232 Decay Series
RAE-104062
Figure 2-1. Principal nuclides, decay modes, and mobilities of the
Uranium-238 and Thorium-232 decay chains.

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of the facilities in every state identified NORM in heater/treaters. A separate estimate based on
Mississippi data indicates that one-half of the wells do produce scale and ten percent of these
have scale with elevated NORM concentrations (BLI88).
In a recent assessment of the characteristics of diffuse NORM for the EPA (EPA91), it was
determined that approximately 620,000 oil and gas production wells operate in the United States.
Additionally, an average of 30 percent of these wells were projected to be operated by equipment
contaminated with NORM scale and sludge. The average total annual volume of NORM scale
and sludge waste generated in the U.S. can be estimated as 230,000 m3 or approximately 1.23
m3/contaminated well (EPA91, RAE92).
In a related study performed for the State of Texas (RAE88), the volume of NORM scale waste
was estimated to be between six percent - ten percent of the total NORM waste volume generated
per well. Total waste evaluated included sludge, scale, tubing, pipes, and valves.
2.1.2	Radionuclide Concentrations
Elevated NORM concentrations in oil and gas production equipment result when Ra-226 and
Ra-228 and their decay products co-precipitate with mineral scales, such as BaS04, that form
deposits on the insides of field production equipment. Concentrations of NORM radionuclides
in scale and sludge of petroleum production equipment can vary from background (about 1 pCi/g)
to hundreds of thousands of picocuries per gram (EPA91). For example, Ra-226 concentrations
as high as 160,000 pCi/g have been found in pipes at storage yards in Michigan (DNR90).
Factors which can affect the magnitudes of NORM concentrations in oil and gas production
equipment include the location of the production facility, the type of equipment, how long the
production well has been in operation, and changes in temperature and pressure that take place
during extraction of the petroleum from the underground formation (EPA91). The State of
Michigan, for example, reports that the precipitates containing radium in Michigan are
predominantly tank sediments rather than pipe scale as found in Louisiana (DNR90).
2-4

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The American Petroleum Institute (API) has conducted an industry-wide survey of external
gamma radiation exposure levels associated with NORM in oil production and gas processing
equipment (API89). Over 36,000 individual observations were made in 20 states and two
offshore areas by participating petroleum companies using similar equipment and data collection
protocols. Radiation exposure levels were measured in units of pR/hr. Background radiation
levels were also measured and reported for each site in order to differentiate the background
effects from contamination effects. The survey showed, as illustrated in Figures 2-2 and 2-3, that
the geographic areas with the highest equipment readings (2-33 pR/hr) were northern Texas and
the gulf coast crescent from southern Louisiana and Mississippi to the Florida panhandle. Very
low levels of NORM activity (0-2 pR/hr) were measured in equipment from California, Utah,
Wyoming, Colorado, and northern Kansas. Assuming 33 percent (EPA91) of the oil wells
produce NORM-contaminated scale, and that an average of 2 tons of scale precipitate for every
3,000 barrels of oil produced (EPA91), median and 90 percentile (calculated as median x GSD1
with t = 1.2817) NORM scale concentrations can be calculated for each state surveyed. Table
2-1 presents the median and 90 percentile scale concentrations as well as the total NORM activity
for the main oil producing states in the United States.
The American Petroleum Institute study also determined that the highest concentrations of radium
(Ra-226 and Ra-228) occurred in the wellhead piping and in production piping near the wellhead
(API89). The concentration of radium deposited in separators is about a factor of ten less than
that found in wellhead systems. Additionally, there is a further reduction of up to an order of
magnitude in the radium concentrations in heater/treaters and in sludge holding tanks.
Concentrations of radium in scale deposited in production tubing near wellheads can range to up
to tens of thousands of picocuries per gram (EPA91, API89). The concentrations in more
granular deposits, found in separators, range from one to about one thousand picocuries per gram
(API89). Higher concentrations are associated with hard scale deposits associated with
precipitation from the water phase. Radium concentrations in sludge deposits in heater/treaters
and tanks are generally around 50 pCi/g (API89).
2-5

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EXTERNAL GAMMA
READINGS (11REM/HR)
OVER 245
RAE- 104041
Figure 2-2. Median of differences of external readings over local
background for NORM contaminated gas production
equipment (API89).
2-6

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EXTERNAL GAMMA
READINGS (pREM/HR)
| | NO DATA
Ex?] BELOW .8
Eg5] .8-1.99
M 2 33
33.01-245
B OVER 245
RAE- 104040
Figure 2-3. Median of differences of external readings over local
background for NORM contaminated oil production
equipment (API89).
2-7

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Table 2-1. Median and 90 percentile gamma radiation levels and NORM concentrations based on (API89) survey data.
Gamma Radiation







90 Percentile



90



Mean Scale
Scale
Mean

Mean
Percentile



Concentration
Concentration
Activity of

Difference
Difference
Oil
Total
NORM
of Above
of Above
NORM

Above
Above
Produced
Scale
Contaminated
Background
Background
Scale

Background
Background
(1000
Produced
Scale Produced
Readings
Readings
Produced
State
(uR/hrV
(uR/hr)'
barrels/vr)b
(tons/vear)c
(tons/vr)d
(pCI/e)e
(pCI/e)®
(Cl/vr/
Alaska
l.OE-fOl
8.SE-f01
7.2E+05
4.8E+05
1.6E+05
4.1E+02
3.5E+03
5.9E+01
Alabama
5.9E+01
2.4E+02
2.6E+04
1.8E+04
5.9E+03
2.4E+03
9.9E+03
13E+01
Arkansas
2.0E-JDO
4.4E+00
1.5E-f04
1.0E+04
3.3E+03
8.2E+01
1.8E+02
23E-01
California
1.0E+O1
5.1E+01
4.0E+05
2.7E+05
8.9E+04
4.1E-t02
2.1E+03
3.3E+01
Colorado
8.5E+00
1.7E+01
3.3E+04
2.2E+04
7.4E+03
3.5E+02
6.7E+02
2.3E+00
Florida
5.9E+01
2.4E+02
9.4E+03
6.2E+03
2.1E+03
2.4E+03
9.9E+03
4.5E+00
Illinois
2.3E+01
2.2E+02
2.4E+04
1.6E+04
5.3E+03
9.4E+02
8.9E+03
4.5E+00
Kansas
l.lE-tOl
1.1E+02
6.8E+04
4.5E+04
1.5E+04
43E+02
4.4E+03
5.9E+00
Kentucky
1.2E+01
6.8E+01
6.8E+03
4.6E+03
1.5E+03
4.9E+02
2.8E+03
6.7E-01
Louisiana
1.2E+01
8.1E+01
5.4E+05
3.6E+05
1.2E+05
4.8E+02
3.3E+03
5.2E+01
Michigan
2.6E+00
5.0E+00
3.0E+04
2.0E+04
6.7E+03
1.1E+02
2.0E+02
6.5E-01
Mississippi
4.6E+00
3.8E+02
2.9E+04
1.9E+04
6.4E+03
1.9E+02
1.6E+04
1.1E+00
Montana
3.7E+01
4.3E+01
2.6E+04
1.7E+04
5.7E+03
1.5E-t03
1.7E403
7.8E+O0
North Dakota
9.0E-tO0
1.7E+01
4.4E+04
3.0E+04
9.8E+03
3.7E+02
7.1E+02
3.3E+00
Nebraska
5.4E+00
1.1E+01
6.1E+03
4.1E+03
1.4E+03
X2E+02
4.5E-t02
2.7E-01
New Mexico
4.0E+00
1.9E+01
8.7E-f04
5.8E+04
1.9E+04
1.6E+02
7.7E+02
2.9E+00
Oklahoma
4.0E+00
3.7E+01
1.7E+05
1.1E+05
3.7E+04
1.6E+02
1.5E+03
5.5E-H30
Texas
5.0E+00
3.0E+01
9.0E+05
6.0E+05
2.0E+O5
2.0E402
1.2E+03
3.7E+01
Utah
5.0E+00
9.0E-fO0
4.0E-tO4
2.7E+04
8.9E+03
2.0E-t02
3.7E+02
1.7E+00
Wyoming
2.3E+00
4.3E+00
1.3E-t05
9.0E+04
3.0E+04
9.4E-f01
1.8E+02
2.5E+00
EFFECTIVE NATIONAL TOTAL


3.3E+06
2.2E+06
7.3E+Q5



EFFECTIVE NATIONAL WEIGHTED MEAN	3.6E+02	2.4E+03 2.4E+02
a	(API89).
b	(EPA91).
c	Based on 2 tons of scale for every 3000 barrels of oil produced (EPA91).
d	Based on 1/3 of all scale is NORM contaminated (EPA91).
e	Based on the correlation that the State of Louisiana is projected to have a median of 480 pCi/g (RAE92) which corresponds to median readings of 11.8 pR/hr.
f	Based on pCi/g for die projected tons of NORM per year.

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The API89 data for the State of Louisiana shows that approximately 60 percent of the total
NORM waste is below 15 pCi/g (based on correlations developed in RAE92). Using the API89
data for the State of Louisiana, the median value of the radium (Ra-226 and Ra-228)
concentration in scale is 270 pCi/g (RAE92). This value includes many measurements that are
within the uncertainty of general detection limits. To characterize actual radium distributions,
the values less than the 15 pCi/g uncertainty limit are removed from the distribution and a
measurable biased median concentration of 480 pCi/g (RAE92) is calculated.
Due to the consistently high measurements found in Alabama, Florida, Mississippi and Illinois,
the national distribution of radium in NORM-contaminated equipment is estimated to have a
median of 180 pCi/g, a seventy-fifth percentile of 900 pCi/g, a ninetieth percentile of 2,000
pCi/g, and a ninety-fifth percentile near 9,000 pCi/g. Removing readings from the national
distribution that are below detection limits gives the distribution found in Table 2-2. The
reusable waste from oil and gas production consists of equipment that is contaminated with scale.
The concentration of radium (Ra-226 and Ra-228) in scale is calculated to have a median value
of 360 pCi/g. A 90 percentile value is calculated using the following equation:
^a90% = ^amedian x ^SD 1
90 percent confidence limit of radium in pCi/g
median radium concentration = 480 pCi/g
effective geometric standard deviation = 5.91
statistical z-score corresponding to the 90 percent confidence limit = 1.28167.
Using equation 2-1, a 90 percentile confidence limit of 2,400 pCi/g is calculated. These values
will be used in this risk assessment As noted, the Ra-226 concentration is three times that of
where
Ra90%
Ramedian ~
GSD
t
2-9

-------
Table 2-2. Median and 90 percentile radium concentrations in NORM
scale (RAE92) (using measurement data exceeding 15 pCi/g
equivalent).
Scale Bearing EauiDment
Median
Concentration
(oCi/c)
Geometric
Standard
Deviation
90.0 Percentile
Concentration
(oCi/e)
Oil Line Piping
4.9E+2
7.3
4.4E+3
Manifold Piping
4.1E+2
6.0
2.9E+3
Injection Well Tubing
1.2E+2
4.5
5.6E+2
Production Well Tubing
1.6E+2
4.2
7.1E+2
Water Lines
1.5E+2
5.5
9.4E+2
Meters, Screens, Filters
1.8E+2
9.0
2.1E+3
SCALE COMPOSITE
3.6E+2
5.9
2.4E+3
2-10

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Ra-228 and is in equilibrium with its daughters. Table 2-3 gives the median and 90 percentile
concentrations of NORM in oil and gas production scale.
For this report, a reference oil and gas production facility consisting of ten production wells is
assumed. The equipment for reuse includes oil flow lines, water lines, injection and production
well tubing, manifold piping and small diameter valves, meters, screens, and filters. This typical
facility (EPA91, RAE92) is estimated to have an average life of 30 years. It is further assumed
that tubing and some of the pipe in the wells will be replaced about every seven years giving a
total of three replacements of the original tubing during the 30-year facility life (EPA91, RAE92).
Estimated quantities of equipment containing scale for reprocessing and reuse are identified in
Table 2-4. The median scale volume per well reported in Table 2-4 (1.206m3/well) is consistent
with the (EPA91) reported median (1.23m3/well) presented in Section 2.1.1 of this report.
2.2 PHOSPHOGYPSUM
Mining of phosphate rock (phosphorite) is the fifth largest mining industry in the United States
in terms of quantity of material mined (EPA84). Phosphate rock is processed to produce
phosphoric acid and elemental phosphorous. The most important use of phosphate rock is the
production of fertilizers, which accounts for about 80 percent of the mining of phosphorite in the
United States (EPA91). Waste generated during the production of phosphoric acid and elemental
phosphorous is in the form of phosphogypsum.
2.2.1	Production Process
Phosphoric acid is processed by beneficiation of phosphate ore. During beneficiation, phosphate
particles are separated from the rest of the ore, creating two types of waste products, phosphatic
clay and sand tailings. After beneficiation, the phosphate ore is digested (dissolved) using
sulfuric acid. This produces a slurry (phosphogypsum) which is discharged from filter pans,
slurried with water, and pumped to large piles (phosphogypsum stacks).
2-11

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Table 2-3. Median and 90 percentile radionuclide concentrations in gas
and oil production NORM scale (RAE92).
Median Concentration 90.0 Percentile Concentration
Radionuclide8	 	(pCi/g)	 	(pCi/g)	
Ra-226
270
2,900
Ra-228
90
950
Radium
360
3,800
Pb-210
270
2,900
Po-210
270
2,900
Th-228
90
950
a For external exposures Po-218, Pb-214, Bi-214, and Po-214 arc assumed to be in secular
equilibrium with radium-226.
2-12

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Table 2-4. Median NORM contaminated equipment volumes for a ten well facility (EPA91, RAE92).
Scale Bearing Eauimnent
Median Total
Volume for
Recycle As Is
(m3)
Median
Scale
Volume
fm3)
Median
Steel
Volume
On3)
Median Total
Volume for
Recycle As Is
(rn3/well)
Median
Scale
Volume
(m3/well)
Median
Steel
Volume
(m3/well)
Oil Line Piping & Valves
111.4
9.3
34.4
11.1
0.9
3.4
Manifold Piping & Headers
0.6
0.0
<0.1
0.1
0.0
<0.1
Injection Well Tubing
6.9
0.8
2
0.7
0.1
0.2
Production Well Tubing
8.5
1.1
3.9
0.9
0.1
0.4
Water Lines & Valves
1.4
0.8
0.4
0.1
0.1
<0.1
Meters, Screens, Filters
0.0
0.0
0.0
0.0
0.0
0.0
COMPOSITE
128.8
12.1
40.7
12.9
1.2
4

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Each phosphoric acid production facility may have one or more phosphogypsum stacks. The
stacks range in size from 5 to 750 acres and range in height from 3 to 60 meters (EPA91). A
total of 63 stacks has been identified nationwide (EPA91). The average base area is largest for
operating stacks, being nearly 230 acres. The average idle or inactive stack is smaller in size,
91 and 55 acres, respectively. The average height is approximately 20 meters (EPA89a). The
production rate of phosphogypsum is estimated using the assumption that 4.5 MT of
phosphogypsum are produced per MT of P205 (GUI75). The yearly phosphogypsum production
averages nearly 40 million MT since 1984 (EPA91). The total phosphate waste volume
generated in the U. S. from 1910 to 1981 has been estimated at 7.7 billion MT (EPA85).
An additional waste product of radiological concern that is associated with this process is
phosphoric acid scale. In the production of phosphoric acid from the raw ore, the
phosphogypsum must be physically separated from the phosphoric acid by a filtration process.
Large stainless steel filter pans are covered with fiberglass fabric which serves to filter out the
phosphogypsum while allowing the passage of acid. During this process, small quantities of
scale are deposited on the surface areas of the pan and fiberglass mat.
2.2.2	Physical and Radiological Properties
Concentrations of uranium in phosphate ores in the U. S. range from 7 to 100 pCi/g (BLJ88).
Most of the impurities, including the primary dose-contributing nuclide, radium-226 and its
radioactive daughters, are separated as phosphogypsum (EPA91).
For this risk assessment, the reference waste form is phosphogypsum, and the median and 90
percentile radionuclide concentrations, as presented in Table 2-5, are those considered to be
typical of phosphogypsum wastes (BID91, HOR88). The risk estimates presented in Chapter 5
are given based on a median radium-226 concentration of 31 pCi/g (BID91) and a 90 percentile
radium-226 concentration of 48.6 pCi/g (BID91). The concentration of Ra-228 is derived from
the activity ratio of Ra-228 to Ra-226 in phosphate fertilizer. Activity ratios for Th-228 and
Th-232 relative to Ra-226 are also those for phosphate fertilizer (BID91). The activity of U-235
2-14

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Table 2-5. Phosphogypsum median and 90 percentile radionuclide concentrations.
Radionuclide
Median Concentration
foCi/fi)
90.0 Percentile
Concentration
(DCi/2)
Ra-226
31.0
48.6
Po-210
32.2
50.5
Pb-210
43.4
68.0
Th-228
4.1
6.5
Ra-228
4.1
6.5
Th-230
5.8
9.1
Th-232
3.8
6.0
U-234
3.7
5.8
U-235
0.2
0.3
U-238
3.4
5.4
2-15

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is assumed to be about five percent of the U-238 activity (BID91). Clay and sand tailings
generated in the production of elemental phosphorous and phosphoric acid are not considered in
this assessment since they are generally not involved in reuse.
Risks associated with the cleaning and reuse of the phosphate scale-contaminated stainless steel
filter pans arc considered. Median and 90 percentile radionuclide concentrations, as presented
in Table 2-6, are those considered to be typical of phosphate scale (EPA91, BID91).
2-16

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Table 2-6. Phosphate scale median and 90 percentile radionuclide concentrations.
Radionuclide
Median Concentration
(DCi/2)
90.0 Percentile
Concentration
(oCi/e)
Ra-226
3.0E+3
3.6E+3
Po-210
3.1E+3
3.8E+3
Pb-210
4.2E+3
5.1E+3
Th-228
4.0E+2
4.8E+2
Ra-228
4.0E+2
4.8E+2
Th-230
5.6E+2
6.8E+2
Th-232
3.7E+2
4.5E+2
U-234
3.6E+2
4.4E+2
U-235
1.9E+1
2.3E+1
U-238
3.3E+2
4.0E+2
2-17

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3. Scenarios and Exposure Pathways for Reuse
This chapter identifies the procedures involved in reprocessing NORM-contaminated equipment
for general reuse. Exposure pathways are presented for individuals exposed during the
reprocessing activities; for individuals exposed to uncleaned equipment; and for individuals
exposed due to the reuse of phosphogypsum. The scenarios considered for the exposure
pathways are summarized in Table 3-1 and discussed below. Current industrial practices are
presented and used as bases for scenario characterization.
3.1 OIL AND GAS PRODUCTION EQUIPMENT
Exposure pathways for reuse and reprocessing of oil and gas production equipment are grouped
into two sections. First, pathways resulting from the general unrestricted release of contaminated
equipment are reviewed. Second, processes and pathways are reviewed for the recycling and
reprocessing of steel from production equipment.
3.1.1	General Unrestricted Release
Before the past decade, oil and gas production equipment was routinely disposed of, recycled,
reused, and released to the general public without restriction. Contaminated pipe has even been
donated to schools and contractors (FUE92). The State of Mississippi found used oil and gas
production tubing contaminated with elevated levels of NORM in school yard fences, playground
equipment, residential and school load supporting beams, residential culinary water plumbing,
and in use as practice welding equipment for school metal shops (FUE92).
Recent awareness and promulgated state guidelines assist in preventing release of contaminated
equipment to the general public. However, evaluation of the public exposures from past practices
and potential exposures from equipment inadvertently released need to be evaluated. Exposures
resulting from the general use of uncleaned contaminated equipment are presented and analyzed
in Chapters 4 and 5.
3-1

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Table 3-1. Exposure scenarios for evaluation.
Scenario
NORM Source
Unrestricted Release
Student at jungle-gym
Teacher at jungle-gym
Welding shop student
Welding shop teacher
Residential construction use
Reprocessing of Steel
Scrap Steel Cleaner (Mechanical, Hydrolaser)
Storage yard worker
Transport operator
Smelter yard worker
Adjacent resident to the smelter yard
Adjacent resident to the storage yard
Adjacent resident to the cleaning facility
Agriculture
Agricultural worker
On-site individual
Member of critical population group
Off-site individual
Road Construction
Construction worker
Vehicle operator
Member of critical population group
Reclaimer
Off-site individual
Research
Researcher
Oil and gas equipment
Oil and gas equipment
Oil and gas equipment
Oil and gas equipment
Oil and gas equipment
Oil and gas and phosphate ore equipment
Oil and gas equipment
Oil and gas equipment
Oil and gas equipment
Oil and gas equipment
Oil and gas equipment
Oil and gas equipment
Phosphogypsum
Phosphogypsum
Phosphogypsum
Phosphogypsum
Phosphogypsum
Phosphogypsum
Phosphogypsum
Phosphogypsum
Phosphogypsum
Phosphogypsum
3-2

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For exposures resulting from the general use of contaminated equipment at schools and in
residential construction, the following scenarios and associated pathways are considered:
• Student at Jungle-gym
-	Direct gamma
-	Dermal exposure
-	Dust inhalation
• Teacher at Jungle-gym
- Dust inhalation
• Welding Shop Student
-	Direct gamma
-	Dust inhalation
-	Indoor radon inhalation
-	Dermal
Welding Shop Teacher
-	Dust inhalation
-	Indoor radon inhalation
-	Contaminant ingestion
Residential Use
-	Contaminant ingestion
-	Indoor radon inhalation
-	Direct gamma
3.1.2	Reprocessing of Scrap Steel
The steel reprocessing technology, as illustrated in Figure 3-1, consists of several stages.
Generally, the scrap or waste from the oil and gas production facility is stored at the facility or
at an independent storage yard for resale (ZAL92). If necessary, the dirt and scale are removed
from the equipment prior to resale. Some of the equipment is then recycled through smelting
into new iron products and released to the general public. Other equipment is recirculated back
to the oil production facility. Several scenarios are considered for exposure from NORM in scrap
steel, including cleaning, storage, transportation and smelting.
3-3

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Figure 3-1. Steel Reprocessing Technology.
3-4

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3.1.2.1
Pipe Cleaning
Reuse of equipment within the industry often requires the removal of NORM deposits from
inside the equipment. Traditionally, this has been done using hand scrubbing (MAD79, EPA87b).
Two such cleaning facilities were located near Laurel and Brookhaven, Mississippi (EPA87b).
The two facilities were used to clean pipe used by the petroleum industry. Pipe taken to the
contractors at these two sites was cleaned using drills to ream material from the pipes. Hand
scrubbing may vary from a simple wipe with a dry or damp cloth to a scouring action with
motor-powered abrasive tools and chemical additives (CHA91). While hand scrubbing is
occasionally effective, worker exposures are significant. Efforts to reduce worker exposures from
hand-cleaning processes include dust vacuuming and filtration systems, protective respirators and
clothing, and equipment for remote handling of contaminated equipment (CHA91). These added
measures have reduced worker exposures up to 90 percent of their original levels (CHA91).
Due to the difficulty and inefficiency of hand cleaning, other decontamination methods have been
developed. The major systems currently being used by the industry are presented in Table 3-2.
Hydrolasers and other high-pressure water cleaners are more commonly being utilized (ZAL92).
Commercially available hydrolasers produce a liquid stream of up to 10,000 psi, and chemical
cleaning agents can be added to the water to increase their effectiveness (MAD79). Even though
the use of hydrolasers reduces dust emissions, allows for remote cleaning, and is significantly
more efficient in cleaning, other waste disposal problems are inherent with such methods. Liquid
wastes, for example, need to be effectively collected and solidified.
Exposures resulting from hand cleaning and remote hydro laser blasting of contaminated
equipment are analyzed conservatively, in this risk assessment, with no further safety features in
place. It is assumed that the following scenarios and pathways will produce limiting doses:
• Pipe Cleaner - Mechanical Scrubbing
-	Direct gamma
-	Dust inhalation
3-5

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Table 3-2. Surface decontamination technology alternatives (CHA91).
Method
Application
Manual Abrasive
Scraping
Liquid Abrasive Blasting
Ultra High Pressure
Water Decontamination
(Hydroblaster/Hydrolaser)
Ultrasonic Cleaning
Advanced
Decontamination Systems
Employs dry grit blasting,
scarifying drilling, vacuum
cleaning, grinding, brushing,
etc.
High volume of water
recirculation of solid grits or
particles (aluminum oxide or
glass beads) bombards the
contaminated surface and
removes scale at 100 psi.
Water particles at pressures
up to 35,000 psi bombard
the contaminated surface
removing heavy scale
coatings.
Effective for small reusable
equipment, valve parts, and
precision components.
Comment
Not an effective cleaning
method for dense scale
deposits. Additional exposure
reduction necessary to reduce
airborne contamination and
direct exposure to worker.
Technique is 95 percent
effective with loose
contamination (CHA91).
Tends to inadequately remove
contamination from cracks,
folds, edges, welds, and from
configurations that serve as
contamination hideout.
Allows for waste minimization
by adapting pressure and
application time. Possible to
recycle contaminated water
through ion-exchange
treatment.
Can penetrate crevices, filter
elements, etc. Limited in use
since the largest size of the
sounding tanks commercially
available is approximately 5' x
3' x 2.5'.
Research currently underway
on: Laser decontamination,
accelerator transmutation of
wastes, and microwave
decontamination
3-6

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•	Pipe Cleaner - Hydro Laser Blasting
-	Direct gamma
-	Dust inhalation
•	Adjacent Resident - Mechanical Scrubbing
-	Dust inhalation
3.1.2.2 Storage Yard
Oil-field equipment removed from service is frequently stored in oil-field equipment yards
(ZAL92). Equipment is stored for possible cleaning, refurbishing, transfer to other fields, sale
to other companies or other uses, and for disposal (ZAL92). As a result of the storage and the
associated handling of equipment, yard employees and adjacent residents are potentially exposed
to gamma emission and respirable dusts from contaminated production equipment For exposures
resulting from the storage of contaminated equipment, the following scenarios and pathways are
considered:
•	Storage Yard Worker
-	Direct gamma
-	Dust inhalation
•	Adjacent Resident to Storage Yard
-	Direct gamma
-	Dust inhalation
3.1.2.3 Transportation
Scrap metal and oil and gas production equipment are generally transported by truck or rail
(KEA92, ZAL92). The exposure pathways from the transportation of contaminated equipment
for this analysis are assumed to result from truck transportation. Rail exposures are not
considered since truck driver exposures are expected to be limiting. The gamma exposures
during the rail transportation are minimal due to the greater exposure distances and thicker steel
sidings of rail cars in comparison to truck trailers.
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Since storage yards for oil and gas production equipment are generally located on site (ZAL92),
it is assumed that transportation does not involve trucking any non-industry scrap metal. Since
most commercial smelters accept scrap from multiple sources (ROW92), the transportation
scenario conservatively assumes a storage yard destination.
• Truck Driver
- Direct gamma
3.1.2.4 Smelting NORM-Contaminated Materials
One method of recycling used steel for other uses is to reprocess the material via smelting.
Melt-refining of NORM-contaminated materials separates the NORM (contained in the scale
deposits) from the steel. The NORM-contaminated scale material is primarily composed of the
Alkali-earth element sulfates (principally BaSO^ (EPA91). The radioactivity in the NORM
comes from the presence of RaS04 in the scale deposits (EPA91). For calculations, the
properties of the scale will be taken as those of BaS04. Currendy, three steel mills are
performing tests involving controlled melting of NORM-contaminated equipment. These are:
Shaparell Steel of Texas, Segean Structured Metals of Texas, and Sheffield Steel of Oklahoma
(TUR92).
A schematic diagram of a smelting furnace is shown as Figure 3-2. A typical batch-smelting
operation of contaminated (recycle) steel handles approximately 50-tons of metal per batch
(ROW92). The furnace is charged with the contaminated steel (approximately 9.0 wt percent,
23 percent by volume, of which is the NORM containing scales) (RAE92) and slagging material.
The slagging material is typically about ten percent of the steel weight (NRC78) (5-tons in this
case). The furnaces operate between 2800 and 3000°F (ROW92). The flow rates of the effluent
gases are 10,000 CFM for natural gas fired furnaces, and 700,000 CFM for electric arc furnaces
(ROW92). A batch cycle lasts between 30 and 50 minutes (ROW92). According to Rowlan
(ROW92), a typical smelting operation does include particulate emission control. In addition,
it has been noted that the bulk of calcium is carried into the baghouse and collected with the
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EFFLUENT GAS
A
SLAG
MATERIAL
FEED
MATERIAL
-~SLAG
SMELTING
FURNACE
^ STEEL
HEAT
RAE -104051
Figure 3-2. Schematic diagram of a smelting furnace.
3-9

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dust (ROW92). The barium concentrations in the dust vary from 0.5 ppm to 490 ppm, but the
specific value, like all the contaminants, is dependent upon the concentrations in the feed material
(ROW92).
As the contaminated steel is melted, the scale deposits are volatilized. The volatilized materials
are then carried out with the stack gases, or they are trapped in the slagging material and
«
removed with the slag. Compounds which are not volatilized or which decompose to form the
metal oxides, migrate into the slag layer as a result of density differences between the molten
steel and the metal compounds. The percent of contaminant removed with the slag depends upon
the material used for slag. According to ROW92, it is estimated that over 95 percent of the
volatile material moves through the slag to the stack gas and is removed. Conversely, references
MAR87, TUR92, and CEC88 indicate that slagging agents can be used to capture virtually all
NORM contaminants. The steel produced from the recycling process is essentially free of
contaminants (ROW92). The stack gas is generally passed through a baghouse where over 99
percent of the particulate emissions are removed (ROW92). Thus, if all the NORM were
vaporized and treated in the baghouse, approximately 90 pounds of the scale deposits charged
to the furnace (per 50-ton batch) could be discharged into the atmosphere with the effluent gases.
The dominant management practices for the waste slag material is onsite storage in large piles.
Properties of critical compounds in the smelting of NORM-contaminated steel are given in
Table 3-3 (CRC85). Although data are not readily available f®r the compounds of Radium, they
are expected to behave similarly to the other Alkali-Earth compounds. It should also be noted
that the values of slag properties will differ depending upon the type of slag used. The primary
function of the slag is to provide an insulating cover on the top of the smelt (ROW92). In
addition to it's primary function, the slag may be useful in removing certain impurities from the
molten steel. According to Rowlan (ROW92), many different slags have been produced which
are capable of entraining and removing certain contaminants.
In order to account for the NORM in a typical smelting operation, it is assumed that the
equipment from a typical ten well facility will be recycled. The median activity of the scale
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Table 3-3. Properties of critical compounds in the smelting of NORM
contaminated steel.8
Material
Density (e/cc)
Melting Point f°F)
Boiline Point (°F)
Basis
Steel
7.80
2760
—
CRC85
Slag
approx. 3.00
	
—
(NRC78)
BaS04
4.50
2876
2100b
CRC85
CaS04
2.96
2642
2179b
CRC85
BaO
5.72
3493
4941
CRC85
CaO
3.31
4689
5162
EPA91, RAE92
Scale
2.60


EPA91, RAE92
a Although data are not readily available for the compounds of radium, they are expected to behave
similarly to the other alkali-earth compounds.
b Transition zone to monoclinic.
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deposits is given as 360 pCi/g. The total recycle volume (RAE92) of steel is 40.7 m3. The total
recycle volume of scale deposits is 12.1 m3. The density of the scale is 2.6 g/cm3 (RAE92,
EPA91). The other properties of the scale are assumed to be the properties of BaS04. The
individual batch weights of the recycle smelting process are 50-tons. The amount of slag added
to each batch is 5-tons. The batch cycle time is taken as 30-minutes (worst case) (ROW92).
Based on these assumptions, the following case scenarios show how the NORM can be removed
in the smelting process:
Case 1: All the NORM is trapped bv the slag (worst case for removal in slag).
Using the densities provided in Table 3-3, the weight percent of the scales is determined to be
9.0 percent. From this value we expect that 4.5-tons of the total recycle charge to the furnace
(50-tons per batch) are expected to be the scale deposits. In addition, 5-tons of slagging material
is added to the furnace. Since the steel is separated from the scale deposits, 9.5-tons of the
slag/scale mixture is expected to be removed. The net effect of this removal is to dilute the
activity per unit weight from 360 pCi/g of radium in the scales to [360 * (4.5/9.5)] or 170 pCi/g
of radium. Thus, the case of removal of the NORM in the slag dilutes the NORM activity by
about a factor of two.
Case 2: All the NORM is removed in the effluent gas, no pollution control equipment is used,
a gas-fired furnace is used in the smelting process, and the batch time is 30-minutes.
The amount of scale deposits is assumed to be the same as in Case 1. With a gas-fired furnace,
a typical effluent discharge rate of 10,000 CFM is assumed. For the 30-minute batch time, the
rate of emission of the scale deposits in the effluent stream is (9,000 lbs/30 min) 300 lbs/min.
By converting this value to an activity per unit volume, the radium concentration in the exiting
gas stream is calculated as follows:
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(300 lbs/min) (453.6g/lb) (360pCi/g)
(10,000 Ft3/min) (28.32 L/Ft3)
= 170 pCi/L radium
(3-1)
Case 3: All the NORM is removed in the effluent gas, no pollution control equipment is used,
an electric arc furnace is used in the smelting process, and the batch time is 30-minutes.
With an electric arc furnace, a typical effluent discharge rate of 700,000 CFM is used. For the
30-minute batch time, the rate of emission of the scale deposits in the effluent stream is
(9,000 lbs/30 min) 300 lbs/min. By converting this value to an activity per unit volume, the
concentration in the exiting gas stream is calculated is calculation as follows:
Case 4: All the NORM is removed in the effluent gas, pollution control equipment that is 99
percent effective in removing particulate emissions is used, a gas-fired furnace is used in the
smelting process, and the batch time is 30-minutes.
With a gas-fired furnace, a typical effluent discharge rate of 10,000 CFM is used. For the
30-minute batch time, the rate of emission of the scale deposits in the effluent stream is (9,000
lbs/30 min) 300 lbs/min. With the pollution control equipment, the emissions of scale material
are reduced to 3.0 lbs/min. By converting this value to an activity per unit volume, the
concentration in the exiting gas stream is calculated as follows:
(3001bs/min)(453.6g/lb)(360pCi/g)
(700,Q00Ft 3/min)(28.32L/Ft3)
= 3pCi/L radium
(3-2)
(3.01bs/min)(453.6g/lb)(360pCi/g)
(10,000Ft 3/min)(28.32L/Ft3)
= 2pCi/L radium
(3-3)
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Case 5: All the NORM is removed in the effluent gas, pollution control equipment that is 99
percent effective in removing particulate emissions is used, an electric are furnace is used in the
smelting process, and the batch time is 30-minutes.
With an electric arc furnace a typical effluent discharge rate of 700,000 CFM is assumed. For
the 30-minute batch time, the rate of emission of the scale deposits in the effluent stream is
(9,000 lbs/30 min) 300 lbs/min. With the pollution control equipment, the emissions of the scale
material are reduced to 3.0 lbs/min. By converting this value to an activity per unit volume, the
concentration in the exiting gas stream is calculated as follows:
(3.01bs/min)(453.6g/lb)(360pCi/g) _ 0>02pCi/L radium	(3-4)
(700,000Ft 3/min)(28.32L/Ft3)
For the purpose of calculating exposures, Case 1 (worst slag case) is used for exposure based on
removal of the NORM in the slag, and Case 2 (worst effluent case) is used for removal of the
NORM in the effluent gas stream. Case 1 may be modified as needed based on the percent
removal for the actual slagging compound used, and also for the amount of slag used. Case 2
may be modified to account for different variations in the smelting process and feed material.
The numerator in Equation 3-1 may be modified for differences in cycle time, pollution control
capabilities, weight of deposits in the recycle steel, and the average activity per unit mass of the
NORM. The denominator of Equation 3-1 may be modified to account for differences in flow
rate of the effluent gas stream.
For exposures resulting from the smelting of contaminated equipment, the following scenarios
and pathways are considered:
•	Adjacent Resident - With NORM Removal in Slag
-	Direct gamma from slag pile
•	Worker in Smelter Yard - No NORM Removal in Slag
-	Dust inhalation from resuspended particles in flue gas
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•	Adjacent Resident - No NORM Removal in Slag
-	Dust inhalation from resuspended particles in flue gas
•	Worker in Smelter Yard - With NORM Removal in Slag
-	Direct gamma from slag pile
3.1.2.5 Steel Mill and Scrap Yard Alarm Systems
Louisiana allows an item to be released for unrestricted use if survey readings are not above 50
jiR/hr (ZAL92, RAE92). This value includes background and is generally equivalent to three
times that of average background Some metal scrap yards and steel mills have emplaced
detectors to serve as alarms for monitoring incoming truck and train loads of scrap steel. In
general, the monitors are located two feet from the side of the load (ZAL92).
Initially, these monitors were installed to detect low-level radioactive waste and sources.
However, these alarm systems also have the ability to detect NORM contamination. An industry
sampling of the average detection criteria for the alarm is presented in Table 3-4. As can be
seen, an average limit can be taken as twice background (or approximately 16 pR/hr). Other
methods of specific NORM detection are currently being developed. Methods currently being
researched incorporate correlations from hand meter readings to NORM contamination (MIL90,
RAE92, SC092).
An additional alarm detection or early warning method, by which the presence and concentration
of radioactive scale can be assessed, is with the use of wireline logs (SMI85). Petroleum
engineers routinely utilize gamma ray logging to enable them to delineate the sand bearing strata
from the natural shales (SMI85). The logging tool detects the natural gamma radiation of the
strata. Consequently, internal NORM deposits can severely interfere with the interpretation of
the natural strata (SMI85).
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Table 3-4. Alarm screening settings for contaminant detection at steel mills, scrap
yards, and landfills.
Alarm Settings
Reference
Twice to ten times background
Twice to three times background
Twice background
400 cpm above background of 400-800 cpm
10 - 15 percent of background above
background
RAE90
ZAL92
FUE92
MIN92
BER92, ZAL92
Most frequently used value: 2 times background.
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A correlation is used between the levels of radioactivity measured during a gamma-logging
survey from the strata and scale, and the levels of radioactivity that can be expected to be
observed once the tubing has been removed from operation (SMI85).
Detection and distribution limits for detecting NORM in contaminated equipment loads are
presented in Chapter 5.
3.2 PHOSPHOGYPSUM
Since there are large volumes of phosphogypsum wastes being produced, use and reuses are
desirable to reduce problems associated with disposal. Past commercial applications of
phosphogypsum, discussed below, include: as a fertilizer and soil conditioner, backfill for road
construction, and as a concrete additive (EPA91). Recent revisions to NESHAPS now restrict
uses to agriculture and research (FR92). The scenarios evaluated in this assessment are based
on actual past practices. In a review by the EPA of the uses and resulting risks of the
phosphogypsum wastes from the FMC elemental phosphorous plant, Simplot phosphate fertilizer
plant, the Monsanto elemental phosphorous plant, and the Kerr-McGee vanadium plant of Idaho,
phosphogypsum slag was found in street paving and as a foundation additive (EPA90).
Additionally, exposures and procedures for cleaning of stainless steel filter pans used in
phosphate production are reviewed.
3.2.1	Phosphogypsum in Agriculture
Uses of phosphogypsum in agriculture include use as a source of calcium and sulfur for soils
deficient in these elements, and as sediment control for soils that have been eroded and leached.
For exposures resulting from the agricultural use of phosphogypsum the following pathways are
considered:
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• Agricultural Worker
-	Direct gamma
-	Dust inhalation
•	On-site Individual
-	Ingestion of contaminated well water
-	Indoor radon inhalation
-	Direct gamma
•	Member of Critical Population Group (CPG)
-	Inhalation of contaminated dust
-	Ingestion of drinking water from contaminated well
-	Ingestion of foodstuffs contaminated by well water
-	Ingestion of foodstuffs grown on fertilized soil
•	Off-site Individual
-	Ingestion of river water contaminated via the groundwater pathway
-	Ingestion of river water contaminated by surface runoff.
3.2.2	Phosphogypsum in Road Construction
Past uses of phosphogypsum in road construction include its use as a secondary road base, and
as a concrete additive for the road surface. Exposures resulting from the use of phosphogypsum
in road construction include the following scenarios and pathways:
•	Construction Worker
-	Direct gamma
-	Dust inhalation
•	Person Driving on Road
-	Direct gamma
•	Member of CPG
-	Direct gamma exposure
-	Ingestion of drinking water from contaminated well
-	Ingestion of foodstuffs contaminated by well water
•	Reclaimer
-	Direct gamma
-	Indoor radon inhalation
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-	Use of contaminated well water
-	Ingestion of foodstuffs grown on-site
•	Off-site Individual
-	Ingestion of river water contaminated via the groundwater pathway
-	Ingestion of river water contaminated by surface runoff.
3.2.3	Phosphogypsum in Research and Development
Uses of phosphogypsum in further research and development activities is also considered in this
assessment Exposures resulting from the use of phosphogypsum in a laboratory environment
include the following scenario and pathways:
•	Researcher
-	Direct gamma
-	Dust inhalation
-	Indoor radon inhalation
3.2.4	Filter Pan Cleaning
The large stainless steel filter pans, which are used to separate the phosphoric acid and the
phosphogypsum, are covered with fiberglass fabric which serves to filter out the phosphogypsum
while allowing the passage of acid (EPA91). During this process, small quantities of phosphate
scale are deposited on the surface areas of the pan and fiberglass mat This scale can also be
found deposited in ancillary piping and filtrate receiver tanks that are associated with the
filtration process (EPA91). Radium concentrations in scales have been found to range from
several picocuries to as high as 100,000 pCi/g (KEA88). While the concentrations of radium are
quite high, the volume associated with this scale is relatively low. One estimate is that a
phosphoric acid production plant will generate about 6 m3 of scale per year (EPA91).
Due to the high cost of filter pans, averaging $20,000 each (KEA92), their reuse is highly
desirable to the phosphogypsum industry. If the filter pans are to be reused, they must be
cleaned similar to the contaminated oil and gas production equipment Current industrial surface
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decontamination practices involve either non-chemical or chemical processes. A summary of the
metal surface decontamination technologies currently in practice is presented in Table 3-2.
Due to the effectiveness, hydroblasting is currently most commonly used in the phosphogypsum
industry for the cleaning of the stainless steel filter pans (KEA92). Grinding and additional
abrasive cleaning are also used to augment decontamination. Hydroblasting and additional
abrasive grinding generally cleans the filter pans sufficiently to allow for unconditional release
to the general public or reuse in the phosphate processes (KEA92). No cost effective cleaning
method, however, has been developed for the decontamination of the fiberglass mats (KEA92).
Currently these are packaged in drums and returned to the phosphogypsum owner (KEA92).
Exposures resulting from the cleaning of the stainless steel filter pans includes the following
scenario and pathways.
• Filter Pan Qeaner - Hvdrolaser
-	Dust inhalation
-	Direct gamma
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4. Risk Assessment Methodology
The purpose of this risk assessment is to analyze the radiological risks associated with alternative
uses of phosphogypsum and gas and oil production wastes and equipment Chapters 2 and 3
briefly discussed the radiological properties, current industrial practices, exposure pathways and
scenarios of phosphogypsum and oil production wastes and current uses for this material. The
PATHRAE, COMPLY, and PRESTO-PILCPG dose assessment models are employed to evaluate
potential doses and risks for the defined exposure scenarios involving the use of these wastes.
This section describes the methodology for this risk assessment, including the PATHRAE,
COMPLY, and PRESTO-PILCPG dose assessment models, the exposure scenarios evaluated, and
the input parameter values and assessment models used for each scenario. The input parameters
and scenario characteristics are based on the cuirent practices of the industry. The results of the
risk assessment are presented in Sections 5.1 and 5.2. Risks to workers, to individuals in the
critical population group (CPG), and to reclaimers are evaluated for agricultural, road
construction, recycling and general public use.
4.1 COMPUTER MODELS
The computer models used to evaluate individual and population risks from uses of these wastes
are described in this section. Dose calculations are performed using the PATHRAE, COMPLY,
and PRESTO-PILCPG dose assessment models (EPA87a, RAE91a, EPA89c). Calculations are
performed for exposure scenarios which included the use of phosphogypsum in agriculture, road
construction and research. Additionally, exposures from the cleaning, recycling and general
public use of NORM-contaminated equipment are analyzed. Where PATHRAE, COMPLY, or
PRESTO-PILCPG do not adequately model the gamma-ray exposure scenarios (e.g., a person
performing experimental analyses on wastes contained in metal drums), the MICROSHIELD
computer code (GR085) is used to augment the analyses. Additionally, the VARSKIN computer
code (NRC87) is used to estimate acute dermal exposures from direct contact with NORM-
contaminated scale. Lifetime risks are computed using annual dose and risk conversion factors,
as illustrated in Table 4-1, from the EPA's Environmental Impact Statement for NESHAPS
radionuclides (EPA89b).
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Table 4-1. Dose and risk conversion factors.
I. DOSE CONVERSION FACTORS (DCF)
Direct Gamma
DCF
Nuclide
Inhalation DCF
(mrem/pCi)a
Ingestion DCF
(mrem/nCi)3
(mrem/yr per
oCi/m2)
Ra-226
8.6E-03
1.3E-03
1.7E-04
Po-210
9.4E-03
1.9E-03
8.6E-10
Pb-210
1.4E-02
5.4E-03
0
Th-228
3.4E-01
4.0E-04
3.4E-04
Ra-228
4.8E-03
1.4E-03
9.0E-05
Th-230
3.3E-01
5.5E-04
8.9E-08
Th-232
1.6E+00
2.7E-03
6.6E-08
U-234
1.3E-01
2.8E-04
8.0E-08
U-235
1.2E-01
2.5E-04
6.4E-08
U-238
1.2E-01
2.7E-04
1.7E-05
(a) 50-year committed dose equivalent from one year of intake (uptake).
IL RISK CONVERSION FACTORSb
Nuclide
Inhalation Risk
per oCi Inhaled
Ingestion Risk
per pCi Ineested
Direct Gamma
Risk per nCi/m2
Ra-226
2.8E-09
9.4E-11
5.7E-11
Po-210
2.4E-09
1.4E-10
2.9E-16
Pb-210
1.4E-09
5.5E-10
0
Th-228
7.2E-08
1.3E-11
4.8E-11
Ra-228
5.8E-10
7.0E-11
3. IE-11
Th-230
2.9E-08
2.3E-11
2.7E-14
Th-232
2.9E-08
2. IE-11
2.0E-14
U-234
2.5E-08
7.5E-11
2.4E-14
U-235
2.3E-08
7.3E-11
5.5E-12
U-238
2.2E-08
7.4E-11
7.23E-13
b.	70-year lifetime risk of fatal cancer from one year of exposure.
m. RADON RISK CONVERSION FACTORS®
Exposure Scenario	Inhalation Risk per pCi/m3
Indoor Exposure	4.4E-08
Outdoor Exposure	4.4E-09
c.	70-year lifetime risk of fatal cancer from one year of exposure to Rn-220 and Rn-222
daughters.
4-2

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4.1.1
The PATHRAE Dose Assessment Model
The PATHRAE dose assessment model (EPA87a) was initially developed as an analytical tool
to assist EPA in developing standards for low-level radioactive waste and below regulatory
concern waste disposal. The PATHRAE model estimates health effects which could occur if
radioactive wastes were disposed of in a near surface facility, sanitary landfill, or other geological
setting. PATHRAE can be used to calculate effective dose equivalents3 to members of the
critical population group from the disposal of radioactive material at sites located in diverse
hydrogeologic, climatic, and demographic settings. An important PATHRAE model feature is
its simplicity in analyzing a comprehensive set of radionuclides, disposal settings, and exposure
pathways. The effects of changes in disposal site and facility characteristics can be readily
investigated with relatively few parameters needed to define the problem.
PATHRAE models both off-site and on-site pathways through which persons may come in
contact with radioactivity from disposed material. The off-site pathways include groundwater
transport to a well and a river, surface water runoff to a river, and atmospheric transport of
radioactive particulates. On-site pathways include direct gamma exposure, dust inhalation,
exposure from foodstuffs grown on-site, and inhalation of radon gas and radon daughters.
4.1.2	The PRESTO-EPA-PILCPG Computer Code
PRESTO-EPA-PILCPG methodology has been developed under EPA direction (RAE91a). The
EPA uses PRESTO-EPA-PILCPG methodology for evaluating maximum annual doses, via
atmospheric pathways, to members of the critical population group (CPG) from the disposal of
NORM wastes. The maximum annual radiation doses to the CPG is calculated for 10
radionuclides. PRESTO-EPA-PILCPG determines the nuclide and pathway specific doses for
each year of exposure. These doses are then summed over all nuclides and pathways.
a Throughout this report the term "dose" refers to the effective whole body dose
equivalent
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4.1.3
The COMPLY Computer Code
The COMPLY computer program was designed to demonstrate compliance with the National
Emission Standards for Hazardous Air Pollutants (NESHAPS) in 40 CFR 61, Subpart I. It has
various levels of complexity, the simplest being a computerized version of the tables of
concentration and possession limits in EPA89c. The most complicated is an air dispersion
calculation using a user-supplied wind rose.
In the analyses reported here, the COMPLY code was used to estimate doses to off-site residents.
The code was used directly to estimate dose rates from dust migration and from the smelt-
refining of NORM contaminated scrap steel.
4.1.4	The MICROSHTF-I J) Computer Code
Where the exposure geometry is not readily modeled by PATHRAE or PRESTO-EPA-PILCPG
(e.g., truck driver transporting NORM-contaminated equipment), MICROSHIELD is used to
estimate the external gamma dose. MICROSHIELD (GR08S) is a microcomputer adaptation of
the ISOSHLD II (ENG66) mainframe code for analyzing gamma radiation shielding.
MICROSHIELD has solution algorithms for 14 different geometries which include point, line,
sphere, disk, cylinder, plane, and rectangular volume sources; and slab, cylindrical, and spherical
shield configurations. MICROSHIELD sorts individual gamma energies from each isotope in the
source term into 21 energy groups. Dose rate calculations are performed by one of three
geometry-based calculational routines which include analytical expressions, Simpson's rule
integration, and point-kernel integration. Execution of the program proceeds by repeating the
solution algorithm for each energy group that has any activity until all 21 energy groups have
been evaluated.
The MICROSHIELD code user supplies input information describing the characteristics of the
exposure scenario to be evaluated This input information includes: distance between the source
and the exposed individual; source inventory; dimensions of the source region; the dimension,
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locations, and orientations of intervening shields; and the material (including air) used for these
intervening shields.
4.1.5	The VARSKIN Computer Code
The VARSKIN code (NRC81) computes the beta radiation dose rate to any specified depth of
the skin from up to five radionuclides on the surface of the skin. The calculational method is
based on the tables of absorbed energy distributions around point sources in water that have been
developed by M.J. Berger (BER71). By running the code several times, the radiation dose from
more than five radionuclides can be computed.
4.2 EXPOSURE SCENARIOS
Scenarios based on the exposure pathways identified in Chapter 3 and the assessment models
used are presented and discussed below. Scenarios have been divided into three groups:
unrestricted general use of contaminated oil and gas production equipment, recycling of oil and
phosphogypsum production equipment, and reuse of phosphogypsum.
4.2.1	Oil and Gas
The scenarios for evaluation of possible health impacts from the commercial uses of oil and gas
production wastes are presented in this section. These evaluations are based on the waste
inventories, current industrial practices, generic site parameters, and radiological properties of the
NORM-contaminated equipment and wastes. Health impacts from the reprocessing and uses of
NORM-contaminated equipment are estimated for workers at the storage and reprocessing
facility, for the persons belonging the critical population group (CPG), and for the general
population in the vicinity of storage and smelter sites.
Certain input parameters are common to all exposure scenarios. Dose and risk conversion
factors, shown in Table 4-1, depend on the radioisotopes. As discussed in Chapter 2, NORM
4-5

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isotopes are the uranium and thorium series. The oil and gas production waste that is reused is
equipment that is contaminated with scale containing NORM. As discussed in Chapter 2, 30
percent of the equipment waste is assumed to be NORM-contaminated, 10 percent of the overall
volume is assumed to be scale and the median and high radium (Ra-226 and Ra-228)
concentration of the NORM, as shown in Table 2-2, are 360 and 2,400 pCi/g.
4.2.1.1 Equipment Released to Schools
NORM-contaminated oil and gas equipment has been donated to schools for use as playground
equipment, fencing, and welding shop practice material (FUE92). Two scenarios, as illustrated
in Figures 4-1 and 4-2, are postulated to estimate school yard exposures from past equipment
releases. Input parameters for describing the two scenarios are presented in Table 4-2. The first
scenario involves a child playing on a jungle-gym built with NORM-contaminated water line
tubing (worst case - RAE92). It is assumed that the playground equipment consists of 7 equal
horizontal, open ended tubes. The child is postulated to be on the average within 0 ft of one,
3 ft. of 2 tubes, and 6 ft of the remaining 4. The child is being supervised by a teacher at
sufficient distance as to not be exposed to direct gamma radiation. However, the teacher is
exposed to the contaminated dust generated from tubal vibrations caused by the children playing.
The child is exposed to direct gamma radiation from the NORM contamination. Additionally,
it is assumed that an area of 0.8 m2 (~0.1 m diameter) of the tubing closest to the child has been
corroded to allow the child to directly contact the NORM-contaminated scale. As the child plays,
scale is shaken loose and allowed to become airborne. A contaminant dust loading factor for the
air surrounding the jungle-gym is calculated, as presented below, assuming a constant
contaminant dust density is maintained within each tube. It is then assumed that the dust is
blown out of the pipe and diluted into the volume of the airspace surrounding the jungle gym.
This air is then blown off site.
4-6

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Dust
Teacher

Child
Jungle-Gym
z
/ / / /



/



/



/



/




/
/
/
/
/
RAE-103860
Figure 4-1. Exposure pathways from a jungle-gym contaminated with NORM.
4-7

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Dust&
Elevated Radon
RAE-103861
Figure 4-2. Exposure pathways from the use of NORM contaminated
scrap steel in a welding shop.
4-8

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Table 4-2. Input parameters for school scenarios.
Parameter	Unit	Value	Basis
Duration of year child plays
on jungle-gym and in shop
Student/child respiration rate
Playground airborne
contaminant loading
Teachers Beverage Volume
Duration teacher spends in
shop
Average distance child is
from contaminated gym bar
Corrosion diameter for
dermal exposure
Teacher's contaminated
beverage consumption rate
Shop total dust loading
Teacher respiration rate
Fraction of dust in shop that
is considered contaminated
Radon emanation coefficient
Dust setde rate into teachers
beverage
Welding student distance to
pipe
hr/yr	400 Average 200 day school year at
2 hours of exposure per day
m3/yr	3700 EPA89b
pg/m3 2.31E-02 See equation 4-1 for 7 pipes
cm3/cup	63 Assumed
hr/yr	1000 Calculated from average 200
day school year at 5 hours of
exposure per day
m	1.3S Calculated from bar distribution
m	0.1 Assumed to be sufficiently
large to allow direct contact
with the scale
m3/yr	4.0E-2 Calculated from 200 mL/day
ingestion
pg/m3	100 EPA91, reuse
m3/yr	8000 EPA89b
percent	10 Assumed
0.10 RAE88, EPA91
m/s	0.01 EPA91
cm	30 Assumed (1 ft)
4-9

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Table 4-2. Continued.
Parameter	Unit	Value	Basis
Duration child is in direct
contact with NORM, exposed
from corroded steel jungle-
gym bar
min/day
10
Assumed
Density of scale
kg/m3
2600
RAE92, EPA91, CRC85
Welding shop ventilation rate
1/hr
2
AVN88
Vertical cross sectional area
of jungle-gym
m2
4.6
Calculated from 7 ft x 7 ft
Air volume of shop
m3
85
20 ft x 20 ft x 7.5 ft
Number of pipes in shop

1
Assumed
Length of pipe in shop and
for jungle-gym
m
2.1
Assumed
Diameter of shop & gym
piping
in
3
EPA91
Scale thickness
in
1
EPA91
Volume of air surrounding
jungle-gym
m3
9.7
Assumed
Fraction of time wind is
blowing parallel to jungle-
gym pipes

9.3E-2
EPA91
Constant internal contaminant
dust loading maintained
within tubes
pg/m3
100
EPA91
Cross sectional open area of
pipes
cm2
1.6
RAE92
Average wind velocity
blowing parallel to pipes
m/s
4.5
EPA91
Steel density
g/cm3
7800
EPA91, GR085, RAE92
Cup Surface Area
cm2
12.6
Assumed
4-10

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where
Peff = Contaminant dust loading factor for air volume surrounding jungle gym
(kg/m3)
RR = f p A1 v = release rate of contaminant from the tubing (kg/s)
v A2
AE = V2 - Air exchange rate of the volume of air surrounding the jungle-gym
(Air Volumes/s)
V2 = Volume of the air surrounding the jungle gym (m3)
f = Fraction of time wind is blowing parallel to tubing
p = Constant dust loading maintained within tubing (kg/m3)
A1 = Cross-sectional area of the tubing opening (m2)
v = Average velocity of the wind when blowing parallel to tubing (m/s)
A2 = Vertical cross section area of the volume of air surrounding the tubing (m2)
The second scenario involves a student practicing welding in an instructional metal shop. The
contaminated equipment is cut into small usable sections and welded. The cutting and welding
allow for dust contamination of the shop environment Additional exposures to the student are
from direct gamma radiation from the contaminated scrap metal. An instructor is also present
in the shop, but at sufficient distance as to not be exposed to the direct gamma radiation. The
instructor is assumed to have a beverage at his desk into which airborne contaminants settle.
4.2.1.2 Unrestricted Residential Reuse
Unrestricted residential reuse of petroleum equipment has occurred under a variety of conditions.
A scenario based on the unrestricted releases of ZAL92, as presented in Figure 4-3, for exposure
4-11

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House
Contaminated Pipe
Used as Structural Support
Culinary Water
Passed Through
Contaminated Pipe
Figure 4-3. Exposure pathways from the unrestricted use of NORM
contaminated equivlant in residential applications.
4-12

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to NORM remaining in former petroleum equipment is that of residential reuse of the equipment.
Tubing, which contains scale, is used by an individual in constructing a domestic water system,
and a piece of larger pipe or other equipment containing scale is used inside the house for
structural support of a floor, ceiling, etc. The tubing used as structural support is assumed to be
used in such a manner to not allow NORM contaminants to become airborne inside the house.
However, indoor radon is assumed to be generated from the scale and allowed to fill the house.
Table 4-3 presents the input parameters for these scenarios.
The methodology used by the NRC in its Environmental Impact Statement for 10 CFR 61
(NRC81) is used to estimate the rate at which radionuclides arc leached from the plumbing used
in the residential culinary water supply. Under this methodology, the rate at which radionuclides
leach from contaminated material is dependent on the rate at which water infiltrates through the
waste, the radionuclide partitioning ratio, and the contact time fraction. Using the NRC
methodology with respect to leaching from irradiated components, the leach rate for the scale was
taken to be factor of 10 less than the rate calculated for standard soil type wastes.
4.2.1.3 Pipe Cleaning
When the equipment is cleaned or refurbished for reuse, workers are within exposure proximity
of the NORM deposits. Reuse within the industry includes removal of NORM deposits from
inside the equipment. Until recently, mechanically abrasive tools were used to ream the scale
from tubular goods and pipes (CHA91).
Presently most of the pipe cleaning is being done with a high pressure water lance (also called
"hydrolaser" for hydroblasting) (ZAL92, CHA91). The high pressure (up to 10,000 psi) fluid is
directed through high pressure hose to an operator-controlled gun (DOE80). The equipment is
operated on a pad to allow complete control of liquids and solids. Pipes to be cleaned are placed
within a metal shroud to contain the spray. The "gun" is slowly fed into the pipe as the pipe is
rotated. The scale is separated from the liquid and stored for disposal. The cleaned pipes have
been sold under unrestricted release (KEA92).
4-13

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Table 4-3. Residential reuse input parameters.
Parameters	 Unit	Value 	
Basis
Duration spent at average	hr/day
distance from support pipe
Average distance from support	m
pipe
Respiration rate	m3/yr
Volume of water consumed from	m3/yr
contaminated plumbing
Pipe density	kg/m3
Scale density	kg/m3
Radon emanation coefficient
Contact time fraction	1/yr
Load bearing pipe height	m
Load bearing pipe diameter	in
Scale thickness	in
Ventilation rate	hr"1
Duration spent in house	hr/day
Leach fraction of NORM scale:
Ra-226	1/yr
Ra-228	1/yr
Th-228	1/yr
Pb-210	1/yr
Po-210	1/yr
Length of pipe used in plumbing	m
Diameter of plumbing pipe	in
House Volume	m3
2.2	EPA91
1.0	assumed
8000	EPA91
0.37	EPA91
(100 percent of average)
7800	EPA91, GR085
2600	EPA91, RAE92, CRC85
0.10	RAE88, EPA91
1.1E-03	calculated
2.3	AVN88
3	AVN88
1	EPA91
0.35	AVN88
18	AVN88
5.14E-07	NRC81
5.14E-07	NRC81
5.14E-07	NRC81
5.14E-07	NRC81
1.29E-07	NRC81
10	assumed
3	assumed
85	assumed
4-14

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Although the use of hydrolases or hydroblasters increases problems associated with waste
disposal, worker exposures are significantly reduced (dust emissions lowered, remote access
capable, exposure duration lowered). Therefore, this scenario, as illustrated in Figures 4-4 and
4-5, considers mechanical abrasive, and remote hydroblasting. It is assumed that the cleaner
works on the waste equipment generated by the reference 10 well facility described in Table 2-4
for a year's duration. Tubing is assumed to be cut to 1.8 m (6 ft) lengths to facilitate cleaning.
Exposures to the worker are assumed to be limited to the pipe being cleaned. Additionally,
exposures to a resident adjacent to the mechanical pipe cleaning facility from dust inhalation is
analyzed. Input parameters characterizing this scenario are listed in Tables 4-4 and 4-5.
4.2.1.4 Storage of Contaminated Equipment
The contaminated equipment is stored for varying times at the oil and gas production facility or
at an equipment storage area (ZAL92). During this storage time, yard and office workers are
exposed to direct gamma exposure and dust inhalation. Additionally, residents living adjacent
to the storage yard are exposed to the direct gamma and dust resuspended from the equipment
piles. Since no refurbishing, cleaning, smelting, or cutting is assumed to take place in the storage
yards, exposures to the adjacent residents due to contaminated dust inhalation is negligible and
not considered in this scenario.
The volume of contaminated equipment at the storage yard is assumed to be that generated from
an average 10 well facility, (see Table 2-4). This equipment is generally stacked in piles at
ground level and exposed to atmospheric conditions (ZAL92). No additional atmospheric
barriers, such as a storage building or protection roof, are considered here. Additionally, it is
assumed that the equipment is generally stored for short term intervals. Source term decay and
groundwater transport due to rainfall are not considered in this scenario. Input parameters
characterizing this scenario, as illustrated in Figure 4-6, are listed in Table 4-6.
4-15

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Adjacent
Resident
Dust&
Elevated Radon
Contaminated
Pipe
RAE-104414
Figure 4-4. Exposure pathways from the mechanical cleaning of NORM
contaminated tubing and pipe.
4-16

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Contaminated
Pipe
Collection
System
RAE-104046
Figure 4-5. Exposure pathways from the hydrolaser cleaning of NORM
contaminated tubing and pipe.
4-17

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Table 4-4. Input parameters for the mechanical abrasive pipe cleaner scenario.
Parameters	 Unit	Value 	Basis
Duration of the year worker is
employed
hr
2000
EPA91
Dust loading
pg/m3
100
EPA91
Respiration rate
m3/yr
8000
EPA91
Density of scale
kg/m3
2600
EPA91, CRC85, RAE92
Density of piping
kg/m3
7800
EPA91, GR085
Average distance to pipe
ft
1
MAD79
Thickness of NORM
in
1
EPA91
Thickness of pipe
cm
0.95
assumed, EPA91
Average length of pipe being
cleaned
m
1.8
assumed
Outer radius of pipe
in
3.0
EPA91
Downwind distance to adjacent
resident
m
100.00
EPA91
Fraction of time wind is
blowing toward resident

9.3E-2
EPA91
Average wind velocity
m/s
4.5
EPA91
4-18

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Table 4-5. Input parameters for the hydroblaster cleaning scenario.
Parameter
Unit
Value
Basis
Duration woiker is employed
m/yr
2000
EPA91
Dust loading
pg/m3
100
EPA91
Respiration rate
m3/yr
8000
EPA91
Scale density
kg/m3
2600
EPA91, CRC85, RAE92
Pipe density
kg/m3
7800
EPA91
Average distance to pipe
ft
10
KEA92, MAD79
Dust collection efficiency
percent
95
KEA92, MAD79
Number of pipes being
cleaned in facility at once

1
assumed
Thickness of NORM
in
1
EPA91
Thickness of pipe
cm
0.95
EPA91
Average length of pipe
m
1.8
assumed
Outer radius of pipe
in
3.0
EPA91
4-19

-------
Dust
Adjacent
Resident
Contaminated Tubes
RAE-104415
Figure 4-6. Exposure pathways from the storage of NORM contaminated tubing.
4-20

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Table 4-6. Storage yard exposure scenario input parameters.
Parameter	 Unit	Value 	Basis
Duration in a year yard
worker is exposed
Average worker distance from
contaminated equipment
Total air dust loading
Average thickness of scale
Average pipe lengths in yard
Respiration rate
Density of scale
Density of pipe
Inner diameter of pipe
Average height of scrap steel
pile
Volume of contaminated
scrap steel stored
Distance to adjacent resident
Fraction of time adjacent
resident is exposed to gamma
Contaminant dust loading
Fraction of time wind is
blowing parallel to pipes
Average wind velocity
hr. 2000	EPA91
m 3	assumed
pg/m3 50	EPA91
in 1	EPA91
ft 10	assumed
m3/yr 8000	EPA91
kg/m3 2600	EPA91, CRC85, RAE92
kg/m3 7800	EPA91, GR085
in 3	EPA91
m 3	assumed
m3 128.8	(reference 10 well facility)
m 100	assumed
0.75	assumed
g/m3 3.23E-6	(e.g., 4-1 for volume of
equipment)
9.3E-2	EPA91
m/s 4.5	EPA91
4-21

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4.2.1.5
Transportation of Contaminated Equipment
Oil and gas production equipment is generally shipped to a storage yard to await further use
(EPA91, ZAL92). During shipment, the truck driver, as illustrated in Figure 4-7, is assumed to
be the only exposed individual. Additionally, it is assumed that the truck driver is responsible
for transporting the volume of used equipment from an average ten well facility to the storage
yard. Using an average volume for a standard semi trailer-truck, 67.3 m3 (ROY92), it is
postulated to take a total of three trips for the truck driver to transport the material to the storage
yard. Conservatively, no additional scrap metal from other sources is assumed to be transported
with the NORM-contaminated oil and gas production equipment. Input parameters characterizing
this scenario are listed in Table 4-7.
4.2.1.6 Steel Mill and Scrap Yard Alarm Systems
Monitors are becoming more commonly used in steel mills and scrap yards. Initially, monitors
were installed to detect low-level radioactive waste and radioactive sources. However, these
alarm systems also have the ability to detect NORM contamination. In fact, the identification
of NORM-contaminated scrap has caused the rejection of scrap metal shipments (ZAL92). The
detection of NORM depends on the radium concentration, location in the load, sensitivity of
alarms, and location of the alarms.
MICROSHIELD is used to calculate the radiation exposure at a monitor two feet from a truck,
as illustrated in Figure 4-7, loaded with NORM-contaminated scrap steel. Conservative radium
concentration estimations in a truck load on NORM-contaminated equipment are determined by
assuming an average of ten percent of the volume of NORM-contaminated scrap steel in the load
is NORM scale (EPA91).
Several loading schemes or NORM distributions are evaluated: the NORM-contaminated
equipment is preferentially loaded on one side (assumed to be the easiest to detect), the NORM
is mainly concentrated on one side, but shielded by one layer of uncontaminated piping; and the
4-22

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Alarm
Detector
RAE-104061
Figure 4-7. Exposure pathways from the transport of NORM contaminated
material.
4-23

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Table 4-7. Transportation scenario input parameters.
Parameter
Unit
Value
Basis
Average miles traveled per trip
miles
50
ZAL92, FUE92
Average speed traveled
miles/hr
40
assumed
Number of trips per year

3
assumed
Cab distance from trailer
m
1
ROY92
Trailer length
ft
40
ROY92
Trailer height
m
2.4
ROY92
Trailer width
m
2.3
ROY92
Scale density
kg/m3
2600
EPA91, CRC85, RAE92
Steel density
kg/m3
7800
EPA91
Volume of trailer
m3
67.3
calculated
Total volume of load
m3
42.9
calculated
Total height
m
1.5
calculated
Fraction of median 10 well

0.33
calculated
volume per load



4-24

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NORM is uniformly distributed throughout the load (assumed to be the hardest to detect). Input
parameters characterizing the evaluation of the alarm systems are listed in Table 4-8.
4.2.1.7 Recycled to Smelter
Although some smelting operations may produce steel for new oil-field equipment from old
NORM-contaminated equipment, other operations produce products to be released to the general
public. In a typical batch-smelting operation of contaminated steel, the furnace is charged with
the steel and slagging material. As the contaminated steel is melted, the scale deposits are
volatilized. The volatilized materials are then carried out with the stack gases, or they are
trapped in the slagging material and removed with the slag. Compounds that are not volatilized
migrate into the slag layer as a result of density differences between the molten steel and the
metal compounds.
The scenarios considered in this assessment conservatively model emissions from a 30-minute
batch processing of the gas-fired furnace described in Case 2 of Section 3.1.2.4. As discussed
above, the slagging agents used directly affect the amount of NORM contaminant that is allowed
to escape in the effluent gases. The two scenarios, as illustrated in Figure 4-8, consider both
extremes (-100 percent of the NORM is volatilized and released with the effluent gases, and
~100 percent of the NORM is captured by the slagging agents and transported to the slag pile).
As discussed in Section 3.1.2.4, the resulting product in either case is considered uncontaminated.
The dust contamination from the flue gas and the gamma emissions from the slag pile expose
both a yard worker and an adjacent resident Input parameters characterizing these scenarios are
presented in Table 4-9. This scenario is considered conservative since some smelters monitor
incoming scrap metal and most reprocess scrap from other sources not associated with the oil and
gas production field.
4-25

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Table 4-8. Alarm scenario input parameters.
Parameter
Unit
Value
Basis
Trailer distance to alarm
ft
2
BER92
Trailer length
ft
40
ROY92
Trailer height
m
2.4
ROY92
Trailer width
m
2.3
ROY92
Scale density
kg/m3
2600
EPA91, CRC85, RAE92
Steel density
kg/m3
7800
EPA91
Volume of trailer
m3
67.3
calculated
Total volume of load
m3
42.9
calculated
Total height
m
1.5
calculated
Fraction of median 10

0.33
calculated
well volume per load
4-26

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Dust
RAE-104060
Figure 4-8. Exposure pathways from the smelting of NORM contaminated
scrap steel.
4-27

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Table 4-9. Smelting input parameters.
Parameters
Unit
Value
Basis
Quantity of metal smelted per batch
tons
50
ROW92
Duration worker is exposed to slag pile
hr/yr
2000
EPA91
Worker respiration rate
m3/yr
8000
NRC81
Dust loading
pg/m3
100
EPA91
Distance to adjacent resident
m
100
assumed
Number of contaminated batches per year
b/yr
5
calculated
NORM concentration in slag if slagging agents used
pCi/g
170
calculated (see
Section 3.1.2.4)
NORM concentration in flue gas if no slagging agents
are used
pCi/L
170
see Section 3.1.2.4
Furnace effluent discharge rate
L/min
2.83E+5
ROW92
Fraction of time resident is exposed to dust or gamma

0.75
assumed
Distance of adjacent resident to smelter stack to slag
pile
m
100
assumed
Fraction of time wind is blowing toward resident

9.3E-2
EPA91
Average wind speed blowing towards resident
m/s
4.5
EPA91
Average Pasquill stability class of air blowing towards
resident
1/2
1/2
C
D
EPA91
Mass of slag per 50 ton batch
ton
9.5
calculated
Average density of slag
g/cm3
3.0
NRC78
Slag pile volumea
m3
14.4
calculated from waste
generated from 10
well facility
Slag pile height
m
2
assumed
Distance of worker to slag pile and smelter stack
m
10
assumed
Average stack gas velocity
m/s
2.7
assumed
Inside stack diameter
m
2.5
assumed
a No additional dilution is utilized for the slag pile.
Generally, slag generated for smelting of non-
contaminated equipment will provide significant dilution.
4-28

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4.2.2	Phosphogypsum
The results of evaluations of possible health impacts from the production and commercial uses
of phosphogypsum wastes are dependent on the waste inventories, generic site parameters and
radiological properties of the NORM wastes. The majority of this information comes from the
recent ORP work, "Development of Background Information and Risk Analyses of Alternative
Phosphogypsum Uses" (BID91).
The exposure scenarios evaluated for this risk assessment include potential exposures to
individuals from the use of phosphogypsum in agriculture, road construction, and research
activities. Additionally, exposures from the cleaning of the stainless steel Alter pans used in the
separation of the phosphoric acid and the phosphogypsum are evaluated. Exposures are
calculated for both the median and high concentrations presented in Table 2-5.
Non-scenario-specific parameters are compiled as Table 4-10.
4.2.2.1 Phosphogypsum in Agriculture
Two scenarios involving the agricultural use of phosphogypsum are evaluated. These scenarios,
as illustrated in Figure 4-9, assume a moderate-sized sand field, used to grow crops, with the
exposed individual being 100 m from the site edge. The first scenario involves the use of
phosphogypsum as a source of calcium and sulfur for soils deficient in these elements. The
second involves its use in sediment control for soils that have been eroded and leached. Values
of environmental and climatological parameters used in the risk assessment are representative of
a humid permeable site.
4.2.2.1.1	Phosphogypsum as a source of calcium and sulfur
Parameters which characterize the scenario involving phosphogypsum as a source of calcium and
sulfur on agricultural fields are shown in Table 4-11. The parameter values in Table 4-11 are
based on the responses by agricultural users of phosphogypsum to a survey by The Fertilizer
4-29

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Table 4-10. Site-specific input parameters for phosphogypsum risk assessments
(Basis for Values: BID91).
Parameter
Units
Value
Phosphogypsum application rate-agricultural
scenarios
Fertilizer
Soil conditioner
Phosphogypsum application interval-
agricultural scenarios
Total years of application-agricultural
scenarios
Agricultural field size
Fertilizer
Soil conditioner
Tillage depth—agricultural scenarios
Fertilizer
Soil conditioner
Agricultural field soil density
Roadbed material density
Distance to nearest residence
Fertilizer
Soil conditioner
Road construction scenarios
Distance to river
River flow rate
Density of aquifer
Porosity of aquifer
Horizontal velocity of aquifer
Vertical distance to aquifer
Fertilizer scenario
Soil conditioner scenario
Construction scenarios
MT/acre/yr
MT/acre/yr
yrs
acre
acre
m
m
kg/m3
kg/m3
m
m
m
m
m3/yr
kg/m3
m/yr
m
m
m
0.66
4.05
biennially
100
138
556
0.22
0.30
1.50E+03
2.25E+03
100
100
100
5.00E403
1.00E+08
1.80E+03
0.33
20
3.0
10.0
3.0
4-30

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Table 4-10. (Continued.)
	Parameter		Units 	Value
Water infiltration rate
Fertilizer scenario	m/yr	0.40
Soil conditioner scenario	m/yr	0.25
Construction scenarios	m/yr	0.40
Fraction of food eaten grown on-site	--	0.50
Adult breathing rate	m3/yr	8.00E-+03
Average dust loading in outside air	kg/m3	5.00E-07
Average dust loading in R&D lab	kg/m3	1.00E-07
Atmospheric stability class	~	4
Fraction of time wind blows toward receptor	~	0.093
Average wind speed	m/sec	4.5
Dust resuspension rate for off-site transport	m /sec	5.0E-07
Dust deposition velocity	m/sec	1.0E-03
Radon emanating power	—	0.30
Radon diffusion coefficient
Soil	m2/yr	2.2E+01
Concrete	m2/yr	1.6E+01
Air change rate in reclaimer house	changes/hr	2
Exposure fraction for indoor exposure	~	0.75
Equivalent exposure fraction for outdoor	—	0.50
exposure
Surface erosion rate	m/yr	2.0E-04
Volume of drinking water consumed	m3/yr	0.37
annually by an individual
Length of road perpendicular to aquifer	mile	10
Aquifer thickness	m	10
4-31

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Aquifer
RAE-103867
Figure 4-9. Exposure pathways from the agricultural use of phosphogypsum.
4-32

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Table 4-11. Phosphogypsum use parameters for agricultural scenarios
(Basis: BID 91).
Soil Additive Sediment Control
Scenario	Scenario
Kilograms of phosphogypsum per acre
Initial
664
8,000
Subsequent

4,000
Acre per farm
138
556
Tillage depth (cm)
22
30
Application rate
Biennial
Biennial
Distance to nearest residence (m)
100
100
4-33

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Institute (TFI89). The reference agricultural field for the first scenario is postulated to be located
in a humid permeable site. Values of environmental and climatological parameters used in the
risk assessment are representative of a humid permeable site.
Dose calculations for the first scenario assumes biennial application of phosphogypsum to the
reference site for a period of 100 years. Phosphogypsum is spread over a field and diluted by
mixing with the soil. Hence the incremental radionuclide concentrations in the soil are much
lower than the concentrations in the phosphogypsum itself. Over time, as phosphogypsum
continues to be applied, the radionuclide concentrations in the soil are expected to increase until
equilibrium is reached with competing mechanisms that remove the gypsum, and its radioactive
constituents, from the soil. These removal mechanisms include plant uptake, leaching by
infiltration of surface water, and wind and water erosion. The Ra-228 part of the radionuclide
content in the soil is also reduced as a result of radioactive decay. A simple mass balance
equation is used to estimate radionuclide concentrations in the reference soil as a result of
biennial applications of phosphogypsum for a period of 100 years.
— = K - kC	(4-2)
dt
where
C = Ra-226 concentration (pCi/g)
K&k = arbitrary constants
The solution to equation 4-2 is obtained through standard differential equation solution
techniques, and is found to be:
C =J£(1 -e'*)	(4-3)
k
4-34

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Using the boundary condition of C=0 at t=0, the arbitrary constants can be solved for. The
resulting solution then becomes:
r,k'CPO,	1	. «	" k<' "i>S (,M)
s W k2+k3+k4+k5
where
Cs	=	Ra-226 concentration in soil (pCi/g)
CpQ	=	Ra-226 concentration in phosphogypsum (pCi/g)
kj	=	application rate of phosphogypsum (g/yr)
W	=	mass of soil (g)
k2	=	Ra-226 decay rate (4.3x1c4 yr*1)
k3	=	rate loss of Ra-226 due to uptake by plants (2.6X10"6 yr"1)
k4	=	rate loss of Ra-226 by leaching (2.8xl0"5 yr"1)
IC5	=	rate loss of Ra-226 by wind erosion (8.9X10"4 yr"1)
Using the data in Table 4-11, the soil Ra-226 concentration can be calculated after 100 years of
biennial phosphogypsum application (see Table 4-12). A summary of the soil Ra-226
concentrations calculated for the scenarios involving phosphogypsum is presented in Table 4-13.
4.2.2.1.2	Phosphogypsum as sediment control for soils that have been eroded ¦
and leached
Parameters which characterize this scenario are also shown in Table 4-11. The reference
agricultural site for this scenario is assumed to be located in the south-western United States.
The phosphogypsum is initially applied at the rate of 8 MT per acre, followed by biennial
applications of 4 MT per acre. As in the first scenario, an application period of 100 years is
postulated. For a median Ra-226 concentration of 31 pCi/g in phosphogypsum, the increase in
4-35

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Table 4-12. Ra-226 soil concentration calculation parameters (Basis: BID91).
Parameter	 	Fertilizer	 Sediment Control
kj (yr"1)	4.3E-04	4.3E-04
k3 (yr"1)	2.6E-06	2.6E-06
k4 (yr'1)	2.8E-05	2.8E-05
kj (yr'1)	8.9E-04	8.9E-04
k| (g/yr)	4.6E+07	1.1E+09
t (yrs)	100	100
W(g)	1.9E+11	1.0E+12
median Cs (pCi/g)	31	31
high (Cs (pCi/g)	48.6	48.6
4-36

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Table 4-13. Ra-226 soil concentrations (Basis: BID91).
Median Ra-226	90 Percentile Ra-226
Concentration Concentration
	Scenario	 	(pCi/g)			(pCi/g)
Fertilize	0.71	1.11
Sediment Control	3.22	5.05
4-37

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the Ra-226 concentration in the tilled soil after 100 years of biannual application is calculated
to be 3.22 pCi/g.
The agricultural worker is assumed to spend 2,000 hours per year at the agricultural site,
performing activities such as plowing, fertilizing, harvesting, etc. The worker would probably
use machinery for most of these activities which would provide some shielding from direct
gamma radiation (as in the construction scenarios, plowing equipment on average provides a
shielding factor of 0.6). However, to ensure conservatism in the results of this risk analysis, no
credit for shielding is taken in calculating the dose from direct exposure to gamma radiation
(BID91).
The on-site individual is assumed to live in a house constructed on a site which was previously
used for agriculture. For conservatism, this individual is also assumed to work at this same site.
The CPG is defined to include individuals who might be exposed to the highest doses as a result
of normal daily activities. For this phosphogypsum risk assessment, the member of the CPG is
assumed to be an adult at the nearest residence as defined in Table 4-11. The person obtains all
water from a well adjacent to the house. Fifty percent of foodstuffs are assumed to be grown
on-site.
4.2.2.2 Phosphogypsum in Road Construction
Two scenarios, as illustrated in Figure 4-10, involving phosphogypsum in road construction are
evaluated. The first involves the use of phosphogypsum in a road base for a secondary road.
The second scenario involves the use of phosphogypsum as a concrete additive.
4.2.2.2.1	Phosphogypsum in a road base for a secondary road
The road base consists of a 1:2 phosphogypsum:soil mixture with a density of 2.25 g/cm3 (2.25
MT/m3). Assuming a Ra-226 concentration of 31 pCi/g in phosphogypsum, the Ra-226
4-38

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•	;H

SCENARIOS 8 AND 9
USE OF PHOSPHOGYPSUM IN A ROAD BASE
'.'.•'•V'•	:* :*
Tr-yn

MWMlMiW
%•
•
SCENARIOS 10 AND 11
USE OF PHOSPHOGYPSUM IN A
CONCRETE ROAD SURFACE
RAE-104416
Figure 4-10. Scenarios involving the use of phosphogypsum in
road construction.
4-39

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concentration in the road base is 10 pCi/g. The road base is 9.15 m (30 ft) wide and 0.25 m (10
inches) thick and is covered by a 0.12 m (5 inch) thickness of asphalt
4.2.2.2.2	Phosphogypsum in a concrete road surface
The concrete road surface incorporates 15 weight percent phosphogypsum. Assuming a Ra-226
concentration of 31 pCi/g in phosphogypsum, the Ra-226 concentration in the road surface is 4.7
pCi/g. The road surface is 7.32 m (24 ft) wide and 0.12 m (5 inches) thick. The road base
under the concrete surface is the same as for the first road construction scenario.
Radium often occurs naturally in concrete constituents. In a study of the radioactive properties
of commercially available concrete for the State of Florida (RAE91b), radium concentrations in
concrete samples from 1.0 pCi/g to 2.4 pCi/g were measured. Radium in commercially available
concrete varies directly with the origin of the constituents (RAE91b). Due to this variance,
radium in the concrete evaluated in this analysis is assumed to be only from the phosphogypsum
additive.
The construction worker is assumed to be engaged eight hours per day for 250 days per year in
constructing a 16-km (10-mile) section of road. Gamma exposures are calculated for a worker
who is employed directly on the road surface and a worker who uses equipment such as a
bulldozer or road grader which provides some shielding from gamma radiation. The shielding
coefficient is 0.6.
The person driving on the road is assumed to use the road from home to work, and return. This
person travels the road one hour per day for 250 trips per year. The automobile in which this
person rides provides some shielding from direct gamma radiation. Hie shielding coefficient is
0.6.
The reclaimer is assumed to build a house on the roadbed at some future time (presumed to be
50 years after road construction) after the road is closed and the road surface has crumbled and
4-40

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been removed. In addition to living in a house at the site, the reclaimer drills a well for water
and plants a vegetable garden in the contaminated soil. The vegetable garden provides 50 percent
of the reclaimer's foodstuffs.
The member of the CPG is assumed to live in a house located 100 meters from the road.
Potential doses to a member of the CPG could result from direct gamma exposure or from the
use of contaminated well water.
4.2.2.3	Phosphogypsum in Research and Development Activities
One scenario, as illustrated in Figure 4-11, is evaluated in which phosphogypsum is used in
research and development to evaluate the properties of this material for commercial applications.
In this scenario, exposures are estimated for a worker who spends four hours per day, 250 days
per year in a laboratory containing one open 55-gallon drum of phosphogypsum. The worker is
exposed via direct gamma radiation, dust inhalation, and radon inhalation pathways.
MICROSHlHLD is used to estimate the external gamma dose; the worker is assumed to be
positioned at an average distance of one meter from the drum of phosphogypsum. To estimate
the exposure from dust inhalation, a dust loading of 100 micrograms/m3 is postulated. This value
is derived from 40 CFR 50.6(b), which specifies a level of 50 pg/m3 as the arithmetic mean level
of primary and secondary standards for airborne particulate matter. The value is doubled to
provide a conservative estimate. To estimate the indoor radon exposure, two air changes per
hour are assumed.
4.2.2.4	Cleaning of Stainless Steel Filter Pans
The production of phosphogypsum involves the separation of phosphoric acid and
phosphogypsum using large fiberglass covered stainless steel filter pans (EPA91). During this
process, scale is deposited on the surface areas of the pan and fiberglass mat. Due to the high
cost of the filter pans, the current industrial practice involves cleaning the pans for reuse
(KEA92). The cleaning of the filter pans exposes workers to direct gamma radiation,
contaminated dust inhalation, and indoor radon inhalation risks.
4-41

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Dust &
Elevated Radon
Researcher
55-Gallon Drum
(Phosphogypsum)
RAE-103869
Figure 4-11. Exposure pathway from research activities using
phosphogypsum.
4-42

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This scenario involves the cleaning of stainless steel filter pans by hydrolasers. The scenario
consists of a worker operating a hydrolaser from the remote distance of ten feet. The Ra-226
concentration of the scale is taken to be 100 times the normal for phosphogypsum 3,000 pCi/g
(EPA91). Additionally, it is assumed that the worker is exposed to a total of six m3 of scale for
the 2000 hour working year. The input parameters characterizing this scenario are presented in
Table 4-14.
4-43

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Table 4-14. Stainless steel filter pan cleaning scenario input parameters.
Parameter
Unit
Value
Basis
Duration workers employed
Dust loading
Respiration rate
Phosphate scale density
Average distance of
exposure3
Dust collection efficiency
Number of pans being
cleaned in facility at once
Volume of scale
Radon emanation
coefficient
m/yr
pg/m3
m3/yr
kg/m3
ft
percent
m
m3/yr
2,000
100
8,000
2,600
10
95
1
6
0.20
EPA91
EPA91
EPA91
CRC85, BID91, KEA92
assumed
KEA92, MAD79
assumed
EPA91
EPA91
a It is assumed that the worker is exposed for a full 2,000 hours to the filter pans being
cleaned.
4-44

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5. Risk Assessment Results
This chapter presents the calculated risks associated with the reprocessing and reuse of NORM-
contaminated oil and gas production equipment and phosphogypsum, according to the scenario
outlined in Chapter 4. Results are reported for median and 90 percentile concentrations of
NORM.
5.1 OIL AND GAS PRODUCTION
Risk assessment results for exposures resulting from NORM-contaminated oil and gas production
equipment are summarized below. Additionally, alarm exposures and distributions are presented.
State and Federal regulations are presented where applicable.
5.1.1	Maximum Individual Exposures
The risks due to the exposures to NORM from the oil and gas production wastes are summarized
in Tables 5-1 through 5-4. The calculated risks are for fatal cancers. If a calculated risk is
7.0E-05, an exposure to the indicated level of radiation for one year will, in a 70-year lifetime,
probably cause seven fatal cancers in an exposed population of 100,000 persons. From Table
5-1 and 5-2, the risks resulting from the unrestricted release of median and 90 percentile NORM-
contaminated equipment are presented The risk to a student playing on a jungle gym
contaminated with median and 90 percentile levels of NORM are 1.2E-05 and 7.8E-05,
respectively. These risks are primarily due to direct gamma exposure. A student in the welding
class that uses median and 90 percentile NORM-contaminated equipment has risks of 1.0E-06
and 7.0E-06. Again, the major contributor is direct gamma radiation. The shop student
experiences higher dust and radon inhalation doses than the child playing on the playground
equipment However, there is less NORM-contaminated equipment in the shop than composed
in the jungle gym, reducing the direct gamma and overall dose to the welder.
5-1

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Table 5-1. Risk assessment results for unrestricted release scenarios with median
NORM concentrations.

Dose
Risk
Person - Pathway
(mrem/vr)
(fatal cancers)
Child on jungle gym


Direct gamma
4.5E+01
1.2E-05
Dust inhalation
1.6E-04
2. IE-11
Dermal
0.0E+00

TOTAL
4.5E+01
1.2E-05
Student in welding class


Direct gamma
4.0E+00
1.0E-06
Dust inhalation
6.6E-02
1.4E-08
Radon inhalation

4.0E-13
Dermal
O.OE+OO
0.0E+00
TOTAL
4.1E+00
1.0E-06
Teacher in welding class


Ingestion
8.2E-03
7.4E-10
Dust inhalation
3.6E-01
7.5E-08
Radon inhalation

2. IE-12
TOTAL
3.7E-01
7.6E-08
Teacher Supervising Jungle Gym


Dust
8.2E-04
1.7E-08
Resident Reuse


Direct gamma
1.8E+00
1.6E-10
Ingestion
2.7E-05
2.4E-12
Radon

8.2E-12
TOTAL
1.8E+00
1.7E-10
5-2

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Table 5-2. Risk assessment results for unrestricted release scenarios
with 90 percentile NORM concentrations.
Dose Risk
Person - Pathway	 	(mrem/vr)		(fatal cancers)
Child on jungle gym
Direct gamma
Dust inhalation
Dermal
3.0E+02
1.0E-03
O.OE+OO
7.8E-05
2.2E-10
TOTAL
3.0E+02
7.8E-0S
Student in welding class


Direct gamma
2.7E+01
6.9E-06
Dust inhalation
4.5E-01
9.2E-08
Radon inhalation

2.6E-12
Dermal
0.0E+00
O.OE+OO
TOTAL
2.7E+01
7.0E-06
Teacher in welding class


Ingestion
5.5E-02
5.1E-09
Dust inhalation
2.4E+00
5.1E-07
Radon inhalation

1.4E-11
TOTAL
2.5E+00
5.2E-07
Teacher Supervising Jungle Gym


Dust inhalation
5.5E-03
1.1E-07
Resident Reuse

-
Direct gamma
1.2E01
1.1E-09
Ingestion
1.8E-04
1.6E-11
Radon

5.5E-11
TOTAL
1.2E+01
1.2E-09
5-3

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Table 5-3. Risk assessment results for the contaminated oil production equipment
reprocessing scenarios for median NORM concentrations.
Dose	Risk
Person - Pathway	 (mrem/vr)	(fatal cancers)
Worker in storage yard
Direct gamma
Dust inhalation
2.0E+01
2.3E+01
5.5E-06
4.9E-08
TOTAL
2.0E+01
5.6E-06
Truck driver
Direct gamma
3.4E-028
9.0E-09®
Resident adjacent to storage yard
Direct gamma
Dust inhalation
7.2E-02
1.1E-03
1.9E-08
5.4E-11
TOTAL
7JE-03
1.9E-08
Worker in smelter yard with no slag
control
Dust inhalation
9.3E+02b
2.0E-04b
Worker in smelter yard with slag control
Direct gamma
5.6E+00
1.5E-06
Resident adjacent to smelter with no slag
control
Dust inhalation
4.3E+01C
9.2E-06C
Resident adjacent to smelter with slag
control
Direct gamma
1.4E-01
3.7E-08
Mechanical abrasive pipe cleaner
Direct gamma
Dust inhalation
5.2E-04
7.2E+00
4.5E-14
1.5E-06
TOTAL
7.2E+00
1.5E-06
Hydrolaser pipe cleaner
Direct gamma
Dust inhalation
7.5E-05
3.6E-01
6.6E-16
7.5E-08
TOTAL
3.6E-01
7.5E-08
Resident adjacent to cleaning facility
Dust inhalation
1.9E-02
4.0E-09
a 1.1E-02 mrcm/yr per trip and 3.0E-09 fatal cancers per trip,
b 1.86E+02 mrem/yr per batch and 4.0E-05 fatal cancers per batch,
c 8.6E+00 mrem/yr per batch and 1.8E-06 fatal cancers per batch.
5-4

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Table 5-4. Risk assessment results for the contaminated oil production equipment
reprocessing scenarios for 90 percentile NORM concentrations.
Dose	Risk
Person - Pathway	 (mrem/vr)	(fatal cancers)
Worker in storage yard
Direct gamma
Dust inhalation
1.4E+02
1.6E+00
3.6E-05
3.3E-07
TOTAL
1.4E+02
3.6E-05
Truck driver
Direct gamma
2.2E-013
6.0E-083
Resident adjacent to storage yard
Direct gamma
Dust inhalation
5.1E-01
7.3E-03
1.3E-07
3.6E-10
TOTAL
5.1E-01
1.3E-07
Worker in smelter yard with no slag
control
Dust inhalation
6.2E+035
1.3E-03b
Worker in smelter yard with slag control
Direct gamma
3.7E+01
1.0E-05
Resident adjacent to smelter with no slag
control
Dust inhalation
2.9E+02C
6.1E-05C
Resident adjacent to smelter with slag
control
Direct gamma
9.2E-01
2.5E-07
Mechanical abrasive pipe cleaner
Direct gamma
Dust inhalation
3.4E-03
5.1E+00
3.0E-13
1.0E-05
TOTAL
5.1E+00
1.0E-05
Hydrolaser pipe cleaner
Direct gamma
Dust inhalation
5.1E-05
2.4E+00
4.4E-15
5.1E-07
TOTAL
2.4E+00
5.1E-07
Resident adjacent to cleaning facility
Dust inhalation
1.3E-01
2.7E-08
a 7.3E-02 mrem/yr per trip and 2.0E-08 fatal cancers per trip,
b 1.2E+03 mrem/yr per batch and 2.7E-04 fatal cancers per batch,
c 5.7E+01 mrem/yr per batch and 1.2E-05 fatal cancers per batch.
5-5

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The risks to the shop instructor and the playground supervising teacher from median levels of
NORM contamination are 7.6E-08 and 1.7E-08, respectively. These risks are higher than the
student's for dust and radon inhalation because of the increased exposure time. However,
without the dominating direct gamma component, the teacher and instructor doses are
significantly less than those experienced by the students.
Tables 5-1 and 5-2 also present the risks to individuals using NORM-contaminated equipment
in residential construction. The resident's risks from the use of median and 90 percentile
NORM-contaminated equipment for plumbing and building materials arc 1.7E-10 and 1.2E-09,
respectively. The major contribution to the overall doses is from direct gamma radiation from
contaminated piping. The direct gamma dose to the individual is significantly less than that
experienced from the student because of the larger average distance from which the resident is
exposed. The estimated radium concentration in the water from median NORM concentration
in scale is 105 pCi/m3 or 0.1 pCi/L. As discussed in chapter 1, this does not violate the National
Drinking Water Standards (40 CFR 141) for radium of 40 pCi/L. In order to exceed the
40 CFR 141 radium limits, radium scale concentrations in this scenario need to be in excess of
1.4E+05 pCi/g.
Exposures resulting from the preprocessing of used oil and gas production equipment are
presented in Tables 5-3 and 5-4. The risks to a truck driver transporting median concentrated
NORM-contaminated oil and production equipment experiences a risk of 9.0E-09. This is
directly resulting from exposure to direct gamma radiation. The risk is significantly less to the
truck driver than that experienced by the child playing on the jungle gym because of the
decreased time of exposure and the increased shielding and distance to contamination.
Other occupational exposures are reported for the pipe cleaners, and the smelter and storage yard
workers. Risks to the mechanical and hydrolaser pipe cleaners from median NORM-
contaminated equipment are 1.5E-06 and 7.5E-08. Exposures to the hydrolaser cleaner are less
than those to the mechanical cleaner primarily due to the added distance and dust control
5-6

-------
provided by hydroblasting. The exposure to the resident adjacent to the mechanical cleaning
facility from median NORM contaminated dust is 4.0E-09.
The risks summarized for the smelter yard worker and adjacent resident are presented in two
parts to allow for the modeling of the effects of varying slagging agents. The risks from
exposure to median concentration NORM equipment to the smelter yard worker if all of the
NORM is captured in the slag is 1.5E-06. However, if slagging agents are used that do not serve
to capture the NORM radionuclides, then the risk to the exposed worker is 2.0E-04. If a
particular slagging agent is used in which 30 percent of the NORM can be captured, then the risk
to the worker is calculated as [(0.30 x 1.5E-06) + (0.70 x 3.0E-04)] or 1.4E-04. Similar
combinations can be made for the adjacent resident [(0.30 x 3.7E-08) + (0.70 x 9.2E-06) =
6.5E-06].
5.1.2	NORM Transportation
The exposures from the several loading schemes of median concentrated NORM distributions
evaluated are illustrated in Figures 5-1 through 5-3. As illustrated in Figure 5-1, if median
concentrated NORM is preferentially loaded on one side (assumed to be the easiest to detect),
the exposure to an alarm would be 2.2E+01 pR/hr. If the NORM is mainly concentrated at one
side but shielded by a layer of uncontaminated piping, the exposure at the alarm would be
1.5E+01 pR/hr. The effects of the shielding provided by clean piping can be seen in Figure 5-2.
Exposures to the alarm are exponentially proportional to the thickness of the clean layer of piping
between the NORM and the detector. Additionally, Figure 5-3 illustrates the alarm-position
exposures from varying concentrations of NORM contamination in a uniformly distributed load
of oil production pipe. As can be seen, NORM radium concentrations need to be as high as 200
pCi/g to be detected by the alarm.
As noted earlier, the DOT defines a regulated radioactive material as "any material having
specific activity greater that 0.002 piCHg" (49 CFR 173). Assuming that 100 percent of the truck
load is NORM-contaminated (~10 percent NORM scale by volume), and a median value of the
5-7

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10
10
10
0.0
AVERAGE ALARM SETTING
AVERAGE BACKGROUND
DISTRIBUTION SCHEMES
~ UNIFORM
~ OUTER EDGE OF LOAD
¦ ONE ROW BACK IN LOAD
0.2	0.4	0.6	0.8
FRACTION OF LOAD THAT CONTAINS
NORM CONTAMINATED EQUIPMENT
1.0
RAE -104076
Figure 5-1. Alarm exposures from NORM contaminated trailers for
varying loading schemes.
5-8

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LOCATION OF NORM CONTAMINATED
EQUIPMENT GROUP IN TRAILER LOAD
RAE-104077
Figure 5-2. Variations in alarm exposures with respect to NORM
contaminated equipment group position in load.
5-9

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RADIUM CONCENTRATION IN NORM (pCi/g)
RAE- 104078
Figure 5-3. Alarm exposures for uniformaly distributed loads of
NORM contaminated equipement vs. radium concentration
of the NORM.
5-10

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total radium concentration in the NORM scale to be 360 pCi/g. This concentration of NORM
would be generally detectable. However, it would not be considered "radioactive material" as
defined by ,49 CFR 173 and as such would not be subject to DOT regulations. In order for a
truck loaded with NORM-contaminated equipment to be regulated by DOT, the radium
concentration in the NORM scale must be 726 pCi/g or higher.
5.2 PHOSPHOGYPSUM
The results of the phosphogypsum risk assessment are given in this section. Results are
presented for the commercial use of phosphogypsum in agriculture, road construction, and
research and development Exposure scenarios used for this risk assessment are described in
Section 4.2.2.
5.2.1	Phosphogypsum in Agriculture
Estimated doses and risks for the soil additive scenario, involving an average phosphogypsum
application rate on a moderate size sand field used to grow peanuts, are shown in Tables 5-5 and
5-6. Estimated doses and risks for the sediment control scenario are also shown in Tables 5-5
and 5-6. The risks shown in Tables 5-5 and 5-6 are estimated lifetime (70-year) risks from one
year of exposure.
For each of the agricultural scenarios, the highest doses and risks result from external gamma
exposure and from indoor radon inhalation to the on-site individual For the fertilizer scenario,
the lifetime risk to the on-site individual from one year of external gamma exposure is estimated
to be 3.7E-06 for 31 pCi/g phosphogypsum. The lifetime risk from one year of indoor radon
inhalation is estimated to be 3.1E-06, for median NORM concentrations. For the sediment
control scenario, the lifetime risk to the on-site individual from one year of external gamma
exposure is estimated to be 1.7E-05. The lifetime risk from one year of indoor radon inhalation
is estimated to be 1.4E-05.
5-11

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Table 5-5. Risk assessment results for agricultural scenarios involving median
phosphogypsum concentrations.
Fertilizer
Agricultural Worker Direct Gamma
Agricultural Worker Dust Inhalation
On-Site Individual Direct Gamma
On-Site Individual Indoor Radon
On-Site Individual Well Water Use
Member of CPG - Inhalation of
contaminated dust
Member of CPG - Ingestion of drinking
water from contaminated well
Member of CPG - Ingestion of foodstuff
contaminated by well water
Member of CPG - Ingestion of foodstuff
grown on fertilized soil
Individual - Ingestion of river water
contaminated by groundwater
Individual - Ingestion of river water
contaminated by surface runoff
Dose3
(mrem)
4.3E+00
8.4E-02
9.0E+00
	c
c
Risk
Sediment Control
Riskb
1.7E-06
6.8E-09
3.7E-06
3.1E-06
Dose®
(mrem)
2.0E+01
9.6E-01
4.0E-KH
	c
c
7.7E-06
7.7E-08
1.7E-05
1.4E-05
8.4E-04 6.8E-11 7.7E-03 6.5E-10
5.9E-02 6.2E-09 2.6E-01 2.7E-08
9.9E-03 9.0E-10 1.7E-01 1.6E-08
a.	Dose or dose commitment from one year of exposure.
b.	Lifetime risk from one year of exposure.
c.	No radionuclides are calculated to reach the on-site well via the groundwater
pathway for almost 10,000 years, or the off-site river or well for at least 100,000
years because of groundwater velocities and retardation factors.
5-12

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Table 5-6. Risk assessment results for agricultural scenarios involving
90 percentile phosphogypsum concentrations.

Fertilizer
Sediment Control

Dose8
fmrem)
Riskb
Dose8
fmrem)
Riskb
Agricultural Worker Direct Gamma
6.8E-KX)
2.6E-06
3.1E+01
1.2E-05
Agricultural Worker Dust Inhalation
1.3E-01
1.1E-08
1.5E+00
1.2E-07
On-Site Individual Direct Gamma
1.4E+01
5.8E-06
6.3E401
2.6E-05
On-Site Individual Indoor Radon
	c
4.9E-06
	c
2.3E-05
On-Site Individual Well Water Use
	c
	C
	c
	c
Member of CPG - Inhalation of
contaminated dust
1.3E-03
1.1E-10
1.2E-02
1.0E-09
Member of CPG - Ingestion of drinking
water from contaminated well
	C
	c
	C
	C
Member of CPG - Ingestion of foodstuff
contaminated by well water
	c
	c
	C
	C
Member of CPG - Ingestion of foodstuff
grown on fertilized soil
9.2E-02
9.7E-09
4.1E-01
4.4E-08
Individual - Ingestion of river water
contaminated by groundwater
	c
	c
	c
	c
Individual - Ingestion of river water
contaminated by surface runoff
1.6E-02
1.4E-09
2.8E-01
2.5E-08
a.	Dose or dose commitment from one year of exposure.
b.	Lifetime risk from one year of exposure.
c.	No radionuclides are calculated to reach the on-site well via the groundwater
pathway for almost 10,000 years, or the off-site river or well for at least 100,000
years because of groundwater velocities and retardation factors.
5-13

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5.2.2
Phosphogypsum in Road Construction
The results of the risk assessment for use of phosphogypsum in road construction are summarized
in Tables 5-7 and 5-8. In evaluating the risk to the construction workers from external gamma
radiation during road construction, two cases (with and without shielding effects) are considered
to bracket the worker doses which could be received from external gamma radiation. Worker
doses were evaluated for the case of no asphalt cover over the roadbed to maximize the resulting
doses.
For the road construction scenarios, the highest doses and risks result from external gamma
exposure and indoor radon inhalation by the reclaimer. For the road base scenario, the lifetime
risk to the reclaimer from one year of external gamma exposure is estimated to be 3.1E-05 for
31 pCi/g phosphogypsum. The lifetime risk from one year of indoor radon inhalation is
estimated to be 7.0E-05 for 31 pCi/g phosphogypsum.
For the concrete additive scenario, the lifetime risk to the reclaimer from one year of external
gamma exposure is estimated to be 5.9E-05 for 31 pCi/g phosphogypsum. The lifetime risk from
one year of indoor radon inhalation is estimated to be 8.1E-05 for 31 pCi/g phosphogypsum.
5.2.3	Phosphogypsum in Research and Development Activities
The results of the risk assessment of the use of phosphogypsum in research and development
activities are summarized in Tables 5-9 and 5-10. For the research and development scenario,
a researcher is postulated to work in a laboratory and be exposed to an open 55-gallon drum of
phosphogypsum. Doses to the researcher from external gamma radiation, dust inhalation, and
indoor radon inhalation are evaluated.
The doses and risks to the researcher from external gamma radiation and dust inhalation are
estimated to be comparable to worker doses from the agricultural and road construction scenarios.
5-14

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Table 5-7. Risk assessment results for road construction scenarios involving median
phosphogypsum concentrations.
Road Base
Concrete Additive
Construction Worker -No Shielding-
Direct Gamma
Construction Worker -With Shielding-
Diiect Gamma
Construction Worker
Dust Inhalation
Person Driving on Road
Direct Gamma
Member of CFG
Direct Gamma
Member of CPG - Ingestion of Drinking
Water From Contaminated Well
Member of CPG - Ingestion of Foodstuff
Contaminated by Well Water
Reclaimer
Direct Gamma
Reclaimer
Indoor Radon Inhalation
Reclaimer
Well Water Use
Reclaimer - Ingestion of Foodstuff
Grown On-Site
Individual - Ingestion of River Water
Contaminated by Groundwater
Individual - Ingestion of River Water
Contaminated by Surface Runoff
Dose*
(mrem)
Risk"
5.0E+01
2.9E+01
1.2E+00
2.6E-01
5.0E-02
8.4E-t01
3.1E-01
2.4E-02
1.9E-Q5
1.IE-OS
1.0E-07
9.6E-08
2.0E-08
3.1E-05
7.0E-05
—c
1.9E-08
1.8E-09
Dose8
(mrem)
Risk"
5.0E+01
2.9E+01
1.2E+00
3.0E+00
5.9E-01
1.7E+02
—c
3.1E-01
2.4E-02
1.9E-05
1.IE-OS
1.0E-07
1.1E-06
23E-07
—c
5.9E-05
8.IE-OS
1.9E-08
—c
1.8E-09
a.	Dose or dose commitment from one year of exposure.
b.	Lifetime risk from one year of exposure.
c.	No radionuclides are calculated to reach the on-site well via the groundwater pathway for almost 10,000 years, or the
off-site river or well for more than 100,000 years because of groundwater velocities and retardation factors.
5-15

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Table 5-8. Risk assessment results for road construction scenarios
involving 90 percentile phosphogypsum concentrations.
Road Base
Concrete Additive
Dose8
fmrem)
Risk
Dose*
(mrem)
Risk"
Construction Woiker -No Shielding-
Direct Gamma
Construction Woiker -With Shielding-
Direct Gamma
Construction Worker
Dust Inhalation
Person Driving on Road
Direct Gamma
Member of CPQ
Direct Gamma
Member of CPG - Ingestion of Drinking
Water From Contaminated Well
Member of CPG - Ingestion of Foodstuff
Contaminated by Well Water
Reclaimer
Direct Gamma
Reclaimer
Indoor Radon Inhalation
Reclaimer
Well Water Use
Reclaimer - Ingestion of Foodstuff
Grown On-Site
Individual - Ingestion of River Water
Contaminated by Groundwater
Individual - Ingestion of River Water
Contaminated by Surface Runoff
7.8E+01
4.6E+01
1.9E+00
4.1E-01
7.8E-02
•—C
13E+02
—c
4.9E-01
—c
3.7E-02
2.9E-05
1.7E-05
1.6E-07
1.5E-07
3.0E-08
4.9E-05
1.1E-04
2.9E-08
—c
2.7E-09
7.8E+01
4.6E+01
1.9E-KX)
4.8E+00
9.2E-01
—c
2.5E+02
4.9E-01
—c
3.7E-02
2.9E-05
1.7E-05
1.6E-07
1.8E-06
35E-07
—c
9.2E-05
13E-04
—c
2.9E-08
-—c
2.7E-09
a.	Dose or dose commitment from one year of exposure.
b.	Lifetime risk from one year of exposure.
c.	No radionuclides are calculated to reach the on-site well via the groundwater pathway for almost 10,000 years, or
the off-site river or well for more than 100,000 years because of groundwater velocities and retardation factors.
5-16

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Table 5-9. Risk assessment results for the research and development scenario involving
median phosphogypsum concentrations.
Dose8
	(mRem/yr)	 	Riskb
Researcher
Direct gamma 3.0E+00	1.1E-06
Dust inhalation 1.1E+00	9.9E-08
Indoor radon inhalation	2.5E-05
Total	4.1E+00	2.6E-05
a.	Dose or dose commitment from one year of exposure.
b.	Lifetime risk from one year of exposure.
5-17

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Table 5-10. Risk assessment results for the research and development
scenario involving 90 percentile phosphogypsum
concentrations.
Researcher
Direct gamma
Dust inhalation
Indoor radon inhalation
Dosea
(mRem/vr)
1.4E+01
4.9E+00
Risk
5.8E-06
2.0E-06
1.2E-04
Total
1.9E+01
1.3E-04
a.	Dose or dose commitment from one year of exposure.
b.	Lifetime risk from one year of exposure.
5-18

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The greatest risk to the researcher is estimated to be from indoor radon inhalation. The indoor
radon inhalation risk is estimated to be 2.5E-05 for 31 pCi/g phosphogypsum.
5.2.4	Cleaning of Stainless Steel Filter Pans
The results of the risk assessment of the cleaning of the stainless steel filter pans used in
separating phosphogypsum from the dissolving acid are presented in Table 5-11. Doses to the
worker from external gamma radiation, dust inhalation, and indoor radon inhalation are evaluated.
The overall doses and risks to the workers are similar to estimated exposures to oil and gas
production equipment cleaners. Risks from cleaning steel filter pans contaminated with median
and 90 percentile NORM concentrations are 2.6E-06 and 3.0E-06 with the main pathways being
direct gamma and dust inhalation.
5-19

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Table 5-11. Risk assessment results for the stainless steel filter pan cleaner
scenarios.
Filter Pan Cl^-nnnr
Direct Gamma
Dust Inhalation
Indoor Radon
TOTAL
Median NORM
Concentration Dose
fmrpm/vr)
4.8E+00
1.0E+01
Risk
1.7E-06
8.7E-07
1.9E-10
1.5E+01 2.6E-06
90 Percentile NORM
Concentration Dose
Risk
(wiraiw/yr)
5.8E+00 2.0E-06
1.2E+01 1.0E-06
1.8E+01
2.3E-10
3.0E-06
5-20

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6. Conclusions
The PATHRAE PRESTO-EPA-PILCPG and MICROSHIELD methodologies are employed to
identify potential radionuclide dose rates and risks to individuals from the transportation,
recycling process, and reuse of NORM-contaminated oil and gas equipment and phosphogypsum.
The pathways that are evaluated for potential radiation exposure include radon inhalation, dust
inhalation, external gamma radiation, contaminant ingestion, and dermal exposures. The external
gamma pathway dominates the listed dose results. However, the indoor radon pathway, for
which doses were not estimated, generally dominates the risk for each scenario where it is
considered. The potential exposure scenarios from oil and gas production equipment include:
the transport operator, scrap and smelter yard workers, school children on a jungle-gym and in
a shop class, teacher of the shop class, resident reusing materials, the adjacent resident to the
smelter, and the storage yard.
The potential exposure scenarios from phosphogypsum use and equipment cleaning include: an
agricultural worker, an onsite individual, construction worker, person driving on a road, a
reclaimer, a researcher, filter pan cleaner, and a member of the CPG.
Scenarios considered are grouped into three main groups: unrestricted release of NORM-
contaminated equipment, reprocessing of contaminated equipment, and alternative uses of
phosphogypsum. Contaminated equipment analyzed generally included pipe and tubing. Typical
NORM concentrations are used in the analysis of the scenarios.
The magnitudes of the dose rates to the individuals were found to be influenced by many
characteristics. Pathway characteristics, contaminant concentrations and thicknesses, and scenario
dependent characteristics all had impact on the dose rates and projected risks. Other findings and
observations are:
1. The past practices of or inadvertent unrestricted reuse of NORM-
contaminated equipment in the school environment does not pose an
elevated risk to the student (1.2E-05) or the teacher (7.6E-08). Use of
6-1

-------
contaminated equipment in house construction also does not pose an
elevated risk to the resident (1.7E-10).
2.	Risks involved in the manual cleaning of contaminated equipment
(1.5E-06) can be reduced by additional safety precautions for dust control,
gamma exposure shielding, radon mitigation, and remote processing
(7.5E-08 for hydroblasting).
3.	For radium-226 concentrations of 31 pCi/g in phosphogypsum, the
dominant risks are to the: on-site individual (6.8E-06) for the fertilizer
scenario; on-site individual (3.1E-05) for the sediment control scenario; the
reclaimer for the road base (1.0E-04) and concrete additive (1.4E-04)
scenarios; and the researcher at 2.6E-05. The exposures involved in the
reuse of phosphogypsum in agriculture and as a road base are directly
proportional to radionuclide concentration.
4.	The risks in all scenarios involving uses of phosphogypsum associated
with the inhalation of radon are significant, and often dominant, and are
increased by disturbance or dispersal of the NORM.
5.	DOT regulations apply to shipments of radioactive material at a
concentration of 2000 pCi/g or higher. However, for truckloads of 100
percent NORM-contaminated equipment, a median NORM radium
concentration of 200 pCi/g is required to set off average steel mill and
scrap-yard alarms (and cannot be released for general reuse if in
Louisiana). A truckload of NORM-contaminated equipment with the
median concentration of 360 pCi/g must be at least 74 percent full to be
detected.
6-2

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