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INDOOR RADIATION EXPOSURE
DUE TO RADIUM-226 IN
FLORIDA PHOSPHATE LANDS
Richard J. Guimond
William H. Ellett, Ph.D.
Joseph E. Fitzgerald, Jr.
Samuel T. Windham
Philip A. Cuny
Revised Printing
July 1979
Criteria and Standards Division
Office of Radiation Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
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PREFACE
The Office of Radiation Programs of the Environmental Protection
Agency endeavors to protect public health and preserve the environment
by carrying out investigative and control programs which encompass
various sources of radiation. Pursuant to this goal, the Office's
Criteria and Standards Division and Eastern Environmental Radiation
Facility initiated a study in June 1975 to examine the radiation
impact of living in structures built on phosphate lands. This study
was carried out in conjunction with the Florida Department of Health
and Rehabilitative Services and the Polk County Health Department.
The purpose of this report is to present the findings of that study;
these include estimates of the radiation levels, evaluations of the
cost-effectiveness of controls, and possible actions that can be taken
to reduce such levels. Readers of this report are encouraged to
inform the Office of Radiation Programs of any omissions or errors.
Comments or requests for further information are also invited.
We wish to express our gratitude to the staffs of the Florida
Department of Rehabilitative Services and the Polk County Health
Department for their cooperation and assistance. Staffs of the
Eastern Environmental Radiation Facility in Montgomery, Alabama, and
the Environmental Monitoring and Support Laboratory in Las Vegas,
Nevada, contributed substantial efforts in sample and data analysis.
We also offer our thanks to officials of the phosphate industry for
their help.
William A. Mills, Ph.D.
Acting Deputy Assistant Administrator
for Radiation Programs (ANR-458)
iii
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TABLE OF CONTENTS
Summary and Findings 1
Section 1.0 Introduction M
Section 2.0 Problem Description 7
Section 3-0 Observed Radiation Levels 17
Section 4.0 Radiation Health Risk Estimates 29
Section 5.0 Analysis of Control Alternatives 56
Section 6.0 Alternatives for Radiation Protection 76
Section 7.0 Socio-Economic Impact 90
Section 8.0 Implementation of Radiation Protection Measures ... 97
References 101
Glossary 107
Appendix A Study Design - Techniques and Procedures
Appendix B Calibration of Track-Etch Films
Appendix C Radiation Exposure Control Measures
Appendix D Evaluation of Field Data
Annex
Individual Structure Data
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TABLES
Table 1 - EPA & DHRS Indoor Radon Decay Product Level
Distribution by Number of Structures 23
Table 2 - Distribution of Indoor Radon Decay Product Levels
by Land Category 24
Table 3 - Distribution of Indoor Radon Decay Product Levels
in Slab and Crawlspace Structures on Reclaimed
and Mineralized Land 25
Table 4 - Outdoor External Gamma Exposure Distribution by
Land Category 27
Table 5 - Distribution of Indoor Radon Decay Product
Levels According to Land Classification
(Track-etch) 28
Table 6 - Observed Increase in Lung Cancer Fatality Rate,
Czechoslovakian Uranium Miners 41
Table 7 - Observed Increase in Lung Cancer Fatality Rate,
Swedish Iron and Zinc Miners 42
Table 8 - Comparison of Typical Aerosol Characteristics 44
Table 9 - Estimated Risk of Lung Cancer per 100,000 Exposed Indivi-
duals Due to Lifetime Residency in Structures Having an
Average Radon Daughter Concentration of 0.02 WL (Relative
Risk Model) 51
Table 10 - Estimated Risk of Lung Cancer per 100,000 Exposed Indivi-
duals Due to Lifetime Residency in Structures Having an
Average Radon Daughter Concentration of 0.02 WL (Absolute
Risk Model) 52
Table 11 - Estimated Lifetime Risk of Excess Fatal Cancer and Genetic
Abnormalities per 100,000 Individuals Exposed
to an Annual Dose Rate of 100 mrem 54
Table 12 - Estimated Average Cost of Control Measures for Structures
Constructed on Florida Phosphate Lands 57
Table 13 - Impact of Alternative Criteria for Indoor Radon
Decay Product Exposure for Structures Requiring
Special Corrective Action 86
vii
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Table B. 1 - Data Used in Analysis B-2
Table C.1 - Estimated Average Cost of Control Measures for
Structures Constructed on Florida Phosphate
Land (same as Table 12) C-10
Table D.1 - Distribution of Mean Gross Indoor Radon Decay
Product Levels D-M
Table D.2 - Number of Structures in Specified WL Ranges by City . D-4
Table D.3 - Number of Structures by Land Category and Mean Gross
Indoor Radon Decay Product Level Ranges D-8
Table D.M - Statistical Comparison of Mean Gross Indoor Radon
Decay Product Levels by Land Category D-8
Table D.5 - Number of Structures by Structure Type and Mean Gross
Indoor Radon Decay Product Level Ranges (N=133) .... D-9
Table D.6 - Statistical Comparsion of Mean Gross Indoor Radon
Decay Product Levels by Structure Type D-10
Table D.7 - Number of Structures by City and Specific Outdoor
Gamma Range D-19
Table D.8 - Average Ratio of Indoor Gamma to Outdoor Gamma Measure-
ments by Structure Type D-21
Table D.9 - Average Ratio of Indoor Gamma to Outdoor Gamma Measure-
ments by Structure Type for Observations Equal to or
Greater than 10 ]aR/hr D-22
Table D-10 - Average Ratio of Indoor Gamma to Outdoor Gamma
Measurements by Structure Type for Observations
Equal to or Greater than 15 uR/hr D-23
Table D-11 - Outdoor Gamma Survey Distribution of All Structure
Sites by Land Category D-25
Table D.12 - Statistical Comparison of Gamma Survey
Distribution for Selected Land Categories D-26
Vlll
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FIGURES
Figure 1 - Phosphate Deposits in Florida 8
Figure 2 - Uranium-238 Decay Series 11
Figure 3 - Typical Profile in Study Area 12
Figure 4 - Factors Influencing Radon Decay Product Concentrations
in Structures 15
Figure 5 - Respiratory Cancer Mortality Reported for U.S. Miners . 31
Figure 6 - Respiratory Cancer Mortality in Ontario (Canada)
Uranium Miners 35
Figure 7 - Respiratory Cancer Mortality Reported in Czechoslovakian
Uranium Miners (1948-1973) 36
Figure 8 - Cost-Effectiveness of Remedial Action to Reduce Indoor
Radon Decay Product Levels for Existing and Planned
Structures 63
Figure 9 - Reduction of Gamma Exposure Rate Resulting from Earth or
Concrete Shielding 66
Figure 10 - Correlation of Observed Indoor Gamma Exposure with
Theoretical Estimation 67
Figure 11a - Cost-Effectiveness of External Gamma Exposure Control for
Planned Structures (Assuming 4" Concrete Slab Construction
@ $550) 70
Figure 11b - Cost-Effectiveness of External Gamma Exposure Control for
Planned Structures (Assuming 8" Concrete Slab Construction
§ $1,500) 71
Figure 11c - Cost-Effectiveness of External Gamma Exposure Control for
Planned Structures (Assuming 12" Concrete Slab Construction
§ $4,000) 72
Figure 11d - Cost-Effectiveness of External Gamma Exposure Control for
Planned Structures (Assuming Excavation and Fill
@ $15,000) 73
Figure 11e - Cost-Effectiveness of External Gamma Exposure Control for
Existing and Planned Structures (Summary) 74
ix
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Figure A.1 - Gamma Radiation Measurements (Reuter-Stokes
Pressurized Ion Chamber and Ludlum Model 125
Micro R Meter) A-2
Figure A.2 - Radon Progeny Integrating Sampling Unit (RPISU) . . . A-4
Figure B.1 - Calibration Formula at 95$ Confidence Level B-6
Figure D.1 - Distribution of TLD Air Sampling Measurements .... D-3
Figure D.2 - Average Indoor Radon Progeny Working Level Distribution
(Gross) for Polk County, Florida (N=133) D-5
Figure D.3 - Distribution of TLD Air Sampling Measurements by
Land Category and Gross Working Level Range D-7
Figure D.4 - Distribution of TLD Air Sampling Measurements by
Structure Type and Gross Working Level Range . . . . D-11
Figure D.5 - Distribution of TLD Air Sampling Measurements by
Structure Type and Gross Working Level Range for
Reclaimed Land D-13
Figure D.6 - Distribution of TLD Air Sampling Measurements
by Gross Working Level Range D-15
Figure D.7 - Distribution of Outside Gamma Radiation
Measurements D-16
Figure D.8 - Average Outdoor Gamma Radiation (Gross) for Polk
County, Florida D-18
Figure D.9 - Distribution of Gamma Exposure Rate by Land
Category D-24
Figure D.10 - Distribution of Indoor Gamma Exposure Rate by
Structure Type for Reclaimed Land D-28
Figure D.11 - Distribution of EPA Track-Etch Data by Gross
Working Level Range D-29
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SUMMARY OF FINDINGS
As a result of the presence of elevated concentrations of
radium-226 and other radionuclides in phosphate ores and mining
wastes, many individuals residing in Central Florida are exposed to
undesirable levels of radiation. In the absence of adequate measures
to protect public health, many more could be exposed in the future,
depending upon developing mining and land use patterns. The major
exposure problem is associated with structures, principally
residences, that are constructed on, near, or using radium-bearing
materials related to phosphate ores. In this study, annual average
indoor radon decay product concentrations in excess of 0.03 working
level (WL) were measured in approximately 15 percent of the structures
surveyed. Normal occupancy at this level of exposure would result in
an annual cumulative exposure of 0.6 working level months (WLM).
Lifetime residence in a structure exhibiting this level could result
in a doubling of the normal three to four percent risk of fatalities
due to lung cancer. At present there are no adequate guidelines to
protect the public from this and most other similar sources.
*Working level month means exposure to one working level (WL)
for 170 hours (a working month). Exposure of non-miners (75%
occupancy) in residential environments to radon daughters at one
working level for one year is approximately equivalent to 27 WLM. A
working level is defined as any combination of short-lived radon
daughter products in one liter of air that can result in the ultimate
emission of 1.3 x 10^ Mev of alpha energy. Normal occupancy is
assumed to be 75 percent residence in this report.
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Areas affected by the radium-bearing phosphate materials also
generally exhibit elevated gamma radiation exposure levels. However, the
health risk accompanying exposure to radon decay products in a structure
is generally much greater than that for the associated gamma exposure.
Therefore, assuring protection from elevated air concentrations of radon
decay products is of primary concern, with protection from gamma exposure
of only secondary importance.
*
Evaluation of the cost-effectiveness of various measures for
controlling airborne radon decay products in new (i.e., planned) and
existing structures suggests that several appear economically
reasonable. The application of control measures in a residence was found
to be warranted on this basis when initial levels are greater than 0.005
WL above normal. Although most of the control measures evaluated have
been tested and used in other situations, none have been thoroughly
tested in Florida.
The cost of controlling gamma radiation in existing structures is
high because remediation would require extensive modifications to the
foundation and to the soil under and around it. It was concluded that
the application of control measures to reduce gamma radiation exposure is
not cost-effective in existing structures. However, in planning
*Meaning the degree to which the economic cost of an action (in
this case, the use of control measures) is justified by the positive
result of the action (e.g., health risk reduction).
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residences, the design and siting of the structure can be arranged to
provide additional gamma shielding for little cost. In most new
residences, it appears to be cost-effective to limit external gamma
radiation exposure rates to 5 yR/h above normal (11 yR/h gross), or less.
Land and wastes associated with other types of ores throughout
Florida, as well as other parts of the United States, may pose similar
health risks due to the presence of radium and other radionuclides in
above normal concentrations. While these findings apply to a specific
situation in Central Florida, Federal, State, or local authorities with
similar problems in other areas may find them useful. Local factors,
including cost and other practical considerations, may have to be weighed
in applying these results to situations other than phosphate-related land
in Florida.
During the course of this study, the Agency also acquired
information about other types of land from the phosphate industry,
universities, and state and local agencies, as well as from its own
measurements. Sizeable areas of land in Florida containing monazite sand
deposits or wastes from the processing of various minerals may also
present health risks similar to those posed by phosphate lands and
wastes. Some of these lands may also pose health risks due to radiation
associated with radionuclides resulting from the decay of thorium-232. A
study carried out by the State of Florida to characterize the health
impact in these areas would appear to be indicated, as a basis for any
control action that may be necessary.
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SECTION 1.0
INTRODUCTION
Naturally-occurring radionuclides such as uranium, thorium, and
their decay products, as well as tritium, carbon-lU, and potassium-40,
are found throughout the environment and are usually fairly evenly
distributed. However, some geological strata, such as marine phosphorite
deposits, contain significantly elevated concentrations of uranium,
thorium, and their decay products. In the United States, the phosphate
deposits of Florida contain concentrations of uranium and its decay
products at levels about 30-60 times greater than those found in average
soil and rock. The presence of this radioactive material in extensive
land areas in Central and Northern Florida creates the potential for
radiation exposure of the general population living on or near this land.
In June 1975, the U.S. Environmental Protection Agency (EPA), in
conjunction with the Florida Department of Health and Rehabilitative
Services and the Polk County Health Department, initiated a pilot study
to examine the radiological impact of living in structures built on
reclaimed phosphate land. The-study was a part of a comprehensive
investigation conducted by EPA of the overall impacts of releases of
radiation and radioactive materials directly or indirectly from the
phosphate industry.
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In September 1975, the Administrator of the Environmental Protection
Agency informed the Governor of Florida that the Agency had found
elevated radon decay product levels in buildings constructed on land
reclaimed from old phosphate raining areas (Tr 75). He noted that the
primary health concern is increased risk of lung cancer to the
occupants. The Administrator recommended that "as a prudent interim
measure the start of construction of new buildings on land reclaimed from
phosphate raining areas be discouraged."
As a result of the Agency's preliminary findings, discussions were
held with appropriate Federal, State, and local agencies, as well as
industry representatives to determine the appropriate course of action.
The following actions were determined to be of principal importance:
1. Complete an assessment of the health risk in the study
structures over a longer period of time.
2. Perform an evaluation of the number of structures affected and
the magnitude of the impacted land within the State of Florida.
3- Develop guidelines for use by the responsible agencies and the
public in determining acceptable indoor radiation levels.
JJ. Develop guidelines for use by the responsible agencies and the
public in evaluating existing structures for possible remedial action.
5. Develop criteria for evaluating the indoor radiation exposure
potential of undeveloped land.
6. Determine if new reclamation techniques are needed and feasible.
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The activities of the Environmental Protection Agency since then
have been focussed on actions one, three, four, and five, with the State
and local health agencies focussing on actions two and four. Industry
efforts have been focussed on action six. However, in order to evaluate
the problem expeditiously, there has been an exchange of data and
information on each of these items among all groups involved.
The purpose of this report is to present data gathered in the EPA
study, estimate the radiation levels in existing structures, evaluate the
cost-effectiveness of controls, evaluate the social and economic impact
of potential radiation protection controls, and delineate the
alternatives available for radiation protection to minimize adverse risk
to the public. A separate report will address item five, i.e., the
development of criteria for the evaluation of undeveloped land to
determine its suitability for residential development.
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SECTION 2.0
PROBLEM DESCRIPTION
2.1 INDUSTRY OVERVIEW
In 1975 about 83 percent of U.S. phosphate mine rock production
occurred in Florida, primarily in the Central Florida Land-Pebble
district with the remainder in Tennessee and several western states (St
77). Figure 1 illustrates the primary Florida phosphate deposit areas.
About 17M million tons of phosphate mine rock was extracted in 1975
through the strip mining of approximately 5,000 acres of land. Over the
80 years that phosphate has been mined in Florida, a total of about 2
billion tons of phosphate mine rock has been extracted from about 120,000
acres of land (St 77, Wa 71*).
2.2 MINING TECHNIQUES & PRACTICES
The standard mining practice in the Florida land-pebble phosphate
fields is to strip the overburden and mine the phosphate matrix with
draglines. Electric-powered walking draglines with 35 to 70 cubic yard
buckets work in cuts varying from 150 to 250 feet in width and from a few
hundred yards to a mile or more in length. The cuts are from 50 to 70
feet deep. Overburden is stacked on unmined ground adjacent to the
initial cut by means of a dragline, until successive cuts allow it to be
cast into adjacent mined-out cuts. As each cut is stripped of overburden
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Hardrock district
Central land-pebble
Figure 1. Phosphate deposits in Florida. (WA 74)
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and then mined, the ore is stacked in a suction well or sluice pit that
has been prepared on unmined ground. High pressure water is used to
produce a slurry of about 40 percent solids from the matrix. This slurry
is then pumped via pipe to the washer plant. In this manner, a typical
operation will mine about 400 acres of land, remove 13 million cubic
yards of overburden, and mine 9 million yards of matrix per year.
Water is used in the phosphate beneficiation or ore refinement
process, in addition to being used as a transportation medium. Both
fresh water from deep wells and reclaimed water from slime settling ponds
are used by the phosphate industry, at a rate of approximately 10,000
gallons to produce one ton of marketable phosphate rock. As the mining
progresses, mined-out areas are used for the disposal of tailings and
slimes, in addition to overburden. Approximately one ton of slimes and
one ton of sand tailings must be disposed of for each ton of marketable
phosphate rock produced. Some of the sand tailings and overburden are
used to construct retaining dams in mined-out areas, behind which
phosphatic clay slimes settle and dewater.
Beneficiation methods differ slightly, depending on screen analysis
of the feed, the ratio of washer rock to flotation feed, the proportions
of phosphate, sand, and clay in the matrix, and equipment preferences.
Through a series of screens, in closed circuit with hammer mills and log
washers, the matrix is broken down to permit separation of the sand and
clay from the phosphate-bearing pebbles. Three concentrations of
marketable phosphate rock are produced: a 3/4-inch by 14-mesh pebble, a
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coarse 14 by 35-mesh fraction, and a fine 35 by 150-mesh fraction. The
washed, oversized pebble fraction is a final product. The 14 by 35-mesh
fraction is called the coarse feed, from which a coarse concentrate is
obtained by gravity and flotation processes. The tailings or waste from
this fraction are used in dam construction or land reclamation. The 35
by 150-mesh fraction is processed through a flotation section to recover
a fine concentrate. The waste, a clay slime, is impounded in areas that
have been mined.
2.3 PRESENCE OF RADIOACTIVE MATERIALS
Uranium is present in the phosphate matrix in concentrations which
generally average about 100-150 ppm (or about 35-55 picocuries natural
uranium per gram of matrix). The uranium is usually in equilibrium with
its radioactive decay products, at least through radium-226 (Gu 75).
This means that for each curie (a measure of radioactivity equal to
3-7x10 disintegrations per second) of the parent radionuclide, one
curie of each daughter radionuclide is also present. The uranium-238
decay scheme is shown in Figure 2.
Radioactivity is also present in parts of the overburden. Figure 3
illustrates the general geological structure found throughout much of the
Florida land pebble district. A "leach zone," which averages five feet
thick and covers much of the pebble deposits, contains uranium in
concentrations comparable to that of the matrix. In some areas other
portions of the overburden also contain elevated radioactivity, although
10
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ATOMIC WGT.
ELEMENT
ATOMIC NO.
HALF-LIFE
Figure 2. Uranium-238 Decay Series
11
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LEACHED ZONE
:0' TO 10'::::
9 (MATRIX);fCLAY • 5 J u **>•. ••
' ^
Figure 3. Typical Profile in Study Area (Fo 72)
12
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not in as high concentrations (Ca 66). The radioactivity is generally
associated with the phosphate, itself, since the uranium replaces the
normal calcium in apatite. Consequently, the marketable ore and slimes
containing most of the phosphate also contain most of the associated
radium. Two-thirds of the phosphate originally contained in the matrix
remains in the marketable rock, with the remainder primarily in the
slimes.
Soil throughout the United States typically contains between 0.2 and
3 pCi radium-226 per gram. One would anticipate that normal Florida
soils would contain this concentration range of radium-226 in areas that
have been undisturbed by mining. However, anomalies may occur in areas
where surface waters have exposed phosphate deposits or where such
deposits are very close to the surface. Measurements indicate that the
latter situation occurs in several areas in Central Florida.
2.4 ORIGIN AND TRANSPORT OF RADON-222
Unmined, reclaimed and disturbed phosphate land can be composed of
widely varying concentrations of radium-226, as a function of the
relative thickness and presence of low activity overburden soil and sand
tailings as compared to higher activity matrix, slimes, or leach zone
material. The presence of radium-226 and its decay products in soil
presents a potential source of gamma exposure to individuals living or
working above the soil. However, of much greater concern is exposure
arising from the release of radon-222, a noble gas decay product of
13
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radium-226 with a 3-85-day half-life. It may diffuse through the soil
into the atmosphere, where observed radon-222 concentrations in the air
are highly variable due to the influence of factors such as precipi-
tation, barometric pressure, and atmospheric thermal stability.
Radon-222 that diffuses up through soil also readily passes through
most concrete slabs and other construction materials. Within a structure,
the principal route of removal of radon is by ventilation or leakage
through the structure's walls, window frames, etc. Radioactive decay of
the material as a removal process is generally small compared to
ventilation and leakage. Radon-222 is probably not in equilibrium with
its decay products in most situations within structures, due to the
effects of ventilation and plate-out of decay products as particulates
*
on inside surfaces. The level of radon-222 and its decay products is
thus dependent upon the rate at which radon diffuses into the structure
and the rate at which it is removed by ventilation, leakage, and decay.
Clearly, if ventilation is low, radon and its decay products have the
potential to build up significantly within a structure. Figure 4 depicts
the movement of radon and daughters into and out of a structure.
The degree to which plate-out is a contributing factor is
highly variable, depending primarily upon exposed surface area and the
free ion fraction; the effect of plate-out, however, is of relatively
small significance in comparison with that due to ventilation.
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EQUILIBRIUM RADON
PROGENY CONCENTRATION
(WORKING LEVELS)
I I'LATF OUT
VENTILATION
RADON
SEEPAGE
THROUGH
DIFFUSION
RADON
EMANATION
SOIL CONTAINING RADIUM 226
FIGURE 4.
FACTORS INFLUENCING RADON DECAY PRODUCT CONCENTRATIONS IN STRUCTURES
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Radon-222 which enters the atmosphere via transport through soil can
originate from hundreds of feet below the surface, but because of its
relatively short half-life and the time required for diffusion through
most soils, the first 20 feet of soil is usually the major source. This
effective source thickness can be reduced to just a few feet if the soil
has a high water content.
16
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SECTION 3.0
OBSERVED RADIATION LEVELS
3-1 NORMAL BACKGROUND LEVELS
3-1.1 General Perspective
Exposure to background radiation results principally from cosmic
radiation sources and normal concentrations of radioactive elements
originating in the atmosphere of the earth's crust. Both of these
components vary throughout the United States, depending upon altitude,
latitude, and the makeup of the terrestrial environment. However, in
some areas the presence of elevated soil radioactivity due to either
natural phenomena or to human alteration of the environment can lead to
radiation exposure significantly in excess of normal background
exposure. The purpose of this section is (1) to place the radiation
levels observed in Central Florida structures built on phosphate land in
perspective with radiation exposure levels generally expected in Central
Florida and in other parts of the country, and (2) to provide a framework
for decision-making regarding measurement of radiation levels and
implementation of radiation protection recommendations in situations
where the exposures are elevated.
17
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3.1.2 Cosmic Ray Exposure
Whole body dose rates at sea level in the United States from Florida
to Alaska range from about 30 to 45 mrem/year (3-4 to 5.1 yrem/h),
respectively. At 45 N latitude, the variation with altitude from sea
level to 8,000 ft. is about 40 to 200 mrem/year (4.6 to 22.8 yrem/h),
respectively (Kl 72). In general, the estimated annual cosmic-ray
whole-body doses in the U.S. range between 30 mrem for Hawaii to 130 mrem
for Wyoming. For Florida it is estimated to be 35 mrem.
In order to verify this estimate for Florida, measurements were at
the center of two reasonably large Central Florida lakes with a
pressurized ion chamber. The measured cosmic-ray contribution, excluding
the neutron component, was 35 mrem/y (4.0 yrem/h) at Lake Pierce and 31
mrem/y (3.5 yrem/h) at Lake Hamilton for an average of about 33 mrem/y
(3.8 yrem/h). The measured values at the two lakes agree quite favorably
with those previously reported. The neutron component could add an
additional 6 mrem/y (0.6 yrem/h), but this will be ignored because
external radiation measurements made in Central Florida as cited in this
document do not record neutron dose (Lo 66).
3.1.3 Terrestrial External Gamma Ray Exposure
Naturally radioactive isotopes are constituents of a number of
minerals present in the terrestrial environment. Naturally-occurring
radionuclides contribute to both external and internal irradiation. The
significant external gamma exposures are produced by potassium-40 and the
decay products of the uranium and thorium series.
18
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Based upon numerous reported measurements, estimates have been made
of the range and mean of whole-body doses due to terrestrial radiation by
population and by area for the United States. Ninety percent of all
areas fall in the range of 15 to 130 mrem/year (1.7 to 14.8 yrem/h),
while ninety percent of the population falls in the range of 30 to 95
mrem/year (3.4 to 10.8 yrem/h). The estimated national mean is 55
mrem/year (6.3 yrem/h).
3.1.4 Total Background External Radiation Levels
Total average background radiation levels in the various States have
been estimated to range between 70 mrem/year (8 yrem/h) and 225 mrem/year
(26 yrem/h) with an overall U.S. average of about 85 mrem/year
(10 yrem/h). The average of 879 measurements of natural background
levels by Levin, et al^., in Florida was 59 mrem/year (6.7 yrem/h) (Oa72).
Measurements of the total normal background in Central Florida were
made by EPA in several locations with various types of detection
equipment. The average outdoor gamma exposure levels measured with
portable scintillation instruments at 26 structures built on unmined
non-mineralized land was 45 mrem/year (5 yrem/h). For these same
structures, indoor gamma exposure levels averaged 43 mrem/year
(4.9 yrem/h). TLD's were placed in Dundee, Lake Wales, and Polk City,
Florida, which are outside the phosphate area, and left for an extended
time period. The average of these measurements was 41 mrem/year
(4.7 yrem/h). Pressurized ion chamber measurements were made at nine
locations outside the phosphate region. The average of these
measurements was 51 mrem/year (5.8 yrem/h). It should be noted that the
19
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measurements by portable scintillation instruments and TLD's will not
reflect cosmic ray exposure as accurately as the pressurized ion
chamber. Considering this, these field data show adequate
intercomparison as well as agreement with the values listed in the
literature. They suggest that the normal external gamma exposure in
Central Florida is about 60 percent of the average for the United States.
3-1.5 Radon-222 and Decay Product Exposure
Natural radionuclides are also present in the air. The greatest
dose to people from airborne natural radioactivity generally arises from
the decay products of Rn-222. Measurements of radon-222 concentration in
air in the U.S. suggest that it is normally present in concentrations
ranging from 40-1000 pCi/m^ (0.04 - 1 pCi/1) (Na75). Radon in the
atmosphere primarily originates from the decay of radium in soils and
rocks. The outdoor radon concentration at ground level depends on the
rate of radon emanation from the soil and how rapidly it is dispersed.
Inside structures the concentration of radon-222 and its decay
products is generally considerably higher than corresponding outdoor
concentrations because of poorer indoor dispersion characteristics.
Although the number of measurements made over extended time periods
throughout the United States is quite limited, the data suggest that the
normal range of radon decay product levels is from about 0.0001 to 0.005
working level (WL), with an average of about 0.002 WL. Although levels
greater than 0.005 WL can be found, these are frequently due to
combinations of larger than normal radium-226 concentrations in soil and
20
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building materials, coupled with poor ventilation. Measurements by EPA
using the TLD air pump system in Central Florida in 26 structures on
non-mineralized land showed an average of about 0.004 WL (.0007-.014
WL). Data obtained by the University of Florida and the State Department
of Health and Rehabilitive Services for this parameter on non-phosphate
land are 0.002 and 0.004 WL, respectively (De ?8, Ro ?8). Review of
these data indicates that the range is within that expected by studies of
other investigators throughout the United States. Further, the three
data sets compare quite favorably, although the University of Florida
data is for a smaller sample of residences measured using only a few grab
samples.
3.1.6 Other Anomalous Radiation Areas in Florida
In addition to the phosphate lands in Florida there are other
regions in the State where elevated radiation levels have been noted,
because of the presence of ores containing trace quantities of uranium,
thorium, and their decay products. These areas are primarily along the
coast between Punta Gorda and Venice, and along the northeastern coastal
region. Deposits of monazite sands are the primary source of radioactive
materials. In these areas, radiation levels are as high as or higher
than those observed in the phosphate region. Little detailed information
is available regarding these areas because they have not been
investigated to any meaningful extent. Limited measurements by EPA
around Punta Gorda and Venice identified external gamma radiation
exposure levels up to 30 viR/h (260 mrem/y). However, the size of the
impacted areas appears to be small. In the northeastern area of Florida,
21
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gamma radiation exposure levels in excess of 100 yR/h (880 mrem/y) have
been reported by the State of Florida Department of Health and
Rehabilitative Services. They also suggested that the impacted area in
this region could be quite large. No information exists on radon-222 and
radon-220 concentrations in these areas.
3.1.7 Background Summary
Based upon EPA's measurements and review of previously reported
data, it is concluded that the normal background radiation level in and
around a Central Florida structure located away from phosphate-related
land can be characterized by the following parameters:
External gamma exposure rate - 6 Urem/h
Indoor radon decay product level - 0.004 WL
Although these values are somewhat variable, as indicated by the
data, they provide a representative basis for most decisions concerning
the need for remedial action for radiation protection.
3.2 SUMMARY OF RADIATION MEASUREMENTS AND EVALUATIONS
3-2.1 Evaluation of Radon Progeny Levels in Structures
Radon progeny levels were evaluated at 133 locations in Polk County
with Radon Integrating Progeny Sampling Units (RIPSU). This device draws
air through a particulate filter, and measures radiation from radon
progeny with a thermoluminescent dosimeter (TLD). These air sampling
units were rotated to the various locations on a periodic basis to insure
several measurements at each structure, and to reflect any seasonal or
22
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diurnal variations in radon decay product concentrations. For the
purpose of evaluation, the 133 locations were categorized according to
structure type (slab, basement, crawl space, or. trailer construction) and
land category (reclaimed, mineralized, or non-mineralized). Of the total
sample, 22 structures were from the original pilot study initiated by EPA
and the remainder were selected later as a part of the group chosen by
the Florida Department of Health and Rehabilitative Services (DHRS). The
distribution of indoor working level measurements in the two samples
differs, although this is expected due to the smaller pilot study sample
size and the practical aspects of selecting the structures. In the
selection of the EPA pilot group, houses known to be on reclaimed land
were chosen on the basis of elevated external gamma measurements made on-
site. The DHRS study group, however, was selected solely by review of
land records to identify reclaimed land. It is understandable,
therefore, that a greater percentage of structures in that group exhibit
lower external gamma and indoor radon decay product levels than in the
EPA pilot group. The distributions of radon decay products in each group
are shown in Table 1.
TABLE 1
EPA and DHRS Indoor Radon Decay Product Level
Distribution by Number of Structures (Percentage in parenthesis)
Level (WL gross) EPA DHRS Composite
Greater than 0.05
0.03 to 0.05
0.01 to 0.03
Less than 0.01
N=22
5 (2350
3 (14$)
4 (18$)
10 (U5$)
N=111
3 (2$)
9 (9$)
22 (20$)
77 (69$)
N=133
8 (6$)
12 (9$)
26 (20$)
87 (65$)
23
-------
From information collected in the survey, the land on which the
structures were constructed was classified according to four categories:
non-mineralized (no deposits), mineralized (deposits present, but
unmined), reclaimed, and other (i.e., missing or incomplete
information). Of the 133 structures, the gross average working level for
each category is 0.003 WL (non-mineralized), 0.015 WL (mineralized),
0.016 WL (reclaimed), and 0.018 WL (other). This distribution, provided
in more detail in Table 2, indicates that mineralized land has as much
radiological impact as reclaimed land.
TABLE 2
Distribution of Indoor Radon Decay Product
Levels by Land Category
Land Use
Reclaimed
Mineralized
Non-mineralized
Unknown
In order to determine the influence of structure design (particularly
foundation design) on radon diffusion, the average working level
measured in various types of structures was evaluated for four typical
structure types found in central Florida: basement, slab-on-grade,
crawl space, and trailers. The average value for each category (with
the number of structures in parenthesis) is 0.020 WL (4), 0.015 WL
(102), 0.01 WL (13), and 0.008 WL (14), respectively. Although sample
N
93
9
29
2
WL<0.01
59$
44$
97$
0
0.01 <.WL <0.03
20$
44$
3$
100$
0.03
-------
size for some of these categories decreases the statistical
significance of this distribution, this data suggests that crawl space
and trailer designs result in less radon diffusion into a structure
than typical basement or slab-on-grade construction.
The evaluations of indoor radon decay product levels by both land
category and structure type can be combined to analyze the
distribution of measurements as a function of these two parameters.
For reclaimed land, the four types of structures were evaluated on the
basis of percent working level distribution. For slab and crawl space
construction the distributions are shown in Table 3.
TABLE 3
Distribution of Indoor Radon Decay Product Levels in Slab and
Crawl space Structures on Reclaimed and Mineralized Land (RPISU)
Level (gross WL) Slab Crawlspace
(including trailers)
N=77 N=22
Greater than 0.05 9% 0%
0.03 to 0.05 12$ 9%
0.01 to 0.03 23% 9%
Less than 0.01 56$ 82$
Ventilation has been identified as a key factor in the buildup of
indoor air concentrations of radon decay products. The use of air
conditioning in the study structures was of interest because it was
initially believed that maintaining a lower indoor temperature at a
reasonable cost would entail reducing the degree of air infiltration
from the outside air. However, studies by EPA show that operation of
25
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a central air conditioning system tends to reduce the indoor radon
decay product levels when compared to no air flow (Wi 78). This is
attributable to the increased influx of outside air due to leakage
surmised to be the result of pressure differences brought about by the
operation of the ventilation system, as well as the deposition or
"plate-out" of decay products in the ventilation system. For
structures with and without air conditioning the average working
levels are 0.012 and 0.016 WL, respectively. This implies that any
significant short term effects caused by operation of the air
conditioning system may be largely balanced over a year by factors
such as decreased usage during the cooler months.
3.2.2 Evaluation of Gamma Exposure Levels
Gamma exposure rate measurements were made at 1102 sites by EPA
and DHRS. The gamma surveys were performed with a standard portable
scintillometer held one meter from the floor or ground level for
indoor and outdoor measurements, respectively. Average indoor and
outdoor gamma exposure rates were estimated from several measurements
in and around each structure.
The distribution of exposure rates was examined for different
land categories. This is summarized in Table 4 for the three primary
categories: non-mineralized, mineralized and reclaimed.
26
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TABLE H
Outdoor External Gamma Exposure
by Land Category ^=107*0*
Level (yR/h) Reclaimed Mineralized Non-Mineralized
N=672
1%
2b%
67%
11 yR/h
N=102
1$
4*
95$
7 yR/h
N=300
0%
3%
97%
6 yR/h
greater than 20
11-20
less than 11
average gamma exposure
*28 sites have unknown classifications
The influence of structural design, especially the degree of
foundation shielding, was evaluated for the four structure types
considered in this study. The average ratio of indoor gamma levels to
corresponding outdoor gamma levels was found to be fairly similar for all
structure types (about 0.8-0.9, as shown in Figure D.8). However, when
controlling for gamma background "noise" contribution (e.g., from
reflected primary radiation and radiation from structural materials
themselves, the differences due to shielding are more pronounced for
foundation (slab and basement) versus non-foundation (crawl space and
trailer) structures. For levels above 10 and 25 yR/h, for example, the
average indoor to outdoor ratio for these respective structure categories
is roughly 0.4 and 0.8 (see Tables D.9 and D.10) These observations are
consistent with the degree of floor shielding present with slab and
basement construction, which have several inches of concrete, and with
crawl space and trailer construction, which have either wood or thin
27
-------
metal flooring. In addition, a distribution plot by structure type for
reclaimed land (Figure D.10) shows that only crawl space and trailer
structures have indoor levels in excess of 20 pR/h.
3.2.3 Evaluation of Track-etch Data
Track-etch film was used in 153 structures selected in the pilot
study for the purpose of providing another estimation of radon progeny
levels. The film was placed in a structure for at least a year, after
which a representative portion of the "etches" were counted to determine
alpha energy deposition. This was translated into an estimate of indoor
radon decay product level through the use of appropriate calibration
curves. The details of this method are discussed in Appendix B. Because
of the errors involved in this technique, particularly at indoor radon
decay product levels less than 0.02 WL, the amount of useful data
obtained is limited. Table 5 shows the distribution of track-etch data
according to land classification.
TABLE 5
Distribution of Indoor Radon Decay
Product Levels According to Land Classification (Track-etch)
(M= Mineralized, N=Non-Mineralized, R=Reclaimed, and U=Unknown)
Level (WL) M N R U
T" 27 112 ~T~
Greater than 0.05 38% 0% 23% 0%
0.03 to 0.05 0% W 12* 0%
0.01 to 0.03 50% 41* 37$ 33/6
Less than 0.01 12* 55% 28% 67%
28
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SECTION 4.0
RADIATION HEALTH RISK ESTIMATES
4.1 THE RISK TO HEALTH DUE TO THE INHALATION OF RADON DAUGHTERS
4.1.1 The Epidemic-logical Data Base
The carcinogenic nature of inhaled radon and its daughter
products became known through observation of fatal lung disease in
some groups of underground miners. The malignant nature of their
disease was recognized as early as 1879 and specifically identified as
bronchiogenic cancer in 1913 (Lu?1). The association between these
cancers and the miners' exposure to radon was first made in 1924.
Although there has been some argument that occupational hazards
other than radon may be important, extensive studies have excluded
many suspected causes of excess lung cancer among underground miners
such as pneumoconioses, water in the mines, heredity, fungal growths,
as well as a number of metals in the ore, i.e., nickel, chromium,
arsenic, and bismuth (Fr48, Hu66). Exhaust fumes from diesel engines
are often mentioned as a causative factor for lung cancer among
uranium miners. Yet from 1869 to 18?8, well before the diesel engine
was patented in 1892, lung cancer caused 75 percent of miner deaths at
Schneeberg (Ha79). The observation of excess lung cancer mortality in
workers in a variety of hard rock and metal mines indicates that
uranium ore dust is not critical to the development of lung cancer
29
-------
(Fr48, Hu66, Lu71). The only common factor identified in all miner
groups studied is the presence of radon and radon-daughter aerosols in
the respired air (Mi?6).
The general recognition of the radon problem has resulted in a
number of epidemiological studies in various countries, including the
U.S.A., Canada, Czechoslovakia, Sweden, and Great Britain. Lung
cancer deaths in U.S. uranium miners have been the subject of an
extensive epidemiological study led by the U.S. Public Health Service
(Lu71, Ar7**, Ar76), which has provided much information on the
etiology of radiation-induced lung disease. Nevertheless, this study
and to a lesser extent other studies of cancer deaths among under-
ground miners have limitations when used for the purpose of providing
risk estimates applicable to the general population. The relative
importance of these limitations has been considered in the risk
estimates made below.
The estimates of the risk to miners have continued to rise as
more epidemiological data have accumulated. In this regard it is of
interest to compare recent information on radiogenic lung cancer with
that available in 1970-1971 when the Federal guide for occupational
exposure of miners was reduced from 12 to 4 Working Level Months (WLM)
per year (Fe71). These guides were based almost exclusively on the
experience of U.S. uranium miners exposed to high concentrations of
radon daughters. At that time 70 lung cancer cases had been observed
30
-------
in the study group. While this number of cases exceeded the expected
number of 12, about half of the cancers followed exposures of more
than 1800 WLM (Lu7D.
Figure 5 shows the number of lung cancer cases observed in the
U.S. uranium miner study group through September 1968, and their
estimated levels of exposure in WLM. The expected number of deaths
depends on the number at risk at each dose level and is based on white
males in the four western states where the uranium mines were in
operation (Lu?1). Three things are worth noting in these early
results: the small number of deaths in each broadly defined exposure
category, the relatively constant ratio of expected-to-observed deaths
below 1800 WLM, and finally the absence of any significant difference
below 120 WLM. For these reasons alone, it is easy to appreciate why
early estimates of the risk due to radon inhalation were controver-
sial; there was essentially no dose response information available.
More recent data, described below, differs considerably from these
1968 results.
A fundamental limitation in this and similar investigations of
lung cancer mortality is that the U.S. study is still in progress.
Survivors in the U.S. study are continuing to die of lung cancer with
the result that more recent data show a much larger number of lung
cancer deaths than was originally projected (Na?6). Another very
serious limitation, peculiar to the U.S. study, is that the cumulative
exposures to the 4000 workers involved were quite large, averaging
31
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WHITE U.S. URANIUM MINERS (1950 — 1968)
3 DEATHS
10
O
UJ
0
Z
r* in
'IRATORY C
C
(0
UJ
•** _
DC 0
-
-
-
=-"
OBSERVED
I I
EXPECTED
* ~
•
M
III I
I
tf \
\
^-~-f/
120 360
840 1800
CUMULATED EXPOSURE IN WLM
3720
Figure 5. RESPIRATORY CANCER MORTALITY REPORTED FOR U.S. URANIUM MINERS (Lu71).
SEE TEXT FOR LIMITATIONS ON DATA
-------
nearly 1000 WLM per miner. There is some evidence that at such high
levels of exposure the risk per unit exposure is somewhat less than
occurs at radon daughter exposures below a few hundred working level
months (Lu?l, Na?6). In addition, the lung cancer mortality data for
Japanese atomic bomb survivors also shows a trend for increasing lung
cancer risk per unit dose at lower doses (Un77). For this reason it
is advisable in risk analysis to limit the use of epidemiological data
for miners to that obtained at moderate exposure levels, i.e., a few
hundred working level months.
The limited information available from the study of the U.S.
uranium miners can be augmented by using results derived from epi-
demiological studies of miner health in other countries and in other
types of mining operations. The occupational environments in these
mines differed substantially from those in the U.S. underground
uranium mines so that the cumulative exposure from radon decay
products was much smaller (Mi?6, Se?6, Sn?2*). In addition, the
reported follow-up period in some of these studies is longer than for
the U.S. study population. In all study groups, however, some miners
are still alive and the final number of lung cancer cases is expected
to be larger. The absence of data from completed lifetime follow-up
studies can lead to a biased underestimation of the risk due to the
inhalation of radon daughters, unless appropriate risk models are
utilized which recognize that current studies have not been
completed. This important topic is discussed below.
33
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The direct proportionality of cancer risk to radon decay product
exposure at levels likely to be experienced in the environment cannot
be demonstrated for either human populations or by animal studies
because of the large number of subjects needed. As shown below, the
available data indicate that the use of a linear response curve for
humans exposed to low concentrations of radon decay products is not
expected to greatly overestimate or underestimate their cancer risk
provided that the exposures do not exceed a few hundred working level
months. Figure 6 illustrates the observed cancer excess in Canadian
uranium miners who were exposed to much lower concentrations of radon
decay products than are common in U.S. uranium mines, (c.f. Figure 5).
Although this study may not be fully adequate to establish a quanti-
tative estimate of the risk per working level month because data on
smoking histories is incomplete, these data have been shown to be
consistent with a linear dose response relationship at relatively low
levels of exposure and strongly argue against a threshold dose for
radiocarcinogensis in the lung (Mi76).
Figure 7 shows results obtained by J. Sevc and co-workers, from
their study of uranium miners in Czechoslovakia whose mining experi-
ence started after 1948 (Se76). In that country, excess lung cancers
had been observed in uranium miners exposed before World War II. An
appreciation of this led to better ventilation of the uranium mines
and resulted in relatively low levels of exposure to miners entering
the work force after 1947. The average follow-up period in this
-------
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group is twenty three years. The high degree of correlation between
exposure and excess cancer shown represents an overall average for
workers of various ages. This study also found that the absolute
cancer risk increased substantially with the age at which a worker
entered this work force.
Tt should be noted also that epidemiological data of the kind
illustrated in Figures 6 and 7 will always overestimate the exposure
to radon decay products needed to initiate a lung cancer. The
exposure considered in these studies is that accumulated throughout
the working life of these miners. The dose received but ineffective
in producing cancer between the period of cancer initiation and its
manifestation is not discounted, For chronic exposure, the same
reasoning applies to determining the minimum exposure level at which a
significant number of cancers occur; an apparent threshold dose will
exist, unless the cancer is initiated on the last day of exposure.
4.1.2 Risk Estimates for Underground Miners
Estimates of the cancer risk due to the inhalation of radon decay
products can be made either on the basis of the dose delivered to the
basal cells of the bronchial epithelium or the cumulative exposure in
WLM. In 1972 the NAS-BEIR Committee used the former method to prepare
their risk estimates so that other types of ionizing radiation could
be considered also (Na 72). More often estimates of the risk due to
radon decay products are based on the cumulative exposure in WLM
(Lu71, Ar76, Na76, Un77, Mi76, Se76,
37
-------
The dose to the bronchial epithelium has been calculated by
several investigators (Wa77, Ha?1*, Ha72). While valuable, these
studies indicate that the dose (in rads) is highly dependent on a
number of factors which have varying degrees of certainty. One
important, but as yet poorly known, parameter is the depth below the
mucosal surface at which the sites in irradiated tissues giving rise
to lung cancer are located. This distance, which is likely to differ
in various portions of the respiratory tract, is not known with any
accuracy. In addition, no information is available on the degree of
uniformity of deposited daughter products in various parts of the
bronchial tree. Furthermore, the in situ absorption and removal
pattern of the radon decay products lead-214 and bismuth-214 is poorly
understood. Recent experimental evidence indicates that to postulate
their complete decay in the mucus near the bronchial epithelium, as is
usually done, is likely to be in error (Ja77). Because of the uncer-
tainty in calculated doses, the Agency prefers to base estimates of
the risk due to radon decay products on the cumulative exposure in
working level months.
The 1972 NAS-BEIR Report used two types of analyses in estimating
the radiation-induced cancer risks from follow-up studies of exposure
groups (Na 72). One, called the absolute risk estimate, is the num-
erical increase in the number of excess cancers per unit of exposure,
averaged over all age groups. The other, tne relative risk estimate,
is the estimated percent increase in excess cancer per unit exposure
38
-------
Either of these models will yield the same number of excess cancers
for a given study population if based on data from a lifetime follow-
up period. Because exposed persons have been followed for a shorter
duration, a choice between these models is needed. In the exposed
groups studied, the risk of radiogenic lung cancer, but apparently not
all cancers, increases with the participants age in about the same
manner as the "natural" incidence of lung cancer, i.e., the relative
risk remains constant. In contrast, the absolute risk estimates
derived from the U.S. study are not constant but have continued to
increase as the length of the follow-up period is increased (Na?6).
Lung cancer mortality among Japanese survivors has shown a similar
pattern (Be77). Moreover, analysis by age shows the Czechoslovakian
and Canadian lung cancer data to be grossly inconsistent with the
absolute risk hypothesis (Mi76, Se76).
More recently, the Japanese cohort data on lung cancer mortality
for those exposed to high LET bomb radiation at age of 50 or more have
been examined for the time of occurrence of excess lung cancer after
exposure (La78). Because of their age, a near lifetime follow-up
study of this group is possible; the youngest surviving member was
nearly 80 at the time of the study. Lung cancer mortality was
compared for two dose ranges, those highly exposed, where three times
the expected number of cancers was observed, and a control group
receiving 0 to ten rads ("tissue kerma" in air). The time to
occurrence of the lung cancers is the same for the two groups, as
would be expected if the increase in lung cancer mortality follows the
39
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temporal pattern predicted by a relative risk model. This is similar
to observed patterns of lung cancer observed in animals following
Plutonium inhalation (Na 76). In the analysis of these data as they
apply to human health risks the 1976 NAS Report stated, "as already
indicated, the steepness with which lung cancer death rates in the
Battelle (Northwest Laboratory) beagles rose as a function of age
strongly suggests that the relative risk estimate is the appropriate
one to use in the present context of assessing lung cancer risk from
alpha emitters." For these reasons, relative risk estimates are
thought to provide a better projection of the risk of lung cancer than
absolute risk estimates. However, both types are included in the set
of risk estimates made below.
As an alternative to these two models, an age-dependent absolute
risk model with age-dependence somewhat different from that for
natural cancer incidence would also be compatible with the observa-
tions made on uranium miner populations. It should be noted that the
estimated risks using such a model would be much closer to those
calculated on the basis of relative risk than for an age-independent
absolute risk model. As yet, parameters for age-dependent lung cancer
risk models have not been published.
The estimate of the absolute risk due to exposure to radon decay
products in the general environment contained in this report are based
on recent mortality experience of U.S. uranium miners (Na76).
Comparable U.S. data on relative risk are not available, the most
recent relative risk compilation was in 1972 for the NAS-BEIR report
-------
(Na?2). Since that time, enough new cancers have occurred so that
absolute risk estimates based on this group have more than doubled
(Na?6). The effect of this longer follow-up period on their relative
risk is unknown, but may be substantial. Therefore the estimates of
relative risk made here are based on studies of underground miners in
Czechoslovakia and Sweden. Relative risk data for the Ontario miners
have not been published. However, an oral presentation indicates the
results of the Ontario study (Mi?6) agree with those for Czech and
Swedish miners (He?8).
The percent increase in excess cancer per WLM for Czechoslovakian
uranium miners is shown in Table 6. These data have been recalculated
TABLE 6
OBSERVED INCREASE IN LUNG CANCER FATALITY RATE
CZECHOSLOVAKS URANIUM MINERS
Mean Exposure (WLM) % Increase per WLM
39 3.6*
80 1.0*
124 1.6
174 2.9
242 2.2
343 2.0
488 1.8
716 1.4
*Not significant at the 5% level of confidence
41
-------
from References Se73 and Se?6 on the basis of an assumed nine-year
latent period between the start of exposure and the occurrence of a
radiation-induced lung cancer. At the exposure levels which occurred
in the Czech uranium miners, the average risk would appear to be
increased by about 2-3 percent per WLM.
Table 7 shows the percent increase per WLM observed in Swedish
miners (Sn74, Ra?6). In this case the increase may be as great as 4
percent per WLM at lower levels of exposure. The variations in the
percent increase in lung cancer found in these epidemiological studies
are not due to statistical sampling variation alone. Each study
reflects differences in the age distribution of those exposed, the
duration of the exposure, and the follow-up periods. Given the
variations shown in Tables 6 and 7, the best that can be done is to
propose a range within which the actual risk may lie, as described in
Section 4.1.3.
TABLE 7
OBSERVED INCREASE IN LUNG CANCER FATALITY RATE
SWEDISH IRON AND ZINC MINERS
Mean Exposure (WLM) % Increase per WLM
15 4*
48 4.2
218 3.3
696 2.5
*Not significant at 5% level.
42
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4.1.3 Applicability of Underground Miner Risk Estimates to the
General Population
As in most cases where the results of epidemiological studies of
occupational exposures are applied to the general population, there is
uncertainty in the extent of comparability between the persons at
risk. Very little information is available on those
non-occupationally exposed. A recent case control study by Axelson
and Edling (AX79) is suggestive that the mortality per WLM for Swedish
residents in homes having presumably high levels of indoor radon
daughters is comparable to that observed in underground miners.
However, the sample size is small and the exposure estimates too
tentative to allow definite conclusions.
Since the only common factor in underground miners with increased
risk of lung cancer mortality is exposure to radon and radon daughter
aerosols, the comparability of mine atmospheres, indoor and outdoor,
should be considered. Jacobi, ejt al., (Ja59), studied aerosol
particle size distributions indoors, outdoors, and in radium mines,
finding similar distributions in each place. Measurements by George
(Ge75a), George, £t aJ., (Ge75b) and others (Ha?6, Lo77, Le75) would
lead to similar conclusions. Holleman has also concluded that the
difference between mine and atmospheric aerosol particle distri-
butions was negligible, with the possible exceptions of the immediate
vicinity of diesel engines and remote areas of the mine where aerosol
concentrations were low (Ho68).
-------
In general, mine atmospheres are not expected to differ greatly
from environmental atmospheres of the same quality. Dusty atmospheres
have low, unattached radon-daughter fractions, clean atmospheres have
high unattached fractions. Well -ventilated areas have low radon-
daughter ratios, poorly ventilated areas have high ratios. There is
no feature which would uniquely identify either mine or environmental
atmospheres, as shown in Table 8.
TABLE 8
Comparison of Typical Aerosol Characteristics
Environment
Aerosol Ventilated Mines Outdoors Indoors
°-"(a'b>0> O.M-0.30'" 0.10W>
Concentration 107(drilling)(c)
(particles/cm3) 103-106 (c) lO^-IO5 (a) 104-105 (a'f)
(a)
Uncombined 0.04 0.08 0.07
Fraction
(Range) (0.002-0.12) (0.005-0.25) (0.003-0.20)
Radon-Daughter 1.0,1.0,0.4,0.3 (c) 1.0,0.9,0.7,0.7 (a>d) 1.0,0.8,0.8,0.7 (a'd'f)
Ratio Range to to to
1.0,0.3,0.03,0.03 1.0,0.8,0.5,0.3 1.0,0.5,0.3,0.2
References:
(a) Ge75a (d) Ha76
(b) Ge75b (e) In73
(c) Ge72 (f) Lo77
-------
There are several reasons for believing that the percent increase
in lung cancer per unit exposure to a general population could be
either more or less than that for miners. Alpha particles from radon
daughters have ranges in tissue comparable to the thickness of the
bronchial mucus and epithelium. The thickness of the bronchial
epithelium of underground miners may be greater than is common in the
general population. The BEIR Committee estimated that the shielding
provided by the thicker epithelium of miners reduced their dose (and
risk) per unit exposure by a factor of two compared to the general
population (Na?2).
On the other hand, miners' lung cancer mortality data reflect a
high frequency of cigarette smoking which tends to increase their lung
cancer risk relative to the general population. The degree to which
smoking in conjunction with exposure to radon daughters may increase
the incidence of radiation-induced lung cancer is not known. While a
study of U.S. uranium miners has suggested a very strong association
between cigarette smoking and radiation-induced lung cancer, the
correlation between age and smoking history in this study precludes
early judgment, particularly since the study also indicates that
nonsmokers have a longer latent period for radiogenic lung cancers
(Ar?6). Some Swedish data on underground miners show that smoking may
increase radiogenic cancers by a factor of about two to four (Ra?6),
however, these results may be dependent on the duration of follow up.
Axelson and Sundell (Ax?8) have reported that in a life span study of
19 exposed miners who died of lung cancer, the lifetime risk of lung
-------
cancer in non-smokers exceeded that of smokers. The latency period,
however, was much shorter for smokers. A sample size this small, of
course, precludes definitive judgments. Unfortunately, the Japanese
data are, as yet, too imcomplete to yield comparable risk estimates
for cigarette smokers or non-smokers or even by sex (Be?7).
Smoking is common in all populations at risk from environmental
radon. While the frequency of smoking in U.S. uranium miners was not
very different from that of other male industrial workers at that
time, it exceeds the current level of cigarette use, particularly by
females (St?6). It is not clear that this will be true in the
future. Cigarette smoking among younger females is continuing to
increase and may approach or exceed cigarette smoking by males. If
so, relative risk estimates for exposure to radon daughters based on
the current incidence of lung cancer mortality, which is now almost
wholly due to male deaths, will be too low. Conversely, if cigarette
smoking in the U.S. becomes less common for both sexes sometime in the
future the incidence of lung cancer may decrease and relative risk
estimates based on the current incidence will be too high. Clearly
cigarette smoking is likely to be a factor in determining the proba-
bility that a lung cancer is induced by exposure to radon daughters.
The Agency recognizes that estimates of the risk due to radon daughter
inhalation have a wide range and may be too high or too low, depend-
ing, among other factors, on the prevelance of cigarette smoking in
the future.
-------
Based on Tables 6 and 7 and the considerations outlined above,
the range of the fractional increase in lung cancer due to radon decay
products in the general environment is thought to lie between one and
five percent per WLM. Studies utilizing longer follow-up times and
relatively low exposures tend to support the latter figure. However,
if miners are atypically sensitive to radon daughters because of other
characteristics in their occupational environment the fractional
increase for the general population could be as low as one percent per
WLM or less.
Another characteristic of the population at risk that differs
from underground miners is age. The estimated risk for miners is
averaged over adult age groups only, children not being at risk. It
is assumed in the absolute risk estimates given below that the risk
due to radon daughters is the same for children as adults. While this
has little effect on the estimates of risk made with an absolute risk
model, relative risk estimates are more dependent on the assumed
sensitivity of children to radiation. The Japanese experience, as
reported in the 1972 BEIR Report, indicates that children irradiated
at the age of nine or less have a relative risk rate of fatal solid
tumors ten times that of adults (Na72). However, none of the observed
cancers in this group has been lung cancer, a cancer of old age.
(There is, of course, no information on lung cancer due to
occupational exposure of children to radon decay products.)
The Agency believes that while it may be prudent to assume some
allowance for the extra sensitivity of children, the factor adopted
should be less than a factor of ten. Therefore, in the Tables below, a
-------
three-fold greater sensitivity for children is assumed in some of the
relative risk calculations of mortality due to inhaled radon decay
products.
Cumulative exposures for a given concentration of radon daughters
differ between miners and the general public. For radon decay pro-
duct exposures occurring to nonoccupationally exposed persons,
consideration must be given to the fact that the breathing rate
(minute-volume, etc.) of miners is greater and the number of hours
exposed per month less than in the general population. Radon decay
product exposures to underground miners are calculated on the basis of
a working level month (defined as exposure for 170 hours to one
working level). Exposure to radon daughters in the general environ-
ment occurs for an average of 730 hours per month. The breathing rate
over this period of time is less than an average breathing rate
appropriate for underground miners engaged in physical activity.
Assuming that the average underground miner (comparatively few of whom
work at the mine face) is engaged in a mixture of light and heavy
activity throughout the working day, his monthly intake of air on the
c
job is about 3 x 10 liters (In 75). An average man (reference man)
n ii
is assumed to inhale 2.3 x 10 liters per day (males) or 2.1 x 10
liters per day (females) (In 75). The average intake for both sexes
c
is 6.7 x 10 liters per month, 2.2 times more than for miners at
work. Therefore, an annual exposure to 1 WL corresponds to nearly 27
WLM for exposures occurring in the general environment.
In the case of radon in residential structures, the time the
residence is occupied must be considered also. On the average,
-------
Americans spend about 75 percent of their time in their place of
5
residence (Mo?6) so that about 5 x 10 liters of residential air is
inhaled each month. This corresponds to about 20 WLM per year for a
radon decay product concentration of 1 WL in residential structures.
Children respire a greater volume of air relative to the mass of
irradiated bronchial tissue than do adults, so that their exposure to
radon daughters is almost a factor of two greater for a few years
(In75). This increase has been included in the Section 4.1.4 risk
estimates.
4.1.4 Risk Estimates for the General Public
Estimates of cancer risk in this report have been derived from an
analysis that considers the following factors: the competing risk from
causes of death other than radiation, the fractional and absolute
increase in lung cancer per unit exposure, the duration of the expo-
sure, the period between the time of exposure and the occurrence of a
clinically identifiable cancer (latency), and the length of time a
person is at risk following the latent period (plateau period) (Bu78).
The risk estimates below assume a fixed latent period of 10 years for
lung cancers (Na76). Although there may be some correlation between
latency and age, relative risk estimates are not too sensitive to this
parameter. Increasing the latency period to 30 years reduces the
estimated risk by between 20 and 40 percent depending on the sensi-
tivity assumed for children. In the case of lung cancer, it is
assumed that following the latent period an individual remains at risk
for the duration of his or her lifetime. While for some cancers a
49
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shorter plateau at risk may be appropriate, the U.S. miner data as
well as the Japanese bomb survivor data reflects a continuing increase
in radiogenic lung cancers beyond 70 years of age.
In these risk estimates it is assumed that the population at risk
is subject to lifetime exposure and the distribution of ages is that
in a stable (stationary) population (Un?5). The Agency recognizes
that residential dwellings are seldom occupied by one family group for
their lifetimes. However, this has little effect on the ultimate
health impact if another family occupies the structure. The health
risk to a particular family is a function of the time they occupy the
dwelling and to a lesser extent their ages. For most practical pur-
poses, the risk due to occupancy of less than 70 years can be found by
taking a fraction of the risk given below as proportional to the years
of occupancy. For example, 7-year occupancy would be expected to
yield one-tenth the estimated risk of lung cancer due to lifetime
exposure, approximately 70 years. Residences which serve primarily as
children's or geriatrie's homes would be obvious exceptions.
The excess cancers due to radiation change the cause of death and
the age at which death occurs in the population at risk. The EPA
analysis provides estimates of the number of premature deaths, the
number of years of life lost per excess death, and the total number of
years of life lost by the population at risk. These parameters are
included in the risk estimates presented below.
Based on the assumptions discussed above, Table 9 lists the
estimated number of premature fatalities due to lung cancer that may
50
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occur in a population of 100,000 persons occupying structures having a
radon decay product concentration of 0.02 WL. The total number of
years of life lost by the population at risk is also tabulated. These
estimates are based on relative risk models which assume a 3 percent
increase in lung cancer per WLM. Two cases are compared in this
Table: (1) that adults and children have the same sensitivity, and (2)
that children below the age of ten are three times more sensitive than
adults. It is seen that the latter assumption increases the estimated
risk by about 50 percent.
Table 9
Estimated Risk of Lung Cancer Per 100,000 Exposed Individuals
Due to Lifetime Residency in Structures Having an
Average Radon Daughter Concentration of
0.02 WL Relative Risk Model*
Excess Cancer Deaths Total Years Lost
Child Sensitivity = Adult 2,000 30,000
Child Sensitivity = 3 x Adult 3,000 50,000
•Assumed mortality 3 percent per WLM (see text)
Table 10 presents absolute risk estimates for a radon decay
product concentration of 0.02 WL and lifetime exposure. This Table
has been calculated on the assumption that absolute risks are
independent of the age at which exposure is received. The estimate of
the number of years of life lost, compared to the relative risk for
the same age sensitivity, is about the same, c.f. Tables 7 and 8. The
estimated number of excess fatalities is a factor of two less than
that estimated using the relative risk model. This is within the
51
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uncertainty of the relative risk estimates since the range of values
for the percent increase in lung cancer per WLM is between 1 and 5
percent per WLM, vis a vis the 3 percent increase assumed in Table 10.
Table 10
Estimated Risk of Lung Cancer Per 100,000 Exposed Individuals
Due to Lifetime Residency in Structures Having An Average
Radon Daughter Concentration of 0.02 WL
Absolute Risk Model*
Excess Cancer Deaths Total Years
Lost
Child Sensitivity = Adult 1,000 27,000
*The assumed risk coefficient is 10 excess lung cancer deaths
per WLM for 10^ person years at risk (Na 76).
For comparison purposes, it is of interest to estimate the number
of excess lung cancers in the U.S. due to ambient levels of radon
decay products in non-contaminated areas. The concentration of radon
decay products in structures has not yet been surveyed extensively.
Most measurements reported in the literature are for either a short
duration, i.e., single samples, or in contaminated areas. An excep-
tion is the long-term radon measurement program of the Environmental
Measurements Laboratory in the Department of Energy. Their measure-
ments of radon decay products indicate average background levels in
residences of 0.004 WL (Ge 78). An ambient indoor background of this
level yields calculated risks one-fifth of those shown in Table 9,
i.e., from about 400 to 600 cases. This is about 10 to 20 percent of
the expected total national lung cancer mortality of 2900 per 100,000
in a stationary population having the 1970 U.S. mortality rates. This
52
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percentage of lung cancer mortality is not necessarily attributable to
radon exposures alone, since many oofactors have been implicated in
the etiology of lung cancer. It is emphasized that these risk esti-
mates are not precise and that the actual risk from radon daughter
exposures could be a factor of two or more larger or smaller.
It should also be noted that the risk estimates made here are
based on a risk analysis using U.S. national health statistics. They
have not been adjusted for the age, sex, or other demographic factors
N
pertinent to persons living on phosphate lands in Florida. To the
extent that the incidence of lung cancers in these areas is higher by
about 40 percent than the national average, the estimated health
impact of radon exposures given above may be low in Florida
residents. In contrast, the persons living on phosphate lands could
have demographic characteristics which differ from the national
average in such a way as to lower their risks compared to those listed
above. For example, if the housing were used primarily by the very
old, there would be appreciably less health impact.
4.2 The Health Risk Due to External Radiation Exposure
Unlike the highly ionizing alpha particles from radon daughters,
external radiation exposures are due to lightly ionizing secondary
particles from interactions along the path of gamma-ray penetration.
High energy gamma-rays penetrate through the body causing a relatively
uniform exposure to all tissues and organs. Since all organs and
tissues are exposed, the complete spectrum of cancers outlined in the
53
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1972 NAS-BEIR Report (Na72) would be expected. In addition, some
genetic risk, resulting from irradiation of the gonads, would be
expected to occur.
In the case of external penetrating radiation, data presented in
the 1972 NAS-BEIR Report (No 72) yields the following estimates for
lifetime whole body exposure to 100,000 persons as shown in Table 11.
TABLE 11
Estimated Lifetime Risk of Excess Fatal Cancer and Genetic
Abnormalities Per 100,000 Individuals Exposed
to an Annual Dose Rate of 100 mrem
Excess Fatal Cancers Total Years Lost
470 a) 6500 a)
Relative risk 150 b) 2700 b)
84 a) 1900 a)
Absolute risk 68 b) 1700 b)
a) life time plateau b) 30 year plateau
Serious genetic abnormalities*
all succeeding
1st generation generations
2-40 10-200
•Birthrate 2% per year
These estimates are based on the assumption that the number of
health effects observed at relatively high doses and dose rates can be
extrapolated linearly to the low levels of radiation usually found in
the environment. Table 11 lists only fatal cancers. The 1972 NAS-
BEIR Committee has estimated that a comparable number of non-fatal
cancers could be induced also.
54
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External exposure to natural background radiation in Florida,
from both cosmic radiation and radiation from radioisotopes present in
the soil, is about 59 millirem per year, except in regions containing
anomalous sources. The estimated lifetime risk associated with this
background is therefore about 60$ of the values listed in Table 10.
55
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SECTION 5.0
ANALYSIS OF CONTROL ALTERNATIVES
5.1 SUMMARY OF AVAILABLE CONTROL MEASURES*
There are five major types of radon decay product control
measures. These are categorized in Table 12 as to their efficacy for
application to existing or planned structures. For existing
structures, air cleaners and polymeric sealants have been shown to be
efficient at either reducing radon decay product levels in the
structure or radon diffusion through the foundations, respectively.
The cost range for these measures is $900-2600 (assuming an average
cost of $1200 for sealant application). These cost values are based
on the sum of capital cost, plus future maintenance charges and
operational costs reduced to their present worth, the discount factor
being 6 percent per year over 70 years, the assumed lifetime of the
average structure. For planned structures, design measures could
include ventilated crawl spaces, excavation and fill, and improved
slab construction. As a result of these measures, radon diffusion can
be reduced before it enters the structure's atmosphere by venting or
reduction of the parent radium concentration. Total costs for
implementing these measures vary from $550 (for crawl space
construction) to $5500 (for excavation and fill). As these are all
A more detailed treatment of the subject can be found in
Appendix C.
56
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TABLE 12
ESTIMATED AVERAGE COST OF CONTROL MEASURES FOR
STRUCTURES CONSTRUCTED ON FLORIDA PHOSPHATE LAND*
(Jl
~J
CONTROL MEASURE
EXISTING STRUCTURES
AIR CLEANERS:
HEPA
ELECTRONIC
ELECTRONIC AND AIR EXCHANGER
POLYMERIC SEALANT-
PLANNED STRUCTURES
VENTILATED CRAWL SPACE:
EXCAVATION AND FILL:
(TO 10' DEPTH)
COMMERCIAL FILL RATE -
FOR 80% RADON REDUCTION (INCLUDES 99%
GAMMA)
FOR 80% GAMMA REDUCTION
W/NOMINAL FILL COST -
FOR 80% RADON REDUCTION (INCLUDES 70%
GAMMA)
FOR 80% GAMMA RED
IMPROVED SLAB CONSTRUCTION:
FOR 80% RADON REDUCTION (INCLUDES 70%
GAMMA)
FOR 80% GAMMA REDUCTION
CAPITAL
COST
$400
$350
$900
S600-S1950
$550
$3250-$5500
$250 -$400
$2550-$2900
$200
$550
$600
ANNUAL
MAIN-
TENANCE
COST
$100
$25+ ***
$25+
UNDEFINED
NONE
NONE
NONE
NONE
NONE
NONE
NONE
ANNUAL
ELECTRICAL
COST
UNDEFINED
$10
$80
NONE
UNDEFINED
NONE
NONE
NONE
NONE
NONE
NONE
TOTAL
AVG. ANNUAL
OPERATING
COST
$100
$35+
$105+
NONE
NONE
NONE
NONE
NONE
NONE
NONE
NONE
PRESENT
WORTH Ol
TOTAL COST
(70 YRS)
$2050
$900
S2600
S600-S1950
$550
S3250-S5500
S250-S400
S2550-S2900
$200
$550
$600
"ASSUMMING 1500 SQUARE FEET FLOOR AREA AND 1977 DOLLAR VALUE (6% DISCOUNT PER YEAR APPLIED) ALL FIGURES ARE FOR RADON
PROGENY REDUCTION EXCEPT WHERE OTHERWISE NOTED
**SEE TEXT
***"+" SIGNIFIES THAT THE ESTIMATE GIVEN IS MOST LIKELY A MINIMAL ONE ALTHOUGH THE ACTUAL AVERAGE IS UNDEFINABLE USING
AVAILABLE COST DATA
-------
passive measures (i.e., having no maintenance or operational
requirements), the total cost involved consists solely of the capital
cost of implementation (although there may be minor exceptions such as
additional heating cost due to increased infiltration of air and heat
conduction through the floor for a crawl space compared to an on-grade
slab).
The control measures listed in Table 12 have been field tested on
a limited basis in a number of locations in this country and Canada.
In the Grand Junction (Colorado) remedial program, for example,
sealants, excavation and fill, and electrostatic precipitators were
used to reduce indoor radiation levels pursuant to the Surgeon
General's Guidelines (see page 77). While the latter two methods
achieved reduction efficiencies at or near 80 and 40 percent,
respectively, results from application of sealants proved
inconsistent. Experience by the Canadian authorities (At78, Fi78) in
applying sealants to structures constructed on radium-contaminated
soils, however, suggests that this lack of consistency in achieving
desired reduction is likely due to inadequate sealing of existing
conduits for radon into the structure's atmosphere. Their objective
of achieving indoor radon decay product level reduction down to .02 WL
(including background) was largely met by a combination of sealant
application and removal of these major radon pathways in the
foundation.
58
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Although none of the radon decay product measures have been field
tested in Florida, on the basis of their demonstrated efficiencies in
these field programs, all of these measures should have an efficiency
of about 80 percent, with the exception of electronic air cleaners
(HO percent), when employed in normally ventilated structures. The
lack of field confirmation is a drawback in determining the
cost-effectiveness for each control. Regardless of this uncertainty,
however, the cost figures are considered representative and permit a
preliminary evaluation of cost-effectiveness.
Control of gamma exposure in existing structures requires either
the addition of shielding or removal of the radium source from under
the structure. Both of these procedures are quite expensive, with an
estimated cost of 15 to 20 thousand dollars per structure. For gamma
exposure reduction in planned structures, improved slab construction
(i.e., additional slab thickness) should be about 80 percent effective
for an additional four inches of concrete at an average cost of about
$600. However, if clean fill at minimal or no cost is available, a
comparable reduction in exposure may be possible at lower cost.
5.2 COST-EFFECTIVENESS
Control cost-effectiveness is defined as the ratio of the present
worth of the cost of control to the reduction in health risk
anticipated. The upper limit of acceptable cost-effectiveness is a
value judgment on the maximum rate of spending that is justified for
59
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averting human health effects. While a detailed discussion of this
issue is outside the scope of this document, such determinations have
been made in other guidance issued by the Federal government. In the
Uranium Fuel Cycle Standard (40CFR190), for example, a limit on
reasonable cost-effectiveness ranging from $200,000-500,000 per health
effect averted was used. While not necessarily applicable to the
Florida case, this example provides some perspective concerning
reasonable limits on acceptable values of cost-effectiveness.
5.2.1 General
As previously noted, two general categories of remedial measures
are involved: those for existing structures which have been
constructed on radium-bearing soil and those for structures which may
be so sited in the future. These are important distinctions (as
discussed further in Appendix C) because different types of controls
have different costs and effectiveness depending on whether they are
applied prospectively or retrospectively. Therefore, this examination
of control cost-effectiveness is divided into four parts: radon decay
product controls for existing structures, radon decay product controls
for new structures, external gamma exposure controls for existing
structures, and external gamma exposure controls for new structures.
In making estimates of the cost-effectiveness of various control
technologies, the following assumptions were used:
1) The average dwelling has 1500 square feet of slab foundation.
60
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2) It is occupied 75 percent of the time by a statistical
average of 3^5 people.
3) Control costs are summed for a 70 year period, the assumed
lifetime of the structure. While this may not be quite
appropriate for existing structures, it does not
significantly change the results because the costs of most
controls are dominated by their capital cost. Further, the
present worth of any annual costs beyond 20 or 30 years
becomes negligible.
5.2.2 Control of Radon Decay Products
As previously estimated, the "normal" background radon decay
product level in a Central Florida dwelling is about .004 WL. A
structure which exhibits an indoor radon decay product concentration
of .030 WL is thus about .026 WL above normal. The discussion on
control technology effectiveness in Appendix C indicates that an
average 80 percent reduction in the average indoor radon decay product
level could be attained using one or more of the control methods
listed. For this assessment it is assumed that the 80 percent
reduction only applies to radon decay product air concentrations in
excess of "normal" background. In many cases "normal" background
radon decay product concentrations would probably also be reduced by
applying these controls, but such potential reductions are not
included in this evaluation of cost-effectiveness. If they were to be
61
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included they would tend to decrease the resource expenditures per
health effect averted, making the application of the control more
cost-effective.
Applying remedial measures to a structure exhibiting an average
indoor radon decay product air concentration of .026 WL above normal
(0.03 WL gross) is estimated to typically result in reducing the
average concentration to about .005 WL above normal (.009 WL gross).
The cost-effectiveness of taking this control action (based upon the
health risk estimates in Section 1) is estimated as follows:
estimated risk of lung cancer per 100,000 exposed due to
lifetime residency at .03 WL = 3000 premature deaths (child
sensitivity = adult)
estimated risk of lung cancer per 100,000 exposed due to
lifetime residency at .009 WL = 900 premature deaths (child
sensitivity = adult)
Therefore, by reducing the level from .03 to .009 WL, an
estimated 2100 lung cancer cases per 100,000 exposed are avertable.
This is normalized to one structure assuming an average occupancy of
3.5 individuals to yield .074 averted lung cancer cases per structure.
From Table 12, the cost for controls ranges from $900 to $2600
per structure. Therefore, the cost-effectiveness is:
$900-$2600/structure _ $12,000 to $35,000 per
.07^ premature deaths averted/structure premature death averted
62
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The above analysis was performed for various indoor radon decay
product concentrations for both existing and proposed structures, (the
latter at a projected cost of $550 per structure), and graphed in
Figure 8 for both initial and achieved indoor radon decay product
levels. For both categories of structures, it is apparent that
cost-effectiveness approaches unreasonably high values asymtotically
at roughly the .01 WL control level. For higher indoor
concentrations, the calculated cost-effectiveness is generally
favorable.
5.3.3 Control of External Gamma Exposure
Average outdoor gamma radiation exposure rates measured around
the dwellings studied ranged from 3 to 42 yR/h (26 to 370 mrem/year).
Average indoor gamma radiation exposure rates for these structures
ranged from 3 to 27 yR/h (26 to 240 mrem/year). Due to the shielding
effectiveness of the materials used in the construction of these
structures, most of them exhibited lower average radiation exposures
rates indoors than outdoors. The principal shielding element
contributing to this effect is the concrete used in the slab
foundations and the masonry walls. Other factors influencing the
ratio of indoor to outdoor exposure include: 1) at lower external
radiation exposure rates (5 to 9 yR/h), much of the exposure is not
readily reducible by adding floor shielding because of the cosmic ray
component and the scatter from the ubiquitous normal radioactive
63
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Q
01
P
ill
LL
Li-
La
I
co
cc
o
Q
LL
O
CO
Q
CO
ID
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LU
LU
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Figure 8
COST-EFFECTIVENESS OF REMEDIAL ACTION TO REDUCE INDOOR RADON
DECAY PRODUCT LEVELS FOR EXISTING AND PLANNED STRUCTURES
60
50
40
30
20
10
EXISTING
(S900-2600/STRUCTURE)
PLANNED
($550/STRUCTURE)
I
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
CONCENTRATION LEVEL AT WHICH REMEDIAL ACTION IS INITIATED (IN WORKING LEVELS )
0.005 0.007 0.009 0.011 0.013 0.015 0.017
CONCENTRATION LEVEL ACHIEVED BY REMEDIAL ACTION (IN WORKING LEVELS)
-------
surroundings, and 2) the construction material may contain significant
concentrations of radioactivity which would offset any shielding
reduction.
Precise calculation of the exposure reduction expected due to
control measures, such as additional slab thickness or removal of
contaminated fill under a structure, is complex. It depends upon the
geometry of the structure, its material makeup, and the radioactive
environment, all of which can be approximated using a general model.
Because the cost of achieving control of gamma exposure in
existing and new (or prospective) structures is vastly different, two
separate evaluations need to be performed. In estimating the control
cost-effectiveness for new structures, the following general
assumptions were used:
1. The structure type in question is slab-on-grade.
2. The normal external gamma radiation exposure rate is 6 uR/h.
3- The impact of shielding, specifically concrete, on exposure
reduction was taken from Figure 9 (SC 71*).
4. Practical control cannot reduce the exposure rate to below
normal background (primarily as a result of unshielded
contributions through the structure walls).
5. The reduction factors are applied only to the difference
between the normal background and unshielded exposure rates
in computing the impact of shielding.
While these assumptions lead to a simplistic model, there does
appear to be sufficient agreement with the field data collected for
65
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1.0
LLJ
h-
<
X
LU
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oo
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0.1
0 01
0.001
PACKED EARTH
ORDINARY CONCRETE
(G% POROSITY)
I
. 1 . i . . . I i . . 1 1 I
0 4 8 12 16 20
THICKNESS OF SHIELDING (Inches)
24
FKJUK; 9. REDUCTION OF GAMMA EXPOSU RE RATE RESU LTING
FROM EARTH OR CONCRETE SHIELDING (Sc 74)
66
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slab-on-grade structures throughout the Central Florida study area as
discussed in Appendix D and graphed in Figure 10. This is
particularly true of structures originally exhibiting outdoor gamma
exposure rates greater than 15 yR/hr. Therefore, it is anticipated
that adding sophistication to the model would not markedly improve the
usefulness of the analysis for decision making.
For new structures, the cost-effectiveness of controlling
external gamma exposure is estimated as follows for a structure that
is assumed to have an unshielded (i.e., external) exposure rate of
40 yR/h:
- A structure with a 4 inch shielding slab is estimated to
have a gamma exposure reduction factor of 0.35 (Figure 9);
therefore, the (model) residual indoor exposure is:
(40 - 6) yR/h x 0.35 +6 yR/h = 18 yR/h
Therefore, the net reduction is:
(40 - 18) yR/h = 22 yR/hr;
which, assuming 75 percent occupancy, 3-5 persons per structure and a
mean lifetime exposure period of 70 years is equal to approximately
600 fatal health effects per 100,000 population (relative risk
model). Assuming a control cost of $550 for a typical 4" concrete
slab, the cost-effectiveness is:
$550
6x10~3 health effect averted
= $28,000 per health effect averted
67
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f.
tr
5
LU
oc
to
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ai
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20
19
18
17
16
15
14
13
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10
Figure 10
CORRELATION OF OBSERVED INDOOR GAMMA EXPOSURE WITH THEORETICAL ESTIMATION
LEGEND: A = 1 DBS, 8=2 DBS, ETC.
I
I
I
A A
,, d 9 10 11 12 13 M 16 16
f-TM\1A|iD ll\noOH GAMMA EXPOSURE (juR/h) (3ASED ON BACKGROUND 6juR/h AND REDUCTION FACTOR OF 0.35 foi 4" CONCRETE SLAB)
-------
This calculation has been performed for several cases involving
both new and existing structures. The results of these calculations
are graphed in Figure 11 (a, b, c, d, e). The three levels of control
for the cases described in Figure 11 (a, b, c) are successive 4"
additional depths of concrete in the foundation, which is the least
expensive control measure. Therefore, Level I (Fig. 11a) is the
normal slab thickness of H inches, Level II (Fig. 11b) is a total of 8
inches, and Level III (Fig. 11c) is a total of 12 inches of ordinary
concrete. The cost-effectiveness for controlling gamma exposure in
existing structures (Fig. lid) is based on excavation and filling with
clean dirt in and around the structure's foundation, at a cost of
$15,000 per structure as derived from the Grand Junction remedial
program (Co?8). A summary of cost-effectiveness for controlling
indoor exposure in both planned and existing structures is provided in
Figure 11e.
In controlling gamma exposure, some reduction in indoor radon
decay products levels might also be achieved. However, because of the
difficulty in reliably predicting such effects the cost-effectiveness
estimates do not take them into account. While it is anticipated that
radon decay product levels would generally be the primary factor in
determining if radiation control is warranted, it would be prudent,
particularly in new structures that require preventative measures and
where acceptable radon decay product control can be achieved by a
number of means, to consider measures which can minimize both
69
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Figure 11a
COST-EFFECTIVENESS OF EXTERNAL GAMMA EXPOSURE CONTROL FOR PLANNED STRUCTURES
(ASSUMING 4" CONCRETE SLAB CONSTRUCTION' $550)
1200
1000
800
600
400
200
Q
CC.
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LL.
D
RESULTING
LEVELS
(ESTIMATED)
10
15 20 25 30
UNSHIELDED GAMMA EXPOSURE RATE (juR/h)
35
40
-------
Figure 11b
COST-EFFECTIVENESS OF EXTERNAL GAMMA EXPOSURE CONTROL FOR PLANNED STRUCTURES
(ASSUMING 8" CONCRETE SLAB CONSTRUCTION@$1,500)
1200
DC
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RESULTING
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(ESTIMATED)
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0
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15
20
25
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10 15
UNSHIELDED GAMMA EXPOSURE RATE (juR/h)
35
40 | INITIAL
20 j RESULTING
-------
Figure 11c
COST-EFFECTIVENESS OF EXTERNAL GAMMA EXPOSURE CONTROL FOR PLANNED STRUCTURES
(ASSUMING 12" CONCRETE SLAB CONSTRUCTION@$4,000)
12001-
OC
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15 20 25 30
10 15
UNSHIELDED GAMMA EXPOSURE RATE (juR/h)
35
40
20
INITIAL
RESULTING
-------
Figure 11d
COST-EFFECTIVENESS OF EXTERNAL GAMMA EXPOSURE CONTROL FOR EXISTING STRUCTURES
(ASSUMING EXCAVATION AND FILL<*$15,000)
3 2400
cc
LU
2000
LU
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- 800
RESULTING
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(ESTIMATED)
INITIAL LEVELS
IV
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UNSHIELDED GAMMA EXPOSURE RATE (xiR/h)
-------
0 1200
LU
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Lu 1000
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Figure 11e
COST-EFFECTIVENESS OF EXTERNAL GAMMA EXPOSURE CONTROL
FOR EXISTING AND PLANNED STRUCTURES
(SUMMARY!
800
600
CO
Q
Z
CO
O
I
b 400
"J 200
EXISTING (EXCAVATION
AND FILL @S15000)
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•a I
10 15 20 25 30
UNSHIELDED GAMMA EXPOSURE RATE (>uR/h)
35
40 INITIAL
-------
radiation exposure components. An example is excavation and fill (for
planned structures), which would remove both the source term for
radon-222 diffusion and gamma radiation.
In conclusion, assuming that it is reasonable to spend about
$200,000 to $500,000 to avert a health effect such as death or serious
genetic damage (Un76), it appears from Table 12 and Figure 8 that it
is cost-effective to apply most control technologies to reducing the
indoor radon decay product levels in new and existing structures from
levels at .005 WL above normal background (.009 WL gross) or higher.
In some cases it may even be cost-effective to apply radon control
technology at indoor radon decay product levels less than .005 WL
above normal background. However, this depends greatly on specific
sites and structures and a case-by-case review is required at such
levels.
In examining cost-effectiveness for control of gamma exposure,
review of Figure 11 suggests that in new structures, Control Level I
is cost-effective for initial gamma exposure rates greater than H uR/h
above normal (10 yR/hr gross), Control Level II is cost-effective for
rates greater than 14 yR/h above normal (20 yR/h gross), and Control
Level III is cost-effective at rates greater than 24 yR/h (30 yR/h
gross). For existing structures, review of Figure 11 indicates that
it does not appear to be cost-effective to retrofit structures with
control measures solely to reduce external gamma radiation exposure.
75
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SECTION 6.0
ALTERNATIVES FOR RADIATION PROTECTION
6.1 EXISTING RADIATION PROTECTION GUIDANCE
At present there are no Federal radiation protection guidelines
specific to radon daughter levels in structures. Recommendations of
«
the former Federal Radiation Council published in 1960 estab-
lished annual guides for exposure of the whole body of 500 mrems to an
individual in the general population and 170 mrems to an average
member of critical population groups. The Council further noted that
"every reasonable effort should be made to keep exposures as far below
this level as practicable." However, these limits excluded natural
background radiation, and it is not clear whether or not they were
intended for application to situations in which man has artificially
increased this natural background.
Another potentially relevant Federal guide is the U.S. Surgeon
General's Guidelines for remedial action in Grand Junction, Colorado
(Pe?0). These guidelines, given below, were developed in 1970, for
use in establishing remedial action criteria for structures having
uranium mill tailings under or around them.
*When the Environmental Protection Agency was established by
Reorganization Plan No. 3 in 1970, the functions and authority of the
Federal Radiation Council were vested in EPA.
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SURGEON GENERAL'S GUIDELINES:
RECOMMENDATIONS OF ACTION FOR RADIATION EXPOSURE LEVELS
IN DWELLINGS CONSTRUCTED ON OR WITH URANIUM MILL TAILINGS
External Gamma Radiation
Level
Greater than 0.1 mR/hr
From 0.05 to 0.1 mR/hr
Less than 0.05 mR/hr
Indoor Radon Daughter Products
Level
Greater than 0.05 WL
From 0.01 to 0.05 WL
Less than 0.01 WL
Recommendations
Remedial action indicated
Remedial action may be suggested
No action indicated
Recommendations
Remedial action indicated
Remedial action may be suggested
No action indicated
The Surgeon General's Guidelines apply specifically to dwellings
constructed with or on uranium mill tailings, and as noted when they
were issued, should not be interpreted as being applicable to other
cases. Since these guidelines were developed, additional information
has become available regarding the risk associated with exposure to
radon decay products.
6.2 BASIC RADIATION PROTECTION PRINCIPLES
For the purpose of developing radiation protection recommenda-
tions for acceptable indoor radiation levels of radon decay products,
the most realistic basis for health risk estimates is epidemiological
77
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studies of groups previously exposed to elevated levels of radon decay
products. A linear nonthreshold dose-effect relationship has been
assumed to be a prudent model for deriving risk estimates for the
general public from these data, in the absence of contrary infor-
ation. This assumption implies that there is some risk to humans no
matter how small the amount of absorbed radiati.on and that the risk at
low dose levels is directly proportional to that observed at higher
doses. In judging the acceptability of such risks, it must be
considered that all persons are exposed to a large number of competing
risks, including other radiation risks, and any reduction of risk from
a single source must be viewed in the overall perspective of the
social and economic impacts involved. The assumption that any expo-
sure to low level ionizing radiation has some degree of associated
adverse health effects is reflected in guidance issued by the Federal
Radiation Council (FRC) in I960 (Fe60) that any necessary exposure
should be reduced to "as low as practical" (ALAP) levels. This
guidance also recommends that any planned exposure above zero (or
background) be justified on the basis of a benefit which, as a
minimum, balances the risks associated with the exposure. Since the
benefits of residence in a particular location or in a specific
structure cannot be quantified on a generic basis (if, indeed, they
can be assessed at all) this latter guidence is not addressed here.
The ALAP criterion was addressed on the basis of an examination of the
cost-effectiveness of control, in terms of dollars per health effect
averted.
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6.3 ALTERNATIVES FOR RADIATION PROTECTION
A number of alternatives are available, both for the form of
radiation protection recommendations and alternative levels of con-
trol. Consideration of administrative alternatives (as opposed to
alternative criteria levels), e.g., no action or delayed action,
however, are not addressed as they are not within the scope of this
discussion. It should be emphasized that the control levels discussed
in this section are provided as examples and do not reflect all of the
options possible.
Three basic alternatives bearing on the level and degree of
control may be considered. In summary, these are:
1. Define a nationally applicable level of unacceptable
continuous radon daughter exposure based on consideration of the
acceptability of the health risk, with remedial measures also taken
below this level, whenever reasonable, based upon local determinations.
2. Define an upper control limit for structures built on
phosphate land in Florida based upon two considerations: 1) the
improvement judged reasonably achievable using remedial measures for
the majority of cases in Florida, and 2) a judgment of the unaccept-
ability of the health risk above this level. Define a lower limit
based upon practical limitations of uncertainty in background, and the
effectiveness of remedial measures, below which no consideration of
remedial action is recommended. Between these limits, the imple-
menting authorities would be advised to assess the practicability of
specific remedial measures on a case-by-case basis.
79
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3. Define a lower limit only, below which consideration of
remedial action is not recommended. Above this level, remedial
action, justifiable on the basis of available cost-effectiveness
information, would be taken. The degree of control warranted would be
determined on a case by case basis taking into account such factors as
cost and effectiveness of available remedial measures, the lifetime
risk averted, the normal background level, the life expectancy of the
structure, and measurement uncertainties.
The principal obstacle to establishing a national recommendation
(first alternative) is limited knowledge of national radon levels.
This makes it difficult to predict, on either an absolute or relative
basis, what levels can be achieved reasonably or the scope of the
public health problem. In addition to variation in air leakage rates
of structures with climate (this variable can have a profound effect
on radon levels), new potential radon problems are still surfacing.
The phosphate situation, itself, was only recently uncovered. Within
the last year, newly identified comparable situations have been
identified arising from thoron, an analogue of radon from thorium
deposits present in monazite sands in Georgia and to a small degree,
in parts of Florida. The magnitude of the potential health risk
associated with chronic exposure to radon decay products at levels
observed on phosphate lands in Florida appears to justify action
independent of consideration of guidance development on a national
level.
80
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Alternative 2 contemplates a lower bound for consideration of
remedial action which would reflect practical limitations on
measurement and the effectiveness of remedial action and an upper
level above which remedial action would be mandatory. This lower
bound to ALARA lies approximately at the 0.005 WL (above background)
level, on the basis of experience with such measurements and
cost-effectiveness of available remedial measures developed in this
study (see Figure 8). The major advantage of this option is its
underlying recognition that, given the limitations of technical
information currently available on radon levels in residences, costs
of remedial action, and the efficacy of remedial measures, it is
desirable to define a reasonable range of flexibility within which
local authorities can address these uncertainties. This flexibility
may also be of importance to individual homeowners who, after
consideration of the reasonableness of reducing their risk, may decide
to take more or less action than called for by strict cost-
effectiveness considerations alone, due to personally overriding
considerations such as their age, the remaining period of usefulness
of the structure, and their ability to pay for the incorporation of
control measures.
An upper bound criterion level above which remedial action would
be mandatory should be based on a balancing of health risk
considerations and the estimated reasonableness of the costs of
control action to bring indoor radon decay product concentration in
the worse cases down to at least this level. As a function of the
81
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level selected, there may be a significant fraction of structures
which will not be remediable to a sufficient degree to satisfy such a
level. For these particular structures, the options would be few,
consisting probably of either forced abandonment or the application of
non-cost-effective remedial action. This inherent disadvantage of a
mandatory criterion, can be minimized if the level chosen can be
projected to be attainable at reasonable cost in all or nearly all
cases.
The overall shortcomings of this alternative, like the advan-
tages, are inherent in the implementation of ALARA. Because its
implementation within the specified range would be left to the
discretion of local authorities or the homeowner, there is the
possibility that ALARA will be implemented incorrectly or not at all.
While education on the subject and government advice might reduce the
instances of misuse, the only means to assure implementation would be
to remove the flexibility provided by two levels. It is also possible
to recommend that remedial action be mandatory within this range with
the degree of control to be applied at the local authorities or the
homeowner's discretion. Despite public education and assistance in
making determinations as to the level of control at which ALARA is
satisfied for individual cases, implementation could still be highly
variable, depending on factors such as the individual's ability to
afford control measures, their ability to comprehend the risk and the
"cost-effectiveness" of control involved, and the extent to which
assistance is available from local authorities.
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Alternative 3 is an option under which the implementation of
remedial action would be called for at all indoor radon decay product
levels, above a minimum level, whenever reduction is reasonably
achievable. All of the difficulties present in the range between the
two levels provided by Alterntive 2 would apply to the whole range of
levels that fall above the single level provided in this Alternative.
In many situations observed in Florida it would be desirable and
practical to reduce the chronic exposure to radon decay product levels
to considerably less than an upper bound criterion level, as provided
for by Alternative 2. Review of the control technology and cost
information indicates that in many circumstances it is not unreas-
onable to achieve a post-control indoor radon decay product level of
less than 0.005 WL above normal background (0.009 WL gross). However,
at indoor radon decay product levels less than 0.009 WL (gross) it
becomes increasingly difficult to accurately measure and differentiate
the observed level from normal background. Other sources of radon
other than those amenable to control by the available technologies may
significantly contribute to the observed indoor radon decay product
air concentrations. These factors tend to increase the implementation
problems for local agencies at and near the 0.005 WL above background
level.
6.4 SELECTION OF RADIATION PROTECTION LEVELS
In developing radiation protection guidance, the following
objectives are important in selecting appropriate action levels:
83
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1. Minimize the health risk to the affected population.
2. Determine that recommended radiation levels can be measured
with reasonable accuracy, and, when necessary, differentiated from
normal background.
3. Determine that suitable control measures exist to reduce
indoor radiation levels to the recommended levels.
4. Determine that application of control measures does not
require the expenditure of unreasonable resources by individuals,
government authoritities or other groups.
5. Determine that the recommendations can be understood and
practically implemented by State and local responsible authorities,
and by the general public.
These objectives call for a series of judgments on the part of the
Agency in its guidance role, and the State or County in their role as
implementing authorities.
6.4.1 Radon Decay Product Levels in Existing Structures
As shown in Figure 8, some control of indoor radon decay product
levels in existing structures can be considered cost-effective at all
initial levels greater than 0.01 to 0.02 WL (including background).
This assumes control costs of $900 - $2600 per structure and 80
percent reduction. However, if the initial level is sufficiently
high, remedial action at these cost levels and at 80 percent reduction
efficiency may not be sufficient to bring a structure down to the
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0.01-0.02 WL range. Therefore, the selection of an action level equal
to or above this lower bound is also dependent more on practical
considerations of the degree of reduction economically achievable. As
illustrated in Table 13, the most basic factor bearing on economically
feasible implementation is the proportion of structures .which require
application of nonconventional control measures (i.e., other than
those listed in Table 12), in order to be brought into compliance with
the numerical criterion selected. At successively lower action
levels, the fraction of structures not easily remediable increases.
At 0.01 WL, for example, 15 percent of structures located on phosphate
land are projected to require more than readily achievable reduction
in levels compared to none expected at .03 WL, as extrapolated from
the EPA/DHRS survey. Using the .03 WL value as a baseline (i.e.,
assuming that no unusual costs are projected at this level), addi-
tional costs of $260,000 - $6MO,000, and $2,600,000 - $6,400,000 would
be accrued,respectively, at 0.02 WL .or 0.01 WL (assuming that 1/3 of
structures not conventionally remediable require special corrective
action at a cost of $10,000 - $25,000 per structure). The cost-
effectiveness of applying these "special" measures is generally in
excess of hundreds of thousands of dollars per health effect averted.
This obvious disparity between the cost-effectiveness of conventional
measures compared to unconventional ones is a result of the latter*s
high cost coupled with the relatively small additional reduction
achievable.
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TABLE 13
IMPACT OF ALTERNATIVE CRITERIA FOR
INDOOR RADON DECAY PRODUCT EXPOSURE
FOR STRUCTURES REQUIRING SPECIAL CORRECTIVE ACTION
(1)
(2)
Number and Percent
of Structures in Excess
Recommended
Remedial
Action Level
(RRAL)
.03 WL
.025 WL
.02 WL
.015 WL
.01 WL
(A)
EPA/DHRS
Survey
(N=104)
20
23
25
30
45
(B)
Extrapolated
(N=4000)
760
880
960
1160
1720
(0
Percent
19
22
24
29
43
(3)
Number and Percent of Structures
not Conventionally Remedial*
(A)
EPA/DHRS
Survey
(N=104)
-
1
2
7
20
(B) (C)
Extrapolated
(N=4000) Percent
-
40 1
80 2
270 7
770 19
(4)
Extrapolated Total Cost
of Special Corrective
Action for Structures
not Conventionally
Remedial**
(N=4000)
-
$130K - $320K
$260K - $640K
$900K - $2,200K
$2,600K - $6,400K
(5)
Cost-effectiveness
of Special
Corrective Actions
(dollars per health
effect averted)***
-
$140K - $430K
$170K - $560K
$220K - $81 OK
$330K - $1,500K
•Assuming 80 percent efficiency of control measures in reducing indoor radon decay product levels which exceed background.
•"Assuming 1/3 of structures not conventionally remediable require special corrective action, at a cost of $10,000-$25,000 per structure.
•••Assuming the above efficiency and costs for reduction from this and the previous RRAL for a structure housing 3-5 people.
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The development of appropriate action level, therefore, requires
judgment as to the most acceptable balancing of overall cost-
effectiveness with practical considerations, such as achievability of
control levels and measurement error. Given the aforementioned cost
of applying unconventional remedial measures and the problems
associated with measurement error at the lower levels, it appears
unreasonable to recommend mandatory action at levels less than 0.02
WL. Within the 0.02 to 0.03 range (the latter again representing a
level projected to be reasonably achievable in all structures), the
acceptability of a projected less than one percent of existing
structures requiring non-cost-effective remedial action must be based
on a judgment on the appropriate allocation of resources to achieve
reductions in health hazard, and the capability and willingness of
responsible parties to provide assistance programs for those
structures requiring additional corrective action.
6.4.2 Radon Decay Product Levels in Planned Structures
Reduction of indoor radon decay product levels is more practical
in new than in existing structures as shown in Figure 8. This is
because structure design, site preparation, selection of construction
materials, and the location can be planned. Through careful con-
sideration of these factors, almost all structures can and should be
designed to achieve ALARA, or 0.005 WL above background, as determined
for construction on phosphate land in Florida. It is possible
87
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that in some cases following construction using what was anticipated
to be properly designed control measures, the indoor radon decay
product level will be greater than 0.005 WL above normal. In some of
these cases additional controls may be warranted but in others the
lowest practical level may already be achieved. Such a determination
will require a case-by-case review. The cost-effectiveness of these
additional controls would, of course, be the same as that for existing
structures as shown in Figure 8.
6.4.3 Gamma Exposure in Existing Structures
The highest indoor gamma radiation dose observed in the exam-
ination of 1102 residential structures in Florida was 190 mrem/yr
(27 yrem/hr assuming 75 percent occupancy). It is not expected that a
significant number of structures with indoor radiation levels much
above or equal to this value will be identified. As shown in Figures
11d and e, the apparent cost of reducing this exposure is high and it
appears unreasonable to attempt reduction of such gamma levels in
existing structures.
6.4.4. Gamma Exposure in New Structures
As is the case for radon, the availability and cost-effectiveness
of control measures for gamma radiation exposure (as shown in Figures
lla-lle and discussed in the preceding section) in residences is such
that in most situations anticipated in Florida on phosphate lands, it
88
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is reasonable to design and site a new residence so that the indoor
gamma radiation exposure rate in the completed structure is less than
5 yR/h above normal gamma radiation background (normal is approxi-
mately 6 yR/hr). Assuming 75 percent occupancy, exposure at this
rate(11 yR/h) is estimated to result in about 100 additional cancer
fatalities annually per 100,000 persons exposed over a lifetime.
Designing structures to achieve an indoor gamma exposure rate less
than about 10 yR/hr (gross) is impractical, since differentiating
between normal background and elevated levels becomes increasingly
difficult below 10 yR/hr. Also, as in the case for radon daughters,
other sources of radioactivity such as construction materials, may be
significant contributors to the overall gamma exposure at these
levels. Because of high retrofitting cost, once a structure is built
using a design and siting plan to minimize indoor gamma radiation
exposure, no additional control is warranted for gamma reduction even
if the recommended gamma ray exposure guide is exceeded.
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SECTION 7.0
SOCIO-ECONOMIC IMPACT
7.1 GENERAL CONSIDERATIONS
At present, the socio-economic impact of implementing remedial
measures can only be evaluated on a qualitative basis, with emphasis
on the identification of probable areas of impact. The actual number
of residences affected, the field effectiveness of control measures
and their specific costs, as well as the availability of financial
aid, are among the factors not totally known at this time. Additional
information in each of these areas may have a substantial effect on
socio-economic impact.
The region under consideration includes about 300,000 acres of
land in central and northern Florida. Three general areas are covered
by the following discussion: impact on public and private
institutions and services, impact on business and employment patterns,
and personal impact.
7.1.1 Impact on Public and Private Institutions and Services
Evaluation of potential impacts in this area includes
modifications in the availability of housing in the region as a result
of radiation protection measures, and the added burden on local health
and building inspection departments. Among the primary forces that
would affect availability and property values negatively are the
90
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reluctance of developers and private builders to use phosphate land,
and possibly, the higher selling price (to cover the additional cost)
and/or poor market for houses that have had remedial action. The
magnitude of these factors depends upon the availability of
alternative construction sites, the ingenuity of construction firms in
incorporating remedial measures into housing plans, and the attitude
of potential home purchasers toward houses with remedial measures.
These factors would, in turn, rely on the type of remedial measure
implemented, its cost, and the degree of assurance for the builder or
homeowner that radiation levels will be effectively reduced.
The effect of the additional workload on local government from
implementing necessary radiation protection measures could be
significant, at least initially. There will be a need for additional
inspections, surveying and recordkeeping, as well as laboratory
facilities for radiological analyses. The availibility of the
necessary additional resources will be dependent on the financial
resources of the individual local health and housing departments. In
some cases either local programs may require cutbacks or the
recommendations may not be implemented fully. To estimate the total
potential economic impact on industry and the housing market
quantitatively would be totally speculative at this time. At a cost
of about $50-100 to determine radiation levels in one structure, the
evaluation of the 4000 structures estimated to be in the region would
cost about $200,000-$400,000. Clearly, these values could vary
depending upon the present capabilities of the local agencies.
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7.1.2 Impact on Business and Employment Patterns
With respect to the local economy, an equilibrium will result
between the positive and negative aspects of implementing a remedial
action program. The positive aspect would primarily be the economic
advantages to business dealing with products or services called for in
the remedial action program. The negative aspect would be the
detrimental effort such implementation could have on businesses
dealing with housing construction or land development. The net effect
for the area in question would be dependent upon a number of
variables, the most important of which is likely to be the impact of
reduced home construction and/or sales, whatever the reason (e.g.,
public attitude). For a high growth area such as Central Florida this
would be of some consequence if realized, although the low cost of
control measures for new residences should make a significant impact
on construction firms from this cause a remote possibility.
7.1.3 Personal Impacts
Some degree of personal impact is likely for those persons
residing in structures which have been found to be in need of remedial
action. Depending upon the type of measure implemented, some degree
of disruption to the occupants' lives, either through the initial
incorporation of a passive remedial measure, or the periodic
maintenance required for one of a non-passive nature, may result. The
cost of the remedial action, if necessary, may also have to be assumed
fully or in part by the homeowner, thereby, posing a significant
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economic burden. However, this negative impact may be merely one
segment of the overall cost to the homeowner, since the presence of
any remedial measures (other than the truly passive ones such as crawl
spaces) may affect the saleability of the residence and its market
value. Other determining factors would be the status of the housing
market in the area and attitudes of buyers towards the radiation
problem and remedial action.
7.2 MAGNITUDE OF THE AREA POTENTIALLY AFFECTED
About 120,000 acres of land have been mined for phosphate rock in
Florida; of that amount, about 50,000 acres have been reclaimed to
various degrees. Estimates suggest that approximately 7>500 acres are
being used for residential housing or commercial purposes, with about
1,500—4,000 structures. The total acreage which contains elevated
radium-226 concentrations near the surface, but is unmined, is unknown
at present, but preliminary research indicates that it may be quite
significant.
Land underlain by phosphate ore is located in the Central Florida
counties of Hillsborough, Polk, Manatee, Hardee, Highlands, Desota,
and Sarasota as well as several Northern Florida counties. Based upon
field experience, we do not believe that all of the land where
phosphate ore is located or all of the disturbed phosphate mine lands
will pose indoor radiation exposure problems to residents of
structures built there. Nonetheless, because of the radium-226
content of phosphate materials, the potential for indoor radon
93
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daughter problems must be anticipated and adequately evaluated
wherever the phosphate materials and associated radium-226 are
present. It is important to note that radium-226 associated with
other minerals in Florida, such as rare earths, titanium, and monazite
sands, may pose similar risks to residents.
7.3 ECONOMIC IMPACT OF REMEDIAL ACTION
Characterization of the economic impact of implementing remedial
measures for both existing and planned structures is performed by
consideration of the cost range of probable implementation scenarios.
Consideration is specifically limited to remedial costs as listed in
Table 12, although it is recognized that impacts as described in the
preceding section would also be applicable. As estimated in the DHRS
Final Report (1978), there are approximately 4000 structures built on
phosphate reclaimed land in Polk and Hillsborough Counties.
Statistics are not readily available on the number of new structures
being built or considered for reclaimed phosphate land. However, a
rough estimate can be made on the basis of annual housing starts for
those cities and towns located in the vicinity of identified areas of
reclamation. From data published by the Bureau of the Census (1977),
approximately 400 housing starts are noted for incorporated munici-
palities located in such areas of Polk and Hillsborough Counties for
1976. There were 3012 housing starts in unincorporated areas of both
counties in 1976. Approximately 50 in Hillsborough County and 950 in
Polk County are assumed to be located in the phosphate area as
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defined-in information derived from the respective county building
permit offices. Of the 1400 total housing starts, as many as 40
percent may need control measures to meet the recommended design
objectives, based on an analysis of the distribution of existing
structures. Therefore about 500 structures, or about 15 percent of
new residential construction starts in the two counties, are projected
to require remedial consideration per year.
From the combined (EPA and DHRS) TLD air sampling data collected
and the application of the findings made in Section 6, the remedial
cost range for the 4000 existing structures can be projected.
With .02 (including background) WL as an upper control level,
approximately 24 percent of the total sample, or 960 structures out of
the estimated 4000 structures, is projected to be in excess. In
addition, one third of 2 percent of structures may require special
corrective action to meet this control level at a cost of $270,000 -
$670,000. At a lower control level of 0.009 WL (0.005 WL + 0.004 WL
background), approximately 40 percent of existing structures or a
total of 1600 structures on reclaimed land would exceed this
criterion. Assuming an average remedial cost per structure of
approximately $1,000, as derived from Table 12 (assuming application
of polymeric sealants), a cost of one to one and a half million
dollars is projected for this range of control levels. Selection of
an appropriate measure and cost for existing structures is difficult
due to lack of data, but, generally, the individual cost of the
various available control measures is similar and this figure ($1000)
95
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is representative of any of them. With more limiting mandatory action
levels (e.g., 0.01 or 0.02 WL), the total cost projected would be
higher commensurate with the number of structures requiring additional
or special corrective action to satisfy the recommended control
level. With a mandatory control level of 0.01 WL, and assuming that
all not conventionally remediable structures identified in Table 13.
require special corrective action, rather than only one third, and,
further, assuming a cost for such special corrective action of $25,000
per structure, the maximum total cost would be $17,000,000.
Estimates for future structures to be built on reclaimed land
assume 500 construction starts per year over a ten year period, with
the cost of control over this period of time being $500 per structure
for a total of about $2,500,000. The economic impact due to remedial
action in both counties for such a ten year period would be about
three to four million dollars (undiscounted 1977 dollars). This
estimate is clearly a function of the rate of new house construction
on reclaimed land, which in turn depends on many variables, including
the growth rate of the counties, availability of reclaimed land,
zoning requirements, etc. Due to the relatively low cost associated
with crawl space implementation, however, this cost estimate is
probably a low one, assuming that other types of structure would also
be built.
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SECTION 8.0
IMPLEMENTATION OF RADIATION PROTECTION MEASURES
8.1 FEDERAL ROLE
These findings were developed through the Agency's authority to
provide technical assistance to States. The U.S. Environmental
Protection Agency has no authority to directly enforce recommendations
in the State of Florida. However, under authority transferred to the
Agency in 1970, EPA can develop Federal guidance for protection of
people exposed to radiation sources associated with structures. Such
guidance would apply to Federal agencies in the conduct of their
regulatory and other programs.
8.2 STATE AND LOCAL ROLE
In order to implement radiation protection measures effectively,
it will be necessary for State and local agencies within Florida to
enforce and carry them out. To this end, appropriate State and local
agencies could adopt measures such as those discussed in this document
through their own regulations which could be in the form of zoning
requirements, building codes, standards, or some other suitable
mechanism. In some cases, in order to provide effective
implementation, additional State and/or local authority may be
necessary.
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8.3 CONDUCT OF STRUCTURE EVALUATIONS
In carrying out remedial action, State and local governments, as
well as private individuals or groups, will need to conduct a variety
of measurements and evaluations to make appropriate decision-making
possible. To assist uniform application of any recommendations, the
Agency has developed suggested measurement guides for assessing
radiation levels in existing structures. Information on indoor radon
decay product exposure is necessary to determine whether remedial
action is warranted. In planning new structures, data on gamma
radiation exposure is necessary. All radiation measurements should be
performed by trained technicians using properly calibrated radiation
detection equipment.
Indoor radon decay product air concentration measurements should
be made using a Radon Progeny Integrating Sampling Unit (RPISU) or
some other appropriate system. If the RPISU or similar device is
used, the average indoor radon decay product level for a test
structure should be the mean of four to six measurements made over a
one-year period. Single measurements totalling less than 2^ hours
integrating time or multiple measurements of less than 125 hours
should not be used in determining the average indoor radon decay
product level unless absolutely necessary. Devices such as
instantaneous working level meters, grab radon or radon daughter
product samples, and track-etch films may be helpful in screening
numerous structures to determine those most likely to exhibit elevated
98
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indoor radon daughter levels. However, they should generally not be
used for remedial action decision-making unless the data is shown to
be of quality comparable to that obtained with the RPISU device. We
anticipate that work by the Agency or other groups may be able to
improve the decision-making usefulness of short-term measurements in
the future.
8.4 CONTROL COST-EFFECTIVENESS ASSESSMENT
Current Federal guidance for radiation protection provides for
reduction of exposures to as low as reasonably achievable (ALARA). It
is recognized that such guidance requires decisions at the local level
regarding which exposure level can be considered ALARA. This value
will differ from case to case and there are several factors to be
considered. First, the reliability of the data should be appraised.
How much measurement error is involved? Second, the normal background
level, which is conventionally the initial baseline for ALARA, should
be considered. Third, the cost to achieve the desired exposure
reduction should be evaluated. This factor is extremely important.
If the cost is minimal, then nearly any reduction (to normal
background) would be desirable. However, if the cost is substantial,
then the associated potential decrease in risk must be weighed by the
homeowner or the local authorities to determine if the application of
control technology is warranted. Fourth, the potential impact of the
dwelling on future inhabitants must be considered. If the structure
99
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is very old and in poor condition and is unlikely to be inhabited to
any significant degree in the future, it will have less long-term
impact on public health. Fifth, the social inconvenience and other
impacts on the inhabitants may be considered. The installation of
control technology may cause a significant disruption to the normal
lifestyle and adverse impact on the well-being of the inhabitants.
Sixth, the economic situation of the inhabitants should be evaluated.
Some residents may be unable to afford to install control technology
due to adverse economic circumstances.
These factors are not listed in order of importance since they
clearly vary from situation to situation, nor do they represent all
factors that may need to be considered. However, it must be
emphasized that the decision on whether remedial action is warranted
at any level should be based upon an overall evaluation of what is
cost-effective and practicable for present and future occupants.
100
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CONF-720805, J.A.S. Adams, W.M. Lowder and T.F. Gesell,.
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Atmospheres, Amer. Ind. Hyg. Assoc. J., ^6:484-490 (1975).
Ge 78 George, A.C. and Breslin, A.J., The Distribution of Ambient
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Gu 75 Guimond, R.J. and Windham, S.T., Radioactivity Distribution
in Phosphate Products, Byproducts, Effluents, and Wastes
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Ha 72 Harley, N.H. and Pasternack, B.S., Alpha Absorption Measure-
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Ha 74 Harley, J.H. and Harley, N.H., Permissible Levels for
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Ha 79 Harting, F.H. and Hesse, W. , Der Lungenkrebs, die
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of the International Radiation Protection Association,
published by the Congress,' Paris, 1977.
Hu 66 Hueper, W.C., Occupational and Environmental Cancers of the
Respiratory System. Springer-Verlag, New York, Inc., New
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In 73 International Atomic Energy Agency, Inhalation Risks from
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In 75 Report of the Task Group on Reference Man, ICRP Report #23,
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Ja 72 Jacobi, W.. Relations Between the Inhaled Potential-Energy of
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Lead-212 Ions from Rabbit Bronchial Epithelum to Blood.
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Estimates of Ionizing Radioactive Doses in the United States
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La 78 Land, C.E., and J. E. Norman, The Latent Periods of
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Le 75 Lefcoe, N.M. and Inculet, I.I., Particulates in Domestic
Premises II Ambient Lefvels and Indoor-Outdoor Relationship.
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Lo 66 Lowder, W.M. and Beck, H.L., Cosmic-Ray lonization in the
Lower Atmosphere, J.Geophys. Res. 71, 4661-68, 1966.
Lo 77 Lowder, W.M., Personal communication, 1977.
Lu 71 Lundin, F.E., Wagoner, J.K. and Archer, V.E., Radon Daughter
Exposure and Respiratory Cancer Quantitative and Temporal
Aspects, NIOSH-NIEHS Joint Monograph No. 1, USPHS USDHEW,
National Technical Information Service, Springfield,
VA 22151, 1971.
Mi 76 Report of the Royal Commission on the Health and Safety of
Workers in Mines, Ministry of the Attorney General, Province
of Ontario, 1976.
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Population Dose Equivalents, Department of Environmental
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Na 72 The Effects on Populations of Exposure to Low Levels of
Ionizing Radiation, Report of the Advisory Committee on the
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National Technical Information Service, Springfield, VA
22151.
Na 75 National Council on Radiation Protection and Measurements
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Report No. 45, Washington, D.C., November 1975.
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Tract. Report of the Ad Hoc Committee on "Hot Particles" of
the Advisory Committee on the Biological Effects of Ionizing
Radiation, Division of Medical Sciences, National Academy of
Sciences, EPA 520/4-76-013, National Technical Information
Service, Springfield, VA 22151.
Oa 72 Oakley, D.T., Natural Radiation Exposure In The United
States, ORP/SID72-1, U.S. Environmental Protection Agency,
Washington, D.C., June 1972.
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Pe 70 Peterson, Paux, Letter of R.L. Cleer of the Colorado State
Health Department transmitting the Recommendation of Action
for Radiation Exposure Levels in Dwellings Constructed on or
with Uranium Mill Tailings, U.S. Public Health Service,
Washington, D.C., July 1970.
Ra 76 Radford, E.P., Report to the National Institute of
Occupational Health on the Status of Research on Lung Cancer
in Underground Miners in Europe, 1976. Order #96,3825,
NIOSH, Cincinnati, OH.
Ro 78 Roessler, C.E., Wethington, J.A., and Bolch, W.E.
Radioactivity of Lands and Associated Structures, Fourth
Semiannual Technical Report, University of Florida,
Gainesville, February 1978.
Se 73 Sevc, V. and Placek, V., Lung Cancer Risk in Relation to Long-
Term Exposure to Radon Daughters in Proceedings of the Second
European Congress of Radiation Protection. Ed. by E. Bujdoso
Akademia Kiado', Budapest (1973).
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Miners and Long-Term Exposure to Radon Daughter Products.
Health Physics, 30:433, (1976).
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Mines in Sweden, pp. 900-911 in Proceedings of the Third
International Congress of the International Radiation
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Type of Employment. J. popup. Med., If}: 743 (1976).
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of Mines, Department of Interior, 1977.
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22,1975.
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Publication (HRA) 75-1150, National Center for Health
Statistics, DHEW, May 1975.
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Un 77 Sources and Effects of Ionizing Radiation, UNSCEAR 1977-
Wa 71* Wang, K.L. Economic Significance of the Florida Phosphate
Industry Information Circular 8653, Bureau of Mines,
Department of Interior, 1974.
Wa 77 Walsh, P.J., Dose to the Tracheobronchial Tree Due to
Inhalation of Radon Daughters, pp. 192-203 in Tenth Midyear
Topical Symposium of the Health Physics Society. Rensselaer
Polytechnic Institute, Troy, N'.Y. 12181, 1977.
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of Home Ventilation on Indoor Radon and Radon Daughter
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GLOSSARY
Activity - The number of nuclear transformations occurring in a given
quantity of material per unit time. The curie is the special unit of
activity. One curie equals 3-7 x 10^ nuclear transformations per
second (abbreviated Ci).
Apatite -Any of a group of calcium phosphate minerals of the approximate
general formula Ca (F, Cl OH,1/2 CO) (PO) occurring variously as
hexagonal crystals and granular masses; or in fine-grained masses as the
chief constituent of phosphate rock and of bones and teeth, specifically
calcium phosphate fluoride CaF(PO).
Benef1ciation- The processing of ores for the purpose of (1) regulating
the size of a desired product, (2) removing unwanted constituents,
(3)iroproving the quality, purity or assay grade of a desired product.
Decay product- A nuclide resulting from the radioactive disintegration
of a radionuclide, formed either directly or as the result of successive
transformations in a radioactive series. A decay product may be
radioactive or stable (also known as a daughter).
Gamma Radiation- Short wavelength electromagnetic radiation of nuclear
origin (range of energy from 10 KeV to 9 MeV) emitted from the nucleus.
Latent Period - The period or state of seeming inactivity between the
time of exposure of tissue to an injurious agent and response.
Matrix - The subsurface of material containing a mineral or metallic ore.
Pressurized ion chamber - A pressurized gas-filled chamber used for the
detection of ionizing radiation. The increased pressure enhances its
ability to monitor low-level gamma radiation (1-200 R/hr).
Radon - A heavy radioactive (alpha and gamma) gaseous element of the
group of inert gases formed by disintegration of radium.
Radiogenic - Produced by radioactivity.
Relaxation length - An absorber thickness which reduces the intensity of
the radiation by a factor of 1/e.
Scintillation instrument - A device for detecting and registering
individual scintillations (flashes) of light produced in a phosphor by an
ionizing event as in radioactive emissions.
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TLD air pump - A device used to measure radon daughter levels utilizing
techniques of thermoluminscent dosimetry.
Track-etch film - A device used to measure radon daughter levels
utilizing a 1/2" x 1" plastic chip which is coated with cellulose
nitrate. The alpha particles (produced by radon daughters) react with
the cellulose nitrate, thus leaving a record.
uR/hr - Microroentgen per hour (1 x 10 roentgen per hour). Unit used
for gamma radiation levels.
WL (Working Level) - The potential alpha energy from short-lived
daughters of radon which will produce 1.3 x 10-> MeV in one liter of air.
108
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APPENDIX A
STUDY DESIGN - TECHNIQUES AND PROCEDURES
I. PILOT STUDY DESIGN
In June 1975, a limited field study was initiated to determine
whether the elevated concentration of radium-226 in reclaimed phosphate
land has an impact on increasing the radon decay product levels in
structures built on the land. A sample was selected of Polk County
structures built on reclaimed and non-reclaimed land. Except for that
variable (i.e., reclaimed versus nonreclaimed), structures were selected
as randomly as practicable. The overall sample size was 125 structures,
with two-thirds of them being reclaimed land sites. The remainder were
nonreclaimed land sites, some in the phosphate district. This limited
study was not intended to evaluate radon decay product levels in all
structures throughout the County, but rather to give a perspective on the
possible problems and thereby point the way to further evaluation, if
needed.
II. GAMMA EXPOSURE INSTRUMENTATION
Gamma radiation levels inside and outside structures were determined
with Ludlum Model 125 Micro R meters that were calibrated with a
Reuter-Stokes Pressurized Ion Chamber relative to a slab source
(phosphate materials). These instruments are shown in Figure A.1.
-------
Figure A.I - Gamma Radiation Measurements
(L to R: Reuter-Stokes Pressurized Ion Chamber
and Ludlum Model 125 Micro R Meter)
-------
III. RADON AND DECAY PRODUCT MEASUREMENT TECHNIQUES
Two techniques were employed for measuring the radon decay product
levels within structures, TLD air samplers and track-etch badges.
a) Radon Progeny Integrating Sampling Unit (RPISU)
The primary air sampling system used by the Environmental
Protection Agency, Office of Radiation Programs (EPA/ORP) was
developed by Colorado State University, Fort Collins, Colorado. It is
known as the Radon Progeny Integrating Sampling Unit (RPISU) and
utilizes the detection techniques of thermoluminescent dosimetry
(TLD). This device is shown in Figure A.2.
The air pump is located inside two pieces of polyvinyl chloride
(PVC) pipe. The PVC pipes are of different diameters and the area
behind the pipes is filled with sound deadening material. The pump is
attached to a sampling head which is located outside of the pump
housing. This sampling head, which is actually a hypodermic syringe
filter holder, contains the TLD's. The filter head is made up at the
EPA facility in Las Vegas, Nevada, or Montgomery, Alabama, and
packaged in a small 3" x 5" envelope. This envelope also provides
space for the entry of the necessary field data.
During operation, air is pulled through the sampling head and the
particulate material containing the radon decay products is trapped on
a one-half inch filter. A TLD (CaF:Dy) is located in the airstream
directly before the filter and the alpha energy from the decay of the
A-3
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Figure A.2 - Radon Progeny Integrating
_ -, • TT_-:J- /'D'DTRTn
A-4
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radon daughters is recorded by this" TLD. A second TLD, separated from
the first by a stainless steel washer, is also located in the filter
head. The first TLD is referred to as the alpha TLD and the second as
the gamma TLD.
The filter head is placed on the sampler, and the starting sampler
information consisting of the reading on a running time meter, a location
number, date and time, and air flow (measured by a calibrated rotometer)
is filled in on the envelope. The sampler is usually left in place for
one week. Information on date, time, and flow rate at cut-off is entered
on the envelope. The envelope with the filter head is then returned to
the Las Vegas facility. The head is taken apart, the TLD's read out on a
Harshaw TLD reader, a data form completed and sent for computer analysis,
*
and the finished printout containing the calculated working level (WL)
retrieved.
The working level is calculated by providing a working level-
liter/nanocoulomb (WL-l/nC) conversion factor for the TLD reader, nC
readout for gamma and alpha TLD, the running time of the sample, the on
and off air flow rates and the'number of the rotometer used.
The net nC value is obtained by subtracting the gamma TLD nC
(background gamma radiation) from the alpha TLD nC (alpha decay energy
plus background). This value, multiplied by the conversion factor and
divided by the correct air balance, produces the WL value average for the
period of exposure.
WL - The working level is defined as the potential alpha energy
from the short-lived daughters of radon which will produce 1.3x!05MEV
in one liter of air.
A-5
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b) Track-etch Films
The track-etch badge consists of a one-half inch by one inch
plastic chip which is coated with cellulose nitrate. As radon and its
decay products are formed, alpha particles are produced. When the
alpha particles strike the cellulose nitrate, a record of their
passage is made. The badges were each numbered, and two of the badges
were usually mounted on a cardboard card which can be positioned on a
wall. The badges were left in place from six months to a year and
collected, then dipped in a caustic solution (NaOH) or "etched". The
alpha particle's passage becomes an etched track, visible with the use
of a microscope.
Each badge, after etching, was read by a technician using a light
microscope with a calibrated field. The number of tracks observed was
p
recorded and the tracks per square millimeter (T/mm ) were
calculated. This value was then compared to a calibration curve and
the working level hours (WL-h) associated with the number of tracks
observed was obtained. The WL short-lived daughters of radon which
will produce 1.3x10 MeV in one liter of air was then calculated,
using the number of hours the badge was in the sampling location.
The badge has the advantage of being a passive dosimeter. That
is, it is put in place and picked up, but no maintenance is required
during the sampling period (no moving parts). However, it has the
disadvantage of measuring or recording not only the alpha energy given
off by radon, but also by polonium-218 (radium A) and polonium-214
A-6
-------
(radium C). Since the alpha energy from radon is not a portion of the
alpha energy used to determine the WL (the radon daughters and not the
radon-222 itself are the prime contributors to adverse health impact),
the system must be calibrated so that the complement from radon can be
subtracted. This calibration will be discussed in depth in a later
section.
IV. INFORMATION COLLECTION AND ORGANIZATION
In the initial survey of structures built on reclaimed phosphate
land, track-etch films were placed in 85 structures built on reclaimed
land and in 40 structures built on nonreclaimed land. Structures
surveyed consisted primarily of private dwellings; however, local
health department buildings and a few office buildings were also
surveyed.
At each structure, data were obtained regarding its
classification (residence, business, etc.), construction type
(basement, slab, crawlspace, etc.), number of levels, material
(masonry, non-masonry), and whether it was air conditioned. A map was
made of each structure showing the indoor and outdoor external gamma
radiation levels. This data was computer coded according to location
identification number and address. Data were added to the computer
file on the indoor radiation level in the structure for both the RPISU
system or track-etch films. Printouts are accessible by keying the
file in several different ways, depending upon the specific variable
of interest.
A-7
-------
After noting elevated levels in some structures in September
1975, the track-etch data base was expanded in November 1975. Since
that time the State of Florida has selected 997 structures for study
either by TLD air pump, track etch film or both. Further, as time has
become available for using the air pumps in additional structures,
they have been added to the TLD air pump data base. The information
from the study collected as of January 20, 1978, for TLD air pump
data are listed in the Annex.
A-8
-------
APPENDIX B
CALIBRATION OF TRACK-ETCH FILMS
I. DEPLOYMENT OF DOSIMETERS
The calibration of the track-etch films used in the study was
accomplished by randomly selecting 23 structures and installing track-
etch films and air sampler (RPISU) devices in each of them. A total of
two or three films were used in each structure. In the structures one
film was deployed for a period of about one year and the other two films
were deployed for consecutive six month intervals coincident with the
film which was in place for a year. The RPISU devices were operated for
approximately a one week period for four to seven weeks during the year,
with at least one week in each of the four seasons.
II. STATISTICAL ANALYSIS OF THE DATA
The data set for statistical analysis included 41 points (N) from 23
locations, using two types of film measurements. The first was the set
of values of track density (T) for films exposed for the entire year,
while the second was constructed by summing results of two films exposed
in consecutive six month periods at the same location. These two types
of measurements did not differ significantly. Corresponding air sampler
measurements (RPISU) for indoor working levels (W) are averages of from
four to seven measurements taken during the study period at each of the
23 locations. The data was analyzed with the air sampler data as the
independent variable and the track-etch film data as the dependent
variable. The data are listed in Table B.1.
-------
Table B.1. Data for Indoor Radon Study
Track-etch density (tracks
Location 1st 2nd 1st+2nd
six mos. six mos.
Air Sampler
entire year (WLh)
70050
70051
70076
70079
70082
70084
70087
7009^
70101
70103
70105
70107
70110
70118
70134
70135
70136
70137
70169
70170
70172
70175
70180
7.6
5.6
26.8
32.2
1.3
1.0
5.3
6.5
10.9
28.9
3.5
1.32
1.16
.98
.95
11
15.37
1.82
2.81
1,
5.
7,
6.45
2.48
29.09
19.00
15.70
3.64
5.29
4.30
6.11
22.64
.65
,48
8.43
1.16
8.10
8.76
6.11
3.80
4.30
2.48
14.05
8.08
55.89
51.20
17.00
4.64
10.59
10.80
17.01
51
5
3
9
1
54
.15
,80
,59
,66
10.08
14.71
13.22
19.17
6.12
5.29
16.20
5.62
49.91
34.54
16.69
.83
4
31
3
,63
07
80
10.08
7.77
52.88
61.97
1.32
.45
.31
,82
8.92
9.42
5.
2.
1,
4.46
4.30
77
163
605
596
182
173
340
304
153
306
373
661
698
107
19
10
10
10
238
69
314
19
28
In order to arrive at an equation which best fits the relationship
between track density on the films and air pump measurements, the
following regression analyses were performed on the data given in Table
B.1:
Option 1
T = 0.4 + .069 W
(t=0.2) (t=11)
R2 = 0.87
F = 124
N = 41
B-2
-------
Option 2
T = -19.5 + 7.57 InW
(t= -2.7) (t=5.1)
R2 = .63
F = 26
N = 1*1
Option 3
InT = 1.4 + .0037W
(t=7) (t=7.3)
R2 = 0.76
F = 53
N = 41
Option 4
InT = .09 + .46 InW
(t=.2) (t=5.0)
R2 = .62
F = 25
N = 41
These options cover the obvious linear and nonlinear cases that
could be considered. (The t statistic is used to test the statistical
2
significance of its corresponding parameter. R is the proportion of
the total variation in the dependent variable explained by the regression
equation. The F statistic tests the presence of a relationship between
the dependent and independent variables of the regression equation.)
B-3
-------
2
Using the R and F statistics as decision criteria for choosing the
best overall fit and prediction ability, Option 1 appears to be the
best. That is, the simple linear form of the relationship between
track-etch and air pump data appears to fit and predict better than
either the log-linear or log-log forms. It can be seen that Option 2 is
consistent with the null hypothesis that the intercept is equal to zero,
based on the t value. This result appears to confirm the theory put
forth by D.B. Lovett that, "the track density resulting from the exposure
of films to alpha particle activity is directly proportional to the time
integral of the total alpha particle activity of the atmosphere to which
it was exposed" (Lo 75). Therefore, a final regression was run in which
the intercept is omitted:
Option 5
T = .070 W
R2 = .75
F = 12
N = 41
This is taken to represent the "best" fit between the track density
on the film and the TLD air pump measurements. The 95 percent confidence
interval for a predicted W from a measured T, based on option 5 is:
T T2
+ 250 .99 +
,069 ~~ 20,000
B-H
-------
This formula is an algebraic manipulation of the confidence interval
given in Equation 10.5 of Brownlee, 1965 (Br 65). It should be noted
that the formula for the confidence interval is -not in standard form,
but has been rearranged for easier computing.
The formulas given here are valid for exposure times of
approximately one year. Results from analyses of six month exposures
suggest some seasonal variation and therefore conversions from track
density to radon exposure based on short term data should not be done
using these formulas. Figure B.1 is a plot of the equation given in
option 5 with the 95 percent intervals identified. As the origin is
approached, the percentage of error rapidly increases. For example,
at 60 tr/mm , the 95 percent interval is about —30 percent whereas
at 20 tr/mm it is about —100 percent.
Reference:
Br 65 Brownlee, K.A. Statistical Theory and Methodology in Science
and Engineering, 2nd Edition. John Wiley & Sons, Inc.: New
York (1965) p.362.
B-5
-------
Figure B.I
1400
w
t
C7V
1200 -
• ANNUAL DATA POINT
X SU;v1 OF 2 CONSECUTIVE 6 MO DATA POINTS
— — 95% CONFIDENCE LEVEL
W=T/ 06978
.1 1 L
40 50 60
TRACK DENSITY (TR/mm2)
100
CALIBRATION FORMULA AT 95% CONFIDENCE LEVEL
-------
APPENDIX C
RADIATION EXPOSURE CONTROL MEASURES
I. INTRODUCTION
This assessment is extracted primarily from a survey of available
measures conducted and published by the Agency in November 1976 (Fi
76). It includes an update on control technology costs that have
changed since publication of the survey. This evaluation focusses on
state-of-the-art radon decay product control measures for proposed
structures which have radon transport through the foundations.
Several of these measures have similar application for reduction of
radon decay product concentrations in existing structures as well as
reduction of external gamma exposure in both new and existing
structures. Five available measures are assessed for
cost-effectiveness: ventilation, polymeric sealants, ventilated crawl
space construction, excavation, and improved slab construction, the
latter two having dual application for gamma and radon. These
measures will be discussed in the context of existing and planned
structures.
II. AVAILABLE TECHNOLOGIES
a) Utilization of Air Cleaners
Air cleaners are designed to remove particulates from the
circulating air of building interiors. The type of air cleaner used
depends upon the particle size and shape, specific gravity,
concentration of the particulates, and the efficiency of removal
-------
desired. Of these, the particle size, along with overall filtering
efficiency required, is the most important characteristic by which an
air cleaner is chosen.
Electronic air cleaners use electrostatic precipitation
principles to collect particulate matter. Unlike their industrial
counterparts, residential electronic air cleaners operate on standard
house current and with normal operation use electricity at the same
rate as a 50-watt lightbulb. The performance of electronic air
cleaners depends upon the rate of air flow and the quality of
installation. A number of commercially available models are designed
to meet these performance parameters, as well as others such as the
volume of air to be cleaned and the size of the heating or cooling
unit.
As no data are available concerning the efficiency of air
cleaners in reducing the concentration of radon daughters, modeling
was performed to make such an estimation (Fi 76). These calculations
show that theoretically, most of the radon daughter level reduction
occurs at effective ventilation rates of less than two air changes per
hour (approximately 70 percent). Therefore, assuming that natural
infiltration accounts for one air change per hour, air cleaners, which
can effectively handle ventilation rates of about one to two air
changes per hour, would have a relatively marginal effect on working
level reduction. For HEPA and electronic air cleaners, a 38 percent
reduction in the equilibrium radon daughter working levels was
calculated. For HEPA filters, though, increased effective ventilation
C-2
-------
rates could lead to an increased tracheobronchial dose (and therefore
a potentially higher total lung dose), due to the resulting increase
in the free ion fraction of radon daughters (Ja 72).
For a combined electronic air cleaner and outside air
exchange system, an efficiency of 62 percent was calculated for
working level reduction. This model assumes a flow rate through the
system of 1.5 air changes per hour and about 25 percent makeup air.
b) Polymeric Sealants
Ideally, if one could completely seal all of the floor and
wall space below ground level for a structure with radon diffusing
through the floor, the problem would be largely alleviated. The radon
gas that would normally diffuse through the floor would be trapped by
this barrier so that it would decay in the structural material and not
*
enter the structure's atmosphere. Polymeric sealants, having low
permeability to radon gas, have been proven to be effective in
reducing in-house radon progeny when properly applied. An EPA funded
study by Culot, et ajl., (Cu 73) showed that radon diffusion into a
structure could be reduced by more than one half by utilizing an epoxy
sealant. An important finding was that a significant reduction of
radon diffusion into structures could be obtained only in a situation
free of other major pathways for radon. From past analyses with test
There is a whole-body gamma exposure related to such decay,
although in regard to potential health effects it is insignificant in
comparison to radon daughter alpha exposure in the lung. From past
field studies, fractional gamma increases of 2 to 20 percent were
measured for a 4-inch concrete slab after sealant application.
C-3
-------
structures on slabs, as well as experience with remedial action in
structures in Grand Junction, Colorado, it was determined that such
pathways do exist and are common in typical residential structures.
One such pathway is minute cracks in the concrete slab at the juncture
of the slab and wall, another is the channel through which pipes and
drains enter the slab. The analyses and field experience have shown
that without complete sealing of these pathways with a
radon-impermeable base, only a relatively small working level
reduction could be obtained. The thoroughness of sealant application,
then, is of prime importance in the implementation of this control
measure.
An efficiency range of 70-90 percent radon progeny reduction for
polymeric sealants was derived from test data by Culot, et al., (Cu
73). Their experiments involved the use of sealed tanks above a
sealed concrete slab with uranium tailings underneath. Assuming an
equilibrium radon progeny concentration over the slab equal to 10
percent of the source term under the slab, which they had previously
determined, the range of reduction was approximately 75-99 percent
*
using polyester styrene, polyester resin, and Omnitech polymers.
From a similar experimental analysis, Auxier, £t al., (Au 74) suggests
that an 88 percent reduction in airborne radon progeny could be
obtained. As these reductions were achieved in an experimental lab
situation, the reduction range of 70-90 percent was
*0mnitech Industries, Inc.
C-1
-------
chosen as a conservative approximation of actual residential
application.' Again, the degree of reduction achievable would be
dependent upon the method and thoroughness of application.
c) Ventilated Crawl Space Construction
The function of building a crawl space for radon progeny
control is to provide a highly ventilated space between the soil
surface and the overlying structure in which the emanating radon gas
can be diluted or removed before diffusion into the structure. The
degree to which such ventilation is effective is dependent upon the
number of air changes per unit time within the enclosure below the
floor. Assuming that a wooden floor would allow radon gas to diffuse
readily, the fractional reduction of radon gas diffusion into the
structure would be proportional to the reduction in partial pressure
of the radon in the crawl space due to ventilation. There are two
means by which the ventilation characteristics of a crawl space can be
enhanced, involving passive and nonpassive measures. First, the crawl
space can be constructed utilizing oversized, properly spaced vents on
all sides of the structure. Second, a fan could be set up for forced
ventilation of the crawl space, thereby establishing a lower limit of
ventilation. Although there is no readily available data concerning
the magnitude or range of the ventilation rate which could be
achieved, with proper construction it could compare favorably with a
well-ventilated house (2-*» air changes per hour). Assuming such
C-5
-------
ventilation rates, radon daughter working level reductions of 80
percent or more would be possible. The level of reduction achievable
could be increased, if desired, through the use of a radon impervious
barrier in the floor. Such a barrier, possibly in the form of a
polymeric sealant underlying a seamless tile floor, would have side
advantages such as moisture proofing and a reduction in heating and
air-conditioning infiltration loss.
d) Site Excavation and Fill
*
A ten-foot layer of soil with a relaxation length of 4.9 feet
(for moist packed earth and dry packed uranium tailings with a
_2
diffusion coefficient of 5x10 cm/s) can be as much as 80 percent
effective at reducing radon emanation from the ground surface (Sc
74). Such data indicate that by removing this depth of reclaimed
phosphate soil and replacing it with non-uraniferous soil of the same
density and porosity, approximately 80 percent of the radon would be
retained in the ground. If such a procedure were done for a home site
on phosphate land, the diffusion rate of radon into the structures to
be built would then be proportionally less, assuming negligible
**
lateral radon diffusion.
*The depth of a uniform layer of material of the same density in
which a diffusing gas (radon in this case) is reduced in concentration
by a factor of "e" (2.703).
**Although no field studies have been performed concerning
lateral diffusion, the cost-effectiveness calculations in Section V
allow for excavation to a distance of three feet from the foundation.
C-6
-------
With regard to gamma exposure reduction, packed earth at
1.6 g/cm density has a tenth value layer of 13 inches (i.e., the
gamma radiation level is reduced by a factor of ten over this thickness
at the assumed density). Therefore, an equivalent 80 percent reduction
in exposure is achievable with only 9 inches of soil, with a 99+ percent
reduction for ten foot depth. These estimates assume no contribution
from terrestrial sources external to excavated soil.
e) Improved Slab Construction
Another technique by which the overall effectiveness of radon
daughter control measures could be enhanced would be improving the
quality of slab (quality control, reinforcement and thickness). As the
pore size present in the cement has a large influence on its radon
stopping ability, utilizing concrete with a low water to cement ratio by
weight (W/C) and dense aggregate material (such as granite or marble)
would decrease radon permeability.
Increasing the thickness of the concrete slab would likewise reduce
the radon diffusion rate, assuming this is the major pathway. As radon
gas has a relaxation distance of about 5 cm (2 inches) in a standard
concrete (density =2.35 g/cm), by doubling the thickness of a normal
4-inch slab to 8 inches, an 80 percent reduction in exhalation is
possible. For controlling gamma irradiation through the foundations,
increasing the thickness of the concrete slab would lead
C-7
-------
to a 70 percent gamma reduction. This estimate is based on concrete
with 6 percent porosity, with an increase in slab thickness from 4 to
8 inches. Unlike radon emanation, the presence of cracks would not
lessen the efficiency of reduction.
III. COST ANALYSIS FOR IDENTIFIED CONTROL TECHNOLOGIES
A cost analysis on the utilization of radon daughter control
technology is critical to any decision-making process in this area.
As with pollution control equipment in industry, the cost of control
measures would probably be passed on to the consumer, or the homeowner
in this case. In order to minimize expenses, the builder must first
determine, from available data, which control measures reduce the
radon progeny concentrations down to acceptable residential levels,
and second, which of these measures can be implemented and maintained
at the least cost to him.
The cost figures utilized in this analysis, as shown in Table
C-1, are best average estimates based on data derived from literature,
government, and private industry. Because of their different sources,
a small degree of variability is to be expected for the actual cost of
application in specific localities of the country. Another source of
variability is inherent in the use of an average value. Such an
estimate is applicable only for an average site and, therefore, cannot
be generally applied. All cost figures utilized in this analysis are
adjusted to present value (6 percent annual discount rate applied).
C-8
-------
TABLE C. 1
ESTIMATED AVERAGE COST OF CONTROL MEASURES FOR
STRUCTURES CONSTRUCTED ON FLORIDA PHOSPHATE LAND*
n
CONTROL MEASURE
EXISTING STRUCTURES
AIR CLEANERS.
HEPA
ELECTRONIC
ELECTRONIC AND AIR EXCHANGER
POLYMERIC SEALANT
PLANNED STRUCTURES
VENTILATED CRAWL SPACE
EXCAVATION AND FILL
(TO 10' DEPTH)
COMMERCIAL FILL RATE -
FOR 80% RADON REDUCTION (INCLUDES 99%
GAMMA)
FOR 80% GAMMA REDUCTION
W/NOMINAL FILL COST -
FOR 80% RADON REDUCTION (INCLUDES 70%
GAMMA)
FOR 80% GAMMA RED
IMPROVED SLAB CONSTRUCTION:
FOR 80% RADON REDUCTION (INCLUDES 70%
GAMMA)
FOR 80% GAMMA REDUCTION
CAPITAL
COST
S400
S350
S900
S600S1950
S550
S3250S5500
S250S400
S2550-S2900
$200
S550
$600
ANNUAL
MAIN-
TENANCE
COST
$100
$25+ * * '
$25+
UNDEFINED
NONE
NONE
NONE
NONE
NONE
NONE
NONE
ANNUAL
ELECTRICAL
COST
UNDEFINED
$10
$80
NONE
UNDEFINED
NONE
NONE
NONE
NONE
NONE
NONE
TOTAL
AVG. ANNUAL
OPERATING
COST
$100
$35+
$105+
NONE
NONE
NONE
NONE
NONE
NONE
NONE
NONE
PRESENT
WORTH O(
TOTAL COST
(70 YRS)
$2050
$900
S2600
S600 $1950
S550
S3250S5500
$250 $400
32550 02900
$200
$550
$600
1977 DOLLAR VALUE (6% DISCOUNT PER YEAR APPLIED), ALL FIGURES ARE FOR RADON
NOTED
'ASSUMMING 1500 SQUARE FEET FLOOR AREA AND
PROGENY REDUCTION EXCEPT WHERE OTHERWISE
*SEE TEXT
*"*-" SIGNIFIES THAT THE ESTIMATE GIVEN IS MOST LIKELY A MINIMAL ONE ALTHOUGH THE ACTUAL AVERAGE IS UNDEFINABLE USING
AVAILABLE COST DATA
-------
There are numerous components of the total cost, both tangible
and intangible, which will be considered. The capital cost is the
most important component to the prospective builder, which would be
incurred in order to implement the control measure. With mechanical
equipment such as air cleaners, maintenance and replacement costs also
become important in calculating the total cost. As most equipment of
this type has a useful life of roughly ten years, some maintenance and
possibly replacement will be required over the average life span of a
building. Another component is electrical cost which is, again,
primarily associated with the use of mechanical air cleaning
equipment. Due to probable increased air infiltration in homes with
crawl spaces, there would be additional electrical costs as a result
of the corresponding increase in the use of air-conditioners or
electrical heating units.
C-10
-------
APPENDIX C REFERENCES
Au 74 Auxier, J.A., Shinpaugh, W.H., Kerr, G.D., and D.J.
Christian, "Preliminary Studies of the Effects of Sealants on
Radon Emanation from Concrete," Health Physics 27:390-392,
No. 4 (1974).
Cu 73 Culot, M.V.J., Olson, H.E., and K.J. Schiager, "Radon Progeny
Control in Buildings," Colorado State University, EPA
R01EC0015.3 and AEC AT (11-D-22733 (May 1973).
Fi 76 Fitzgerald, J.E., Guimond, R.J., and R.A. Shaw, A Preliminary
Evaluation of the Control of Indoor Radon Daughter Levels in
New Structures, EPA-520/4-76-018, U.S. Environmental
Protection Agency, Washington, D.C., November 1976.
Ja 72 Jacobi, W., "Relations Between the Inhaled Potential -Energy
of Ra-222 and Ra-220 Daughters and the Absorbed -Energy in
the Bronchial and Pulmonary Region, Health Physics 23;3-11,
No. 7 (1972).
So 74 Schiager, K.J., Analysis of Radiation Exposures on or Near
Uranium Mill Tailing Piles, Radiation Data and Reports, U.S.
Environmental Protection Agency, 15:411-425, No. 7 (1974).
C-11
-------
APPENDIX D
EVALUATION OF FIELD DATA
I. Evaluation of Radon Decay Product Level Data
D.1.1 General
Data on indoor radon decay product levels were obtained for over
200 structures throughout Central Florida. However, not all of these
data are useful in describing the radiological situation. In order to
represent a year's exposure condition in a structure, it is desirable
to operate the air pumps (RPISUs) four to six times spaced throughout
the year for approximately a week each time. This proved to be
difficult to achieve in many structures for several reasons. First,
some residents refused to allow the devices to be operated for those
time periods. Second, smoking and other environmental factors within
a structure sometimes clogged the filters and automatically stopped
the pumps after only a few hours of operation. And third, exchanges
of property sometimes precluded necessary followup measurements.
During the study it was also learned that, in addition to not
being representative of long time periods of exposure, short air pump
operational times (generally less than 24 hours) sometimes were
predictive of indoor radon decay product levels considerably higher
than extended runs in the same structure. All of the reasons for this
observed phenomenon have not been discerned, although to minimize the
use of erroneous data, short run times were not utilized to determine
-------
structure averages. In order to further improve the validity of the
measurements made, we have decided to report average indoor radon
decay product levels from structures with air pump operating times of
more than 24 hours. Also, the three or more measurements must total
more than 125 hours of combined operation to be included.
Using the above data selection criteria, 133 structures were
identified from those in the original EPA pilot study and the group
chosen by DHRS. TLD's from these air pumps were analyzed by the
Eastern Environmental Radiation Facility in Montgomery, Alabama, the
Radiation Office in Las Vegas, Nevada, and Department of Health and
Rehabilatative Services, Orlando, Florida. All of the data from these
sources were combined, with each of these groups participating in
quality control checks and intercalibrations. As a result of such
intercomparisons, all the data is believed to be within +30 percent of
the true value. This is very important to consider when trying to
draw conclusions about the need for remedial action in a structure.
Figure D.1 depicts the breakdown of the observed indoor radon
decay product data according to percentage distribution of the mean
gross indoor level for the entire 133 structures in the composite
EPA-DHRS population. This data is summarized in Table D.1 by
percentile in excess of selected radon decay product levels for the
EPA, DHRS, and composite groups; and for houses on reclaimed or
mineralized land only.
D-2
-------
35
30
a
CO
2b
en
LU
CC
I-
u
cc
t-
l/}
u.
o
20
N=133
15
10
.002WL .004 006 008 .010 .012 .014 .016 018 020 022 024 .026
MEAN GROSS WORKING LEVELS (FOR INTERVENING RANGES)
.032
034
.036
038
.040 WL > 040
Figure D.I PERCENT DISTRIBUTION CF TLD AIR SAMPLING MEASUREMENTS
-------
TABLE D.1
Distribution of Mean Gross Indoor Radon Decay
Product Levels (percent equal to or in excess of level noted)
Level (WL)
0.005
0.01
0.015
0.02
0.030
0.040
0.050
EPA
DHRS
N=22 *N=15
64$ 93$
55$ 80$
50$ 73$
41$ 60$
36$ 53$
23$ 33$
23$ 33$
N=111 «N=89
65$ 76$
31$ 37$
17$ 21$
14$ 18$
11$ 13$
3$ 3$
2$ 2$
Composite
N=133 »N=104
65$ 79$
35$ 43$
29$
24$
19$
8$
23$
19$
15$
6$
5$
7$
•Excludes houses on non-mineralized lands
D.1.1 Geographical Distribution
The mean indoor radon decay product levels in the structures were
examined to determine if any trends could be noted in the geographical
distribution patterns. These data are shown in Table D.2 and
represented on a general map of Polk County in Figure D.2.
City
TABLE D.2
Number of Structures in Specified
WL Ranges by City
WL<0.01 0.01£ WL <0.03 0.03-WL<0.05 WLlO.05
N
- 1
Auburndale
Bartow
Bradley Junction
Davenport
Dundee
Eagle Lake
Eaton Park
Fort Meade
Haines City
Lake Alfred
Lakeland
Lake Wales
Mulberry
Pierce
Polk City
Winter Haven
2 (100$)
2 (22.2$)
0
2 (100$)
2 (100$)
1 (100$)
2 (50$)
1 (33.3$)
9 (90$)
1 (100$)
42 (68$)
3 (100$)
16 (64$)
0
2 (100$)
5 (100$)
0
2 (22.2$)
0
0
0
0
1 (25$)
2 (66.7$)
1 (10$)
0
11 (18$)
0
5 (20$)
1 (100$)
0
0
0
2 (22.2$)
1 (100$)
0
0
0
1 (25$)
0
0
0
5 (8$)
0
4 (16$)
0
0
0
0
3 (33.3$)
0
0
0
0
0
0
0
0
4 (6$)
0
0
0
0
0
2
9
1
2
2
1
4
3
10
1
62
3
25
1
2
5
TOTAL
90
23
13
133
D-4
-------
LEGEND
GROSS WORKING LEVELS WL> 05—<-/"pV— WL< 01
03
-------
Of 25 locations outside the general bounds of the phosphate
mineralized region in Polk County only one location had an average
indoor radon decay product level greater than .01 WL. The level for
this structure was .011 WL. This finding lends support to the
conclusion that normal soil unrelated to the phosphate region in Polk
County generally exhibits low average indoor radon decay product
levels. From the figure it can be seen that the highest levels are
generally observed in the southwestern region of the county. Clearly,
from the standpoint of focusing control on the areas of principal
impact at present this region is of primary concern.
D.1.3 Evaluation by Land Category
The land on which the structures in the study are built was
classified according to four categories: non-mineralized (no phosphate
deposits), mineralized (deposits present, but unmined), reclaimed, and
"other" (due primarily to lack of information). Of the 133
structures, the average gross indoor radon decay product level for
each category is .003 WL for non-mineralized land (N=29), .015 WL for
mineralized land (N=9), .017 WL for reclaimed land (N=93), and .009 WL
for land of unknown designation (N=2). The data for these categories
are given in Table D.3 and graphed in Figure D.3-
D-6
-------
100
90
80
70
in
£ 60
o
^—
o
cc
k 50
U-
O
H
Z
oJ
O
30
20
N=2
WL< 01
03^WL< 05
05
WL< 01 03*£WL< 05 WL< 01 03 05 01
-------
TABLE D.3
Number of Structures by Land Category and Mean Gross
Indoor Radon Decay Product Level Ranges
Land Use WL<0.01 0.011 WL< 0.03 0.031WL< 0.05 WL>. 0.05
Reclaimed 55 19 12 7
Mineralized 44 10
Non-mineralized 28 1 00
Unknown 02 00
A statistical analysis of these data indicate that levels in the
structures on non-mineralized land are different from those on reclaimed
land at the 99 percent confidence level as shown in Table D-4:
TABLE D.4
Statistical Comparison of Mean Gross
Indoor Radon Decay Product Levels by Land Category
(Mineralized (M), Non-mineralized (N), Reclaimed (R))
Land Use N Mean WL F-test value PR * F«
M
N
R
N
R
M
R
M
N
9
29
93
29
93
9
93
9
29
0.015
0.003
0.0.17
0.003
0.017
0.015
0.017
0.015
0.003
6.90
13.24
0.09
29.46
.0014
.0004
.7677
.0001
•Probability that the sample distributions are a product of random
variability.
D-8
-------
Further, it is observed that the levels in structures on mineralized
land are not different from reclaimed land at the 90 percent
confidence level. This suggests that structures on mineralized land
may present similar indoor radon decay product levels as reclaimed
land. Therefore, based on present information, it would be extremely
difficult to differentiate the two categories with respect to control
recommendations.
D.1.4 Evaluation by Structure Type
The data was classified according to four structure types:
basement, slab on grade, crawl space, and trailer. Of the 133
structures, the average gross indoor radon decay product level for
each structure type is 0.02 WL (Basement, N=4), 0.014 WL (slab on
grade, N=102), 0.010 WL (crawl space, N=13), and 0.008 WL (trailer,
N=14). The sample distribution by selected working level ranges is
provided in Table D.5.
TABLE D.5
Number of Structures by Structure Type and Mean
Gross Indoor Radon Decay Product Level Ranges (N=133)
Structure Type WL<0.01 0.0'\<.VL< 0.03 0.031 WL< 0.05 WL>. 0.05
Basement
Slab
Crawlspace
Trailer
TOTAL
2
66
10
11
89
0
20
2
2
24
2
9
1
1
13
0
7
0
0
7
D-9
-------
The data for these structure types are summarized in Figure D.4.
Review of these data do not indicate any statistically significant
differences among the four structure types at the 40 percent
confidence level, as shown in Table D.6. Therefore, though inspection
of the data suggests that basement and slab-on-grade structures have
higher indoor radon decay product levels, this cannot be shown to be
statistically significant. One of the problems in showing such
significance is the small number of structures in the categories other
than slab-on-grade.
TABLE D.6
Statistical Intercomparison of Mean Gross
Indoor Radon Decay Product Levels by Structure Type
(Basement (b), Slab (s), Crawlspace (c), Trailer (T))
Structure type N Mean WL F-test value PR > F *
B
S
C
T
B
S
C
T
S
C
S
T
4
102
13
14
4
102
13
14
102
13
102
14
0.020
0.014
0.010
0.008
0.020
0.014
0.010
0.008
0.014
0.010
0.014
0.008
0.99
0.27
0.14
0.87
1.70
.4012
.6035
.7067
.3523
.1948
•Probability that the sample distributions are a product of random
variability
D-10
-------
D
I
O
D
DC
CJ
tr
WLX.01 03=WL< 05
01 05
SLAB-ON-GRADE
WL< 01 .03 05 01 05
CRAWL SPACE TRAILER
Figure D.4 PERCENT DISTRIBUTION OF TLD AIR SAMPLING MEASUREMENTS BY STRUCTURE TYPF
AND GROSS WORKING LEVEL RANGE
-------
Of the 93 structures built on reclaimed land, the average gross
indoor radon decay product level for each structure type is 0.026 WL
(basement, N=3), 0.018 WL (slab on grade, N=70), 0.013 WL (crawlspace,
N=7), and 0.008 WL (trailer, N=13). The data for these structure
types is shown according to its percent distribution in Figure D.5.
Review of these data suggests that trailers have the least
average gross indoor radon decay product levels, followed in
increasing order by crawl space, slab-on-grade, and basement
structures. This appears reasonable based upon an understanding of
the characteristics of each structure type. Trailers are generally
constructed off the ground with good ventilation under the trailer.
When the trailer's "crawl space" is fully enclosed by cement block or
other materials, ventilation through the space is reduced and the
potential is increased for undesirable indoor radon decay product
levels in the trailer. Additions to trailers which are constructed on
slab-on-grade foundations provide a pathway for radon to enter the
trailer. It is evident therefore, that trailers generally exhibit low
indoor radon decay product levels unless they are situated in such a
manner as to provide a pathway for radon to enter the trailer.
The average gross indoor radon decay product level in structures
built with crawlspaces was not as low as anticipated, probably because
several crawlspace structures were enclosed, which restricted air flow
under the structure or otherwise provided a pathway for radon to enter
it. Therefore, to minimize the radon decay product levels in such
D-12
-------
o
I
cc
13
h-
O
D
QC
(—
CO
u_
O
O
cr
90
80
70
60
50
40
30
20
10
WL< 01 03
-------
structures restrictions on air flow should be minimized. For example,
piping and supports should be constructed so as not to allow for a
radon pathway.
Slab-on-grade and basement structures exhibited the highest radon
decay product levels. This was anticipated because of the direct
interaction between the foundation and the soil where the radon is
generated. Clearly, these types of design present the greatest
opportunity for radon to readily enter the structure.
D.1.5 Evaluation by the Presence of Air Conditioning
It was believed that the presence of air conditioning might have
a dramatic influence on the indoor radon decay product level because
the exchange of outdoor and indoor air would be reduced substant-
ially. However, examination of the data, provided in Figure D.6, did
not confirm this theory. In non-air conditioned structures, the
average gross indoor radon decay product level was 0.016 WL (N=47)
whereas in air conditioned structures the level was 0.012 WL (N=86).
Other studies of the effect of ventilation on indoor radon decay
product levels (Un 78) indicated that operation of the central air
conditioning system in a structure can have a pronounced effect on
reducing the indoor radon decay product levels. Reduction up to a
factor of 10 have been observed during steady state operation of the
ventilation system versus a minimal ventilation of about 0.7 air
changes per hour. It appears that this reduction is due to plateout
D-14
-------
WL 0!
01 WL 03 03 WL C5
WITH A/C
WL - 05
W L 01
Or WL- 03 03 WL 05 vVL 05
WITHOUT A/C
Figure D.6 PERCENT DISTRIBUTION OF TLD AIR SAMPl ING MEASUREMENTS BY GROSS WORKING LEVEL RANGE
-------
of radon decay products within the system as well as increased
ventilation caused by pressure differences between the indoor and
outdoor environments. These factors seem to combine so that over an
extended time period the short term difference between air conditioned
and non-air conditioned structures are greatly eliminated.
II. Gamma Radiation Measurements
D.2.1 General
Outdoor gamma radiation measurements were obtained for 1102 sites
in Polk County. The gamma surveys were performed with a standard
portable scintillometer held one meter above the ground, with
precautions taken to eliminate "hot spots", i.e., localized areas of
anomalous radiation. The values given in the appended printout and
plotted in Figure D.7 are averages of approximately 8-10 outdoor
readings for each surveyed site. Assuming an average background gamma
level of 6yR/hr, as established by the EPA/DHRS survey, approximately
97 percent of the outdoor gross gamma measurements performed were
equal to or in excess of background. For the total survey, 87 percent
were between 6 and 15 yR/hr, with 9 sites or about one percent, in
excess of 30 yR/hr.
D.2.2 Geographical Distribution
The gamma survey was performed in nineteen cities and towns in
the County with a predominant number of surveys (853) being performed
in Lakeland, Mulberry, Winter Haven and Bartow, as shown in Table D.7.
D-16
-------
100
C/5
UJ
tr
O
oc
u
OC
90
80
70
60
50
40
30
20
10
N-1102
6 10
11 15
>30
1620 21-25 26-30
OUTSIDE GAMMA (jjR'hri
Figure D.7 PERCENT DISTRIBUTION OF OUTSIDE GAMMA RADIATION MEASUREMENTS
D-1 7
-------
TABLE D.7
NUMBER OF STRUCTURES BY CITY AND SPECIFIC OUTDOOR GAMMA RANGE
City 0-10yR/hr 11-20yR/hr 21-30yR/hr 30yR/hr N
15
1
67
5
25
23
1
23
23
30
37
1
1
2 616
35
3 101
5
24
69
5 1102
Figure D.8 provides a geographical representation of this data with the
number of sites and average gamma range for each city noted. The "Pebble
55-70 percent BPL" boundary denotes the approximate extent of the
phosphate mineralized zone. As the site data illustrates, all of the
measurements except for one in excess of 10 UR/hr were located on
mineralized land (reclaimed or otherwise). Average measurements in
excess of 20 yR/hr (53 sites or about 5 percent of the sites) were
obtained in Bartow, Eaton Park, Fort Meade, Lakeland, Mulberry, and
Pierce.
Auburndale
Babson Park
Bartow
Bradley
Davenport
Dundee
Eagle Lake
Eaton Park
Fort Meade
Frostproof
Haines City
Highland City
Lake Alfred
Lakeland
Lake Wales
Mulberry
Pierce
Polk City
Winter Haven
TOTAL
15
1
44
4
25
22
1
18
9
23
37
1
1
466
35
41
2
24
69
838
19
1
1
3
10
7
127
47
2
217
4
2
4
21
10
1
42
D-18
-------
NO. OF
STRUCTURES
SAMPLED
AVG. OUTDOOR
GAMMA LEVEL
(GROSS)
2675
025
r*-1 STRUCTURE SAMPLED
10/^R/hr
21-30AiR/hr
LAKE COUNTY
ORANGE COUNTY
OSCEOLA COUNTY
EATON PARK WINTER HAVEN
MULBERRY BARTOW
HARDEE COUNTY
HIGHLANDS COUNTY
Figure D.8 AVG OUTDOOR GAMMA RADIATION DISTRIBUTION (GROSS) FOR
POLK COUNTY, FLORIDA (NM102)
D-I9
-------
D.2.3 Indoor/Outdoor Gamma Radiation Ratio
Indoor gamma levels are measured in a manner similar to the outdoor
survey. For the indoor survey, a minimum of one reading was made in each
room of a structure with at least 10 readings per 1000 square feet of
floor space. The ratio of the average indoor gamma level to the average
outdoor gamma level would be expected to provide a general measure of the
shielding.characteristics of a structure type. As shown in Table D.8,
four structure types were evaluated: basement, slab-on-grade, crawl
space, and trailer. In calculating these ratios, the cosmic radiation
contribution, estimated at 4 pR/h, is subtracted from the indoor and
outdoor values.
TABLE D.8
Average Ratio of Indoor Gamma to Outdoor
Gamma Measurements by Structure Type
(minus cosmic contribution of 4 yR/h)
Average Ratio
Structure Type Indoor/Outdoor # of Structures
Basement .79 13*
Slab-on-grade .83 765**
Crawl Space .91 60+
Trailer .90 215+
* 2 structures have no ratio given
**32 Structures have no ratio given
+15 Structures have no ratio given
For the total sample of 1102 structures, an average ratio of 0.9
was calculated for all four structure types. The lack of
differentiation is not unexpected recognizing that approximately
two-thirds of the structures had outdoor gamma readings of less than
D-20
-------
10 yR/hr. These readings roughly approximate the observed background
level of 6yR/hr, thereby leading to a high "noise" level by which a
representative relationship between outdoor to indoor gamma is
masked. This effect is supported by ratio calculations for
observations equal to or greater than 10 and 15 yR/hr, respectively.
As shown in Tables D.9 and D.10, the average ratio for all structure
types is less for these observations. The ratio for basements and
slabs is as much as a factor of two less than the total sample, which
corresponds to an attenuation factor of 0.4 for a four inch layer of
concrete (6 percent porosity). Accepting this premise, structures with
underlying layers of concrete appear to be between two and three times
as effective in reducing gamma flux than those that do not (i.e.,
crawl space and trailers, with a underlying layer of air and
flooring). In summary, inside gamma was greater than outside gamma
for 80 sites (7 percent), less than outside gamma for 606 sites (55
percent), and about equal for 404 sites (38 percent).
D-21
-------
TABLE D.9
A. Average Ratio of Indoor Gamma to Outdoor
Gamma Measurements by Structure Type for
Observations equal to or greater than 10 R/hr
(Basement (B), Slab (S), Crawlspace (C), Trailer (T))
(minus cosmic contribution of 4 R/h)
Structure Type
B
S
C
T
Average Indoor/Outdoor
0.44
0.53
0.77
0.80
# of Structures
4
257
28
52
B. Statistical Comparison of Average Gamma Ratios
Type
Avg Ratio
B
S
C
T
S
C
T
C
T
S
C
4
257
28
52
257
28
52
28
52
257
28
0.44
0.53
0.77
0.80
0.53
0.77
0.80
0.77
0.80
0.53
0.77
F-test Value
28.47
PR F*
0.0001
42.19
0.32
28.40
0.0001
0.5727
0.0001
"Probability that the sample distributions are a product of random
variability
D-22
-------
TABLE D.10
A. Average Ratio of Indoor Gamma to Outdoor Gamma Measurements
by Structure Type for Observations Equal to or Greater than
15 yR/hr (Basement (B), Slab (S), Crawl Space (C),
Trailer (T)) (minus cosmic contribution of 4 yR/h)
Structure Type Average Indoor/Outdoor # of Structures
B 0.42 1
S 0.41 87
C 0.81 13
T 0.79 22
B. Statistical Intercomparison of Average Gamma Ratios
Type N Avg. Ratio F-test Value PR > F«
B 1 0.42
S 87 0.41 45.50 .0001
C 13 0.81
T 22 0.79
S 87 0.41
C 13 0.81 67.14 .0001
T 22 0.79
C 13 0.81 0.03 .0001
T 22 0.79
S 87 .41 54.90 .0001
C 13 .81
•Probability that the sample distributions are a product of random
variability
D-23
-------
100 i-
90 -
c
I
ro
0 10
,11 R/HR
RECLAIMED
Figure D.9
•Ranges not shown indicate N=0
11 20
PR/HR
MINERALIZED
010 1120
JJR/HR ^JR/HR
NON MINERALIZED
0 10
l R/HR
11 20
>JR/HR
UNKNOWN
21 30
PR/HR
PERCENT DISTRIBUTION OF GAMMA EXPOSURE RATE BY LAND
CATEGORY*
-------
D.2.4 Evaluation by Land Category
As part of the overall survey, outdoor gamma measurements were
evaluated according to the land category of the site. Four primary
categories were delineated on the basis of the presence or absence of
phosphate matrix, and past mining and reclamation: reclaimed raining
sites, mineralized sites, non-mineralized sites, and sites of unknown
designation. In Table D.11 and Figure D.9, a distribution of
measurements in increasing increments of 10 yR/hr is given for these
categories.
A statistical (F-test) intercomparison of the data shows a probable
difference between the three distributions (excluding the "unknown"
category) at the 99 percent confidence level. This evaluation, summarized
in Table D.12, suggests that on the basis of the sample data collected,
these land categories have statistically unique gamma distributions
associated with them.
TABLE D.11
Outdoor Gamma Survey Distribution of all structure
• sites by Land Category
Range of Outdoor Gamma Measurement ( y R/hr)
Use N 0-10 11-20 21-30 >30 Average
Reclaimed (R) 672 429 198 40 5 10.7
Mineralized (M) 102 97 5 0 0 7.2
Non-Mineralized (N) 300 292 8 0 0 5.6
Unknown (U) 28 20 7 10
TOTAL 1102 838 218 41 5
D-25
-------
M
N
R
M
R
N
R
M
N
102
300
672
102
672
300
672
102
300
7.0
5.8
10.7
7.0
10.7
5.8
10.7
7.0
5.8
39.64
244.34
139.26
55.35
TABLE D.12
Statistical Comparison of Gamma Survey
Distribution for Selected Land Categories
(reclaimed (R) mineralized (M) non-mineralized (N))
Use N Avg Gamma F test-Value PR >F*
0.0001
0.0001
0.0001
0.0001
•Probability that the sample distributions are a product of random
variability
D.2.5 Evaluation by Structure Type and Land Category
Indoor gamma exposure was evaluated on the basis of both
structure type and land category. As a preponderance of structures
(677) in the survey are located on land identified as being reclaimed,
the gamma measurement distribution for the four structural categories
were taken for structures so located, as provided in Figure D.10.
III. Track-Etch Measurements
Radon decay product levels were estimated in 153 structures with
track-etch film. In this pilot study, the film was placed in a
D-26
-------
100 i—
D
10
N 426
N 20?
010
1120
BASEMENT
0 10
0 10
1120 2130
TRAILER
1120 010 1120 2130
SLAB ON GRADE CRAWL SPACE
INDOOR GAMMA EXPOSURE (;iR/HR GROSS)
Figure D.10 PERCENT DISTRIBUTION FOR INDOOR GAMMA EXPOSURE RATE B\ STRUCTURE TYPE FOR RECLAIMED LAND
• RANGES NOT SHOWN INDICATE NO
-------
structure for at least a year, after which a representative count was
taken of the "etches" caused by alpha energy deposition. This count
is translatable into radon decay product levels (see Appendix B of
this report).
In Figure D.11, a percent distribution of working level estimates
in increments of .006 WL is provided. Approximately 70 percent of
these measurements were less than or equal to 0.03 WL, with 7 percent
in excess of 0.09 WL.
D-28
-------
35
30
25
O
I
10
vD
u
20
N 1 53
15
o
cr
10
WL *~ 006 012
018 .024 030 036 042 048 .054 060 066 .072 078
TRACK ETCH DATA IN INCREMENTS OF OOG WLMMTfRVtNINC., RAMu F RS'
090 VVL • 090
Figure D.ll PERCENT DISTRIBUTION OF EPA TRACK-ETCH DATA BY GROSS WORKING LEVEL RANGE
-------
ANNEX
-------
ANNEX KEY
"CLASS"
CLASSIFICATION
"TYPE"
TYPE STRUCTURE
"LEVELS"
FLOOR LEVEL
"MATRIAL"
MATERIAL
"A-C"
AIR CONDITIONING
0. Vacant Lot
1. Residence
Single Family
2. Multiple
(4 families)
3. Apartment (Gt 4)
4. Motel, hotel
5. Single business
6. Multiple business
7. School
8. Church
9. Other
1. Basement
2. Slab-on-grade
3. Crawl space
4. Trailer
5. Unknown
0. Unknown 0. Unknown 0.
1. One floor 1. Masonry 1.
2. Two floors 2. Non-masonry 2.
3.
4.
5.
6.
7.
8.
A.
B.
Unknown
Yes
No
Yes, never used
Central always
Central seasonally
Central occasionally
Window recirculating
always
Window recirculating
seasonally
Window recirculating
occasionally
Window makeup always
Window makeup
seasonally
Window makeup
occasionally
"AP-Mean": Air Pump Mean Working Level (WL)
"TE-Mean": Track Etch Mean Working Level (WL)
"GF-Gamma": Mean Indoor Ground Floor Gamma Exposure Rate ( yR/hr)
"Out-Gamma": Mean Outdoor Gamma Exposure Rate ( yR/hr)
"USE": "R"-Reolaimed, "M"-Mineralized, "N"-Non-mineralized, "U"-Unknown Land
Use
-------
AIK PUMP ANfl TRACK ETCH AVERAGES ANC ALL LOCATION DATA
LCCATION AP_MEAN TE_MEAN GF_GAMMA OUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
70C50
7CC51
70052
70C53
70054
70055
70056
70057
70058
70059
70060
70061
70062
7C063
7CC64
70065
70C66
70067
7CC68
70069
7CC70
70C7L
70072
7CC73
70C74
70075
7CC76
70C77
70C78
70 079
70080
7CC81
7CC82
7CC83
0.0075
C.0173
0.0626
O.C599
C.0226
C.01C2
0.0083
C.0209
0.0091
C.0096
C.0151
C.0089
C.OG8V
C.0223
0.0152
C.0086
0.0069
G.U202
0.0340
C.U147
0.0047
C.0179
0.0316
C.UJ82
C.0042
C.0183
0.0040
C.1248
0.0790
C.0248
0.0405
C.0619
0.0415
C.0029
0.0251
12
9
3
6
4
10
7
5
7
5
6
6
8
8
7
7
7
5
7
8
4
4
8
7
5
18
16
10
15
10
17
9
20
10
11
12
7
10
11
15
12
12
9
11
14
13
12
11
10
9
10
11
8
12
9
8
8
8
25
26
14
11
12
16
7
9
3
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
K
R
9
9
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
L
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
1
1
1
1
1
1
L
1
1
L
1
1
2
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
7
1
2
2
2
5
5
6
6
6
6
0
5
6
6
6
5
6
6
6
5
6
6
6
6
6
6
6
5
6
6
6
6
6
6
0
2
2
2
LAKELAND
EATON PARK
LAKELAND
LAKELAND
EATON PARK
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
EATON PARK
EATON PARK
EATON PARK
EATON PARK
EATON PARK
LAKELAND
BARTOW
BAHTOW
BARTGW
BARTOW
BARTOW
BARTOW
BARTOW
FT MEADE
FT MEADE
-------
AIR PUMH AND TKACK ETCH AVERAGES ANC ALL LOCATION DATA
LCCATILN
7CC£4
7CC€6
K C 6 7
7CCfc8
7CC89
7CC90
7CC91
7CC92
7CC93
7CC94
7CC95
7CC96
7CC97
7CC98
7CC99
701CO
7C1C1
7C102
7C1C3
7C1C4
7C1C5
701C6
7C1C7
7G1C8
7C1C9
7C110
7C111
7C112
7C113
7C114
7C115
7C116
7C117
AP_MEAN
0.0176
0.0322
O.IC45
C.0365
0.0673
0.0721
G.GC36
N oF_GAMMA CUT_GAPA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
O.OC12
O.OC17
C.OC68
O.OC37
0.0227
O.GC89
0.0208
0.0012
0.0107
O.U46fa
0.0598
0.0170
0.0217
O.OC13
0.0187
O.OC57
0.0250
0.0157
0.0186
0.0939
0.0768
C.OC87
O.OG32
0.0839
O.OG82
O.OC99
0.0252
0.0210
O.OC48
0.0155
0.0900
27
15
15
28
7
14
9
15
8
8
12
16
14
15
20
3
5
12
7
9
9
10
15
15
11
12
12
16
9
19
16
16
5
11
29
23
16
29
1 7
18
14
16
£
5
23
28
24
24
25
8
13
2C
15
7
14
2 1
3C
31
23
2C
22
17
23
33
15
15
9
23
U
R
R
R
R
R
ft
R
R
R
R
R
R
R
R
U
U
U
U
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
9
1
1
1
1
1
1
9
1
1
1
1
8
3
3
3
3
2
2
2
2
1
2
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
2
2
1
I
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
2
2
2
3
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
3
1
1
1
2
0
2
6
2
2
2
2
1
6
6
6
6
6
0
6
6
6
5
6
2
6
6
6
2
6
6
6
0
6
6
2
2
6
FT MEADE
FT MEADE
FT MFADE
FT MEAOE
BARTCW
BARTGW
BARTGW
BARTGW
MULBERRY
MULBERRY
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
AUBURNDALE
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
MULBERRY
MULBERRY
MULBERRY
MULBERRY
PIERCE
BRADLEY JUNCTION
PIERCE
-------
A IK PUMP AND TRACK fcTCH AVERAGES ANC ALL LOCATION DATA
CCATIuN
7C118
7C119
7C120
7C121
70122
7G123
7C124
7C125
7C126
7C127
7C128
70129
7C130
7C131
7C132
7C134
7C135
7C136
7C137
7C138
7C139
70140
7C141
7C146
7C147
7C148
7C149
7C150
70151
7C152
7C166
7C167
7C168
7C169
AP_MEAN T£_M£AI
0.0106 0.0050
0.0565
0.0702
0.0277
0.0162
0.0154
0.012C
0.0154
0.0053
0.0057
0.0096
0.0297
0.0166
0.0013 O.J069
C.COC8 O.UG89
O.C013 0.0026
O.C009 0.0143
0.0027
0.0250
0.0141
0.0089
0.0102
0.0034
0.0088
0.0052
0.0198
0.0666
0.1256
O.C252 0.0203
GF_GAMMA uUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
PIERCE
LAKELAND
LAKELAND
LAKELAND
MULBERRY
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
WINTER HAVEN
LAKE ALFRED
EAGLE LAKE
KINTEP HAVEN
WINTER HAVEN
HAINES CITY
LAKE HALES
BA8SCN PARK
AUBURNDALE
AUEURNOALE
AUBUKNDALt
PCLK CITY
BARTOk
FT MEAOE
FT MEADE
LAKELAND
LAKELAND
LAKELAND
MULBERRY
7
12
14
8
6
14
6
6
5
7
6
12
14
15
13
3
3
4
4
3
3
3
3
3
3
3
4
7
10
6
9
18
15
10
8.0
17. C
15.0
15. C
13.0
2C.O
16, C
s.o
7.0
1C.O
1C.C
35.0
17, C
1£,C
15.0
6.0
6.0
7.C
6.0
5,5
6.C
fc.C
6.C
3.C
4.0
8.0
4.0
7.0
7.0
6.C
16.0
13.0
17.0
11. C
R
R
R
R
R
R
R
R
K
R
R
R
R
R
R
N
N
N
N
K
N
N
N
N
N
N
N
U
M
N
M
M
M
M
1
1
1
9
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
9
i
1
1
I
1
9
2
2
2
2
2
2
2
3
3
2
1
2
2
2
2
2
2
1
2
2
3
2
I
2
3
3
3
1
3
-y
£.
2
2
3
2
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
2
1
1
I
1
1
1
I
1
1
I
I
I
1
1
0
1
1
1
1
1
1
2
2
1
1
2
1
1
2
1
1
1
1
1
2
1
1
1
1
1
2
1
2
1
1
I
3
1
2
6
6
5
5
6
6
2
2
6
6
0
6
6
6
5
2
2
6
6
5
6
6
2
0
6
2
5
6
6
6
6
0
5
-------
AIR t^UMP ANi) TRACK ETCH AVERAGES ANC ALL LOCATION JATA
TE_HEAN GF_GAMMA CUT_GAMA USE CLASS TYFfr LEVELS MATRIAL A_C CITYNAME
7C17C
7C171
7C172
7C173
7C174
7C175
7C176
7 C 1 7 7
7C178
7C179
7C180
7C181
7C182
7C183
7C1C4
7C185
7C186
7C187
7C188
7C189
7C190
7C191
7C1S2
7C3CO
7C3C1
70302
7C3C3
7C3C4
7C3C5
703C6
1C3C7
7C3C8
703C9
70310
O.CC65 0.0192
0.0604
0.0329 0.0288
0.0135
0.0338
0.0022 0.1
-------
AIR PUMP ANO TRACK ETCH AVERAGES AND ALL LOCATION DATA
LCCATICN AP_MEAN TE_KEAN GF_GAMMA CUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7C3H
7C312
7C313
7C314
7G315
7C316
1C317
7C318
70319
70320
7C321
7C322
7C323
7C324
70325
7C326
70327
7C330
7C331
7C332
10333
7C334
7C335
1C336
70337
7C338
70339
7C350
70351
7C352
7C353
7C354
7C355
7C356
0.0296
0.0387
0.0232
0.01L8
0.0795
0.13L1
0.0554
0.0778
0.1373
0.0915
0.0872
0.0£79
0.0567
O.OC49
O.OC47
O.OC78
0.0074
O.OC60
O.OC53
O.OC77
0.0550
O.OC26
0.0072
0.0226
O.OC96
0.0830
0.0321
0.0456
0.0159
6
7
7
6
8
10
8
7
5
6
5
8
10
8
7
4
3
3
4
8
8
6
6
15
5
7
13
8
8
6
6
14
15
16
20
17
3C
18
13
13
3C
8
15
25
25
16
6
5
4
13
11
14
9
14
6
9
12
13
7
6
28
24
16
21
15
ft
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
I
1
1
5
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
2
3
2
2
2
2
2
3
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
2
1
1
1
1
1
2
1
1
1
1
2
1
1
1
0
1
5
5
6
3
4
1
5
5
4
5
1
1
1
1
1
1
2
2
1
1
1
1
1
1
1
1
1
1
1
6
1
1
6
3
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
BARTCW
BARTOW
BARTOW
BARTCW
BARTOW
BRADLEY JUNCTION
BRADLEY JUNCTION
BARTGW
BARTOW
BARTOW
BARTOW
BARTOW
BARTOW
BARTOW
BARTOW
BARTOW
PIERCE
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIK PUMP AND TRACK ETCH AVERAGES ANC ALL LOCATION DATA
LCCAT10N AP_MEAN TE_MEAN 6F_GAMMA OUT_GAMA USE CLASS TYPE LEVcLS MATRIAL A_C CITYNAMc
70357
70358
70359
70360
70361
70362
70363
70367
70401
7C402
70403
70406
70407
70408
70409
70410
70411
70412
704 13
70414
70415
70416
70417
70418
70419
70420
70421
70422
70423
70424
70425
70426
70427
70428
C.0926
0.0837
0.0076
0.0043
0.0035
8
6
11
9
7
6
10
6
7
a
3
6
7
6
7
8
9
9
9
10
7
7
8
7
7
6
7
10
12
8
6
6
6
6
22
15
25
20
23
IS
11
6
11
9
9
7
7
7
7
8
9
10
11
1C
7
7
9
6
7
7
7
11
11
8
6
6
6
7
R
R
R
R
R
R
R
R
R
R
R
R
R .
R
R
R
R
R
R
R
R
k
R
K
R
K
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
6
1
1
6
1
6
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
I
1
I
I
1
2
1
I
I
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
AUBUKNQALE
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA
LOCATION AP_MEAN TE_MEAN GF_GAMMA CUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
70429
70430
70431
7C432
70433
70434
70435
70436
70437
70433
70439
70440
7044L
70443
70444
70445
70446 0.0046
10447
70448
70449
70450
70451
70452
70455
70454
70455
7C456
70457
70458
70459
70460
70461
70462
70463
6
6
5
5
10
9
7
9
10
6
7
7
7
7
7
6
7
7
8
12
12
12
6
6
8
7
8
6
7
7
6
6
6
7
6
6
5
5
11
9
8
9
11
6
7
6
8
7
7
6
7
7
9
14
13
13
6
6
8
7
7
6
7
7
7
6
6
7
U
U
U
U
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4'
4
4
4
4
4
4
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
I
1
1
2
2
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
Alk PUMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA
LOCATION AP_MEAN TE_/*tAN GF_GAMMA CIT.GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7C464
70 46 5
7U466
7C467
7C463
7C469
7U47U
7G471
70472
70473
70474
7C475
70476
7C477
7C478
7C479
704dO
7C481
7C482
70483
7G4d4
70435
70486
704b7
70488
70489
70490
70491
7C492
70493
7C494
70495
7C496
7C497
C.0033
7
6
6
6
6
7
7
6
6
6
5
6
6
8
10
6
6
7
6
7
6
6
6
6
7
7
7
7
7
6
6
5
6
6
7
6
6
6
6
7
7
6
6
7
6
6
6
7
7
7
7
7
7
7
7
7
6
7
7
7
8
7
7
6
6
fc
7
7
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
L
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
1
1
1
1
1
1
1
L
1
1
1
1
1
1
L
1
1
1
1
1
1
L
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
4
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
L
1
1
1
1
1
1
1
1
1
1
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AlK PUMP AND TRACK ETCH AVERAGES AND 4LL LOCATION DATA
LCCATIGN AP_MEAN T£_MEAN GF_GAMMA CLT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
70498
7C499
70500
70501
70502
70503
7C504
70505
70506
70507
70508
70509
70510
70511
70512
70513
70514
70515
70516
70517
70518
7C519
70520
70521
70522
7C523
70524
70525
70526
70527
70528
70529
70530
70531
5
5
5
5
5
5
6
f>
5
6
5
8
5
5
5
6
5
5
5
6
5
5
5
5
6
5
5
20
8
7
6
5
5
5
5
6
6
6
5
6
5
6
6
6
5
8
6
6
6
6
6
5
5
8
5
5
6
6
6
6
5
8
8
7
6
6
5
6
R
K
R
R
R
R
R
R
R
R
R
R
R
K
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
1
1
1
1
1
1
I
1
1
1
1
1
1
1
i
1
1
1
1
1
1
i
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
i
1
1
1
1
1
1
1
1
1
1
I
1
1
1
I
LAKELAND
LAKtLAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKtLAND
LAKELAND
LAKELAND
-------
AIR PUMP AND TXACK ETCH AVERAGES ANC ALL LOCATION DATA
LOCATION AP_MEAN Tfc_MEAN bF_GAMKA CUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
70532
70533
70534
70535
70536
70537
70538
7053S
70540
70541
70 542
70543
70544
70545
70546
70547
7C548
70549
70550
70551
7C552
70553
70554
70555
70556
70557
70558
70559
70560
70561
70562
70563
70564
7C565
C.0384
0.0858
C.0106
C.0313
7
7
7
7
6
7
7
13
7
3
7
9
8
7
8
7
7
6
6
7
7
7
11
7
7
7
7
6
8
7
7
7
7
7
8
6
8
3
7
8
8
8
1C
12
11
11
a
10
11
9
8
7
8
8
8
7
15
7
8
8
10
8
S
11
15
16
7
8
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
k
R
R
R
R
R
R
R
R
K
R
R
K
R
R
R
R
1
1
1
1
1
3
3
1
1
1
I
1
3
3
1
I
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
2
I
1
1
1
1
2
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
2
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
i
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUMP ANO TKACK ETCH AVERAGES AND /*LL LOCATION OATA
LOCATION AP_MEAN TE_MEAN GF_GA^A CUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAHE
II
70566
70567
70568
70569
7C570
7G571
70572
7C573
70574
70575
70576
70577
70578
7G579
70580
70581
70582
70583
70584
70585
70586
705&7
7C588
70589
7C590
70591
7C592
70593
70594
7C595
70596
70597
70598
70599
G.0066
0.0086
C.0042
0.0064
0.0089
C.0168
0.0177
C.0108
7
7
7
6
6
6
6
6
6
6
7
6
7
6
7
6
6
6
7
6
6
7
a
6
7
7
7
6
7
6
6
7
8
7
8
7
7
8
6
6
7
7
8
9
6
6
7
7
6
7
8
11
7
8
9
8
9
8
8
8
8
8
6
6
8
R
R
R
R
R
R
R
k
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
3
3
2
2
2
1
1
3
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
I
2
1
1
2
2
1
I
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
Alk PUMP AND TRACK ETCH AVERAGES AND *LL LOCATION DATA
12
LOCATION AP_MEAN TE_MEAN GF_GAMMA CUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7C6UC
7C601
7C602
7C603
7C604
7C605
70606
7C607
70608
7C609
70610
70611
70612
7C613
70614
70615
70616
7G617
70618
7C619
7C620
7C621
70622
70623
70624
70625
7C626
70627
70628
70629
70630
70631
70632
70633
C.0066
0.0091
0,0056
0.0034
C.C096
0.0041
0.0138
7
7
5
5
5
6
6
8
7
7
7
7
8
7
6
7
7
8
7
8
7
6
6
8
10
9
8
8
8
8
7
7
6
7
10
10
7
5
6
6
6
9
10
11
11
13
9
12
6
12
10
10
10
10
8
6
9
12
11
12
9
9
9
11
9
9
10
10
R
R
R
R
R
k
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
K
R
R
R
1
3
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
I
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
I
1
I
1
1
1
1
1
1
1
1
1
1
I
I
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUMP AND TRACK ETCH AVERAGES ANC *LL LOCATION DATA
LOCATION AP_MEAN Tt.MtAN GF.GAMMA CUT.GAMA USE CLASS TYPE LEVELS MATRIAJ. A_C CITYNAME
13
70634
7C635
7C636
7C637
7C638
70639
7C640
7C641
7C642
70643
70644
7C645
7C646
70647
7C648
7C649
7C650
70651
7C652
7C653
7U654
7C655
70656
70657
7C658
7G659
70660
7C661
70662
7C663
70664
7C665
70666
70667
C.0050
0.0044
0.0058
C.0040
0.0048
8
7
7
6
7
9
8
7
6
8
9
8
8
7
7
8
7
7
3
6
6
10
10
6
8
6
7
7
10
7
7
7
6
7
11
9
10
10
11
8
10
9
6
9
18
11
10
12
10
13
10
11
12
7
8
9
1C
6
7
7
8
7
11
8
8
7
5
8
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUMP AND TRACK ETCH AVERAGES AND *LL LOCATION DATA
LOCATION AP_MEAN TE_NEAN GF_GAMMA CUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7C668
7C669
70670
70671
7C672
7C673
70674
7C675
70676
7C677
70678
7C679
7C680
7C681
70682
70683
7C684
70685
70686
7C687
70688
70689
7C690
7C691
7C692
70 693
7C694
7C695
70696
70697
7C698
70699
70700
7C701
0.0046
0.0052
0.0039
0.0063
0.0053
0.0075
0.0025
C.0055
7
7
8
8
7
6
6
6
10
6
7
6
7
6
7
7
7
7
7
7
8
8
8
8
8
10
7
8
7
7
7
6
7
7
7
8
10
7
7
7
7
6
9
8
9
7
6
6
12
9
9
8
10
8
9
9
9
9
8
11
10
12
10
8
8
7
7
8
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
I
2
1
1
*
4
4
4
4
4
2
2
4
4
4
4
4
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
2
2
2
2
2
1
1
2
2
2
2
2
1
1
1
1
1
1
2
1
1
2
1
1
1
1
1
1
1
1
2
1
2
2
1
1
1
1
1
1
2
1
1
1
1
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA 15
LCCAFIGN AP_MEAN TE.rtEAN GF_GAMMA ObT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYKAME
7C7G2
70703
7C7G4
70705
707Cf
707C7
7C7C8 C.0131
70709
7C7LU
70711
7C712
7C713
70714
70715
70716
70717
7C71B C.OC79
7C719
70720
7C721
70722
7C723
70724
7G725
70726
70727
70728
70729
70730
70731
7J732
70733
7C734
70735 O.OG84
8
0
6
8
6
8
a
9
10
6
7
12
15
17
8
13
7
10
9
7
8
12
10
8
8
13
6
6
8
7
12
9
6
6
S
9
6
7
6
8
e
11
13
6
8
15
20
21
13
15
8
10
7
7
7
12
11
9
10
16
8
7
7
9
13
6
7
1C
R
R
a
R
R
H
R
k
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
4
4
4
4
2
2
2
2
4
4
4
4
4
4
4
2
2
2
2
2
4
4
4
4
4
2
4
2
2
4
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
4
2
2
1
1
1
2
1
2
2
2
2
2
1
1
1
1
2
2
2
2
2
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
2
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
2
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
EATON PARK
EATON PAKK
EATON PARK
LAKELAND
LAKELAND
EATON PARK
EATON PARK
EATON PARK
-------
A1K PUMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA
LLCATION AP_MEAN TE_MEAN GF_GAMMA OUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C
15
CITYNAME
70736
70737
7C738
70739
7C74G
70741
7C742
70743
70744
7G74b
7G746
70747
70748
70749
70750
70751
70752
70753
70754
70755
70756
70757
70758
70759
70760
70761
70762
70763
70764
70765
70766
70767
70768
70769
0,0072
0.0255
C.0047
0.0395
0.0127
6
7
6
13
9
6
7
12
7
8
7
8
21
6
6
7
10
6
5
6
12
7
6
7
7
8
8
8
8
8
11
7
7
7
7
7
7
25
16
8
13
20
14
14
14
7
23
9
7
9
12
6
6
6
13
10
10
1C
12
11
1C
8
11
10
2C
9
1C
10
R
R
R
R
R
R
R
R
R
R
K
R
R
R
R
R
R
U
U
U
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
4
2
2
2
3
2
2
2
4
2
2
2
2
4
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
I
1
1
1
1
1
1
1
2
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
EATON PARK
EATON PARK
EATON PARK
LAKELAND
LAKELAND
EATON PARK
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
EATON PARK
LAKELAND
EATON PARK
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
MULBERRY
MULBERRY
MULBERRY
MULBERRY
-------
AIR PUrtP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA
LCCATION AP_MEAN TE_M£AN GF_GAM,MA CUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNArtE
17
7C770
70771
7C772
7C773
70774
7C775
7C776
7C777
7C778
7C779
7C780
7C781
7C782
7C783
7C784
70785
7C786
7C787
7C788
7C789
7C79G
7C791
7C792
7C793
7C794
7C795
7C796
7C797
7C798
7C799
70800
7C80L
7G802
7C803
0.0071
0.0032
0.0094
C.0326
0.0042
0.0040
0.0096
C.0139
G.0343
0.0110
C.0072
10
a
7
9
8
5
5
7
6
10
6
7
8
11
9
8
8
7
10
Q
7
7
11
8
19
7
9
10
7
7
8
10
11
17
9
8
8
10
10
5
5
7
7
19
11
12
10
8
8
10
8
9
14
12
9
11
14
9
22
11
14
3C
9
17
11
14
20
24
R
R
R
R
R
N
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1'
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
4
4
4
4
4
4
4
4
2
2
2
3
2
2
2
2
2
2
2
2
2
2
2
3
2
2
2
2
2
3
2
2
3
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
2
1
1
1
1
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
2
1
1
2
1
1
1
1
1
1
1
1
1
2
1
1
I
1
1
1
2
2
2
1
2
2
2
1
2
2
1
1
1
1
1
2
2
1
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MUL6ERHY
-------
AIR PUMP ANJ TRACK ETCH AVERAGES ANC flLL LUCATIGN OATA
18
LCCATICN AP_MEAN
TE_MEAN GF_GAMMA CUT_GAMA USE CLASS TYPE LfcVhLS MATRIAL A_C CITYNAME
7C8U4
7C805
7C806
70807
7C808
7C809
7C810
7C811
7C813
7C814
7C815
7C816
7C817
7C818
7CB19
7C820
7C821
70822
7C823
7C824
7C825
70826
7C827
7C828
7C829
70831
7C832
7C833
7C834
70835
7C836
7C837
7C836
7C839
C.0057
C.0098
0.0100
0.0034
C.0114
0.0100
0.0495
C.0034
7
12
9
7
19
7
7
9
14
12
9
7
6
6
6
5
5
5
13
11
9
23
9
a
8
11
10
16
11
9
7
5
7
8
7
14
8
7
34
11
8
10
16
14
8
10
7
7
7
5
5
5
6
13
11
14
28
8
10
12
9
21
21
20
10
6
7
9
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
ft
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
4
2
2
2
2
3
4
4
4
2
2
2
2
4
4
4
4
4
4
3
3
3
3
3
3
3
4
2
2
2
4
4
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
2
1
1
1
2
2
2
2
1
1
1
1
2
2
2
2
2
2
2
2
1
1
1
2
2
2
1
1
2
2
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
2
2
2
2
2
1
2
2
2
1
2
1
MULBERRY
MULBERRY
MULBERRY
MULPERKY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUMP AND TRACK ETCH AVERAGES ANC ALL LOCATION DATA
19
LOCATION AP_MEAN TE_MEAN GF_GAMMA CLT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7C840
7C841
7C842
7C843
7C644
708*5
7C£46
7C847
7C848
76850
7C851
7C852
7C853
7C854 u.0113
7C655
7C856
7C837
7C858
7C£59
7C860
7C861
7C662
7C863
7CE64
70865
7C866
7C667
7C868
7C869
7CS70
7C871
7C872
7C873 C.OQ57
7CS74
7
8
3
7
9
10
7
8
7
7
6
7
10
12
8
8
7
7
8
7
8
9
8
7
9
7
7
6
8
6
6
8
7
10
8
S
8
8
9
12
9
S
9
8
8
8
16
15
12
13
8
12
11
11
11
14
16
15
11
8
6
9
7
6
10
7
11
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
3
3
3
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
4
4
4
4
2
3
4
2
2
2
2
2
2
4
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
i
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
2
2
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
2
I
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
2
1
2
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
MULBERRY
MULBERRY
FT WEAOE
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
FT MEADE
FT MEADE
FT MEAOE
MULBERRY
FULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AlK PUMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA
20
LLCATItlSi AP_MEAN Tt_MEAN GF_GAMMA CLT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7C875
7CE76
7C877
7C878
7C879
71880
7C801
7C882
7C833
7C884
7C8S5
7C836
7C887
7C888
7C88S
7C890
7C891
7C892
7C893
7C894
7C895
7C896
7C897
7C898
7C899
7C900
70901
7C902
7C903
70904
70905
7C906
7C907
7C9C8
0.0143
C.0064
0.0075
C.0051
0.0054
0.0341
6
8
11
7
6
8
8
9
6
7
10
7
7
6
7
6
5
a
12
9
23
13
15
a
9
9
Q
8
7
9
19
14
19
18
7
9
15
11
9
10
13
17
8
10
11
11
9
7
8
7
6
11
18
11
24
14
19
10
10
12
10
12
10
10
23
17
31
27
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
4
3
3
4
4
2
2
2
2
2
3
3
3
4
4
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
2
2
2
1
1
1
1
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
1
1
2
1
1
1
1
2
1
1
2
2
2
1
1
1
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
LAKELAND
LAKELAND
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
-------
AIR PUMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA
LOCATION AP_MEAN TE_MfcAN GF_GAMMA CUT_GAMA USE CLASS TYPE LEVELS NATRIAL
21
A_C CITYNAME
7C909
7C910
7G9L1
7C912
7C913
7C9i4
7C915
7C916
70917
7C918
7C919
7C920
70921
7C922
70923
70924
70925
70926
70927
7C928
7C929
7C930
7C931
7C932
7C933
70934
7C935
70936
7C937
70938
7C939
70940
70941
7G942
0.0069
0.0148
0.0373
0.0513
0.0261
C.0305
0.0075
C.0098
13
11
8
7
7
7
7
7
7
10
7
8
o
11
11
10
10
10
8
11
10
8
9
9
8
7
8
8
8
7
3
10
7
6
15
13
11
10
10
9
9
10
8
1U
10
9
10
21
18
17
19
14
10
14
18
0
10
10
10
10
10
10
9
10
12
15
8
8
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
1
1
1
3
3
3
3
5
1
1
1
1
1
1
1
1
1
1
1
1
1
3
3
3
3
3
1
1
1
1
1
1
1
1
4
2
3
2
1
2
2
2
3
2
2
2
2
2
2
2
2
3
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
2
1
1
1
1
L
1
1
1
1
1
2
1
1
2
1
1
1
1
1
1
1
1
1
2
1
2
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
1
1
1
2
2
2
2
2
2
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
MULBERRY
MULBERRY
BARTOW
BARTOW
BAR TOW
BARTOW
BARTOW
BARTOW
BARTOW
BARTOW
BARTOH
FT MEAOE
BARTOW
FT MEAOE
BARTOW
FT MEADE
FT MEAOE
BARTOW
FT MEAOE
FT MEADE
FT MEADE
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
MULBERRY
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUMP AND TRACK ETCH AVERAGES ANC ALL LOCATION DATA 22
LCCATION AP_MEAN T£_MEAN Gh_GAMMA JIT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7C943
70944
7C945
70946 C.OC84
7C947
70948
70949
70950
70951
70952 0.0351
70953
7G954
70955
70956
70957
7C958 C.0179
70959
7C960
70961
7C962
7C963
7C964
70965
7C966
7C967
70968
70969
70970
7C971
70972
7C973
70974
7C975
7G976
7
9
20
16
21
15
18
9
6
22
11
9
12
8
11
10
7
6
7
6
7
7
6
6
6
6
6
8
6
6
5
6
5
5
8
10
22
16
24
17
19
14
9
20
15
13
15
10
14
17
7
6
6
6
6
7
6
6
6
6
6
8
6
6
5
5
5
5
U
U
R
R
R
R
R
U
R
R
R
R
R
U
U
U
U
U
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
4
4
4
4
4
4
2
2
4
2
2
3
2
4
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
2
2
2
2
2
2
1
1
1
1
2
1
2
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
2
1
1
1
2
1
1
2
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
LAKELAND
LAKELAND
EATON PARK
EATON PARK
LAKELAND
LAKELAND
LAKELAND
LAKELAND
EATON PARK
EATON PARK
LAKELAND
MULBERRY
MULBERRY
LAKELAND
MULBERRY
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
MULBERRY
LAKELAND
MULBERRY
MULBERRY
MULBERRY
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUMF ANO TRACK ETCH AVERAGES ANC £LL LOCATION DATA
23
LCCATIUN AP_MEA,M TE_MEAi4 GF_GAMMA UtT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7C977
7CS78
7CS79
70S 80
70S 81
7C982
7GS83
7CS84
7CS85
70S86 0.0029
70S67
7CS88
7CS89
7C99Q
7C991
70992
7C993
7C994
7C99t>
7C996
7C9S7
7C988
7C999
71000
71001
71CC2
71003
710C4
71005
710C6
71007
710C8
71CC9
71010
6
5
7
7
7
5
12
11
10
6
5
5
5,
5
5
7
5
5
8
5
5
7
5
5
6
6
6
6
6
6
6
6
6
5
5
5
11
9
7
6
<;
10
10
6
5
5
5
6
5
7
5
5
6
5
6
7
5
5
6
6
7
6
6
6
6
6
6
6
N
N
U
U
U
U
U
J
U
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
i.
2
2
4
2
2
2
2
3
2
2
2
2
2
2
2
2
2
3
2
2
3
2
2
2
2
2
2
2
2
2
3
1
1
1
1
L
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
2
L
1
1
2
1
1
1
1
1
1
1
1
2
2
1
I
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
2
2
2
1
1
1
1
2
1
2
1
2
2
2
1
1
1
1
1
1
1
1
1
1
LAKELAND
LAKELAND
BARTCW
HARTDW
BARTGW
PIERCE
BARTLW
6ARTOW
BARTON
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPGKT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
LAKELAND
MULBERHY
MULBCRftY
MULBERRY
MULBERRY
MULBERRY
MULBERRY
POLK CITY
POLK CITY
POLK CITY
-------
AIR PUMP AND TRACK ETCH AVERAGES ANC ALL LOCATION DATA
24
LOCATION AP_MEAN TE_ME/>N GF_GAMMA GUT_GAMA USfc CLASS TYPE LEVELS MATRIAL A_C CITYNAME
71011
71012
71013
71014
71015
71016
71017
71C18
71019
71020
71021
71022
71023
71024
71025
71026
71027
71028
71C29
71030
71031
71032
71033
71034
710-5
71036
71037
71C38
71039
71040
71041
71042
71043
71044
0.0038
0.0024
O.C041
0.0025
O.C011
O.C045
7
6
6
5
5
6
6
7
7
6
6
5
5
5
6
b
5
5
5
b
5
5
6
6
6
6
5
5
5
5
5
3
5
5
8
7
6
6
6
6
7
8
7
6
6
5
5
5
6
6
6
5
5
5
5
5
6
6
6
5
6
5
5
5
5
5
5
5
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
1
1
1
1
1
1
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
i
1
3
3
3
1
3
1
2
2
2
2
2
2
2
1
2
2
2
2
2
2
2
2
2
2
3
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
2
1
2
2
2
2
1
1
1
2
2
1
1
2
1
2
2
2
2
1
1
1
1
1
1
1
POLK CITY
POLK CITY
POLK CITY
POLK CITY
POLK CITY
POLK CITY
POLK CITY
POLK CITY
POLK CITY
POLK CITY
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
DAVENPORT
hAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES C[TY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
-------
AIR PUMP ANO TRACK ETCH AVERAGES AND ALL LOCATION DATA
LOCATION AP_HFAN T E_MEAN GF_GAMMA GUT_GAMA USE CLASS IYPE LEVELS MATRIAL
5
5
5
5
5
5
7
5
5
5
6
6
5
6
5
5
5
5
5
5
5
5
6
8
5
5
5
5
5
5
5
25
A_C
C1TYNAHE
71045
71046
71047
71048
71049
71050
71051
71052
71053
71054
71055
71056
71057
71058
71059
7106C
71061
71062
71G63
71064
71065
71066
71067
71068
71069
71070
71071
71072
71C73
71074
71C75
71C76
71C77
71078
0.0028
O.C025
O.C030
0.0033
0.0022
0.0118
O.C027
5
5
5
5
5
5
6
5
6
6
5
6
6
7
6
5
6
5
5
5
5
5
5
5
5
5
10
6
5
5
5
6
5
5
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
3
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
i
1
1
1
2
2
3
2
2
3
2
2
2
2
2
2
2
2
2
2
3
2
3
2
2
2
2
2
2
2
2
2
2
2
2
2
3
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
2
1
1
1
I
1
1
i
I
1
1
1
1
2
1
1
1
1
1
1
1
2
1
1
2
1
1
2
1
1
1
I
1
2
1
1
1
2
1
2
1
2
1
1
1
1
2
1
2
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HA1NFS CITY
HAINtS CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
HAINES CITY
FROSTPROOF
FKGSTPKOGF
FROSTPROOF
FRCSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
-------
AIR HUMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA
26
LCCATION AP_MEAhi TE.MEAN GI-_GAMMA GIT_GAMA USE CLASb TYPE LEVELS MATRIAL A_C CITYNAME
71C79
71C80
71081
71082
71C33
7108-*
71CB5
71C86
71C87
71C8d
71 CSS)
71090
71G91
71092
71C93
71C94
71U95
71C96 C.OG41
71CS7
71093
71 C !9'*
71100
71101
711C2
71103
71104
7 1106
71107
71103
711C9
71110
71111
71112
5
5
6
6
7
5
6
6
7
b
5
5
5
5
5
5
5
6
6
5
b
5
6
7
6
5
5
5
5
5
5
Lu
5
b
5
5
5
6
8
5
6
6
6
5
5
6
6
5
5
6
6
5
5
6
7
6
6
6
6
6
5
6
5
12
5
6
N
N
Ni
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
\
N
N
N
N
N
N
N
N
N
N
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
I
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
3
2
2
3
4
4
2
4
2
2
2
2
2
2
2
2
2
1
3
2
3
2
2
3
2
3
2
3
2
I
I
1
2
1
1
I
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
2
2
1
2
1
1
1
1
1
1
1
I
1
2
1
2
1
1
2
L
1
1
2
1
1
1
1
1
I
1
1
2
2
2
2
1
2
I
1
2
1
1
1
1
2
2
2
2
1
2
1
2
2
1
1
1
1
1
FRUSTPHOLF
PCLK CITY
POLK CITY
PCLK CITY
PCLK CITY
PCLK CITY
PCLK CITY
PCLK CITY
PCLK CITY
PCLK CITY
PCLK CITY
PCLK CITY
PCLK CITY
DUNDEE
DUNOFF
DUNDEE
CUNOEE
DUNDEE
DUNDEE
DUNOFE
DUNDEE
DUNDEE
DUNDEE
DUNDEE
DUNDEE
DUNDEE
DUNDEE
CUNDCE
DUNDEE
DUNDEE
DUNDEE
DUNDEE
DUNDEE
DUNDEE
-------
A Ik PUMP AND TRACK ETCH AVERAGES ANC ALL LOCATION DATA 27
LLCATION AP_MEAi\ TE_MEAN GF_uAMMA OUT_GAMA USE CLA. S TYPE LEVELS MATRIAL A_C CITYNAME
7111J
71114
7111i>
71116
71117
71118
71119
71120
71121
71122
71123
71124
71125
71126
71127
71123
71129
71130
71131
71132
71133
71134
71135
71136
71137
71136
71139
7114J
71141
71142
71143
71144
71145
71146
0.0024
C.UL81
C.0035
C.0033
5
6
5
6
6
5
5
5
5
5
6
8
6
5
5
5
5
6
5
5
5
5
5
9
5
6
6
5
5
5
6
5
5
s
5
5
5
6
6
5
5
5
5
6
5
6
5
6
5
5
5
6
5
5
5
5
5
7
5
5
5
6
6
5
5
5
5
N
\
N
IM
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
1
1
3
3
3
3
3
3
3
3
3
3
5
3
1
1
I
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
3
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
4
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
I
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
2
1
1
2
2
DUNDEE
DUNDEE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
LAKE
WALES
WALES
WALES
WALES
WALES
WALES
HALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
WALES
-------
AIR FJMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA
28
LCCATIGN AP_MbAN TE_ME«I GF_GAMMA UUT.GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
71147
71148
71149
71150
71151
71152
71153
71154
71155
71156
71157
71158
71159
71160
7U61
71162
71163
71164
71165
71166
71167
71168
71169
71170
711,1
71172
71173
71174
71175
71176
71177
71178
71179
71180
0.0018
5
5
6
6
6
5
5
5
t>
5
5
5
5
5
5
5
5
5
5
5
7
5
5
6
5
5
10
10
10
9
7
5
9
10
5
5
6
6
6
5
5
5
5
5
5
5
5
6
5
5
5
5
5
5
6
5
5
7
5
5
11
10
13
1C
9
5
1C
11
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
L
1
1
I
1
1
2
I
1
1
2
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
1
2
2
2
1
2
2
1
1
1
2
2
2
2
2
1
1
2
1
2
2
1
LAKE WALES
LAKE KALES
BARTON
BARTGfe
BARTCW
8ARTGW
BARTOW
BARTOW
BARTGfc
BARTGW
BARTOW
BARTON
BARTOW
BARTOW
BARTOh
BARTOW
BARTOte
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
BARTOW
FROSTPROOF
FROSTPROOF
FROSTPROOF
-------
AIR PUMP AND TRACK ETCH AVERAGES AND ALL LOCATION DATA 29
LCCATIGN AP_MEA.\ TE.MEAU GF_GAMMA OUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
71181
71182
71183
711S4
71185
711 80
71187
71188
71189
71191
71192
71193
71194
711S5
71196 G.0224
71197
71198
71199
71200
71201
71202
71203
71204
71205
71206 C.0204
71207
712C8
71209
71210
71211
71212
71213
71214
71215
5
5
5
9
10
10
11
11
8
7
8
10
10
9
9
7
7
7
6
7
6
7
6
6
6
6
0
6
6
6
6
9
a
6
5
5
5
S
11
11
11
12
9
9
9
10
1C
10
8
7
8
7
6
7
7
7
7
7
6
6
6
6
6
7
6
a
8
6
N
N
N
N
N
N
N
N
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
N
M
M
M
M
M
M
H
M
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
3
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
2
2
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
2
2
2
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
FROSTPROOF
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
-------
AIR PUrtP AND TRACK ETCH AVERAGES *ND 4LL LOCATION DATA
33
LOCATION AP_MEAN TE_MEAN Gf_«AMMA OUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
71216
71217
71218
71219
71220
71221
71222
71223
71224
71225
71226
71227
71228
71229
71230
71231
71232
71233
71234
71235
71236
71237
71238
71239
712-iO
71241
71242
71243
71244
71245
71246
71247
71248
71249
6
6
8
8
11
6
6
7
7
7
8
6
7
6
6
7
7
9
6
8
6
6
6
6
6
6
8
6
7
7
6
8
6
5
7
6
7
6
6
7
7
8
7
8
7
6
8
6
5
8
7
8
6
7
6
6
7
7
6
6
9
6
7
7
7
6
6
5
M
M
M
M
M
M
M
M
M
M
M
N
M
M
M
M
M
M
M
M
M
M
M
M
N
N
N
N
N
N
N
N
N
N
1
1
1
1
1
1
1
1
1
1
1
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
2
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
2
2
2
2
2
2
2
2
LAKELAND
LAKELANO
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELANO
LAKELAND
LAKELAND
LAKELANO
LAKELAND
LAKELAND
LAKELAND
LAKELANO
LAKELAND
LAKELAND
LAKELAND
LAKELANO
LAKELAND
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
-------
Alk PUMH AuU TRACK cTCH AVERAGES 4.\ C ALL LGCATIGN DATA
31
LGCATILN AP_MEAN TE_MfcAN GP_oAM>4A UUT_GAfA USE CLASS TYPE LEVELS MATKlAL A_C CITYNAML
7 12 50
71251
71252
71253
71254
71255
71256
71257
71258
71259
71260
71261
712b2
71263
71264
71265
71266 O.CObO
71267
71268
71269
71270
71271 O.C056
71272
71273
71274
71275
71276
71277
71278
7127S
71280
71281
71282
71283
5
5
6
5
5
5
6
b
6
5
7
f>
5
5
5
5
6
5
6
6
5
4
5
5
5
5
5
5
5
23
5
5
5
5
5
5
6
5
6
6
7
5
6
5
6
c
K
5
5
6
8
5
5
5
5
5
5
5
c
-*
5
C
^f
5
c
-^
5
5
5
5
5
N
(Si
N
K
N
N
N
f.
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
iNi
N
N
N
N
N
N
N
N
N
N
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
1
i
1
1
1
1
I
1
1
I
1
1
1
1
2
2
2
2
1
i
1
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
WIMFR
WlMfcR
WIMEH
hIMEk
VvIMEfc
fclNTEk
WlKTtH
WINTER
WIMFK
to I N T E K
wINTEK
BAfcTUw
BAR TO,
BARTOfc
BARTOk
BARTC*
BARTCw
WINTER
WINTEK
WINTER
wINTEK
WINTEK
bINTEK
WINTER
vilisTEH
WINTER
hINTEK
WINTER
WINTER
WINTER
WINTEK
WINTER
WINTER
WINTER
HAVEN
HAVEN
HAVEN
HAVLN
HAVEN
HAVtN
HAVEN
HAVfcN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
HAVEN
-------
AlK PUMP AND TKACK ETCh AVERAGES AND ALL LOCATION DATA
LCCATlLiM AP_i-lEAiN4 TE_ME/»N GF_GAMMA GJT_GAMA USE CLASS TYPE LEVELS MATRIAL
A_C
712E5
712S6
7128 1
71288
71290
71291
71292
71293
71294
71295
71296
71297
71298
71299
71300
71360
71361
71362
71363
71364
71365
71366
71368
71369
71370
71371
71372
71373
71374
71375
71376
71377
71378
0.0043
O.C070
5
to
9
fa
9
7
7
8
6
6
6
7
9
7
8
7
5
to
6
6
6
6
6
5
5
5
5
5
5
to
6
6
c
5
6
7
e
7
7
6
6
7
6
6
6
e
7
7
8
6
6
6
6
6
6
£
5
5
5
5
5
5
6
6
6
N
N
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
R
R
R
P
M
M
M
M
M
M
M
M
M
M
1
1
1
1
1
1
i
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
I
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
CITYNAME
WINTER HAVEN
WIMEn HAVEN
LAKEL.AND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
LAKELAND
AUbURNOALE
AUBURNDALE
AU6URNDALE
AUBURNOALE
AUBURNOALE
WINTER HAVEN
HINTS* HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
AUBURNDALE
AUBUKNOALE
AU6URNDALE
AUBURNOALE
-------
A Ik PUMP ANO TRACK ETCH AVERAGES ANQ ALL LOCATION DATA
LOCATION AP_MtAN TE_MEAN GF_GAMMA GUT_GAMA USE CLASS TYPE LEVELS MATRIAL A_C CITYNAME
7137S
71380
71331
71382
71383
71384
71385
71386
71387
71388
71389
71390
7 1391
71392
71393
71394
71395
713S6
71397
O.C029
O.C100
6
6
5
5
5
5
5
5
5
5
5
5
5
5
5
8
14
16
7
6
6
6
6
6
5
5
5
5
5
5
5
5
5
5
1C
12
18
7
M
M
M
M
M
M
M
K
M
M
M
M
M
M
M
M
R
R
M
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
I
2
3
2
2
2
2
2
2
2
2
2
2
2
2
2
3
4
4
4
I
I
1
1
1
1
1
1
1
1
1
1
1
1
1
1
L
1
1
1
1
1
1
1
1
I
1
1
1
1
1
2
2
2
1
2
1
I
1
1
1
1
1
1
1
1
1
1
1
2
2
1
1
AUBURNOALE
AUBURNDALE
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
WINTER HAVEN
FT MEAOE
FT MEADE
FT MEAOE
FT MEADE
OU.S. GOVERNMENT PRINTING OFFICE: 1979 281-147/94 1 -3
------- |