United States
Environmental Protection
Agency
Air And
Radiation
(ANR-459)
402-R92-002
May 1992
EPA
Potential Uses Of
Phosphogypsum And
Associated Risks
Background Information
Document
Printed an Recycled Paper
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40 GFR 61 Subpart R
National Emission Standards for
Radon Emissions from
Phosphogypsum Stacks
402-R^92-002
POTENTIAL USES OF PHOSPHOGYPSUM
AND
ASSOCIATED RISKS
BACKGROUND INFORMATION DOCUMENT
for
40 CFR 61 Subpart R
National Emission Standards for
Radon Emissions from
Phosphogypsum Stacks
Craig Conklin
Work Assignment Manager
Prepared Under
Contract No. 68P90170
Work Assignment No. 1-106
Prepared for
U.S. Environmental Protection Agency
Office of Radiation Programs
401 M Street, S.W.
Washington, D.C. 20460
May 1992
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DISCLAIMER
Mention of any specific product or trade name in this report does not imply an
endorsement or guarantee on the part of the Environmental Protection Agency
11
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PREFACE
The Environmental Protection Agency (EPA) is promulgating revisions to 40 CFR
Part 61, Subpart R, National Emission Standards for Radon Emissions From Phosphogypsum
Stacks. This Background Information Document (BID) has been prepared in support of the
rulemaking. This BID contains an introduction, a general description of the fertilizer
industry, a discussion of the physical and radiological characteristics of phosphogypsum, a
discussion of the uses of phosphogypsum, analyses of the radiological risks associated with
various uses of phosphogypsum, and an analysis of the availability and costs of substitute
materials.
Copies of this BID, in whole or in part, are available to all interested persons. For
additional information, contact Craig Conklin at (703) 308-8755 or write to:
Director, Criteria and Standards Division
Office of Radiation Programs (ANR-46OW) . .. •
U.S. Environmental Protection Agency
401 M Street, SW
Washington, D.C. 20460
111
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LIST OF PREPARERS
Various staff members from EPA's Office of Radiation Programs contributed to the
development and preparation of the BID:
Albert Colli
Craig ConMin
Fran Jonesi
Dan Hendricks
Larry Gray
Byron Bunger
Cheng-Yeng Hung
Chief, Air Standards and
Economics Branch
Health Physicist
Attorney Adviser
Environmental Scientist
Environmental Scientist
Economist
Hydrologist
Reviewer
Project Officer
Reviewer
Reviewer
Reviewer
Reviewer
Reviewer
An EPA contractor, S. Cohen & Associates, Inc., McLean, VA, provided significant
technical support in the preparation of the BID.
IV
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TABLE OF CONTENTS
Preface ii
Disclaimer . 4 ...-..' iii
List of Preparers . iv
List of Tables ... .viii
List of Figures xi
1. INTRODUCTION . .................'...... 1-1
1.1 Federal Regulatory Background . . ; , . . . 1-1
1.2 Purpose and Scope of the BID ..;.... 1-1
2. GENERAL DESCRIPTION OF THE FERTILIZER INDUSTRY 2-1
2.1 Fertilizer Production 2-1
2.1.1 Phosphate Rock 2-1
2.1.2 The Wet Process .;. . .2-2
2.2 Phosphogypsum 2-6
,t 2.2.1 Composition of Phosphogypsum 2-6
2.2.2 Phosphogypsum Stacks .2-8
2.2.3 Production Rate of Phosphogypsum . 2-9
3. USES OF PHOSPHOGYPSUM . . .3-1
3.1 Introduction . .3.1
3.2 Agricultural Applications . 3-2
3.3 Road Construction .3-4
3.4 Concrete and Cement Blocks 3-5
3.5 Sulfur Recovery , . - . . . . . .3.5
3.6 Mine Reclamation 3-6
3.7 Research Activities .3-7
3.7.1 Agricultural Uses .3-8
3.7.2 Construction Materials . 3-8
3.7.3 Purification of Phosphogypsum .3-9
3.8 Summary of Phosphogypsum Utilization . 3-9
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TABLE OF CONTENTS (Continued)
4. RADIOLOGICAL ASSESSMENTS OF PHOSPHOGYPSUM USE 4-1
4-1
4.1 Introduction V ' ,' A i
4.2 Radiological Effect of Amending Soils With Phosphogypsum 4-1
4.2.1 Long-Term Study -
4.2.2 Short-Term Study 4_2
4.2.3 Leaching Studies ' ' ' 4-3
4.3 Risk Assessment Methodology • "
4.3.1 The PATHRAE Dose Assessment Model • • • • '.
43.2 The MICROSHIELD Computer Code £J
4.3.3 Exposure Scenarios •
4.3.3.1 Phosphogypsum in Agriculture ™
4332 Phosphogypsum in Road Construction •«-»
4.3'.3.3 Phosphogypsum in Research & Development Activities . . 4-11
4.3.4 Input Parameters ~
4.3.4.1 Radionuclide Concentrations '*'IL
4.3.4.2 Dose and Risk Conversion Factors 4-ii
4.3.4.3 Site-Specific Input Parameters . . •. 4-i4
4.4 Results 4_14
4.4.1 Phosphogypsum in Agnculture
4.4.2 Phosphogypsum in Road Construction ?•.•••• ^'^
4A3 Phosphogypsum in Research & Development
Activities 4 37
4.4.4 Ingestion of Treated Soil
5. AVAILABILITY AND COSTS OF COMPETING MATERIALS 5-1
5.1 Peanut Farming in Georgia ^
5.1.1 Availability ' ^
5.1.2 Cost ^
5.2 Peanut Farming in North Carolina • 5_6
5.3 Peanut Farming in Virginia 5_6
5.4 Agriculture in Florida • • ' ' ' ' ^
5.5 Agriculture in Idaho . . .........•••• ^
5.6 Agriculture in California . - 5_7
5.7 Road Building in Florida • • ' ' 5_7
5.7.1 Availability 5_9
5.7.2 Cost g_u
5.8 Reclaiming Mined Land ^^
5.8.1 Availability ^_^2
5.8.2 Cost
VI
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TABLE OF CONTENTS (Continued)
6. REFERENCES . . 6-1
APPENDICES
Appendix A PATHRAE Pathway Equations A-l
Appendix B Ra-226 Soil Concentration Calculations . B-l
Appendix C Risk Assessment for the Ingestion of Treated Soil C-l
VII
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LIST OF TABLES
2-1 Wet process phosphoric acid plants
,2-4
2-2 Trends in phosphate fertilizer demand and application 2-5
2-3 Average radionuclide concentrations in phosphogypsum, pCi/g dry weight 2-6
2-4 Radium-226 concentrations in Florida phosphogypsum samples -.2-7
2-5 Radium-226 concentrations in phosphogypsum, listed by state 2-7
2-6 Average activity ratios of major radionuclides in composite phosphogypsum
samples
.2-9
2-14
.3-3
3-10
2-7 The location and characteristics of phosphogypsum stacks in the United States , 2-10
2-8 Summary of the phosphogypsum stacks in each state - 1989 ; . . . . 2-13
2-9 Annual phosphate fertilizer production rates . •
3-1 Quantities of phosphogypsum sold at eight facilities - 1988
3-2 Estimated quantities of phosphogypsum used per year
4-1 Phosphogypsum use parameters for Scenarios 1 through 4 4-6
4-2 Phosphogypsum use parameters for Scenarios 5 and 6 4-7
4-3 Phosphogypsum reference radionuclide concentrations 4-12
4-4 Dose and risk conversion factors 4-13
4-5 Site-specific input parameters for PATHRAE risk assessments 4-15
4-6 Risk assessment results for Scenario 1 : use as fertilizer-average site (clay) ... 4-18
4-7 Risk assessment results for Scenario 2 - use as. fertilizer-average site (sand) . . . 4-19
4-8 Risk assessment results for Scenario 3 - use as fertilizer-maximum site (clay) . . 4-20
4-9 Risk assessment results for Scenario 4 - use as fertilizer-maximum site (sand) . . 4-21
vm
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LIST OF TABLES (Continue^)
4-10 Risk assessment results for Scenario 5 - use as sediment control, (clay) .... . . . 4-22
4-11 Risk assessment results for Scenario 6 - use as sediment control (sand) ; . '.'.". . 4-23
4-12 Risk assessment results for Scenario 7 - radon exposure risks to the on-site
individual as a function of phosphogypsum application rate and Ra-226
concentration ........ . . . . : . . . .... . . . . . '. . . . . . . . . . 4,24
4-13 Risk assessment results for Scenario 7 - external gamma risks to the on-site
individual as a function of phosphogypsum application rate and Ra-226
concentration ... ... ...... ... . . . ... . . . .-. . ... . ... ...... .4-24
4-14 Risk assessment results for Scenario 7 - Total risks to the on-site individual as
a function of phosphogypsum application rate and Ra-226 concentration 4-25
4-15 Risk assessment results for Scenario 8 - use of phpsphogypsum in road base
for secondary road (clay) .-...' 4-31
4-16 Risk assessment results for Scenario 9 - use of phosphogypsum in road base
for secondary road (sand) . . . 4-32
4-17 Risk assessment results for Scenario 10 - use of phosphogypsum in a concrete
road surface (clay) T . .4-33
4-18 Risk assessment results for Scenario 11. - use of phosphogypsum in a concrete
road surface (sand) 4-34
4-19 Risk assessment results for Scenario 12 - use of phosphogypsum in R&D
activities 4-36
4-20 The estimated total risks due to the ingestion of soil treated with
phosphogypsum 4.37
5-1 Pod yields per acre of peanuts for various gypsum materials, estimated cost of
various materials and estimated net return, Georgia 5-2
5-2 Gypsum material cost per pound of peanuts for competing gypsum materials . . . 5-3
5-3 Fertilizer cost indices for competing materials relative to phosphogypsum at
point of sale .5-3
IX
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LIST OF TABLES (Continued)
5-4 Fertilizer cost indices for competing materials relative to phosphogypsum
incorporating transportation costs into the fertilizer cost 5-4
5-5 The comparison of material costs per acre 5-5
5-6 Gypsum sources and application rates for peanuts in North Carolina . 5-6
5-7 Economic returns using phosphogypsum on selected Florida crops . . 5-8
5-8 Estimated maximum distances phosphogypsum can be hauled for road use and
remain competitive with conventional materials 5-11
x
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4-1
4-2
4-3
4-4
4-5
LIST OF FIGURES
Scenarios involving the use of phdsphogypsum in road construction . ... ; .... 4-9
Risk assessment results for Scenario 4 - radon exposure risks to the on-site
individual as a function of the Ra-226 content of phosphogypsum for the six
application rates (Ibs/acre) shown in parenthesis 4-27
Risk assessment results for Scenario 4 - external gamma exposure risks to the
on-site individual as a function of the Ra-226 content of phosphogypsum for
the six application rates (Ibs/acre) shown in parenthesis 4-28
Risk assessment results for Scenario 4 - total radon and gamma exposure risks
to the on-site individual as a function of the Ra-226 content of phosphogypsum
for the six application rates (Ibs/acre) shown in parenthesis , 4-29
Application rate of phosphogypsum as a function of Ra-226 concentration
for a lifetime risk of SxlO"4
4-30
5-1 Road building cost comparison-traditional material versus phosphogypsum .... 5-10
XI
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1. INTRODUCTION
1.1 FEDERAL REGULATORY BACKGROUND
The off-site use of phosphogypsum was prohibited by the final National Emission
Standards for Hazardous Air Pollutants (NESHAPs) for radionuclides promulgated at 40 CFR
Part 61, Subpart R, National Emission Standards for Radon Emissions from Phosphogypsum
Stacks (54 FR 51654, December 15, 1989). This rule requires that as of the effective date
of the rule (March 15, 1990), phosphogypsum be disposed of in stacks or in mines,
prohibiting uses of phosphogypsum in construction, agriculture, or research and
development.
Because of concerns about the potential impact on farmers, researchers, and other
users of phosphogypsum, a Notice of Limited Reconsideration was published in the Federal
Register on April 10, 1990 (55 FR 13480). Simultaneously EPA issued a limited class
waiver allowing the continued use of phosphogypsum for agricultural application during the
1990 growing season. This waiver had an expiration date of October 1, 1990. However, the
waiver was extended on September 28, 1990 with an expiration date of June 1, 1991 (55 FR
40834), and again on May 16, 1991 with an expiration date of October 1, 1991 (56 FR
23519). When the waiver expired on October 1, 1991, all persons holding stacks of
phosphogypsum became subject to the work practice requirements in subpart R.
In conjunction with the Notice of Limited Reconsideration, EPA issued a notice of
proposed rulemaking at 55 FR 13482 which contains the following options:
1) Retain Subpart R as promulgated on December 15, 1989;
2) Establish a threshold level of radium-226 which would further define the term
"phosphogypsum";
3) Allow, upon prior EPA approval, the use of discrete quantities of
phosphogypsum for the research and development of processes to remove
radium-226 from phosphogypsum, to the extent that such use is at least as
protective of public health as is disposal of phosphogypsum in stacks or mines;
and/or
4) Allow, upon prior EPA approval, other alternative use(s) of phosphogypsum to
the extent that such use(s) is at least as protective of public health as is
disposal of phosphogypsum in stacks or mines.
1.2 PURPOSE AND SCOPE OF THE BID
This Background Information Document (BID) provides information relative to the
management, disposal and potential uses of phosphogypsum. It also contains an assessment
1-1
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of the radiological risks associated with agricultural, construction, and research and
development applications of phosphogypsum.
The BID contains a detailed description of the Agency's procedures and methods for
estimating the radiological risks associated with the potential uses of phosphogypsum. The
material is arranged as shown in the following descriptions of the chapters and appendices.
• Chapter 2 - A general description of the phosphoric acid industry, including
phosphate rock, fertilizer, and phosphogypsum production rates and the nature
and composition of phosphogypsum.
• Chapter 3 - A description of the potential uses of phosphogypsum, including
the quantity of material utilized for each use, and the scope of ongoing
research activities.
• Chapter 4 - A detailed description of the risk assessment performed and the
results obtained.
• Chapter 5 - A discussion of the availability of nonradioactive materials that
could compete with phosphogypsum and the costs associated with their use.
• Chapter 6 - References.
• Appendix A - A description of the PATHRAE pathway equations used in the
assessments.
• Appendix B - A description of the Ra-226 soil concentration calculations used
in the assessments.
• Appendix C - The risk assessment for the ingestion of soil treated with
phosphogypsum based on different application rates and exposure periods.
1-2
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2. GENERAL DESCRIPTION OF THE FERTILIZER INDUSTRY
2.1 FERTILIZER PRODUCTION
Modern agricultural practice uses large amounts of chemical fertilizers to replenish
and supplement the nutrients that growing plants take up from the soil. A number of
chemical elements are required to support vigorous plant growth. Most soils contain
adequate trace amounts of the minor chemicals required, but to maintain the long-term
fertility of the soil, quantities of nitrogenous material, phosphates, and compounds of
potassium and sulfur must be replaced.
Phosphorus fertilizer requirements can be met by the application of chemicals derived
from natural deposits of what is known as phosphate rock. Phosphate rock does not have a
definite chemical composition, and the composition varies in different mining-areas. The
major phosphorus materials in the rock are geologically in the apatite group, which in high
grade ores is about seventy percent calcium phosphate and is mixed with a large number of
impurities, such as calcium fluoride, chlorides, chromium, rare earths, and radionuclides.
Extensive deposits of phosphate rock are found in Florida, Tennessee, and North
Carolina. Workable deposits are also found in Idaho. The phosphate rock is recovered by
open pit mining. Phosphate rock is transported to a washing plant where it is separated from
accompanying soil, stones, etc. Particles less than 200 mesh size are called slimes and are
separated from the ore at the washing plant creating a slurry of up to one third the total
mined tonnage. The slurry is discharged to slime ponds. The material larger than 200 mesh
size is treated in an amine flotation circuit to remove the silica sand from the ore, dried, and
ground into particle sizes of 150 micrometers or less. The calcium phosphate is nearly
insoluble in water and, to be useful as fertilizer, must be converted into a soluble form. This
is most commonly done by converting the phosphate content of the rock into phosphoric
acid. There are wet and dry processes for doing the conversion. United States production
facilities utilize a wet process where the prepared material is digested with sulfuric acid to
produce the phosphoric acid. Phosphoric acid is water soluble and can be concentrated, as
desired, by evaporating water from the mixture. The byproduct remaining after the acid
conversion is largely calcium sulfate arid has been given the name phosphogypsum. Gypsum
is the common tradename for calcium sulfate, a common building material.
The phosphogypsum product appears as the dihydrate or the hemih'ydrate form (water
molecules attached to the calcium sulfate molecule), depending on the specific processing
details. This byproduct material, filtered from the phosphoric acid, is transferred as a water
slurry to open air storage areas known as stacks. A stack can be created by filling a
previously mined area or constructed directly on the land surface.
2.1.1 Phosphate Rock
Phosphate rock, mined in open-pit mines, consists of about one-third quartz sand,
2-1
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one-third clay minerals, and one-third phosphate particles. After mining, the ore is
processed by beneficiation (washing and flotation processes), followed by drying of the
marketable rock. The production of phosphate rock in the United States during 1988 was
estimated to be 38 million metric tons (MT){a) (TFI89). Production in the United States
peaked in 1980 when 54 million MT were produced (TVA86), and has since declined at a
rate of about 3 percent per year (TVA86, TFI89, BOM88). Phosphate rock inventories have
also decreased, from 15 to 7.5 million MT in 1985 and 1988, respectively (TFI89).
Phosphate ores mined in the United States contain uranium concentrations ranging
from about 7 to 67 pCi/g (20-200 ppm)® (SCA91). This is 10 to 100 times higher than the
uranium concentration in typical rocks (1 to 2 ppm). Uranium decay products, such as
radium-226, exist with the uranium at near secular equilibrium levels. Actual radium-226
concentrations in central Florida phosphate ore range from 18-84 pCi/g, with an average
value of 38 pCi/g (Ro87a). Thorium-232 occurs in the ore at much lower concentrations,
ranging between 0.1 to 0.6 pCi/g (SCA91).
2.1.2 The Wet Process
In general, the wet process for manufacturing phosphoric acid involves four primary
operations: raw material feed preparation, phosphate rock digestion, filtration, and
concentration. The phosphate rock is generally dried in direct-fired rotary kilns, ground to a
fineness of less than 150 /tm for improved reactivity, and digested in a reaction vessel with
sulfuric acid to produce the product, phosphoric acid, and the byproduct, phosphogypsum.
Specific wet-acid processes used include the classic Prayon and Nissan-H processes
which generate a dihydrate form of phosphogypsum (CaSO4»2H2O), and the Central-Prayon
and Nissan-C processes which generate a hemihydrate form of phosphogypsum
(CaS(VteH2O) (EPA90). The processes that'generate the hemihydrate form result in
phosphoric acid concentrations of 40 to 50 percent without evaporation, as opposed to the 30
to 35 percent normally produced by the dihydrate processes. It is uncertain which of the
above processes are used by each of the phosphoric acid facilities; however, indications are
that only two or three facilities use one of the processes which generate the hemihydrate
phosphogypsum while the large majority of the facilities use one of the processes which
generate the dihydrate phosphogypsum (EPA90). All four processes generate two special
wastes: process wastewater and phosphogypsum.
The phosphogypsum is transferred as a slurry to onsite disposal areas referred to as
phosphogypsum stacks. These stacks are generally constructed directly on unused or mined-
out land with little or no prior preparation of the land surface. The gypsum slurry is pumped
wOne metric ton (MT) is approximately 1.1 tons.
wl ppm U-238 = 0.33 pCi/g or 0.67 pCi/g total uranium, U-238 + U-234.
2-2
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to the top of the stack where it forms a small impoundment, commonly referred to as a
gypsum pond. Gypsum is dredged from the pond on top of the stack and used to increase
the height of the dike surrounding the pond. The phosphogypsum stacks become an integral
part of the overall wet process. Because the process requires large quantities of water, the
water impounded on the stack is used as a reservoir that supplies and balances the water
needs of the process. Thus, the stack is not only important as a byproduct storage site, but
also contributes to the production process.
As of September 1989, the phosphoric acid production industry consisted of 21 active
facilities that use the wet-acid production process (EPA90). Two additional facilities,
Agrico's Fort Madison, IA and Hahnville, LA facilities, were on standby at that time. The
locations of these facilities are shown in Table 2-1. The majority of the 21 facilities are
located in the southeast, with 12 in Florida, three in Louisiana, and one in North Carolina.
The combined annual production capacity of 19 reporting facilities is over 11 million MT.
In 1988, the aggregate production of nearly 8.5 million MT yielded a capacity utilization rate
of about 77 percent (EPA90). Several facilities, however, operated at low utilization rates,
e.g., three facilities reported rates of 15.8, 30.1, and 37.5 percent. The generation of 8.5
million MT of P2O5(c) would produce an estimated 38 million MT of phosphogypsum, based
on 4.5 MT of phosphogypsum per MT P2O5 (Gu75).
In 1985, 51 million MT of marketable phosphate rock were produced, of which 41
million MT (80 percent) were used to produce 12 million MT of P2O5 by the wet acid
process (EPA89a). By 1988, these production figures had dropped to 38 million MT of
marketable phosphate rock producing 8.5 million MT of P2O5. The main cause for this
reduced production, nearly 30 percent, was the poor financial condition of the fertilizer
industry during much of the 1980s. These conditions were the result of low domestic
demand and reduced foreign purchases (EPA90). About 95 percent of the commercial
phosphoric acid produced by the wet process is used in the production of fertilizers and
animal feed, with a small portion used as a feedstock in chemical processing operations
(BOM87). The data shown in Table 2.2 reflect the use of phosphate fertilizers on major
crops, such as coarse grain, wheat, soybeans, and cotton and, as can be seen, the demand for
fertilizer closely parallels the acreage of major agricultural crop production. However, the
domestic demand for phosphoric acid is expected to increase as a result of the 1988 recovery
of the farm economy, and should continue to grow as crop prices and planted acreage
increases (EPA90). Non-fertilizer uses of phosphoric acid also declined during the 1980s,
due to strict regulations governing the use of phosphates in household products, such as
detergents, and a decline in industrial demand (SP88).
(c)By convention, the phosphate industry relates the production of phosphoric acid to P2O5
rather than H3PO4.
2-3
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Table 2-1. Wet process phosphoric acid plants (EPA90).
Operator
Location
Parent Company
Agrico
Agrico
Agrico
Arcadian
Central Phos.
CF Chemicals
Chevron Chemical
Conserv
Farmland, Inc.
Fort Mead Chemical
Gardinier
IMC Fertilizer
Mobil Mining
Nu-South Ind.
Nu-West
Occidental Chem.
Royster
Royster
Seminole Pert.
J.R. Simplot
Texasgulf
Argico00
Agrico(a)
(a) On standby in 1989.
Donaldsonville, LA
Mulberry (Pierce), FL
Uncle Sam, LA
Geismar, LA
Plant City, FL
Bartow (Bonnie), FL
Rock Springs, WY
Nichols, FL
Bartow (Pierce), FL
Fort Meade, FL
Riverview (Tampa), FL
New Wales (Mulberry), FL
Pasadena, TX
Pascagoula, MS
Soda Springs, ID
White Springs, FL
Mulberry, FL
Palmetto (Piney Pt), FL
Bartow, FL
Pocatellp, ID
Aurora, NC
Ft. Madison, IA
Hahnville, LA
Freeport-McMoRan
Freeport-McMoRan
Freeport-McMoRan
Arcadian
CF Industries
CF Industries
Chevron Corp.
Conserv
Farmland Ind.
US Agric ChemAVR Grace •
Gardinier
IMC Fertilizer
Mobil Corp.
Nu-West Industries
Nu-West Industries
Occidental Petroleum
Cedar Holding Co.
Cedar Holding Co.
Seminole Fertilizer
J.R. Simplot
Texasgulf
Freeport - McMoRan
Freeport - McMoRan
2-4
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Table 2-2. Trends in phosphate fertilizer demand and application (BOM88).
~ Year -
Actual/Proj ected
1980
1981
1982
1983
1984
1985
1986
19.87
1988
1990
1995
Average*'
Fertilizer
Demand
(million MT)
5.5
5.6
5.0
4.4
5.2
4.9
4.5
4.2
4.2
4.4
5,0
4.8
Major Crop(a)
Harvested Areas
(million acres)
331
351
336
297
324
331
311
289
296
309
333
319
ApplicationRates
(Kg/acres)
16.6
15.8
15.0
15.0
16.2
15.0
14.2
14.2
14.2
14.2
15.0
15.0
(a)
Major crops include coarse grain, wheat, soybeans, and cotton.
Does not include 1990 or 1995 projections.
2-5
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2.2 PHOSPHOGYPSUM
2.2.1 Composition of Phosphogypsum
Phosphogypsum, which has an average particle diameter of less than 0.2 mm, is
primarily calcium sulfate dihydrate, CaSO4»2H2O, in association with varying amounts of
silicon, phosphate and fluoride. Phosphogypsum is only slightly soluble in water, about 2g
per liter (EPA89a). Phosphogypsum contains appreciable quantities of radium-226, uranium,
and other uranium decay products. This is due to the high uranium concentration in
phosphate rock which was discussed in Section 2.1.1. The radionuclides of significance are:
uranium-238, uranium-234, thorium-230, radium-226, radon-222, lead-210, and polonium-
210. When the phosphate rock is processed through the wet process, there is a selective
separation and concentration of radionuclides. Most of the radium-226, about 80 percent,
follows the phosphogypsum, while about 86 percent of the uranium and 70 percent of the
thorium are found in the phosphoric acid (Gu75).
Table 2-3 shows the average radionuclide concentrations measured in 50
phosphogypsum samples collected in 1985 by EPA from five stacks in central Florida
(Ho88). For comparison, the radionuclide concentrations normally observed in
uncontaminated rock and soil are also presented. The concentrations measured in the
phosphogypsum samples are similar to those previously reported (Gu75) and exceed those in
background soil by factors of 10 (uranium) to 60 (radium-226). These radionuclides and
radon-222 are possible sources of airborne radioactivity. Radon-222, a decay product of
radium-226, is a gaseous element which may diffuse into the air. Also, these radionuclides
in particulate form may be resuspended into the air by wind and vehicular traffic. Wind and
vehicular traffic are the two principal mechanisms for airborne releases of radioactivity from
phosphogypsum stacks.
Table 2-3. Average radionuclide concentrations in phosphogypsum, pCi/g dry weight
(Ho88).
Material
Ra-226
U-234
U-238
Th-230
Po-210
Pb-210
Phosphogypsum 31 3.3 3.2 5.1
Background 0.5 0.3 0.3 0.3
Soil
27 36
0.5 0.7
The radium-226 concentration in phosphogypsum varies significantly at different
sampling locations on a single stack and also in phosphogypsum from different stacks within
the same geographical area. This variation is illustrated by the data in Table 2-4. All stacks
were active except Estech, which was inactive (closed). The ranges of radium-226
concentrations measured in phosphogypsum collected from stacks in six states are presented
2-6
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Table 2-4. Radium-226 concentrations in Florida phosphogypsum samples (Ho88).
Phosphogypsum
Stack
Gardinier
W.R. Grace
Royster
Conserv
Estech
(a). Mean concentration
each stack.
Mean Concentration Concentration Range
(pCi/gdry)a (pCi/gdry)
33+2
30+9
30+11
34+18
25 ±4
with the standard
31-37
. 19-48
16-49
23-81
19-31
deviation of samples from 10 locations on
Table 2-5. Radium-226 concentrations in phosphogypsum, listed by state (EPA90).
State
Florida
Idaho
Louisiana
Mississippi
North Carolina
Texas
Phosphogypsum
Generated in 1988
(MT) '
29,777,000
2,646,000
7,280,000
474,000
5,425,000
1,157,000
Ra-226 Concentration
in Phosphogypsum
(pCi/g)
5.9-36
7.9-23
1.4-26
5.9-36
4.3-46
13-15
2-7
-------
in Table 2-5. The radium-226 concentrations observed in phosphogypsum from Louisiana
and Mississippi are similar to those observed in Florida, as might be expected since Florida
phosphate rock is processed in those states.
The average activity ratios of the major radionuclides in the composite
phosphogypsum samples from the central Florida study are shown in Table 2-6. For
example, the activity ratio of Ra-226/U-238 is the average radium-226 concentration in
phosphogypsum divided by the average uranium-238 concentration in phosphogypsum.
These activity ratios indicate that concentrations of uranium and thorium isotopes are
depleted in phosphogypsum relative to their concentrations in phosphate rock. However, the
concentration of Ra-226 in phosphogypsum is similar to that in phosphate rock. Thus, most
of the radium-226 follows the phosphogypsum in the wet process, while most of the uranium
and thorium are in the phosphoric acid product.
In addition to radionuclides, phosphogypsum contains some trace metals in
concentrations which the EPA believes may pose a potential hazard to human health and the
environment (EPA90). Two contaminants, chromium and arsenic, were identified in
phosphogypsum from some facilities at concentrations that may pose significant health risks.
The concentrations of these contaminants vary greatly in phosphogypsum from different
facilities, ranging over three orders of magnitude. Trace metals may also be leached from
phosphogypsum, as are radionuclides, and migrate to nearby surface and groundwater
resources. The EPA has identified a number of potential constituents in phosphogypsum
from some facilities that could, under the appropriate conditions, cause adverse health effects
or the restriction of potential uses of nearby surface or groundwater resources. Elements
identified include arsenic, lead, cadmium, chromium, fluoride, zinc, antimony, and copper
(EPA90). The presence of these trace metals in phosphogypsum is mentioned here in order
to provide a more complete description of phosphogypsum, but they will not be addressed in
the risk assessment.
2.2.2 Phosphogypsum Stacks • '
A total of 63 phosphogypsum stacks were identified nationwide in 1989 (EPA89a).
Table 2-7'gives the location, size, and status, as of 1989, for each stack. Phosphogypsum
stacks were present in 12 different states, with two-thirds located in just four states, Florida,
Texas, Illinois and Louisiana. Of the stacks identified, 26 were operating, 24 were inactive,
and 13 were considered idle. An operating or active stack is one that is currently receiving
gypsum, and an inactive stack is one that is permanently closed. A stack was classified as
idle if there were definite plans to reactivate it and it has the characteristics of an active
stack, e.g., water may be maintained on the stack top surface and utilized in the water
balance for the facility. The phosphogypsum stacks ranged in area from approximately 5 to
almost 741 acres, and heights of the stacks ranged from 3 to about 60 meters.
The number of phosphogypsum stacks in each state is given in Table 2-8. The
information in this table relates the phosphogypsum stacks to individual states and gives the
2-8
-------
Table 2-6. Average activity ratios of major radionuclides in composite phbsphogypsum
samples (Ho88). :,: ,,
Radionuclides
Activity Ratio
Ra-226 / U-238
Th-230/ U-238
Pb-210 /U-238
Pb-210 / Ra-226
Po-210 / Pb-210
U-234 / U-238
9.1
1.7
13.0
1.4
0.74
1.1
distribution of stack and stack areas within each category (operating, idle, and inactive).
Over half of the operating stacks are in Florida, which accounts for 57 percent of the total
base area of all operating stacks. In 1989, the total base area of all phosphogypsum stacks in
the United States was approximately 8,490 acres, of which 69 percent was associated with
operating stacks, 14 percent with idle stacks, and 17 percent with inactive stacks. From
Table 2-8, it is apparent that older inactive stacks are generally much smaller than the newer
operating stacks. For example, the average base area of an operating stack was 224 acres,
while the average base area of an inactive stack was only 60 acres.
In addition to their large sizes, operating phosphogypsum stacks are characterized by
other physical features. Large areas of the stack top are covered by ponds of water, ditches,
or beaches (saturated land masses that protrude into the ponds). These surface features may
cover up to 75 percent of the top of the stack. Other surface features include areas of loose,
dry materials, access roads, and thinly-crusted stack sides. Inactive stacks are characterized
by a hard, thick-crusted top and dry, thinly-crusted sides.
2.2.3 Production Rate of Phosphogypsum
The production of phosphogypsum can be estimated by applying the rule of thumb of
4.5 MT of phosphogypsum per Mt of P2O5 (Gu75). For illustrative purposes, the annual
phosphate rock, phosphoric acid, and phosphogypsum production rates are provided in Table
2-9 for selected years since 1965 (TFI89, TVA86).
2-9
-------
Table 2-7. The location and characteristics
States (EPA89a).
of phosphogypsum stacks in the United
Facility Name
Districhem Ihc.w
Agrico Fertilizer Co.
Royster Phosphate,!^1*
Brewster Phosphates
CF Industries, Lie.
CF Industries, Lie.
Conserv, Inc. I00
2
Estech, Inc.
Farmland Industries,Inc.
Gardinier, Lie.
Seminole Fertilizer 1
Corp. 2
IMC Corp.
Occidental Chem.Co. 1
(Suwanne River) 2
Occidental Chemical Co.
(Swift Creek)
Royster Co. 1
2
USS Agri-Chemicals,Ihc.
USS Agri-Chemicals,Lic.
Nu-WestInd.,Lic.w
J.R. Simplot Co. 1
2
Bunker Hill Co. 1
2
3
General Chemical Corp.
Location
Helena, AR
Bartow, FL
Palmetto, FL
Bradley, FL
Plant City, FL
Bartow, FL
Nichols, FL
Bartow, FL
Bartow, FL
Tampa, FL
Bartow, FL
Mulberry, FL
White Spgs, FL
White Spgs, FL ,
Mulberry, FL
Bartow, FL
Ft. Meade, FL
Conda, ID
Pocatello, ID
Kellogg, ID
E.StLouis, IL
Stack
Status
Inactive
Operating
Operating
Inactive
Operating
Idlew
Operating
Operating
Inactive
Operating
Operating
Operating
Operating
Operating
Operating
Operating
Operating
Operating
Operating
Inactive
Operating
Operating
Idle
Operating
Inactive
Inactive
Inactive
Inactive
Stack
Height(m)
23
22
20
18
18
24
18
23
24
12(d)
20(d)
g(e)
8»
8<0)
9
Base
Area(acres)
22
346W
299
124
400
361
79
77
27«o
227
341
158
561
388(c)
99
99
131
74
44
49
151
89
42»
200
5»
12w
49(0)
21
2-10
-------
Table 2-7. The location and characteristics
States (EPA89a) (continued).
of phosphogypsum stacks in the United
Facility Name
F&W Flying Service, Inc.
Mobil Mining & Minerals
Northern Petrochem. Co.
Olin Corp.
Smith Douglas/Borden
Quantum Chemical Corp.
Agrico pert. Co.
Agrico Fertilizer Co.
Arcadian Corp.
Agrico Pert, Co.(a)
Agrico Fert. Co.00
Nu-SouthInd.,Inc.(a)
Fanners Chemical Co.
W.R. Grace and Co.
Texasgulf Chem. Co.
Amoco Oil Co.
Co.
1
2
1
2
3
1
2
3
4
1
2
1
2
3
4
5
1
2
Location
Marseilles, IL
Depue, IL
Morris, IL
Joliet, IL
Streator, IL
Tuscola, IL
Ft. Madison,IA
Donaldsonville, LA
Geismar, LA
Hahnville, LA
Uncle Sam, LA •
Pascagoula, MS
Joplin, MO
Joplin, MO
Aurora, NC
Texas City, TX
Stack
Status
Inactive
Inactive
Inactive
Idle(a)
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Operating
Idle
Idle
Idle
Operating
Operating
Operating
Operating
Inactive
Inactive
Inactive
Idle"0
Idle60
Idle""
Idle(a)
Operating00
Idle
Idle
Stack
Height(m)
6
13
4
27
V5
18
16
30
9
5 -•
12
2QW-
12w
12w .
6(al ,
4
20
20
15
10w
10w
26(a>
:18w
38(a)
19w
20(a)
11
3
Base
Area(acres)
65
135
69
210(a)
20(a)
25(a>
79
49
49
59
502(0
94<">
35
-------
Table 2-7. The location and characteristics of phosphogypsum stacks in the United
States (EPA89a) (continued).
Facility Name
Kerley Agricultural
Chem. of TX Inc.
Mobil Mining and 1
Location
Pasadena, TX
Pasadena, TX
Stack
Status
Inactive
Inactive
Stack
Height(m)
11
27
Base
Area(acres)
27
59
Minerals Div.
Phillips Chemical Co.
Four Court Incorporated
Chevron Chemical Co.
2
3
Pasadena, TX
Magna, UT
Rock Sp., WY
Inactive00
Operating
Idle
Inactive*'
Operating
27
30
27
5
10®
89
151
35
299
450
(a) Jo88b.
(b) Numbers 1,2,3, etc. refer to different stacks at a facility.
(c) Ba88; (d) Si88; (e) Ap88; (f) Wa88b; (g) Wa88a; (h) Co88; (i) Default value.
Note: Information in this table is from PEI85, except for that identified by footnotes (a), and (c) to (i), and
relates to 1988-1989 conditions.
These production figures reflect the capacity of the phosphate mining industry for the
last 20 years. It is evident from Table 2-9 that the yearly phosphogypsum production has
averaged nearly 40 million MT since 1984. However, this estimate may be low, as the
estimated quantity of phosphogypsum produced in 1988, 41.9 million MT, is less than the
total reported by the EPA for the same year for six of the larger production states, 46.8
million MT (see Table 2-5). The total phosphate waste volume generated in the U.S. from
1910 to 1981 has been estimated at 7.7 billion MT (EPA85). In Central Florida, the
phosphoric acid industry produces about 32 million MT of phosphogypsum each year, with a
current stockpile of nearly 400 million MT (SCA91).
The amount of phosphogypsum that will be produced in future years is uncertain.
Predictions of the amount of phosphogypsum that will be produced during the next 20 years
are reported to range from 310 to 910 million MT (SCA91). Thus, although the amount of
phosphogypsum that must be managed in future years will certainly be large, it is not
possible to predict with a reasonable degree of certainty the growth of the total
phosphogypsum inventory in the U.S.
2-12
-------
Table 2-8. Summary of the phosphogypsum stacks in each state-1989 (EPA89a).
State
Arkansas
Florida
Idaho
Illinois
Iowa
Louisiana
Mississippi
Missouri
N. Carolina
Texas
Utah
Wyoming
Number of
Stacks
1
20
6 ' .
8
3
7
1
3
5
7
1
1
Total Base Areas, acres(a)
Operating
0
3319(16)
289 (2)
0
0
1248 (4)
250(1)
0
126 (1)
151 (1)
0
450 (1)
Idle
0
361(1)
42(1)
210(1)
0
156(3)
0
0
366 (4)
74 (3)
0
0
Inactive
22 (1)
200 (3)
67(3)
410(7)
158 (3)
o
0
119 (3)
0
175 (3)
299 (1)
0
Total
63
5833 (26)
1209 (13) 1450 (24)
Average Stack Area
224
93
60
(a)
Number of stacks is shown in parentheses.
2-13
-------
Table 2-9. Annual phosphate fertilizer production rates.
Year
Phosphate Rock
(million MT)
Phosphoric Acid
(million MT)
Phosphogypsum
(million MT)
1965
1970
1975
1980
1984
1985
1986
1987
1988
26.8
35.1
.44.3
54.4
49.2
44.8
32.8
35.7
38.3
3.5
5.2
7.0
9.8
9.9
8.9
7.4
8.1
9.3
15.8
23.4
31.5
44.1
44.6
40.1
33.3
36.5
41.9
2-14
-------
3. USES OF PHOSPHOGYPSUM
3.1 INTRODUCTION
Phosphogypsum is currently being used in several commercial applications with
additional research being conducted, primarily by the Florida Institute of Phosphate Research
(FIPR), in order to identify new applications and expand existing ones. Currently,
applications include (SCA91):
1) fertilizer and conditioner for soils where peanuts and a variety of other crops
are grown;
2) backfill and road-base material in roadway and parking lot construction;
3) additive to concrete and concrete blocks;
4) mine reclamation; and
5) recovery of sulfur.
Each application is discussed below. Agriculture, and to a lesser extent mine
reclamation, presently utilizes the largest quantities of phosphogypsum. Other uses have not
moved past the development stage of field testing in the U.S. However, this could change in
the future if present restrictions on the disposal of phosphogypsum are removed. Research is
continuing on additional uses of phosphogypsum as a soil conditioner, as well as other uses,
e.g., sulfur recovery, in ceramic products, as anti-skid aggregate, and as a concrete
aggregate (SCA91). ,
Due to the absence of low-cost natural gypsum and the lack of long-term storage
space, the use of phosphogypsum in Europe and Japan has been much more widespread than
in the U.S. These countries have used phosphogypsum extensively in cement, wallboard,
and other building materials (SCA91).
Because of the elevated levels of radionuclides, primarily radium-226, in
phosphogypsum, building construction materials containing phosphogypsum could result in
elevated radiation exposures to building occupants. Phosphogypsum was used by a New
Jersey based company in the manufacture of wallboard, partition blocks, and plaster for
distribution in the northeastern United States between 1935 and 1946 (Fi78). No wallboard
containing phosphogypsum is currently manufactured for commercial use in the United
States. Therefore, the use of phosphogypsum in wallboard and the associated risk will not be
addressed in this assessment.
Radon measurements conducted in a room constructed of Japanese phosphogypsum
wallboard at EPA's National Air and Radiation Environmental Laboratory did not detect any
3-1
-------
increase in indoor radon concentrations (Se88). The emanation fraction was estimated to be
less than 2 percent. However, a modular structure constructed of ferrocement panels
containing 50 percent phosphogypsum, 25 percent cement, and 25 percent fine aggregate
resulted in radon levels, measured under worst-case ventilation conditions (i.e., the structure
was made as air-tight as possible) that averaged 4 to 5 pCi/L (Ch87). The upper end of this
range is above the level at which the EPA recommends that homeowners take action to
determine the long-term average radon concentration in their home (EPA86).
The amount of phosphogypsum currently being used in the U.S. for the above
purposes is small compared to the total amount being produced. It has been estimated that
only about 5 percent of the U.S. phosphogypsum output is utilized in some way (An88).
The quantities of phosphogypsum sold each year are compared in Table 3-1 to the annual
production rates at eight facilities (Va89). The phosphogypsum sold at these facilities was
primarily for agriculture. Although this survey does not include all facilities, it does indicate
the small scale use of phosphogypsum in the United States.
3.2 AGRICULTURAL APPLICATIONS
For more than 30 years, phosphogypsum has been used in the United States as a
conditioner for clayey and sodic(a) soils because of its moisture retaining and salt leaching
properties. Its use is considered critical to maintaining soil productivity in the southeastern
states where highly weathered soils have poor physical properties and high erodability
(TFI90a). In addition, phosphogypsum provides needed nutrients, such as calcium and
sulfur, to deficient soils. The phosphogypsum in the southeast is used primarily by peanut
growers in Georgia, North Carolina, Virginia, and Alabama. Studies have also indicated that
phosphogypsum, may be beneficial to southeastern soils used to grow tobacco, corn, small
grain, and sugar cane. Currently, the state of Georgia is the largest consumer of
phosphogypsum, applying 120,000 to 180,000 MT annually to its peanut fields. Application
rates vary depending on the crop, soil type, and purpose of the amendment. Phosphogypsum
is a source of calcium for peanuts and is added at rates of 0.2-0.4 MT/acre per year. It is
applied at higher rates, 0.8-1.2 MT/acre per year, on acidic, crusting soils to improve
physical properties and mitigate subsoil acidity (Mi91).
There is also a large demand (estimated 500,000 to 750,000 MT/yr (TFI90a, Va89)
for agricultural use of gypsum in California to amend sodic soils growing such crops as
citrus, almonds, vegetables, and tomatoes. In 1985, more than 270,000 MT of
phosphogypsum were applied to fields in California. The sales of phosphogypsum for
agriculture declined sharply to about 84,500 MT in 1988, due primarily to the depletion of
phosphogypsum stacks in that state. As a result, phosphogypsum is currently being shipped
into California from Utah.
(a)Soils containing elevated levels of sodium.
3-2
-------
Table 3-1.
Quantities of phosphogypsum sold at eight facilities-1988 (Va89).
Facility Name
Arcadian Corp.
Farmland
Industries, Inc.
Four Court, Inc.
Mobil Mining &
Minerals Div.
Occidental
Chemical Co.
Royster Co.
J.R. Simplot Co.
Texasgulf
Chemicals Co.
Location
Geismer, LA
Bartow, FL
Magna, UT
Pasadena, TX
White Springs, FL
Mulberry, FL
Pocatello, ID
Aurora, NC
Tons Sold
Per Year
5,000
0-5,000
200,000(a)
(c)
100,000
(c) :
40,000-50,000
100,000-150,000
Percent of
Annual
Facility
Production
0.7
0 - <0.2
(b)
10- 15
<1
<1
, 3-4
2-3
(a)
Shipped to San Joaquin Valley, CA.
Facility is inactive, but has about 8 million tons stockpiled.
Information not provided.
3-3
-------
The Fertilizer Institute (TFI) circulated a questionnaire to which eight farmers in
California and 30 farmers in Georgia who regularly apply phosphogypsum to their fields
responded (TFI90a, Appendix 38). The crops grown in the amended soils in California were
almonds and walnuts (69 acres), peaches (40 acres), grapes (20 acres), alfalfa, corn, beans,
and oats (1080 acres), and trees (75 acres). The farms in Georgia were used exclusively for
growing peanuts, a total of about 4,200 acres. The following results were obtained from this
survey.
Georgia
California
Application, tons/acre
Acres Amended per Farm
Years of Application
Average Tillage Depth,
inches
0.06 - 1.0 (0.44)(a)
5-700 (139)
3-40 (17.3)
1-15 (8.3)
1.0-2.0(1.3)
7-1,000(183)
2-15 (10.5)
0-18(7.4)(b)
(b)
Average values are given in parenthesis.
Depended significantly on crop.
This is a small sampling of the total farmers that apply phosphogypsum to their fields;
however, it probably presents a representative cross-section of this practice, particularly for
the peanut farmers in the southeastern United States.
3.3 ROAD CONSTRUCTION
Phosphogypsum, mixed with fly ash, sand, gravel, or cement, has been successfully
used in the United States as a base for roads, parking lots, and storage areas. The use of
phosphogypsum for road bed construction has been most extensive in the Houston, Texas
area (L185, Kr88), with some application in Florida (FIPR88). The quantities of
phosphogypsum sold for roadbed construction in Texas and Florida in 1988 was estimated to
be about 140,000 MT per year (Kr88). The quantities of phosphogypsum used in North
Carolina are not available. However, considering the large amount of phosphogypsum in
Florida and the strong demand for aggregate in that state, the use of phosphogypsum in road
construction could significantly increase. Some applications of phosphogypsum in roadway
and parking lot construction are described below (EPA90, TFI90a).
3-4
-------
1) Phosphogypsum from Mobil's facility in Pasadena, Texas was mixed with fly
ash or cement and used as road base on five sections of city streets in La
Porte, Texas, near Houston.
2) In Polk County, Florida, 2.4 km of road base was constructed of a compacted
mixture of phosphogypsum and granular sand, and surfaced with one to two
inches of asphalt.
3) In Columbia County, Florida, a 2-mile stretch of road base was constructed
using both 100 percent dihydrated phosphogypsum and mixtures of
phosphogypsum and sand in ratios of 1:2, 1:1 and 2:1. The road base was
then surfaced with one to two inches of asphalt.
4) Phosphogypsum has been used commercially in North Carolina as a fill and
sub-base in roads crossing swampy areas.
5) A mixture of phosphogypsum (13 percent) and concrete was used to pave
1,670 m2 (2,000 yd2) of driveways and parking areas at the Florida Institute of
Phosphate Research in Bartow, Florida.
Several investigators have studied direct radiation exposures from gamma-rays and
radon-222 resulting from the use of phosphogypsum in roadbed construction. Roessler
reports external gamma-ray exposures ranging as high as 20 ^R/hr over a roadbed
constructed on a 100 percent phosphogypsum base, to 10-11 ^R/hr over roadways
constructed of a 25 percent phosphogypsum/gravel or sand base and paved with asphalt
(Ro87b). Radon flux measurements over the roadways generally ranged between 1 to 2
pCi/m2-s. When the roadbed was sealed with asphalt, the radon flux was less than 1
pCi/m2-s. Exposures along the sides of the roadways were near the background gamma-ray
and flux levels of 8-10 juR/hr and less than 0.1 pCi/m2-s, respectively. Another source cites
similar exposure levels (An88).
3.4 CONCRETE AND CEMENT BLOCKS
Phosphogypsum has been used on a very limited basis in the manufacture of building
materials, e.g., concrete and cement blocks. Phosphogypsum is not currently being used in
the United States in the manufacture of building materials. It is widely used for this purpose
in Europe and Japan. It is believed that the utilization of phosphogypsum as a raw material
for building materials will require further evaluation and probably the establishment of
standards for final construction materials. The potential demand for phosphogypsum for this
purpose is not known, but would probably not be great. An exception may be in Florida
where there are large quantities of phosphogypsum and a high demand for cement.
Currently, natural gypsum is used extensively in cement; about 19 percent of the natural
gypsum used in the United States is used as an additive to cement (EPA90).
3-5
-------
3.5 SULFUR RECOVERY
Extensive research has been conducted to develop a technology to.recover sulfur from
phosphogypsum. The development stage appears to be complete and the process could
become commercially available should the price of sulfur, currently at $110.00/long ton,
increase significantly (L191). In general, sulfate is converted to sulfur dioxide (SO2) by a
hish temperature decomposition of calcium sulfate (CaSO4) in the phosphogypsum. The
sulfur dioxide is scrubbed from the gaseous emissions and sent to the facility's chemical plant
where it is converted to sulfuric acid (H2SO4) which is utilized in the wet-acid process.
A pilot project to produce sulfuric acid and aggregate has operated successfully at the
Asrico plant near Uncle Sam, LA (L191). Using the circular grate process, the plant utilized
about 35 tons of phosphogypsum and other materials to produce about 30 tons of sulfunc
acid and 25 tons of aggregate per day. The plant began operation in 1988 but is presently
mothballed, a result of the low price of sulfur.
Consolidated Minerals, Inc. proposes to construct on a 17,100 acre site in DeSoto
County, Florida, a multi-production facility that will include a sulfur recovery process. The
sulfur dioxide recovered will be converted to sulfuric acid and used" in the phosphate
fertilizer production unit to precipitate calcium sulfate. In addition to the usual phosphate
fertilizer products, the process will also produce calcium oxide for use in Portland cement.
The waste products from the plant will include a more pure phosphogypsum (dihydrate with
some hemihydrate and anhydrate forms) containing lower radium-226 concentrations
(reported to be less than 5 pCi/g) and the insoluble impurities that contain most of the .
radium-226. It is planned to return the latter to the mine site as part of the reclamation
process. The plant is presently scheduled to begin operation in late 1994.
3.6 MINE RECLAMATION
An alternative to the disposal of phosphogypsum directly in stacks has been developed
in which the phosphogypsum is mixed with a phosphatic clay suspension (a waste from the
beneficiation of phosphate rock) in the approximate ratio of 3 parts phosphogypsum to 1 part
clay The suspension is then pumped to the disposal site. The mixture will dewater and
become consolidated in about one year, after which the surface can be revegetated with grass
and trees.
There are two factors that must be considered in determining if a phosphogypsum
facility can utilize this disposal method. First, the facility must be located near the disposal
site (mine) to keep transportation costs to a minimum. Second, the phosphatic clay
suspension must contain sufficient base (e.g. calcium carbonate) to neutralize the acids
remaining in the phosphogypsum.
3-6
-------
Currently, only Texasgulf's facility near Aurora,; North Carolina is using this disposal
process. At this facility, phosphogypsum is disposed in a mine adjacent to the plant at about
the same rate as it is produced (EPA90). Facilities in Florida and Idaho are close enough to
mines to make this disposal process feasible. In 1988, mine reclamation could have utilized
more than 32 million MT. However, this use is not viable for facilities in Louisiana,
Mississippi, and Texas because their phosphate rock is shipped from Florida, nor at the
facility in Rock Springs, Wyoming that receives phosphate rock mined in Utah. In 1988, the
combined total phosphogypsum generated at these facilities was nearly 10 million MT
(EPA90). '' . -.
Mine reclamation as a means of phosphogypsum disposal is a viable option that may
become more prevalent in the future. Two distinct advantages of mine reclamation over the
current practice of placing the material in large stacks are the aesthetic advantage of
revegetating the mined-out area, and the greatly reduced potential for the waste to be
released to surface water by erosion and to the atmosphere by the wind.
3.7 RESEARCH ACTIVITIES
Extensive research is being conducted under the sponsorship of the Florida Institute of
Phosphate Research (FIPR) and other organizations to develop commercial uses for
phosphogypsum (FIPR87, FIPR89a, FIPR89b, FIPR90a, FIPR90b). Some current and
potential uses for phosphogypsum were listed in Section 3.1 and briefly discussed in Sections
3.2 to 3,6. Research and development projects were being actively pursued in all of these
applications until the prohibition on its use was enacted on December 15, 1989 (54 FR
51654).
Numerous research efforts have been directed at expanding and developing beneficial
uses for phosphogypsum. The major goals Of FIPR, an agency of the State of Florida
supported financially by the state severance tax on phosphate, are the prevention of further
accumulation of phosphogypsum and the reduction of current inventories. FIPR is engaged
in research directed toward the recovery of sulfur and other valuable by-products from
phosphogypsum; the possible production of building materials such as aggregate, lime, and
cement; the use of phosphogypsum as a road-base material; and its use as an agricultural
amendment to enhance calcium and sulfur values in the soil.
FIPR and the phosphate industry are not alone in conducting research on possible uses
for phosphogypsum, Louisiana State University has established an Institute for Recyclable
Materials, one objective of which is the study of beneficial uses of phosphogypsum. Other
southeastern universities, including the University of Florida, the University of Miami, and
the University of Georgia are also involved in phosphogypsum research.
Research activities related to a few specific potential uses of phosphogypsum are
discussed below. This is not intended as a complete listing of current or planned research
projects. It is included here only to provide a perspective of the effort being made to
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identify beneficial uses of phosphogypsum and to point out the diversity of the uses being
considered.
3.7.1 -Agricultural Uses
AGRO Services International, Inc., under a grant sponsored by FIPR, researched the
use of phosphogypsum as a fertilizer on several Florida crops (AGRO89). As part of this
study, field trials were conducted using various rates and placement of phosphogypsum
(holding constant the addition of other fertilizer containing nutrients not found in gypsum) in
order to determine the yield response of several crops to phosphogypsum. The study
demonstrated that the application of phosphogypsum on crops, other than cowpeas, is very
likely to result in strong economic returns.
Other research studies indicate that phosphogypsum can be an important source of
calcium and sulfur for soils that are deficient in these elements (FIPR89b, FIPR90a,
Da ). In a study of phosphogypsum as a source of sulfur to improve the yield of wheat
grown for forage on sandy loams in Florida and Alabama, phosphogypsum was added at
annual rates varying between 12 and 121 kg/acre (FIPR90a). Significant increases in yield
were observed at an annual application rate of about 40 Kg/acre. Various studies have also
indicated the usefulness of phosphogypsum on crops such as tobacco, corn, wheat, and sugar
cane grown in Alabama, Louisiana, and North Carolina (Ba80, Go83),
Phosphogypsum has been found useful in controlling soil erosion and maintaining soil
productivity on agricultural fields in the southeastern states where highly weathered soils
have poor physical properties and are highly erodable (Mi89, Su80, Oa85). Experimental
data indicate that phosphogypsum maintains a higher rate of water infiltration for soils
compared with mined gypsum. Higher dissolution of the smaller phosphogypsum crystals
provides a relatively high electrolyte concentration in the surface soil, sufficient to prevent
, crust formation. The improvement in water infiltration rates by phosphogypsum application
has resulted in significant reductions in surface water runoff which leads to a reduction in
soil erosion. Reductions in soil erosion approaching 60 percent have been observed (Wa89).
3.7,2 Construction Materials
Phosphogypsum use in road construction has been tested in the United States. Several
research studies have demonstrated that phosphogypsum is suitable for use as a construction
aggregate for various applications, including road construction, road embankments, and
railroad beds (Ch89, Ch90). Phosphogypsum has been used on an experimental basis for
paving and highway construction in both Texas and Florida (see Section 3.3). The addition
of gypsum to cement appears to retard the setting times, counteracts shrinkage, increases the
strength of the cement product, and provides resistance to sulfate etching.
Phosphogypsum has the same basic properties as natural gypsum and may be used as
a substitute for natural gypsum in the manufacture of commercial construction products such
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as plasterboard and plaster of Paris, Phosphpgypsum has hbeen used extensively in the
manufacture of construction materials in Japan, Australia, and Europe. Currently, however,
there are no major uses of phosphogypsum in commercial construction materials in the
United States due to the low-cost availability of other suitable materials'and to the ban on the
utilization of phosphogypsum under 40 CFR Part 61, Subpart R. If the ban on the use of
phosphogypsum is lifted, research might well lead to the development of building materials
that are suitable for the U.S. market.
3.7.3 Purification of Phosphogypsum
The major disadvantage to the commercial use of phosphogypsum is the presence of
potentially hazardous concentrations of radium-226. Research is being conducted in the
United States and in other countries to reduce or remove the radium from raw
phosphogypsum to ensure its safe use in the agriculture and construction industries. Methods
for the removal of radium include hydrocycloning, a physical separation process, and
calcining raw phosphogypsum into the hemihydrate form which eliminates most of the
radium.
The physical process involves the use of a hydrocyclone to separate the smaller
phosphogypsum crystals (less than 30 ^m) which contain the greatest portion of the
radionuclides from the rest of the phosphogypsum (Pe85). Although this process has proven
effective in reducing radium concentrations by factors of 2 to 5, it does not remove all of the
radium from the phosphogypsum. A new process, which shows promise of producing
phosphogypsum of a much lower radioactive content, involves calcining the raw
phosphogypsum into the hemihydrate form (CaSO4« 1/2H2O) and dissolving the hemihydrate
in water (Mo90). The solution is quickly filtered and the radium salts are collected on the
filter media.
Although the hemihydrate process generates a relatively low volume of waste, it is
concentrated in radium-226, up to 600 pCi/g, and may pose disposal problems that are equal
to or even greater than those associated with the original phosphogypsum (EPA90). No
information is available on the volume or radium-226 concentration of the waste resulting
from the physical separation method, but it too would probably produce wastes with
relatively high concentrations of radium-226. This waste disposal problem will need to be
resolved if the purification of phosphogypsum is to become viable.
3.8 SUMMARY OF PHOSPHOGYPSUM UTILIZATION
Probably less than 500,000 MT per year of phosphogypsum are being used in the
United States today. The majority is for agricultural applications in California and the
peanut producing states in the southeast (approximately 220,000 MT/year). The remaining
quantity is for road construction in Texas and Florida (approximately 140,000 MT/yr).
Quantities used for mine reclamation are not presently available, but could be substantial in
the future if it were decided to dispose of the phosphogypsum by this process. The quantities
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of phosphogypsum used for building materials and research are very small.
The historic usage of phosphogypsum from 1984 through 1987 shows a general
decline, primarily due to the closing of the California facilities and the depletion of the
phosphogypsum generated in that state. This decline is demonstrated in Table 3-2 (Jo88a,
EPA89a).
Table 3-2. Estimated quantities of phosphogypsum used per year (EPA89a).
Year
Total Estimated MT(a)
1984
1985
1986
1987
660,000
460,000
540,000
360,000
(a)
These totals are based on the results of a mail survey (Jo88a). Since some of the
companies failed to respond to the survey, it does not represent a total response for
the industry; however, it is believed that the survey gives an approximate total usage
rate.
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4. RADIOLOGICAL ASSESSMENTS OF PHOSPHOGYPSUM USE
4.1 INTRODUCTION
The purpose of this assessment is to analyze the radiological risk associated with
various uses of phosphogypsum. The PATHRAE dose assessment model is employed to
evaluate potential doses and risks for plausible exposure scenarios involving the commercial
use of phosphogypsum. Section 4.3 provides a discussion of the methodology for this risk
assessment, including a brief description of the PATHRAE dose assessment model, the
exposure scenarios evaluated, and the input parameter values used in the PATHRAE
analysis. The results of the risk assessment are summarized in Section 4.4. Risks to
workers, to individuals in the critical population group (CPG), and to reclaimers are
evaluated for agricultural, road construction, and research and development (R&D) uses of
phosphogypsum.
There is some concern that crops grown in soils amended with phosphogypsum may
contain elevated concentrations of radionuclides, primarily radium-226, polonium-210, and
lead-210 (see Table 2-3). To better understand the significance of this pathway, both Iting-
and short-term uptake studies were conducted at the University of Georgia for the EPA
(Mi91). As part of the study, the leachability of radionuclides in amended soils was
investigated. The results of the University of Georgia study are presented in Section 4.2.
4.2 RADIOLOGICAL EFFECT OF AMENDING SOILS WITH PHOSPHOGYPSUM
Both long- and short-term studies were conducted by the Agronomy Department at the
University of Georgia to determine the significance of the uptake of radionuclides by plants
grown in soils treated with phosphogypsum (Mi91). Locations having two different soil
types were selected for study: one at Athens, GA where there is a sandy loam topsoil (25-30
cm) overlying a clayey subsoil, and at Tifton, GA where there is a very sandy topsoil (50
cm) over a sandy clay loam subsoil.
4.2.1 Long-Term Study
In 1985, 2 m by 5 m plots were established at both locations and treated with an
equivalent of 4 MT/acre (simulating 5 to 10 years of field treatment) of phosphogypsum from
Bartow, FL. The phosphogypsum was mixed with the top 15 cm of soil and planted with
alfalfa. Similar untreated plots were used as controls. All plots were treated with
commercial nitrogen, phosphorus, and potassium fertilizers. Plant tissues were randomly
harvested from each plot in 1990, after which five core samples, 5 cm in diameter and 90 cm
deep, were obtained from each plot, divided into three sections (0-15 cm, 15-30 cm, and 75-
90 cm depths), and combined with respect to the depth increment.
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4.2.2 Short-Term Study
This study was conducted in 1990 at the Athens, GA farm. Plots of 4 m by 5 m
were treated with an equivalent of 4 MT/acre of the same phosphogypsum that was used in
the long-term study. The phosphogypsum was lightly raked into the soil surface immediately
after soybeans had been planted in June. Untreated plots were used as controls. The
soybeans were harvested in the fall and separated into leaves (including stems) and seeds.
Prior to analysis, the plant samples were dried at 60°C and ground in a Wiley mill.
The soil samples were air-dried and sieved to <2 mm. All samples, including samples of
the phosphogypsum used in the studies, were analyzed for isotopic uranium and thorium,
radium-226, lead-210, and polonium-210.
Of the pertinent radionuclides, only Ra-226 was consistently present above the
detection limit in the soil samples; however, concentrations in samples from the treated plots
were no higher than those from the control plots, about 2 pCi/g. The analysis of core
samples from fields treated five years earlier with phosphogypsum showed no detectable
elevated levels of radionuclides at any depth. These results were attributed to the small
quantities of radionuclides added in the phosphogypsum relative to the amounts naturally
present in the soil.
Radium-226 was the only radionuclide associated with phosphogypsum that was
detected in either alfalfa or soybeans. There were no statistical differences in the
concentration of Ra-226 measured in plant tissues grown in the treated and control plots.
Although the uptake of Ra-226 was measurably higher in alfalfa grown in Tifton soil than in
alfalfa grown in Athens soil (2 pCi/g dry weight vs less than 1 pCi/g dry weight), it was not
statistically significantly greater in plants from treated soils than in the controls at the two
sites. The dominant radionuclide was potassium-40 in both plant types, ranging from about 7
to 20 pCi/g dry weight.
4.2.3 Leaching Studies
A series of leaching studies was performed as part of the uptake studies (Mi91).
Intact soil columns, 10 cm diameter and 30 cm deep, were taken of both Tifton and Athens
soils using a truck-mounted hydraulic ram. Two columns of each soil type were treated with
an equivalent of 4 MT/acre of the phosphogypsum used in the uptake studies. The
phosphogypsum was applied as a powder to the soil surface. Two columns of each soil type
were untreated and used as controls. Deionized water was ponded on the surface at a
constant 2-cm depth and allowed to perculate through the column until a total of 8 liters of
leachate in 1-liter increments had been collected from the column base. This is equivalent to
about one year of precipitation.
The leachate was filtered to remove suspended clay particles prior to analysis. The
columns were cut into 5-cm sections, and the soil in each section analyzed separately for the
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same radionuclides as listed above for the soil samples.
Only Ra-226 was consistently detected in the leachate of the soil columns. The
amount of Ra-226 leached from the treated and untreated Athens soil columns was about the
same, totaling 2.2 pCi in the 8 liters collected. However, the Ra-226 concentrations in the
leachate of Tifton soil treated with phosphogypsum was 3 to 5 times higher than in the
control leachate. The Ra-226 concentration in the leachate peaked at 3 liters (0.8 pCi/L),
and then decreased to near the control level after 8 liters were collected. The total amount of
Ra-226 collected in the Tifton soil leachate was 6.5 pCi, equivalent to about 5 percent of the
Ra-226 initially added in the phosphogypsum. The higher leachability of Ra-226 in the
Tifton soil was attributed to the sandy nature of the soil allowing rapid percolation of water
with limited adsorption capacity of the soil. No discernable trend was observed in the Ra-
226 concentration with soil depth.
Considering the relative immobility of the principal radionuclides associated with
phosphogypsum in soil and the small quantities added in the phosphogypsum relative to the
amounts naturally present in the soil, 0.7 pCi/g and 1.9 pCi/g of radium-226 in Tifton and
Athens soils, respectively, University of Georgia investigators concluded that short-term
treatments (5-10 years) of farm lands with phosphogypsum does not pose an acute
environmental hazard.
Studies conducted earlier to characterize the radiological hazards associated with soils
amended with phosphogypsum produced similar results and conclusions. A University of
Florida study of radionuclide uptake by foods grown in soil receiving one ton of
phosphogypsum per acre every four years concluded that there would be no significant
radiation problems for up to at least 50 years (Ro88). Another study measured the radon
flux on three fields that had been amended with varying amounts of phosphogypsum for
different periods of time (Po90). The mean of 13 flux measurements, using charcoal
canisters, made on each field ranged from 0.4 to 1 pCi/m2-s. The background flux,
measured on areas receiving no application, was 0.4 pCi/m2-s. It was difficult to correlate
the radon flux measurements with the amount of phosphogypsum applied.
4.3 RISK ASSESSMENT METHODOLOGY
The methodology employed in evaluating individual and population risks from
commercial uses of phosphogypsum is described in this section. Dose calculations were
performed using the PATHRAE dose assessment model (EPA87). Calculations were
performed for exposure scenarios which included the use of phosphogypsum in agriculture,
road construction, and R&D activities. Where PATHRAE does not model the exposure
scenario (e.g., a person performing experimental analyses on phosphogypsum contained in
metal drums), the MICROSHIELD computer code (GRO85) was used to augment the results
of the PATHRAE analyses. Lifetime risks from one year of exposure were obtained from
the PATHRAE dose assessment results using the risk conversion factors in the EPA's
Environmental Impact Statement for NESHAPS radionuclides (EPA89b).
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4.3.1 The PATHRAE Dose Assessment Model
The PATHRAE performance assessment model (EPA87) 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 potentially 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 equivalents'8' to members of a 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 ot
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. See Appendix A for a detailed description of the PATHRAE pathway equations.
For this risk assessment, the phosphogypsum is assumed to be mixed with soil in^n%
agricultural field or mixed with other construction materials to construct roadbeds and
concrete highways. Exposure scenarios and values for some important input parameters used
in modeling these scenarios are described later in this section.
4.3.2 The MTCRQSHIELD Computer Code
Where the exposure geometry is not readily modeled by PATHRAE (e.g., person
exposed to the radioactivity in phosphogypsum contained in metal drums), MICROSHIELD
was used to estimate the external gamma dose. MICROSHIELD (GRO85) 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.
« Throughout this report the term "dose" refers to the effective whole body dose
equivalent.
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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 dimensions, locations, and orientations of intervening shields; and the
material (including air) used for these intervening shields.
4.3.3 Exposure Scenarios
The exposure scenarios evaluated for this phosphogypsum risk assessment include
potential exposures to individuals from the use of phosphogypsum in agriculture, road
construction, and R&D activities.
4.3.3.1 Phosphogypsum in Agriculture
Seven scenarios involving the agricultural use of phosphogypsum are evaluated.
Scenarios 1,3, and 5 assume a clay soil base type, with the exposed individual being greater
than 100 m from the site edge. Scenarios 2, 4, and 6 consider similar pathways, using a
sand soil base type, and exposed individuals 100 m from the site boundary. Scenarios 1
through 4 involve the use of phosphogypsum as a source of calcium and sulfur for soils
deficient in these elements. Scenarios 5 and 6 involve its use in sediment control for soils
that have been eroded and leached. Scenario 7 evaluates the effect of using phosphogypsum
containing a range of Ra-226 concentrations with different application rates.
Scenarios 1 through 4: Phosphogypsum as a source of calcium and sulfur for soils
deficient in these elements. Parameters which characterize the four scenarios involving
phosphogypsum as a source of calcium and sulfur on agricultural fields are shown in Table
4-1. Four scenarios are evaluated: two involving an average phosphogypsum application
rate on a moderate size clay or sand field, and another for a maximum application rate on a
large clay or sand field. The parameter values in Table 4-1 are based on responses by
agricultural users of phosphogypsum to a survey by The Fertilizer Institute (TFI). The
reference agricultural fields for Scenarios 1 through 4 are postulated to be located in the
southeastern United States. Values of environmental and climatological parameters used in
the risk assessment are representative of a humid permeable site.
The dose calculations for Scenarios 1 through 4 assume biennial applications 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 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
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Table 4-1. Phosphogypsum use parameters for Scenarios 1 through 4.
Kilograms of phosphogypsum per acre
Acres per farm
Tillage depth (cm)
Application rate
Distance to nearest residence (m)
Soil Type
Average Site
(Scenario 1&2)
Maximum Site
(Scenario 3&4)
n per acre
J(m)
664
138
22
Biennially
890 & 100
Clay, Sand
2,032
1,000
46
Biennially
6,440 & 100
Clay, Sand
reference soil as a result of biennial applications of phosphogypsum for a period of 100
years For a Ra-226 concentration of 30 pCi/g in phosphogypsum, the increase in the
Ra-226 concentration in the soil after 100 years of biennial application is calculated to be
0 69 pCi/g for Scenarios land 2 and 1.02 pCi/g for Scenarios 3 and 4. A detailed
description of the Ra-226 soil concentration calculation method is presented in Appendix B.
Scenarios 5 and 6: Phosphogypsum as sediment control for soils that have been
eroded and leached. Parameters which characterize Scenarios 5 and 6 are shown in Table
4-2 The reference agricultural site for this scenario is assumed to be located in south-central
California. The phosphogypsum is initially applied at the rate of 8 MT per acre followed by
biennial applications of 4 MT per acre. As in Scenarios 1 through 4, an apphcation period
of 100 years is postulated. For a Ra-226 concentration of 30 pCi/g in phosphogypsum, the
increase in the Ra-226 concentration in the soil after 100 years of biennial application is
calculated to be 3.12 pCi/g for Scenarios 5 and 6.
For Scenarios 1 through 6 the following exposure pathways are evaluated:
• Agricultural Worker
- Direct gamma exposure
- Dust inhalation
• On-site Individual
- Direct gamma exposure
- Indoor radon inhalation
- Use of contaminated well water
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• Member of CPG .
- Inhalation of contaminated dust - ;
- Ingestion of drinking water from a 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.
Table 4-2. Phosphogypsum use parameters for Scenarios 5 and 6.
Kilograms of phosphogypsum per acre
.-- Initial application 8,000
- Subsequent applications 4,000
Acres per farm 555
Tillage depth (cm) 30
Application rate biennially
Distance to nearest residence (m) 1,000 & 100
Soil Type '• Clay, Sand
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
provide 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.
The on-site individual is assumed to live in a house in a development 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 Tables 4-1 and
4-2. The person obtains all water from a well adjacent to the house. Fifty percent of
foodstuffs are assumed to be grown on-site.
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Scenario 7: Use of phosphogypsum as a soil amendment based on the application
rate and Ra-226 concentration. The purpose of this scenario is to determine if the
phosphogypsum containing various concentrations of Ra-226 can be applied for agricultural
purposes based on various application rates. To evaluate the feasibility of this approach, risk
estimates are performed for the two limiting exposure pathways identified from Scenarios 1-
6, direct gamma and indoor radon exposures to the on-site individual. The risks for these
exposure pathways are estimated using the following combinations of phosphogypsum
application rates and Ra-226 concentrations:
Application Rate
(Ibs/acre)
Ra-226 Concentration
(pCi/g)
3, 7, 15, 20, 30, 45, 60
3, 7, 15, 20, 30, 45
3, 7, 15, 20, 30
3, 7, 15, 20
3, 7, 15
3, 7, 15
501)
1,000
1,500
2,500
5,000
10,000
A nine-inch tillage depth is assumed. All other parameters remain constant and are
those given above for the average site in the southeastern United States.
4.3.3.2 Phosphogypsum in Road Construction
Four scenarios involving phosphogypsum in road construction are evaluated.
Scenarios 8 and 9 involve the use of phosphogypsum in a road base for a secondary road.
Scenarios 10 and 11 involve phosphogypsum as an additive to increase the strength of a
concrete road surface. These scenarios are shown schematically in Figure 4-1.
Scenarios 8 and 9: 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 30 pCi/g in phosphogypsum, the Ra-226
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.
Scenarios 10 and 11: Phosphogypsum in a concrete road surface. The concrete road
surface incorporates 15 weight percent phosphogypsum. Assuming a Ra-226 concentration
of 30 pCi/g in phosphogypsum, the Ra-226 concentration in the road surface is 4.5 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 Scenarios 8 and 9.
For Scenarios 8 through 11 the following exposure pathways are evaluated:
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12 cm
9.15m
7.32m
25cm
SCENARIOS 8 AND 9
USE OF PHOSPHOGYPSUM IN A ROAD BASE
12cm
25cm
SCENARIOS 10 AND 11
USE OF PHOSPHOGYPSUM IN A
CONCRETE ROAD SURFACE
RAE-103855
Figure 4-1. Scenarios involving the use of phosphogypsum in road construction.
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• Construction Worker
- Direct gamma exposure
- Dust inhalation
• Person Driving on Road
- Direct gamma exposure
• Member of CPG
- Direct gamma exposure
- Ingestion of drinking water from a contaminated well
- Ingestion of foodstuffs contaminated by well water
• Reclaimer
- Direct gamma exposure
- Indoor radon inhalation
- 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.
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.
The shielding coefficient is 0.6.
The reclaimer is assumed to build a house on the roadbed at some future time after
the road is closed and the road surface has crumbled and 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 or 1,000 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.
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4.3.3.3 Phosphogypsum in Research & Development Activities
One scenario (Scenario 12) 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.
MICROSHIELD 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 ^g/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.
4.3.4 Input Parameters
Values of input parameters used in PATHRAE to evaluate potential doses to
individuals and the attendant risks from the commercial use of phosphogypsum are presented
in this section. These input parameters include radionuclide concentrations, dose and risk
conversion factors, and parameters used to characterize the exposure scenarios described in
Section 4.3.3.
4.3.4.1 Radionuclide Concentrations
The relative radionuclide concentrations in phosphogypsum providing the basis for the
risk assessment are shown in Table 4-3. The concentrations in Table 4-3 are based on a
radium-226 concentration of 1 pCi/g. The risk estimates presented in Section 4 are given as
a function of Ra-226 concentration.
The relative concentrations of Pb-210, Po-210, Th-230, U-234, and U-238 are based
on average activity ratios of these radionuclides to Ra-226 in phosphogypsum reported in
Ho88. The relative concentration of Ra-228 is derived from the activity ratio of Ra-228 to
Ra-226 in phosphate fertilizer, reported in SCA9L Activity ratios for Th-228 and Th-232
relative to Ra-226 are also those for phosphate fertilizer, reported in SCA91. Because
concentrations of thorium in phosphogypsum are depleted relative to concentrations in
phosphoric acid, the use of thorium to radium-226 activity ratios for phosphate fertilizer may
tend to overestimate these thorium concentrations. The activity of U-235 in phosphogypsum
is assumed to be about 5 percent of the U-238 activity,
4.3.4.2 Dose and Risk Conversion Factors
The dose and risk conversion factors used in this analysis are shown in Table 4-4.
Dose conversion factors for ingestion and inhalation are from the EPA's Federal Guidance
4-11
-------
Table 4-3. Phosphogypsum reference radionuclide concentrations.(a>
Radionuclide
Ra-226
Po-210
Pb-210
Th-228
Ra-228
Th-230
Th-232
U-234
U-235
U-238
Concentration
(pCi/g)
1.000
1.040
1.400
0.133
0.133
0.187
0.123
0.120
0.005
0.110
w Based on a Ra-226 concentration of 1 pCi/g. See text for explanation of activity
ratios of other radionuclides relative to Ra-226.
Report No. 11, which provides guidance for control of occupational exposures to radiation
(EPA88).
Dose conversion factors for inhalation, ingestion and direct exposure to gamma
radiation are from guidance for modifying PRESTO-EPA-CPG to reflect major recent
changes in EPA's dose calculation methodology. The inhalation and ingestion conversion
factors represent the effective whole body dose equivalents resulting from a unit curie of
intake, and the conversion factors for the direct gamma represent the effective whole body
dose rates resulting from the exposure to a unit concentration of a curie per square meter on
the ground surface. Risk conversion factors in Table 4-4, except those for radon, are based
on the radiation risk factors in Table 6-27 of Volume I of EPA's "Environmental Impact
Statement for NESHAPS Radionuclides" (EPA89b). As a result of a recommendation by
EPA's Science Advisory Board, EPA reduced the radon risk conversion factors by about 37
percent to 4.4xlO'8 and 4.4xlO'9 for indoor and outdoor exposures, respectively (Co92). The
risk conversion factors represent average lifetime (i.e., 70-year) risks of fatal cancer per unit
4-12
-------
Table 4-4. Dose and risk conversion factors.
I. DOSE CONVERSION FACTORS
Nuclide
Inhalation DCF
(mrem/pCi)"
Ingestion DCF
(mrem/pCi)*
Direct Gamma
DCF
(mrem/yr per
pCi/m2)
Ra-226
Po-210
Pb-210
Th-228
Ra-228
Th-230
Th-232
U-234
U-235
U-238
8.6E-03
9.4E-03
1.4E-02
3.4E-01
4.8E-03
3.3E-01
1.6E+00
1.3E-01
1.2E-01
1.2E-01
1.3E-03
1.9E-03
5.4E-03
4.0E-04
1.4E-03
5.5E-04
2.7E-03
2.8E-04
2.5E-04
2.7E-04
1.67E-04
8.55E-10
0
3.37E-04
9.04E-05
8.88E-08
6.56E-08
8.00E-08
6.41E-08
1.67E-05
50-year committed dose equivalent from one year of intake (uptake).
II. RISK CONVERSION FACTORS"
Nuclide
Ra-226
Po-210
Pb-210
Th-228
Ra-228
Th-230
Th-232
U-234
U-235
U-238
Inhalation Risk
per pCi Inhaled
2.8E-09
2.4E-09
1.4E-09
7.2E-08
5.8E-10
2.9E-08
2.9E-08
2.5E-08
2.3E-08
2.2E-08
Ingestion Risk
per pCi Ingested
9.4E-11
1.4E-10
5.5E-10
1.3E-11
7.0E-11
2.3E-11
2.1E-11
7.5E-11
7.3E-11
7.4E-11
Direct Gamma
Risk per pCi/m2
5.7E-11
2.9E-16
0
4.8E-11
3.1E-11
2.7E-14
2.0E-14
2.4E-14
5.5E-12
7.23E-13
™ 70-year lifetime risk of fatal cancer from one year of exposure.
III. RADON RISK CONVERSION FACTORS6
Exposure Scenario Inhalation Risk per pCi/m3
Indoor Exposure
Outdoor Exposure
4.4E-08
4.4E-09
70-year lifetime risk of fatal cancer from one year of exposure to Rn-220 and Rn-222 daughters.
4-13
-------
of intake or exposure. A quality factor of 1 has been used to convert from rads to rems for
low-LET (i.e., gamma) radiation, and a relative biological effectiveness of 8 has been used
to convert from rads to rems for the induction of cancer by high-LET (i.e., alpha) radiation.
4.3.4.3 Site-Specific Input Parameters
Values of all important site-specific input parameters used by PATHRAE in the risk
assessments are shown in Table 4-5.
4.4 RESULTS
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 4.3.
4.4.1 Phosphoevpsnm in Agriculture
The results of the risk assessment for the use of phosphogypsum in agriculture are
summarized in Tables 4-6 through 4-14. Estimated doses and risks for Scenarios 1 and 2
involving an average phosphogypsum application rate on a moderate size clay or sand field
usS to grow peanuts, are shown in Tables 4-6 and 4-7. Estimated doses and risks for
Scenarios 3 and 4, involving a maximum phosphogypsum application rate on a large clay or
SndTeld, are shown in Tables 4-8 and 4-9. Estimated doses and risks ^ Scenarios; 5 and
6, involving the use of phosphogypsum for sediment control, are shown in Tables 4-10> and
441. Estimated risks for Scenario 7, based on various phosphogypsum application rates and
Ra-226 concentrations, for radon and gamma exposures to the on-site individual are shown in
Tables 4-12 and 4-13, respectively; the total risks from both pathways are shown in Table 4-
14. The risks shown in the tables are estimated lifetime (70-year) risks from one year of
exposure.
As explained in Section 4.3, phosphogypsum applications to agricultural fields are .
assumed to occur biennially. Equilibrium is reached with competing mechanisms that
remove gypsum and its radioactive constituents at 1100 yrs for Ra-226 and 1600 yrs for
uranium and thorium. Doses and risks are evaluated for fields that have been repeatedly
fertilized on a biennial basis over a 100-year period. Results of Scenarios 1 through 6 are
shown for Ra-226 concentrations in phosphogypsum ranging from 26 pCi/g to 3 pU/g. me
actual Ra-226 concentrations in the agricultural fields are lower due to dilution of the
phosphogypsum with the soil and depletion mechanisms such as plant uptake and leaching
which tend to remove radionuclides.
4-14
-------
Table 4-5. Site-specific input parameters for PATHRAE risk assessments.
Parameter
Phosphogypsum application rate-agricultural
scenarios
Fertilizer— average
Fertilizer— maximum
Soil conditioner
Phosphogypsum application interval-
agricultural scenarios
Total years of application-agricultural
scenarios
Agricultural field size
Fertilizer—average
Fertilizer— maximum
Soil conditioner
Tillage depth—agricultural scenarios
Fertilizer— average
Fertilizer-maximum
Soil conditioner
Agricultural field soil density
Roadbed material density
Distance to nearest residence
Fertilizer—average
Fertilizer—maximum
Soil conditioner
Road construction scenarios
Distance to river
River flow rate
Density of aquifer
Porosity of aquifer
Horizontal velocity of aquifer
Units
MT/acre/yr
MT/acre/yr
MT/acre/yr
—
yrs
acre
acre
acre
m
m
m
kg/m3
kg/m3
m
m
m
m
m
nWyr
kg/m3
-- .
m/yr
Clay Value, Sand Value
0.66
2.03
4.05
biennially
100
138
1,000
556
Q.22
0.46
0.30
1.50E+03
2.25E+03
890, 100
6,440, 100
1,000, 100
1,000, 100
5.00E+03
l.OOE+08
1.80E+03
0.33
20
4-15
-------
Table 4-5. Site-specific input parameters for PATHRAE risk assessments (continued).
Parameter
Vertical distance to aquifer
Fertilizer scenarios
Soil conditioner scenario
Construction scenarios— humid site
Construction scenarios—dry site
Water infiltration rate
Fertilizer scenarios
Soil conditioner scenario
Construction scenarios-humid site
Construction scenarios— dry site
Fraction of food eaten grown on-site
Adult breathing rate
Average dust loading in outside air
Average dust loading in R&D lab
Atmospheric stability class
Fraction of time wind blows toward receptor
Average wind speed
Dust resuspension rate for off-site transport
Dust deposition velocity
Radon emanating power
Radon diffusion coefficient
Soil—humid site
Soil-dry site
Concrete
Air change rate in reclaimer house
Exposure fraction for indoor exposure
Equivalent exposure fraction for outdoor
exposure
Surface erosion rate
Units
m
m
m
m
m/yr
m/yr
m/yr
m/yr
—
m3/yr
kg/m3
kg/m3
—
—
m/sec
nWsec
m/sec
—
m2/yr
m2/yr
m2/yr
changes/hr
—
—
m/yr
Clay Value, Sand Value
3.0
10.0
3.0
10.0
0.40
0.25
0.40
0.25
0.50
8.00E+03
5.00E-07
l.OOE-07
4
0.093
4.5
5.0E-07
l.OE-03
0.30
2.2E+01
6.3E+01
1.6E+01
2
0.75
0.50
2.0E-04
4-16
-------
Table 4-5. Site-specific input parameters for PATHRAE risk assessments (continued).
Parameter
Units
Clay Value, Sand Value
Distribution coefficients (KJ
Ra-226
Po-210
Pb-210
Th-228
Ra-228
Th-230
Th-232
U-234
U-235
U-238
Volume of drinking water consumed
annually by an individual
Length of road perpendicular to aquifer
Aquifer thickness
m3/kg
m3/kg
rrrVkg
m3/kg
mVkg
m3/kg
mVkg
m3/kg
mVkg ,
mVkg
m3/yr
mile
m
0.45,
0.50,
0.90,
150.0,
0.45,
150.0,
150.0,
0.45,
0.45,
0.45,
0.07
0.50
0.90
150.0
0.07
150.0
150.0
0.07
0.07
0.07
0.37
10
10
It is observed that the doses from the groundwater pathways are all zero. As an
added sensitivity analysis, scenarios 2, 4, 6, 9 and 11 were created as replicates of 1, 3, 5, 8
and 10, modifying the distance to the offsite individual (100 m). Additionally, the kj for
uranium and radium was reduced to 70 ml/g. Using these modifications, PATHRAE
projected a peak risk at year 4200 of l.Sxia8. These changes also caused, as illustrated in
the summary tables, an increase in the risk to members of the CPG from-dust inhalation.
For a well placed onsite, and a k,, of 70 ml/g for uranium and radium, a risk of 6.7xia9
occurred by the year 1000, for scenario 4. A peak risk of 2xia8 occurred in year 3100 for
the same scenario.
For Scenarios 1 and 2, a Ra-226 concentration of 26 pCi/g in phosphogypsum is
estimated to correspond to an increase in the soil Ra-226 concentration of 0.60 pCi/g at the
end of the 100-year period. For Scenarios 3 and 4, a Ra-226 concentration of 26 pCi/g in
phosphogypsum is estimated to correspond to an increase in the soil Ra-226 concentration of
0.88 pCi/g at the end of the 100-year period. For Scenarios 5 and 6, a Ra-226 concentration
of 26 pCi/g in phosphogypsum is estimated to correspond to an increase in the soil Ra-226
concentration of 2.70 pCi/g at the end of the 100-year period. As shown in the tables, for
each scenario, the doses and risks are directly proportional to the Ra-226 concentration in the
original phosphogypsum.
4-17
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4-23
-------
Table 4-12. Risk assessment results for Scenario 7 - radon exposure risks to the on-site individual as a
function of phosphogypsum application rate and Ra-226 concentration.00
Application Rate
(Ibs/Acre)
500
1,000
1,500
2,500
5,000
10,000
Ra-226 Concentration in Phosphogypsum (pCi/g)
3
l.OE-07
2.1E-07
3.1E-07
5.1E-07
l.OE-06
2.1E-06
7
2.4E-07
4.8E-07
7.5E-07
1.2E-06
2.4E-06
4.8E-06
15
5.1E-07
l.OE-06
1.6E-06
2.6E-06
5.1E-06
l.OE-05
20
6.8E-07
1.4E-06
2.1E-06
3.4E-06
—
—
30
l.OE-06
2.1E-06
3.1E-06
—
—
—
45
1.6E-06
3.1E-06
~
—
—
, —
60
2.1E-06
—
—
—
—
—
Lifetime risk from one year of exposure.
Table 4-13. Risk assessment results for Scenario 7 - external gamma risks to the on-site individual as a|
function of phosphogypsum application rate and Ra-226 concentration/*
Application Rate
(Ibs/Acre)
500
1,000
1,500
2,500
5,000
10,000
Ra-226 Concentration in Phosphogypsum (pCi/g)
3
1.1E-07
2.3E-07
3.4E-07
5.7E-07
1.1E-06
2.3E-06
7
2.6E-07
5.3E-07
7.9E-07
1.3E-06
2.6E-06
5.3E-06
15
5.7E-07
1.1E-06
1.7E-06
2.8E-06
5.7E-06
1.1E-05
. 20
7.5E-07
1.5E-06
2.3E-06
3.8E-06
—
—
30
1.1E-06
2.3E-06
3.4E-06
—
—
—
45
1.7E-06
3.4E-06
—
—
—
— •
60
2.3E-06
• —
~
—
—
~
Lifetime risk from one year of exposure.
4-24
-------
Table 4-14. Risk assessment results for Scenario 7 - Total risks to the on-site individual as a function of
phosphogypsum application rate and Ra-226 concentration.(a>b)
Application Rate
(Ibs/Acre)
500
1,000
1,500
2,500
5,000
10,000
Ra-226 Concentration in Phosphogypsum (pCi/g)
3
2.2E-07
4.4E-07
6.5E-07
1.1E-06
2.2E-06
4.4E-06
7
5.1E-07
l.OE-06
1.4E-06
2.5E-06
5.1E-06
l.OE-05
15
1.1E-06
2.2E-06
3.3E-06
5.4E-06
1.1E-05
2.2E-05
20
1.4E-06
2.9E-06
4.4E-06
7.2E-06
—
—
30
2.2E-06
4.4E-06
6.5E-06
— .--
— •
, ~
45
3.3E-06
6.5E-06
—
—
—
.
60
4.4E-06
—
•
—
•
—
(a) Lifetime risk from one year of exposure.
^ The sum of the risks from Tables 4-12 and 4-13.
4-25
-------
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
Scenario 1, the lifetime risk to the on-site individual from one year of external gamma
exposure is estimated to range from S.Oxia6 for 26 pCi/g phosphogypsum to 3.4xlO'7 for 3
pCi/g phosphogypsum. The lifetime risk from one year of indoor radon inhalation is
estimated to range from 2.6xia6 for 26 pCi/g phosphogypsum to S.OxlCr7 for 3 pCi/g
phosphogypsum.
For Scenario 3, the lifetime risk to the on-site individual from one year of external
gamma exposure is estimated to range from 4.6xlfr6 for 26 pCi/g phosphogypsum to
5.2xlO"7 for 3 pCi/g phosphogypsum. The lifetime risk from one year of indoor radon
inhalation is estimated to range from e.SxlO"6 for 26 pCi/g phosphogypsum to 7.5xlO-7 for 3
pCi/g phosphogypsum.
For Scenario 5, the lifetime risk to the on-site individual from one year of external
gamma exposure is estimated to range from 1.4xlO-s for 26 pCi/g phosphogypsum to
1.6xlO'6 for 3 pCi/g phosphogypsum. The lifetime risk from one year of indoor radon
inhalation is estimated to range from 1.2xlQ-5 for 26 pCi/g phosphogypsum to 1.4xia6 for 3
pCi/g phosphogypsum.
The results of the first four scenarios prompted Scenario 7; an evaluation of the risks
associated with the two principal exposure pathways, radon and direct gamma exposures,
with varying phosphogypsum application rates and Ra-226 concentrations. Combinations of
application rates and Ra-226 concentrations varied from 500 to 10,000 Ibs/acre and 3 to 60
pCi/g, respectively. The affect of these two variables on the estimated risk is best illustrated
by the family of curves represented in Figures 4-2 to 4-4, which illustrate the increase in risk
as the Ra-226 concentrations increase with each application rate. The risks presented in the
figures are those listed in Tables 4-12 to 4-14 multiplied by a 70-year exposure period.
Thus, they represent the estimated lifetime risk resulting from a 70-year exposure. The total
lifetime risk to the on-site individual from 70 years of external gamma and radon exposures
is estimated to range from l.SxlO'5 for 3 pCi/g phosphogypsum applied at a rate of 500
Ibs/acre to LSxlO'3 for 15 pCi/g phosphogypsum applied at a rate of 10,000 Ibs/acre. Using
Scenario 7, the combinations of phosphogypsum application rates and Ra-226 concentrations
that yield an estimated lifetime risk of SxlO4 is plotted in Figure 4-5. For example, a
lifetime risk of 3xlO" will result when phosphogypsum, containing 1 pCi/g of Ra-226, is
applied at a rate of 25,000 Ibs/acre; whereas, to produce the same risk when the application
rate is 1,000 Ibs/acre will require a Ra-226 concentration of 30 pCi/g.
4.4.2 Phosphogypsum in Road Construction
The road construction scenarios evaluated in this risk assessment are shown
schematically in Figure 4-1. The results of the risk assessment of the use of phosphogypsum
in road construction are summarized in Tables 4-15 to 4-18. Estimated doses and risks for
Scenarios 8 and 9, involving the use of phosphogypsum in a road base, are shown in Tables
4-26
-------
10
-5.
10'
10
20
30
40
50
60
70
Concentration of Ra-226 in Phosphogypsum (pCi/g)
Figure 4-2. Risk assessment results for Scenario 7 -
radon exposure risks to the on-site individual as a function
of the Ra-226 content of phosphogj psum for the six
application rates (Ibs/acre) shown in parenthesis
4-27
-------
10 -.
•
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X
-------
£
1
10
-5
) 10 20 30 40 50 60 70
Concentration of Ra-226 in Phosphogypsum (pCi/g)
Figure 4-4. Risk assessment results for Scenario 7 -
total radon and gamma exposure risks to the on-site individual
as a function of the Ra-226 content of phosphogypsum for the
six application rates (Ibs/acre) shown in paraenthesis
4-29
-------
Figure 4-5. Application rate of phosphogypsum as a/unction of Ra-226
concentration for a lifetime risk of 3x10-*.
£
u
CO
£
25
20
15
10
£ 5
5 10 15 20 25
Radium-226 Concentration (pCi/g)
30
4-30
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4-15 and 4-16. Estimated doses and risks for Scenarios 10, and 11, involving the use of
phosphogypsum in both a concrete road surface and a road base, are shown in Tables 4-17
and 4-18.
In evaluating the risk to the construction worker from external gamma radiation four
cases were analyzed - two in which the worker stands directly on the roadbed for the entire .
work day (no shielding), and two in which the worker uses equipment, such as a road
grader which provides some protection from external gamma radiation (with shielding)
-These four cases are considered to bracket the worker doses which could be received from
external gamma radiation. Worker doses for Scenarios 8 and 9 were evaluated for the case
of no asphalt cover over the roadbed to maximize the results of the dose calculations
Worker doses from dust inhalation were evaluated for a humid site, (with characteristics
typical of a southeastern site) and a dry site (with characteristics typical of a southwestern
Reclaimer doses were evaluated for a time (presumed to be 50 years after road
construction) when the road is closed and the road' surface has crumbled and been removed
The reclaimer is assumed to live in a house constructed on the site and to obtain 50 percent
of his food from a garden grown on the site. Indoor radon doses to the reclaimer were
evaluated for both a humid site and a dry site.
For the road construction scenarios, the highest doses and risks result from external
gamma exposure and indoor radon inhalation to the reclaimer. For Scenarios 8 and 9 the
lifetime risk to the reclaimer from one year of external gamma exposure is estimated to range
from 2.6x10- for 26 pCi/g phosphogypsum to 3.2xia6 for 3 pCi/g phosphogypsum The
lifetime risk from one year of indoor radon inhalation is estimated to range from 6 2xias for
26 pCi/g phosphogypsum to 7.5xlO-6 for 3 pCi/g phosphogypsum;
For Scenarios 10 and 11, the lifetime risk to the reclaimer from one year of external
gamma^exposure is estimated to range from S.lxlQ-5 for 26 pCi/g phosphogypsum to
5.9x10- for 3 pCi/g phosphogypsum. The lifetime risk from one year of indoor radon
inhalation is estimated to range from S.lxlO'5 for 26 pCi/g phosphogypsum to 9 3xia6 for 3
pCi/g phosphogypsum.
4-4.3 Phosphogypsum in Research & Development Activities
The results of the risk assessment of the use of phosphogypsum in Research &
Development activities are summarized in Table 4-19. For the Research & Development
scenario (Scenario 12), 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
4-35
-------
8.
-8
4-36
-------
construction scenarios. The greatest risk to the researcher is estimated to be from indoor
radon inhalation. The indoor radon inhalation risk is estimated to range from 2.1xlO'5 for 26
pCi/g phosphogypsum to 2.4xlQ-6 for 3 pCi/g phosphogypsum.
4.4.4 Ingestion of Treated Soil
A final risk assessment was conducted of ingesting soil that had been treated with
phosphogypsum. Two scenarios are considered: Scenario 13, which assumes a biennial
application rate for 100 years of 664 kg/acre of phosphogypsum containing 10 pCi/g Ra-226,
and scenario 14, which assumes an initial application of 8,000 kg/acre of phosphogypsum
containing 26 pCi/g Ra-226 followed by biennial applications of 4,000 kg/acre for 100 years.
These application rates are the same as those used for scenarios 1/2 and 5/6, respectively
(see Section 4.3.3.1). The detailed calculations and the results of this risk assessment are
provided in Appendix C. The exposure periods and soil ingestion rates selected for this
assessment are also listed in Appendix C.
The total estimated risks for each scenario are given in Table 4-20. The estimated
risks from ingesting treated soil are small in comparison to those estimated earlier in this
section for exposure to either direct gamma radiation or indoor radon-222. As might be
expected, the highest estimated lifetime risk, 7.4E-6, is for a 70-year exposure period
combined with using the phosphogypsum containing the highest Ra-226 concentration, 26
pCi/g. This risk is similar to that estimated for exposure to either direct gamma radiation or
indoor radon when phosphogypsum containing only 3 pCi/g Ra-226 is applied at a rate of
227 kg (500 Ibs) per .acre (see Tables 4-12 and 4-13). Over 85 percent of the total risk is
due to the presence of Pb-210 and Po-210, while the Ra-226 present contributes only about
10 percent of the risk.
Table 4-20. The estimated total risks due to the ingestion of soil treated with
phosphogypsum00. -
(a)
(b)
Condition
Scenario 13
Scenario 14
Results from
Lifetime risk
Exposure Period00
70 year 30 year
1.9E-6 8.8E-7
7.4E-6 3.5E-6
Appendix C.
for the specified exposure period.
9 year
3.7E-7
1.5E-6
4-37
-------
-------
5. AVAILABILITY AND COSTS OF COMPETING MATERIALS
5.1 PEANUT FARMING IN GEORGIA
5.1.1 Availability
Georgia grows almost half of the peanuts produced in the United States. Of the more
than 600,000 acres of peanuts grown in Georgia, approximately a third require some form of
gypsum. Traditionally, 60-70% of that demand has been supplied by phosphogypsum
(GDA90). But since the ban on phosphogypsum, there have been numerous entrants into the
Georgia market for gypsum materials, even though there have been waivers for the
agricultural use of phosphogypsum. New products in the Georgia ^rea include: Nutcracker-
a by-product of sulfuric acid neutralization distributed out of Tampa, Florida; Kemira~an
industrial acid neutralization product distributed out of Savannah, Georgia; and Fluorolite-
another acid neutralization product distributed out of Louisiana and Alabama. According to
Agrobusiness, one of the largest distributors of gypsum materials in Georgia, these new
products, as well as pure gypsum products, are abundant and available in the Georgia peanut
growing area (JA91).
5.1.2 Cost
Dr. Carley, an agricultural economist at the University of Georgia, presented cost and
effectiveness data for different types of gypsum fertilizers, including phosphogypsum, during
public testimony on the limited reconsideration and proposed rule NESHAP for radionuclide
emissions from phosphogypsum stacks in May 1990. He compared the four phosphate
fertilizers in Table 5-1 with a control (no gypsum material added) to determine the economic
return when using the four different types of gypsum materials. Carley found that
phosphogypsum gave the highest return at $1218 per acre. U.S.G. 500, a gypsum product
still available on the Georgia market today, provided a slightly lower return of $1212 per
acre. The other two products analyzed, granular and pelleted substances, gave significantly
lower returns.
By analyzing Dr. Carley's information, it is possible to compare the cost of increasing
peanut yield from the control level for each of the gypsum materials. This comparison is
shown in Table 5-2. Phosphogypsum provides.the lowest cost per pound of peanuts when
increasing yield. Gypsum costs are 1 cent for every pound of increased peanut yield if
phosphogypsum is used as the source of gypsum. It costs four times as much, 4 cents per
pound, to increase crop yield using U.S.G. 500. The two other materials, granular and
pelleted substances, have considerably higher costs per pound to provide an increased yield.
Further analysis of phosphogypsum cost compared to substitutes "is presented in Table
5-3. The analysis makes no assumption about comparative yield when using one gypsum
fertilizer or another. It presents cost indices for gypsum materials competitive with
phosphogypsum. Only two products, Fluorolite and Nutcracker have indices less than 1.
5-1 . - .
-------
Table 5-1. Pod yields per acre of peanuts for various gypsum materials, estimated cost of
various materials and estimated net return, Georgia.
Gypsum Material00
Experimental
Yields
(pds/acre)(a)
Control (no gypsum material) 2708
Phosphogypsum - Occiwet.
Crystalline - U.S.G. 500
Granular - Abssgram
Pelleted - Abpellet
3917
4000
3091
2768
Gross
Return
($/acre)w
854
1236
1262
975
873
Cost of
Gypsum
Material
($/acre)(c)
0
17.5
50
45
37.5
Return Minus
Gypsum Cost
($/acre)
854
1218
1212
930
835
(c)
From reference A189.
Priced at 1990 quota support price of $631 per ton, no adjustment made for grade.
Based on Carley's personal communication with Coastal Plain Experimental Station
research personnel; 1990 price quotations. Costs include transportation costs to Tift
County Georgia.
Kemira is identically priced to phosphogypsum, with a cost index of 1. All of the other
gypsum products are at least two and one-half times as expensive as phosphogypsum, with
cost indices of 2.69 or greater. These cost indices are misleading, however, because they do
not include transportation costs in the cost of the fertilizer. The two products which seem
most competitive with phosphogypsum are both produced great distances from the Georgia
peanut growing district ~ in Tampa, Florida and Geismar, Louisiana. The Table 5-3 cost
indices were revised by including estimated transportation costs from the point of sale to
Tifton, Georgia for each of the fertilizers. The new cost indices are shown in Table 5-4.
Tifton, Georgia was chosen as the final destination for determining transportation costs
because it is in the center of the Georgia peanut growing area. The revised fertilizer cost
indices show that no gypsum treatments are less expensive than phosphogypsum. Only
Kemira, with a cost index of 1.28 approaches phosphogypsum. All other applications cost at
least twice as much as phosphogypsum, with the exception of A.C.G.2000 and Nutcracker
which cost 1.86 and 1.95 times as much as phosphogypsum, respectively.
As different soil amendments are not applied at the same rate, the application rate
should be considered in the comparative pricing of different products. For example, the
University of Georgia Cooperative Extension Service recommends a minimum application
5-2
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Table 5-2. Gypsum material cost per pound of peanuts for competing gypsum materials.
Gypsum Material Cost of
Material
($/acre)
None (Control)
Phosphogypsum - Occiwet.
Crystalline - U.S.G. 500
Granular - Abssgram
Pelleted - Abpellet
0
17.5
50
45
37.5
Experimental Change in
Yield Cost From
(pds/acre) Control
($)
2708
3917
4000
3091
2768
17.5
50
45
37.5
Change in
Yield From
Control
(pds)
1209
1292
383
60
Change in
Cost/Change
in Yield
($/pd)
0.01
0.04
0.12
0.63
Source: Table 5.1
Table 5-3. Fertilizer cost indices for competing materials relative to phosphogypsum at point
of sale. ' • -
Fertilizer
Phosphogypsum
U.S.G. 500
Gold Bond Bag (bagged)
(bulk)
Domtar (bagged)
(bulk)
A.C.G. 2000
Nutcracker
Kemira
Fluorolite
Granular (made from Kemira
by Florida Favorites)-
Point Price at Point
of of Sale
Sale(a) .($/ton)w
White Springs, FL
Brunswick, GA
Savannah, G A
Savannah, GA
Savannah, GA
Savannah, GA
Cordele, GA
Tampa, FL
Savannah, GA
Geismar, LA
Columbia, AL
Moultrie, GA
Macon, GA
13
38
41.5
35
47
35
40
10
13
7.5
47
63
63
Fertilizer Cost
Index
1.00
2.92
3.19
2.69
3.62
2.69
3.08
0.77
1.00
0.58
3.62
4.85
4.85
(a)
(b)
Prices obtained from a phone conversation with Jim Arnold of Agrobusiness in Albany,
Georgia on August 13, 1991.
The fertilizer cost does not include equipment and labor cost for applying the fertilizer
or transportation costs to the farm. Equipment costs can be considered the same for all
fertilizers, but labor costs are higher for the two dry gypsums, Gold Bond Bag and
Domtar, than for the damp gypsums.
5-3
-------
*^rJt\JOJCMfM«-*-«-CMCMCMM
0) O
u. o. *•»
'£ A
8.
in i. 15 •
•8 e £
5-4
-------
rate (broadcasting) for phosphogypsum and USG 500 of 1000 Ibs/acre and 750 Ibs/acre,
respectively (USG90). Thus, a complete comparative pricing for phosphogypsum and
substitute products will include their respective application rates. Table 5-5 presents the
results of such an analysis for phosphogypsum and three substitute materials. It is estimated
that USG 500 will cost $6.56 (about 55 percent) more per acre than phosphogypsum. Gold
Bond and Kemira are 132 and 150 percent more costly per acre, respectively, than
phosphogypsum.
Table 5-5. The comparison of material costs per acre.
Material
Phosphogypsum
USG500
Gold Bond
Kemira
Costs (dollars/ton)
Product
(Table 5-3)
13
38
35
63
Transportation
(Table 5-4)
10.70
11.10
17.40
2.90
Application
Rates
(Ibs/acre)
(USG90)
1000
750
1050
900
Cost
($/acre)
11.85
18.41
27.51
29.66
Cost/Acre
Differential
($)
0
6.56
15.66
17.81
5.2 PEANUT FARMING IN NORTH CAROLINA
The North Carolina Agricultural Extension Service recommends that gypsum be
applied to all peanuts regardless of soil type or soil nutrient levels. Although soil calcium is
usually sufficient for good plant growth, it is inadequate for pod development and good
quality peanuts. Application rates are balanced with the calcium content of the gypsum.
Table 5-6 provides the application rates recommended by the North Carolina Agricultural
Extension Service for four forms of gypsum (NC90).
According to the Department of Agriculture of the State of North Carolina,
approximately two-thirds of peanut growers used phosphogypsum on crops in 1990. They
estimate that the banning of phosphogypsum for agriculture use on peanuts would cost North
Carolina peanut farmers approximately $2 million per year in producing 160,000 acres of
peanuts (Gr90). In March 1991, the North Carolina Peanut Growers Association wrote that
other gypsum sources may be available in North Carolina, but that "Phosphogypsum is less
expensive, easier to handle, and convenient (Su91)." The Plant Food Association of North
Carolina, which includes fertilizer manufacturers and dealers, materials suppliers, NC State
University Research and Extension, and NC Department of Agriculture, wrote in April 1990,
"Phosphogypsum provides a readily available and economical source of nutrients for our
5-5
-------
Table 5-6. Gypsum sources and application rates for peanuts in North Carolina.
Source
Bagged (finely ground)
420 Granular
By-Product Wet Bulk
Granular By-Product
Percent
Calcium
25
25
17
20
Application Rate
16-18 in. Band
600-800
600-800
—
750-1,000
(Ibs/acre)
Broadcast
—
1,200-1,600
1,800-2,300
1,500-2,000
Eastern North Carolina peanut crop. There are other sources available, but excessively
expensive (Yo90)."
5.3 PEANUT FARMING IN VIRGINIA
According to S. Mason Carbaugh, Commissioner of the Commonwealth of Virginia's
Department of Agriculture and Consumer Services, and his staff, "an adequate supply of
gypsum is available in Virginia to meet the needs of Virginia farmers (Ca90)." Carbaugh
investigated prices for substitutes and found a price of $24.30 an acre for gypsum from U.S.
Gypsum and $15.75 an acre for gypsum from Materials Byproducts, Inc. Phosphogypsum,
available in Virginia from Texasgulf, was comparatively priced at $15.75 an acre. All prices
are FOB at a dealer warehouse. The Virginia Farm Bureau Association estimates that
banning the use of phosphogypsum would cost southeast Virginia peanut farmers, who
currently use phosphogypsum, $20 more an acre for an alternative. The Association
estimates that this increased cost would translate into a cost of several million dollars a year
for the farmers of the approximately 100,000 acres of peanuts in Virginia (As90).
5.4 AGRICULTURE IN FLORIDA
AGRO Services International, Inc., under a grant sponsored by the Florida Institute of
Phosphate Research, researched the use of phosphogypsum as a fertilizer on several Florida
crops (AGRO89). As part of this study, AGRO Services completed field trials using various
rates and placement of phosphogypsum (holding constant the addition of other fertilizers
containing nutrients not in gypsum) in order to determine the yield response of several crops
to phosphogypsum. As well as determining yield response for each crop tested, AGRO
determined the economic returns due to the use of phosphogypsum on the crops. By
assigning a cost to phosphogypsum and its application, assigning a selling price to the tested
crops, and by using the percentage yield increases of the experiment, AGRO found that only
5-6
-------
cowpeas present a real risk in obtaining an economic return on investment in phosphogypsum
among the crops tested. See Table 5-7 for a summary of the AGRO study. Application of
phosphogypsum on the crops, other than cowpeas, is highly likely to result in strong
economic returns, because the percentage increases in the last column of Table 5-7 are
substantially higher than the break-even levels.. ',
5.5 AGRICULTURE IN IDAHO
Simplot operates a plant in Pocatello, Idaho. In 1988 Simplot sold approximately
40,000 to 50,000 tons of phosphogypsum for use on alfalfa, onion, and potato crops in
Idaho. In 1991, Simplot only sold approximately 4,500 tons of phosphogypsum for use on a
ranch which produces corn, potatoes, and wheat. Due to the regulatory uncertainty
surrounding the use and sale of phosphogypsum, they no longer promote sales (Mc91).
5.6 AGRICULTURE IN CALIFORNIA
According to The Fertilizer Institute, phosphogypsum is used on a variety of crops in
California including citrus, almonds, vegetables, and tomatoes. The 1988 sales of
phosphogypsum in California were 84,507 tons. The Fertilizer Institute estimates, however,
that 1990 demand for gypsum for agricultural use in California is at 500,000-750,000 tons
per year (TFI90b). Four Court, Inc., whose 1990 sales of phosphogypsum to California
sources were 50,000 tons, questions the use of alternative mined gypsum from Utah. They
suggest that mined gypsum from one Utah source contains high levels of uranium and
thorium (Se90).
5.7 ROAD BUILDING IN FLORIDA
5.7.1 Availability
In a study considering the use of phosphogypsum for secondary road construction, the
University of Miami writes, "Traditional road building materials, such as limerock,
shellrock, shell, and clay are in short supply in many parts of Florida. Significant tonnages
of aggregates used in road construction are now imported from foreign countries. The U.S.
Bureau of Mines has forecasted that Florida will have to import all its aggregate by the year
2000 (UoM89)." The study suggests phosphogypsum as an alternative. According to the
Florida Department of Transportation, however, limestone - the primary material used as a
roadbase in the state of Florida - is plentiful from local sources throughout the state of
Florida with a few exceptions. Natural sand-clay material and natural shellrock are also
available in limited supply in some areas (He91). Thus, there appears to be differing
opinions on the availability of roadbase materials in Florida, and the need for
phosphogypsum in road construction is unclear.
5-7
-------
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ra co
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•8
•8
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5-8
-------
5.7.2 Cost
The University of Miami in conjunction with the Florida Institute of Phosphate
Research constructed one and one-half miles of secondary road (Parrish Road) utilizing
phosphogypsum(UoM89). They then compared the costs of building the road to the costs
encountered in building two similar roads. The roads used for comparative purposes, Tanner
Road and Windy Hill Road, were built in Polk County about the same time as Parrish Road,
but were built with clay. The building of Parrish road was broken down into 9 tasks for
which economic data (labor, capital, and energy expense) were collected. The tasks
included: setting stakes and grading, hauling gypsum, spreading gypsum, boxing out and
shaping up, mixing subgrade and gypsum, watering, final blade, compaction, and foreman's
work. According to the analysis, the total cost for building Tanner Road and Windy Hill
Road were $98,339 per mile and $129,320 per mile, respectively.' In comparison, the cost
of building Parrish Road was $23,485 per mile. Figure 5-1 breaks these costs down by
vehicle, material, and labor costs. The road built with phosphogypsum materials has no
material costs as the road was built close to the source of the phosphogypsum and the
phosphogypsum was donated to the project. In order for the cost of building Parrish Road to
equal the cost of Tanner Road and Windy Hill Road, the amount of phosphogypsum
necessary to build one mile of road and the transportation of that amount of material would
have to cost $74,854 and $105,835, respectively.
It is possible to estimate the cost of phosphogypsum to construct one mile of roadway
using information provided in the BID; however, it is difficult to estimate the transportation
costs. Because the transportation cost is a function of the haulage distance, it is possible,
however, to estimate the distance phosphogypsum can be transported and not exceed the cost
of using conventional materials ($74,854 and $105,835). The following information was
provided earlier in this document.
• Roadbed Dimensions (Figure 4-1) - 0.25 m thick x 9.15 m wide x 1613 m long
• Roadbed Material Density (Table 4-5) - 2250 kg/m3
• Cost of Phosphogypsum (Table 5-3) - $13.00/ton .
• Transportation Cost (Table 5-4)-$0.10/ton-mile
Using this information, one mile of roadbed will contain 3690 m3 of material
weighing 9,151 tons. Phosphogypsum is usually mixed in various ratios with soil (clay/sand)
in roadbed preparation. The amounts of phosphogypsum required and its cost for three
commonly used mixtures are:
Phosphogypsum: Soil Mixture
1:2
1:1
2:1
Amount (tons)
3,050
4,576
6,101
Cost ($V
39,650
59,488
79,313
5-9
-------
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.2 CO
n_ Q.
CO >
Q. O)
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0 •
0)
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ccg
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E? £
u. •*-
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O
O
v.
O
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C3
U
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O
0)
•*-•
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CO
O
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O
O
CO
5-10
-------
Thus, the amount of money for transportation costs not to exceed the cost of Tanner
($74,854) and Windy Hill ($105,835) roads will be:
Phosphogypsum: Soil Mixture Tanner Road ($) Windy Hill Road ($)
1:2 35,204 66,185
1:1 15,366 46,347
2:1 -4,459 26,522
The distance phosphogypsum could be shipped and not exceed the cost of using conventional
materials is presented in Table 5-8.
Table 5-8. Estimated maximum distances phosphogypsum can be hauled for road use and
remain competitive with conventional materials.
Phosphogypsum: Soil Mixture
1:2
1:1
2:1
Tanner Road (miles)(a)
115
34
0
Windv Hill RoadCmilesV^
217
101
43
miles = Trans, dollars available 4- tons required x $ 0.10/ton-mile.
From this analysis, the economical advantage of using phosphogypsum in roadbed
construction is not conclusive, but will depend in great part on the transportation costs.
Therefore, the viability of using phosphogypsum in road construction will be dependent upon
the location of the phosphogypsum in relation to the road construction site and the
availability, cost, and location of competing materials.
5.8 RECLAIMING MINED LAND .
5.8.1 Availability
°\
Texasgulf produces phosphogypsum as a by-product at its wet phosphoric acid
producing plant in Aurora, North Carolina (Pe91). The company's chemical processing
facility is adjacent to their phosphate rock mine. In light of the proximity of the two sites,
the company spent time and energy developing a method to mix clay, separated from the
mined phosphate rock, and by-product phosphogypsum to reclaim mined land. This process,
although economical for Texasgulf, may not be economical for other companies because the
mines and the chemical processing plants of the other companies may not be close enough
5-11
-------
together to make the blending process economical, and the clay recovered from the phosphate
rock in other locations may not be suitable for this type of process.
5.8.2 Cost
Quantitative figures on the savings Texasgulf achieves by reclaiming mined land were
not available. However, obvious savings include the cost of building and maintaining
phosphogypsum stacks and clay settling ponds. Additionally, land reclaimed with the
phosphogypsum/clay blend is available for use sooner than when it is reclaimed with only
clay. Texasgulf estimates that land reclaimed with the phosphogypsum/clay mixture is
suitable for revegetation approximately 9 months after reclamation. Alternatively, land
reclaimed with only clay may take 20 plus years before it is suitable for revegetation.
5-12
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6. REFERENCES
AGRO89 AGRO Services International, Inc., "Use of Phosphogypsum Fortified With
Other Selected Essential Elements as a Soil Amendment On Low Cation
Exchange Soils", under a grant from the Florida Institute of Phosphate
Research, November 1989.
A189 Alva, A.K., Gascho, G.J. and Guang, Y., "Gypsum Material Effects on
Peanut and Soil Calcium," Communication in Soil Sci. Plant Anal. 20, 1727-
1744, 1989.
An88 Anderson, N, Mobil Mining and Minerals Div., personal communication with
Jack Faucett Associates, Bethesda, MD, June 14, 1988.
Ap88 Appel, B. D., Woodward-Clyde Consultants, Oakland, CA, written
communication, July 1988.
Ar91 Arnold, J., Agrobusiness, Albany, GA, personal communication with Jack
Faucett Associates, Bethesda, MD, August 13, 1991.
As90 Ashworth, C. W., President, Virginia Farm Bureau Federation, written
communication to U.S. Environmental Protection Agency, January 24, 1990.
Ba80 - Baird, J. V., and E. J. Kamprath, "Agricultural Use of Phosphogypsum on
North Carolina Crops", Presented at the International Symposium on
Phosphogypsum sponsored by Florida Institute of Phosphate Research, Bartow,
Florida, November 5-7, 1980.
Ba88 Baretincic, J. M., IMC Fertilizer, Inc4, Mulberry, FL, written communication
to T. R. Horton, SC&A, Montgomery, AL, June 1988.
BOM87 Bureau of Mines, "Minerals Yearbook", 1987.
BOM88 Bureau of Mines, "World Demand for Fertilizer Nutrients for Agriculture",
Open File Report, OFR 24-88, Department of the Interior, Washington, D.C.,
April 1988.
Ca90 Carbaugh, S. M., Commissioner, Virginia Department of Agriculture and
Consumer Services, written communication to U.S. Environmental Protection
Agency, May 21, 1990.
6-1
-------
Ch87 Chang, W. F., "Reclamation, Reconstruction, and Reuse of Phosphogypsum
for Building Materials", Florida Institute of Phosphate Research, Publication
No. 01-014-048, 1987.
Ch89 Chang, W. F., D. A. Chin, and R. Ho, "Phosphogypsum for Secondary Road
Construction", Publication No. 01-033-077, Florida Institute of Phosphate
Research, Bartow, Florida, June 1989.
Ch90 Chang, W. F., and M. I. Mantell, "Engineering Properties and Construction
Applications of Phosphogypsum", Phosphate Research Institute, University of
Miami Press, Coral Gables, Florida, 1990.
Co88 Cook, L. M., Chevron Chemical Co., written communication to R. Guimond,
Office of Radiation Programs, EPA, Washington, D.C., August 1988.
Coc88 Cochrane, J. F., J. R. Simplot Co., Pocatello, ID, written communication to
Doug Chambers, SENES Consultants, LTD., Richmond Hill, Ontario,
Canada, April 15, 1988.
Co92 Colli, A., Personal Communication, USEPA, Office of Radiation Programs,
Washington, D.C., January 15, 1992.
Da Daughtery, J. A., and F. R. Cox, "Effect of Calcium Source, Rate, and Time
of Application on soil Calcium Level and Yield of Peanuts", Paper No. 4352
of the Journal Series of the North Carolina Agricultural Experiment Station,
North Carolina State University, Raleigh, North Carolina, (no date).
Eng66 Engel, R. L., et al., "ISOSHLD, A Computer Code for General Purpose
Isotope Shielding Analysis", BNWL-2316, U.S. Department of Energy,
Richland, Washington, June 1966. .
EPA85 U.S. Environmental Protection Agency, "Report to Congress, Wastes From
the Extraction and Beneficiation of Metallic Ores, Phosphate Rock, Asbestos,
Overburden From Uranium Mining, and Oil Shale", EPA/530-SW-85-033,
1985.
EPA86 U.S. Environmental Protection Agency, "A Citizen's Guide to Radon: What it
is and What to do About it", U.S. Government Printing Office, Washington,
D.C., OPA-86-004, 1986.
EPA87 U.S. Environmental Protection Agency, "PATHRAE-EPA: A Performance
Assessment Code for the Land Disposal of Radioactive Wastes, Documentation
and Users Manual", EPA 520/1-87-028, Washington, D.C., December 1987.
6-2
-------
EPA88 U.S. Environmental Protection Agency, "Limiting Values of Radionuclide
Intake and Air Concentration and Dose Conversion Factors for Inhalation,
Submersion, and Ingestion", EPA 520/1-88-020, September 1988.
EPA89a U.S. Environmental Protection Agency, "NESHAPS for Radioriuclid.es -
Background Information Document - Volume 2", Office of Radiation
Programs, EPA/520/1-89-006-1, September 1989.
EPA89b U.S. Environmental Protection Agency, "Risk Assessment Methodology,
Environmental Impact Statement for NESHAPS Radionuclides, Volume 1,
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September, 1989.
EPA90 U.S. Environmental Protection Agency, "Report to Congress on Special
Wastes From Mineral Processing", USEPA, Solid Waste and Emergency
Response, EPA/530-SW-90-070C, July 1990.
Fi78 Fitzgerald, J. E. and Sensintaffar, E. L., "Radiation Exposure From
Construction Materials Utilizing Byproduct Gypsum-From Phosphate Mining",
Radioactivity in Consumer Products, U.S. Nuclear Regulatory Commission,
NUREG/CP0001, August 1978. '
FIPR87 Florida Institute of Phosphate Research, "Reclamation, Reconstruction, and
Reuse of Phosphogypsum for Building Materials", Publication No. 01-014-
048, Bartow, Florida, January 1987.
FIPR88 Florida Institute of Phosphate Research, Newsletter, Vol. VIII, No. 4, Winter
1988.
FIPR89a Florida Institute of Phosphate Research, "Phosphogypsum for Secondary Road
Construction", Publication No. 01-041-077, Bartow, Florida, June 1989.
FIPR89b Florida Institute of Phosphate Research, "Use of Phosphogypsum Fortified
With Other Selected Essential Elements as a Soil Amendment on Low Cation
Exchange Soils", Publication No. 01-034-081, Bartow, Florida, November
1989.
FIPR90a Florida Institute of Phosphate Research, "Use of Phosphogypsum to Increase
Yield and Quality of Annual Forages", Publication No. 01-048-084, Bartow,
Florida, May 1990.
FIPR90b Florida Institute of Phosphate Research, "Proceedings of the Third
International Symposium on Phosphogypsum". Two Volumes, Publication No.
01-060-083, Bartow, Florida, December 1990.
6-3
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GDA90 Georgia Department of Agriculture, written communication to U.S.
Environmental Protection Agency, May 17, 1990.
Go83 Golden, L. E., "Twenty-Five Years of Research in Soil Fertility and Nutrition
Studies with Sugar Cane in Louisiana", Agronomy Research Report No. 78,
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Gr90 Graham, J. A., Department of Agriculture, State of North Carolina, written
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GRO85 GROVE Engineering, Inc., "MICROSHIELD, User's Manual", Washington
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Gu75 Guimond, R. J. and Windham, S. T., "Radioactivity Distribution in Phosphate
Products, By-Products, Effluents, and Wastes", Technical Note ORP/CSD-75-
3, U.S. Environmental Protection Agency, Office of Radiation Programs,
Washington, D.C., August 1975.
He91 Hendricks, D., Soil Materials Engineer, Florida Department of Transportation,
Gainesville, FL, personal communication with Jack Faucett Associates,
Bethesda, MD, August 14, 1991.
Ho88 Horton, T. R., Blanchard, R. L., and Windham, S. T., "A Long-Term Study
of Radon and Airborne Particulates at Phosphogypsum Stacks in Central
Florida", U.S. Environmental Protection Agency Report, EPA 520/5-88-021,
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Jo88a Johnson, K., The Fertilizer Institute, Washington, D.C., written
communication to Barry Parks, USEPA, ORP, Las Vegas, NV, August 1988.
Jo88b Johnson, K., The Fertilizer Institute, Washington, D.C., written
communication to Barry Parks, USEPA, ORP, Las Vegas, NV, October 4,
1988.
Kr88 Kramer, C., Jack Faucett Associates, Bethesda, MD, written communication
to T. R. Horton, SC&A, Inc., Montgomery, AL, June 24, 1988.
L185 Lloyd, G. M., "Phosphogypsum - A Review of the Florida Institute of
Phosphate Research Programs to Develop Uses for Phosphogypsum", Florida
Institute of Phosphate Research, Publ. No. 01-000-035, December 1985.
6-4
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L191 Lloyd, M., Florida Institute of Phosphate Research, Bartow, PL, personal
communication with R. Blanchard, SC&A, Inc., Montgomery, AL, August 8,
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Mc91 McGinnis, J., Simplot Co., personal communication with Jack Faucett
Associates, Bethesda, MD, August 14, 1991.
Mi89 Miller, W. P., "Use of Gypsum to Improve Physical Properties and Water
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of Phosphate Research, Bartow, Florida, December 1989.
Mi91 Miller, W.P. and Sumner, M.E., "Impacts From Radionuclides on Soil
Treated With Phosphogypsum", Final Report, Agronomy Department,
University of Georgia, Athens, GA, April 28, 1992.
Mo90 Moisset, J., "Complete Removal of Radium From Phosphogypsum",
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sponsored by Florida Institute of Phosphate Research, Bartow, Florida,
December 1990.
NC90 North Carolina Agricultural Extension Service, "Peanuts 1990", North
Carolina State University, Agricultural Extension Service, Publ. AG-331,
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Oa85 Gates, K. M., and A. G. Caldwell, "Use,of By-Product Gypsum to Alleviate
Soil Acidity", Soil Sci. Soc. Am. J., Vol. 49, pp 915-918, 1985.
Pe85 Penn, N., "Utilization of the Phosphogypsum Produced in the Fertilizer
Industry", United Nations Industrial Development Organization,
UNTOO/IS.533, May 1985.
Pe91 Peacock, B., Texasgulf, Aurora, NC, personal communication with Jack
Faucett Associates, Bethesda, MD, August 13, 1991.
PEI85 PEI Associates, Inc., "Data Describing Phosphogypsum Piles", EPA
Contractor Report, Contract No. 68-02-3878, Work Assignment No. 10,
Cincinnati, OH, May 1985.
Po90 Post, Buckley, Schuh and Jernigan, Inc., "Radiological Evaluation of Farm
J^ands Amended With Phosphogypsum in Bainbridge, GA", Post, Buckley,
Schuh, and Jernigan, Inc., Orlando, FL, October 1990.
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Ro87a Roessler, C.E., "The Radiological Aspects of Phosphogypsum", Proceedings
of the Natural Radiation and Technologically Enhanced Natural Radiation, in
Florida Symposium, Winter Haven, Florida, May 1987.
Ro87b Roessler, C.E., "Gamma Radiation and Radon Flux From Roads Constructed
With Bases Having Phosphogypsum- Bearing Aggregates", Department of
Environmental Engineering Sciences, University of Florida, Gainesville, FL,
Draft, November 30, 1987.
Ro88 Roessler, C.E., "Radiological Assessment of the Application of
Phosphogypsum to Agricultural Land", Proceedings of the Second
International Symposium on Phosphogypsum, January 1988.
SCA91 S. Cohen and Associates, Inc., "Diffuse Norm Wastes - Waste
Characterization And Risk Assessment (Draft)", Prepared for U.S.
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Radon Branch, personal communication to R. Blanchard, SC&A, Inc.,
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Se90 Sepehri-Nik, E., Four Court, Inc., written communication to U.S.
Environmental Protection Agency, January 18, 1990.
Si88 Simplot Company, written communication from J.F. Cochrane, J.R. Simplot
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Hill, Ontario, Canada, April 15, 1988.
SP88 Standard and Poor's, "Chemical: Basic Analysis", Industry Surveys. Section 3,
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Su80 Summer, M. E., W. P. Miller, D. E. Radcliffe, and M. McCray, "Use of
Phosphogypsum as an Amendment for Highly Weathered Soils", Proceedings
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Environmental Protection Agency, March 12, 1991.
TFI89 The Fertilizer Institute, "Fertilizer Facts and Figures", Washington, D.C.,
1989.
6-6
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TFI90a The Fertilizer Institute, "Comments to the U.S. Environmental Protection
Agency Concerning Noticrof Limited Reconsideration And Proposed Rule -
NESHAPS for Radionuclides Reconsideration: Phosphogypsum", Docket No.
A-79-11, 1990.
TFI90b The Fertilizer Institute, Comments submitted to the U.S. Environmental
Protection Agency, June 11, 1990.
TVA86 Tennessee Valley Authority, "Fertilizer Trends", TVA/OACD-86/12, Bulletin
Y-195, Muscle Shoals, Alabama, October 1986.
UoM89 University of Miami, "Phosphogypsum for Secondary Road Construction",
under a grant from the Florida Institute of Phosphate Research, June 1989.
USG90 United States Gypsum Company, "Comments to the U.S. Environmental
Protection Agency on NESHAPS for Radionuclides Reconsideration;
Phosphogypsum 55 Fed. Reg. 13480 (April 10, 1990)", with Exhibit D - The
University of Georgia Cooperative Extension Service, Gypsum Sources For
Seed Peanuts, Docket No. A-79-11, June 18, 1990. '
Va89 Van De Verg, E., "Economic Analysis - Proposed NESHAPS for
Radionuclides", Chapter 9, Jack Faucett Associates, Bethesda, MD, February
10, 1989.
Wa88a Walker, R., Freeport Chemical Company, Uncle Sam, LA, oral
communication to T.R. Horton, SC&A, Montgomery, AL, January 1988.
Wa88b Walker, R., Freeport Chemical Company, Uncle Sam, LA, oral
communication to T.R. Horton, SC&A, Montgomery, AL, July 1988.
Wa89 Warrington, D., I. Shainberg, M. Agassi, and J. Morin, "Slope and
Phosphogypsum's Effects on Runoff and Erosion", Soil Sci. Soc, Am. J., Vol.
53, pp 1201-1205, 1989.
Yo90 Younts, C., President, Plant Food Association of North Carolina, Raleigh,
NC, written communication to U.S. Environmental Protection Agency, April
27, 1990.
6-7
-------
-------
APPENDIX A
PATHRAE PATHWAY EQUATIONS
A-l
-------
APPENDIX A
PATHRAE Pathway Equations
A.I PROGRAM DESCRIPTION
The PATHRAE methodology models both offsite and onsite pathways through which man
can come in contact with the waste. For each of the pathways, the dose from each nuclide is
calculated as a function of time. These doses are then summed to give the total dose for the
pathway. The dose to the CPG from all pathways is then computed, assuming the entire nuclide
inventory is accessible through each pathway.
In this assessment, the PATHRAE code considered eight pathways by which radioactivity
may reach humans. These pathways were:
1. Ground water migration with discharge to a river.
2." Groundwater migration with discharge to a well.
3. Surface erosion of the cover material and subsequent contamination of
surface water.
4. Food grown on the site.
5. Direct gamma exposure.
6. Inhalation of radioactive dust on site.
7. Inhalation of radon gas and radon daughters on site.
8. Inhalation of radioactive particulates offsite (dust resuspension).
A.2 PATHWAY EQUATIONS
The equations used to calculate the doses, D, for each of the eight pathways are presented
in this section. References are given to aid the reader in understanding the assumptions on
which the equations are based and, where appropriate, some discussion is given of the important
features of the equations. In general, the equations can be grouped into three components
representing the waste form or release rate, the transport pathway, and environmental uptake.
For simplicity, the results of the environmental foodchain analysis are represented in the
equations by the symbol, U, called the equivalent uptake factor.
A.2.1 Pathway One - Groundwater to a River
Groundwater migration with discharge to a river is calculated from the following equation:
A-2
-------
D =
QV«U,(DF)
(A-l)
where
f°
V
u,
DF
= inventory of the isotope available in a given year (pCi)
= flow rate of the river (rnVyr)
= fraction of inventory arriving at the river from transport through the aquifer
= fraction of each nuclide leached from the inventory in a year (1/yr)
= annual equivalent uptake by an individual (m3/yr)
= dose conversion factor (mrem/pCi)
The components of the equation are:
Release Rate = Q XL
Transport Pathway = f0
Environmental Uptake = Uj / qw (DF)
The term f0 can be calculated for dispersive groundwater transport using two methods.
For the first case, a constant fraction leach model is used to obtain a non-dispersion solution,
which is modified by the Hung Correction Factor(4) to obtain a dispersion solution form for f0
given by:
f0 =0 fort <"t, - t0
fo = T^- [l-expE-VCt-Ctj-g)]] for t,-t0
-------
kj = sorption coefficient in the aquifer (mVkg)
p = aquifer density (kg/m3)
Fh = correction factor for dispersion
XL = length of waste site in direction parallel to aquifer flow (m)
v, = interstitial horizontal aquifer velocity (m/yr)
xw = distance of groundwater flow for nearest edge of burial pits to the river (m)
p = aquifer porosity.
The term Fh is strictly applicable to a time integration of the release and is given by:(4)
(L+0.5xw)
R = exp
2D
va2
(A-3)
where
D.
u
= longitudinal dispersivity (m)
= RXD,
For dispersive groundwater transport a band release leaching model is used and f0 is given by:(5)
fo = E [ Fj
where
Fj(t)
U(t)
z+
= 0.5 U(t) [erfc (z-) + exp(dj) erfc (z+)]
= unit step function
N
2/t/(Rtwj)
= distance from sector center to access location, divided by the dispersity
= water travel time from sector center to access location (yr)
= number of mesh points in numerical integration.
The numerical integration referred to above is a means by which the point source
analytical solution for dispersive transport can be extended to approximate an area source. The
A-4
-------
disposal facility of length L is divided into N sectors of equal length. A point source of the
appropriate magnitude is placed at the center of each sector. The distance, djh, is proportional
to the distance from the center of sector j to the access location. The point source analytical
solutions are then summed over all sectors to approximate an area source.
A.2.2 Pathway Two - Groundwater to a Well
Groundwater migration with discharge to a well is calculated from:
QXLf0U2(DF)
(A-5)
The aquifer dilution water flow rate qw is given, in this case, by:
Qw
WLP for Hw > Lp
WLV.p for Hu
(A-6)
where
W = width of waste pit perpendicular to aquifer flow (m)
L = length of waste pit parallel to aquifer flow (m)
P = water percolation rate (m3/m2-yr)
Lp = length of well casing in aquifer (m)
Hw — vertical dimension of contaminated zone in aquifer (m)
va = horizontal velocity of aquifer (m/yr)
p = aquifer porosity
U2 = annual equivalent total uptake of well water by an individual (m3/yr).
The vertical dimension of the contaminated zone, Hw, is related to the other parameters as
follows:
P L
H.
P Va
A well that intercepts the contaminated zone of the aquifer may also draw in uncontaminated
water if the length of the well casing, Lp, exceeds Hw. This is why Equation A-6 gives two
forms for the dilution rate based on the relative magnitudes of H,, and Lp. In the general use
A-5
-------
of PATHRAE, the factor U2 differs from U, in that contaminated seafood is not included.
In addition to modeling the effects of longitudinal dispersion in the aquifer, the well
pathway can account for any transverse dispersion that may occur. This reduces the
conservatism when calculating nuclide doses for the well pathway. When modeling transverse
dispersion, the term f0 in Equation 2-5 is modified by an additional multiplicative term, ft, given
by:
F, - ^ erf
2i/D t
W/2)R i
-j erf
" W/2)R
2t/D t
(A-7)
where
yw = distance to well from center of water area in the direction perpendicular to
the aquifer flow (m)
Dy = transverse dispersion coefficient (m2/yr).
For the limiting case in which Dy goes to zero, ft> becomes equal to one. Therefore, the
effects of transverse dispersion can be ignored by choosing Dy equal to zero.
The groundwater pathways to the (river and the well) can also accommodate transport
in the vertical unsaturated zone between the waste and the aquifer. This is accomplished in the
same manner as in the PRESTO codes.*2-4' The vertical water velocity and retardation are given
by:
V = P/(pS)
R = 1 +
(A-8)
p*s
where
S = fraction of saturation.
The term S can either be input or calculated from the expression:
S = Sr + (1 - Sr) Jl
SNO
(A-9)
where
Sr = residual saturation
SNO = soil index
A-6
-------
Kh = vertical zone saturated hydraulic conductivity (m/yr).
A.2.3 Pathway Three - Erosion and Transport to a River
The dose for sheet erosion of cover material and waste and its subsequent deposition in
a nearby river is given by:
D =
(A-10)
where
fdil = fraction of solids entering river that originated in waste trenches (calculated
internally in the code)
fe = fraction of waste eroded each year
qw = river flow rate (m3/yr). ,
The parameter fe is calculated from the surface erosion rate, Er, which is an input
variable, according to the relation fe = £/!„,, where ^ is the waste thickness (m) and Er is
expressed in m/yr.
A.2.4 Pathway Four - Food Grown Onsite
The equation for D for food grown over the disposal site is:
D =
QfdfE(DF)U3
(A-ll)
V
where
V
Ps
fd
fg
u,
= volume of waste (m3)
= soil density (kg/m3)
= dilution factor representing the dilution of waste in the soil
= fraction of individual's diet consisting of food grown over the disposal site
= total equivalent uptake factor for food (kg/yr).
Equation A-ll assumes that at some future time a reclaimer moves onto the waste
disposal site and builds a house. By excavating a basement for the house and by drilling a well
on the property, some of the waste material is brought to the surface and is mixed with the
A-7
-------
surface soil to some depth (tg). Using these assumptions, the factor fd representing the dilution
of waste in the surface soil is given by:
where
(A-12)
tm - tc x tw
ls
[H
tg
A' -1
Aw
A,
Ah
/*«/
= thickness of the waste (m)
= dilution of waste in the trench before reclaimer activities occur
= thickness of cover (m)
= depth of maximum mechanical disturbance (m)
= depth to which contaminants are mixed with surface soil (m)
= lot area (m2)
= house area (m2)
= cross sectional area of wells drilled (m2).
The first term in the brackets of Equation A-12 is the component due to the excavation
of a basement. The second term is the well drilling component. A complete derivation of
Equation A-12 is given in Reference 6.
A.2.5 Pathway Five - Direct Gamma
The dose from direct gamma exposure to an intruder is calculated from:
D =
4E
fexp (8760)(DFG)
(A-13)
where
BOit)
= 1 +
gamma attenuation constant of the waste (1/m)
gamma attenuation constant of the cover (1/m)
A-8
-------
t,, = thickness of the waste (m)
tc = thickness of the cover (m)
f = fraction of the year the individual is exposed
A = plane area of the waste, the waste is assumed to be a circular horizontal plane
with the exposed individual standing at the center (m?)
E7 = weighted average gamma energy emitted by nuclide (MeV)
DFG = infinite ground plane dose conversion factor (mrem/hr per pCi/m2).
The function, B, in Equation A-13 is the gamma buildup factor which is used to account
for the effects of gamma-ray scattering in the waste and in the cover. It is an empirical relation
based on gamma scattering data at energies from 0.25 MeV to 1.0 MeV.w
The term in brackets in Equation A-13 accounts for self-shielding and buildup in the
waste.
The weighted average gamma energy is computed by taking the average of all gamma
energies emitted by a particular nuclide, each energy being weighted by its probability of
occurrence.
There are three alternatives available when calculating direct gamma doses using
PATHRAE. The first alternative allows the calculation of the gamma dose from the undisturbed
buried waste. The second alternative assumes that plant roots penetrate the waste and transport
some nuclides to the surface. Each year the plants die and deposit their absorbed nuclides on
the ground surface, so there is continual transport of nuclides and deposition on the ground
surface. The gamma dose is calculated from the nuclides deposited on the surface, as well as
the nuclides remaining in the original burial trenches. The third alternative assumes that a
reclaimer builds a house and digs a well on the site, as is described under Pathway Five. This
brings some of the waste material to the surface where it is mixed with the existing soil. The
gamma dose is calculated from the waste on the surface and from the waste that remains
underground.
The three options in Pathway Five are selected by the value of the PATHRAE variable
IGAMMA which can have the value 0, 1, or 2.
A-9
-------
A.2.6 Pathway Six - Onsite Dust Inhalation
by:
The dose, D, for the inhalation of resuspended dust by an inadvertent intruder is given
(A-14)
where
pw = waste density (kg/m3)
pd = dust loading in the air breathed (kg/m3)
fexp = fraction of the year the individual is exposed to dust
U{ = volume of air breathed in a year (m3/yr)
V = total volume of waste (m3)
fd = dilution factor representing the dilution of waste in the soil.
The assumptions for this pathway are similar to those for Pathway Four. That is, a
reclaimer builds a house and drills a well over the waste site. The dose arises as a result of
inhalation of contaminated dust during the excavation of the house's basement and the drilling
of the well. As in Pathway Four, the dilution factor, fd, is calculated using Equation A-12.
A.2.7 Pathway Seven - Inhalation of Radon in Structures
The dose from inhalation of radon and radon daughters in a structure built over the waste
is calculated from:
D- Q
h\rVF
tanh(100bwtw)exp(-100b1t1 -
(A-15)
where
Q
E
h
r
V
inventory of Ra-226 (pCi)
fraction of radon which can emanate upward from the waste
height of rooms in structure built over the waste (cm)
air ventilation rate of the structure (air changes/sec)
volume of waste (m3)
A-10
-------
X
tw
tl
t2
D
= decay constant of radon (I/sec)
= waste thickness (m) >: ;
= thickness of earthen cover (m)
= thickness of concrete floor in reclaimer house (cm)
= radon diffusion coefficient of the waste (cm2/sec)
= radon diffusion coefficient of the cover (cnWsec)
= radon diffusion coefficient of concrete floor (cm2/sec)
= /X/D. (i = w, 1, 2)
j.
2
J.
2
2
1 + A/a, tanh(bwtw)
tanh(bt)
exp(-2(100 b,t, + b
. • a, = pf-Djl -(l-k)mi]2
m = 0.01 Mp/p
M = moisture content (dry weight percent)
k =0.26 pCi/m3 in water per pCi/m3 in air
p . = porosity
Uj = total volume of air breathed in a year (m3/yr).
A.2.8 Pathway Eight - Atmospheric Transport of Contaminants
The dose from the inhalation of airborne contaminants from dust resuspension (also valid
for incinerator or trench fire) is given by:
" X ''
W
D = r f, f
V f v
\ (df)
(A-16)
where
= dust resuspension rate or burn rate of incinerator or trench fire (m3
waste/sec)
A-ll
-------
ff
X
Q'
= deposition velocity for dust resuspension (m/sec) or fraction of the year the
burning occurs for incinerator and trench fire
= nuclide-specific volatility factor for incineration or trench fire (fraction of
nuclide released to atmosphere)
= downwind atmospheric concentration (pCi/m3)
= atmosphere source release rate (pCi/sec).
PATHRAE uses Gaussian plume(9) expressions for X/Q':
w
2irx
(A-17)
where
fw = fraction of time wind blows in direction of interest
crw = standard deviation of plume concentration in vertical direction (m)
u = average wind speed (m/sec)
n = number of sectors or wind directions (usually 16)
x = distance'from source to receptor (m)
h = effective release height including momentum and thermal plume rise effects
(m).
Plume depletion effects from deposition are represented by a reduced source release rate
calculated internally to the code.(9)
The actual release height is modified to account for momentum and thermal plume rise
effects by the following equations:(9)
1.5 v. d
(A-18)
where
actual release height (m)
stack gas velocity (m/sec)
stack inside diameter (m)
A-12
-------
QH = heat emission rate from stack (cal/sec).
Equation A-18 is valid as long as the distance to the receptor location is less than ten
times the stack height. For greater distances the receptor distance, x, is replaced with 10 K,.
If some parameters are unknown or poorly characterized, a default option, based on the
location of the maximum plume concentration, is used. In this case:
_X_ = 2
Q' Th2eu
(A-19)
where
= Euler's number (2.71828).
Equations A-17 and A-19 are from Reference 10 and are expressions for point sources.
For the trench fire scenario it is assumed that the fire involves a relatively small amount of
waste (for example, the amount received by the facility in one day). For an incinerator the only
source is a single incinerator stack. Since the extent of the source is small in these cases, the
use of the point source expression is justified.
If an area source is desired it can be represented by the virtual point source
approximation, where x is replaced by x', given by(1)
x' = x + 1.5137 y
where
= width of the facility (m)
The
-------
Appendix A References
1. U.S. Environmental Protection Agency, "Radiation Exposures and Health Risks Resulting
From Less Restrictive Disposal Alternatives for Very Low-Level Radioactive Wastes,"
U.S. Environmental Protection Agency report, (in press).
2. M.W. Grant, et al., "PRESTO-CPG: Users Guide and Documentation for Critical
Population Group Modifications of the PRESTO Code," U.S. Environmental Protection
Agency report, (in press).
3. U.S. Nuclear Regulatory Commission, "Calculation of Annual Doses to Man From
Routine Releases of Reactor Effluents for the Purpose of Evaluating Compliance with 10
CFR Part 50," Appendix I, Regulatory Guide 1.109, March 1976 and October 1977.
4. "PRESTO-EPA-POP: A Low-Level Radioactive Environmental Transport and Risk
Assessment code - Methodology Manual," EPA 520/1-85-001, 1985.
5. H.C. Burkholder and E.L.J. Rosinger, "A Model for the Transport of Radionuclides and
Their Decay Products Through Geologic Media," Nucl. Techl. 150. 1980.
6. V.C. Rogers, et al., "Low-Level Waste Disposal Site Performance Assessment with the
RQ/PQ Methodology," Electric Power Research Institute report, NP-2665, December
1982.
7. K.Z. Morgan, I.E. Turner (eds), "Principles of Radiation Protection," John Wiley &
Sons, Inc., p. 270, 1967.
8. V.C. Rogers and K.K. Nielson, "Radon Attenuation Handbook for Uranium Mill
Tailings Cover Design," U.S. Nuclear Regulatory Commission report NUREG/CR-3533,
February 1984.
9. R.E. Moore, et al., "AIRDOS-EPA: A Computerized Methodology for Estimating
Environmental Concentrations 'and Dose to Man from Airborne Releases of
Radionuclides," EPA 520/1-79-009, December 1979.
10. D.H. Slade (ed.), "Meteorology and Atomic Energy," U.S. Atomic Energy Commission
report, July 1968.
11. V.C. Rogers, et al., "A Radioactive Waste Disposal Classification System - The
Computer Program and Groundwater Migration Models," U.S. Nuclear Regulatory
Commission report NUREG/CR-1005, V-2, September 1979.
A-14
-------
APPENDIX B
RA-226 SOIL CONCENTRATION CALCULATIONS
B-l
-------
APPENDIX B
Ra-226 Soil Concentration Calculations
Radium-226 soil concentrations, resulting from periodic applications of
phosphogypsum, can be calculated by solving a standard mass balance equation:
dC
dt
= K - kC
The solution to equation B-l is obtained through standard differential equation
solution techniques, and is found to be:
C = . (1 - e-*)
(B-l)
(B-2)
Using the boundary condition of C=0 at t=0, the arbitrary constants can be solved
for. The resulting solution then becomes:
where
k;
W
k2
k3
k C
Cs = ! PG *
W
1
Cs
k4 + k5)
(B-3)
Ra-226 concentration in soil (pCi/g)
Ra-226 concentration in phosphogypsum (pCi/g)
application rate of phosphogypsum (g/yr)
mass of soil (g)
Ra-226 decay rate (4.3X104 yr1)
rate loss of Ra-226 due to uptake by plants (2.6xlO~6 yr1)
IQ, = rate loss of Ra-226 by leaching (2.8xlO"5 yr1)
ks = rate loss of Ra-226 by wind erosion (8.9X104 yr1)
Using the data in the table presented below, the Ra-226 soil concentration can be
calculated after 100 years of biennial phosphogypsum application.
B-2
-------
Table B-l. Ra-226 soil concentration calculation parameters.
Parameter
My'1)
k3 (yr1)
k.Cyr1)
k5 (yr1)
k; (g/yr)
t (yrs)
W(g)
CpL (pCi/g)
Scenario 1 & 2
4.3E-04
2.6E-06
2.8E-05
8.9E-04
4.6E+07
100
1.9E+.11
30
Scenario 3 & 4
4.3E-04
2.6E-06
2.8E-05
8.9E-04
l.OE+09
100
2.8E+12
30
Scenario 5 & 6
4.3E-04
2.6E-06
2.8E-05
8.9E-04
1.1E+09
100
l.OE+12
30
A summary of the Ra-226 soil concentrations calculated for scenarios 1-6 is presented
in Table B-2.
Table B-2. Ra-226 soil concentrations.
Scenario
1 & 2
(Agriculture: Average Case
3 &4
(Agriculture: Maximum Case)
5&6
(Soil Amendment)
Ra-226 Concentration fpCi/g)
0.69
1.02
3.12
B-3
-------
-------
APPENDIX C
RISK ASSESSMENT FOR THE INGESTION OF TREATED SOIL
C-l
-------
APPENDIX C
Risk Assessment for the Ingestion of Treated Soil
The risks that result from the direct ingestion of treated soil has been estimated using
the following information:
1. Exhibit 6-14 of the Superfund Risk Assessment Guidance handbook
a. Ingestion Rate - 200 mg/d 1-6 yrs of age
- 100 mg/d 6-70 yrs of age
- 365 days/yr
b. Exposure Periods
- 70 yrs - lifetime
- 30 yrs - 90 percentile residency
- 9 yrs - national average residency
c. Total Uptake
9 Year Exposure
(200 mg/d)(365 d/y)(6 y)+(100 mg/d)(365 d/y)(3 y)= x mg
438,000 mg + 109,500 mg = x mg
547,500 mg = x mg
547.5 g
30 Year Exposure
(200 mg/d)(365 d/y)(6 y)+(100 mg/d)(365 d/y)(24 y)= x mg
438,000 mg + 876,000 mg = x mg
1,314,000 mg = x mg
1,314 g
70 Year Exposure
(200 mg/d)(365 d/y)(6 y)+(100 mg/d)(365 d/y)(64 y)= x mg
438,000 mg + 2,336,000 mg = x mg
2,774,000 mg = x mg
2,774 g
C-2
-------
Table C.I. Scenario 13 - Based on 10 pCi Ra-226/g of phosphogypsum applied at the rate
of 664 kg/acre biennially for 100 years.
Nuclide
Ra-226
Po-210
Pb-210
Th-228
Ra-228
Th-230
Th-232
U-234
U-235
U-238
'
Relative1
Concentration
(pCi/g soil)
0.69
0.66
0.89
0.09
0.09
0.12
0.08
0.08
0.003
0.07
• - .
RF2
(Risk/uCi)
9.4 E-5
1.4E-4
5.5 E-4
1.3 E-5
7.0 E-5
2.3 E-5
2.1 E-5
7.5 E-5
7.3 E-5
7.4 E-5
TOTAL RISK
======
70 YR
Risk
1.8 E-7
2.6 E-7
1.4 E-6
3.3 E-9
1.8 E-8
7.7 E-9
4.7 E-9
1.7 E-8
6.1E-10
1.4 E-8
1.9 E-6
30 YR
Risk
8.5 E-8
1.2 E-7
1 6.4 E-7
1.5 E-9
8.3 E-9
3.6 E-9
2.2 E-9
7.9 E-9
2.9E-10
6.8 E-9
8.8 E-7
======
=====
9 YR
Risk
3.6 E-8
5.1 E-8
2.7 E-7
6.4E-10
3.5 E-9
1.5 E-9
9.2E-10
3.3 E-9
1.2E-10
2.8 E-9
3.7 E-7
Soil concentrations after 100 years of application taking into consideration removal
mechanisms.
Risk factors from Table A-5 of EPA89b.
C-3
-------
Table C.2. Scenario 14 - Based on 26 pCi Ra-226/g of phosphogypsum applied at the rate
of 8,000 Kg/acre initial application followed by biennial applications of 4,000 Kg/acre for
100 years. .
Nuclide
Ra-226
Po-210
Pb-210
Th-228
Ra-228
Th-230
Th-232
U-234
U-235
U-238
Relative1
Concentration
(pCi/g soil)
2.74
2.64
3.55
0.34
0.34
0.47
0.31
0.30
0.013
0.28
RF2
(Risk/uCi)
9.4 E-5
1.4E-4
5.5 E-4
1.3 E-5
7.0 E-5
2.3 E-5
2.1 E-5
7.5 E-5
7.3 E-5
7.4 E-5
TOTAL RISK
1 1
70 YR
Risk
7.1E-7
1.0 E-6
5.4 E-6
1.2 E-8
6.6 E-8
3.0 E-8
1.8 E-8
6.3 E-8
2.6 E-9
5.7 E-8
7.4 E-6
=====
30 YR
Risk
3.4 E-7
4.8 E-7
2.6 E-6
5.8 E-9
3.1 E-8
1.4 E-8
8.8 E-9
3.0 E-8
1.2 E-9
2.7 E-8
3.5 E-6
=====
9 YR
Risk
1.4 E-7
2.0 E-7
1.1 E-6
2.4 E-9
1.3 E-8
6.0 E-9
3.6 E-9
1.2 E-8
5.0 E-10
1.1 E-8
1.5 E-6
===== —
Soil concentrations after 100 years of application taking into consideration removal
mechanisms.
Risk factors from Table A-5 of EPA89b.
C-4
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