United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington DC 20460
EPA 520/6-83-026
June 1983
Radiation
£EPA
Evaluation of
Radon Sources and
Phosphate Slag in
Butte, Montana
-------
EPA 520/6-83-026
of Radon Sources and
Phosphate Slag in Butte, Montana
Larry L. Uoyd
Occupational Health Bureau
Montana Department of Health
and Environmental Sciences
June 1983
This report was prepared under
EPA Contract No. 68-01-6100
Project Officer
Michael F. O'Connell
Office of Radiation Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
-------
DISCLAIMER
The work upon which this report is based was supported in part by funds
provided by the U. S. Environmental Protection Agency, Office of Radiation
Programs.
Contents of this report do not necessarily reflect the views and policies
of the U. S. Environmental Protection Agency. Mention of trade names or com-
mercial products does not constitute their endorsement or recommendation for
use by the U. S. Environmental Protection Agency or by the Montana Department
of Health and Environmental Sciences.
-------
FOREWORD
In 1977, The Montana Department of Health and Environmental
Sciences (DHES) initiated an investigation of the use of phos-
phate slag in Butte and Anaconda, Montana. Phosphate slag, a
waste product from a nearby elemental phosphorus smelter, was of
concern because of its elevated content of natural radioactivity,
particularly radium-226.
During the investigation of phosphate slag, DHES discovered
elevated radon and radon progeny concentrations in many structures
in Butte. The cause of these elevated concentrations was unknown.
DHES requested assistance from the U.S. Environmental
Protection Agency (EPA). The EPA's Office of Radiation Programs
subsequently entered into a contract with DHES to identify the
sources of radon and radon progeny in structures and in the
ambient air in the Butte area. The scope of the contract was
expanded in 1981 to include an intensive sampling program designed
to evaluate the state-of-the-art in indoor radon measurement
equipment and methods.
This report is the first of a series summarizing the EPA
sponsored work conducted in Butte. The DHES investigation into
the contribution of phosphate slag and the mineralized geology as
sources of elevated radon and radon progeny levels in Butte struc-
tures are described in this report.
Future reports will summarize the extensive indoor air
measurement data, describe the statistical relationships between
the various sampling methodologies, and discuss sampling and data
management.
iii
-------
ACKNOWLEDGEMENTS
This project was made possible by the U. S. Environmental
Protection Agency's (EPA) Office of Radiation Programs through a
contract (EPA Contract No. 68-01-6100) with the Montana Department of
Health and Environmental Sciences (DHES).
It could not have been completed without the cooperation and
assistance of numerous federal, state, and local governmental agencies,
private individuals, and particularly the homeowners in Butte, Montana,
and the surrounding areas.
t
The EPA's Las Vegas Facility and the Eastern Environmental
Radiation Facility (Montgomery) provided both technical and laboratory
support as needed throughout the duration of the study.
The U. S. Bureau of Mines provided radon and radon progeny
calibration facilities and technical consultation at its Denver Research
Center. The Bureau of Mines' Spokane Research Center computerized the
bulk of the data acquired by DHES in addition to available geological
information pertaining to the Butte area. The Bureau of Mines computer
was used for data comparison and evaluation and for the graphic
production of numerous figures in Section 5 of this report.
The U. S. Department of Energy/s Environmental ^Measurement
Laboratories (EML) provided DHES with 'semi-annual radon 'measurement
intercomparison exchanges to assure the accuracy of radon measurement
calibrations.
The Montana Bureau of Mines assisted in the evaluation and
understanding of the Butte geology and with the description of the Butte
geology.
The Anaconda Company provided DHES with a detailed geological map
of the Butte area which was used extensively to locate veins, fractures,
and surface geological formations.
The cooperation and assistance provided by the Butte/Silver Bow
Government's Chief Executive's Office and Health Department helped to
maintain good public relations throughout the study.
The friendly cooperation of Butte homeowners in allowing DHES to
perform measurements in their homes was essential to the completion of
the project.
A special appreciation is expressed to the DHES staff members who
conducted the field operations of the study. Their continued commitment
to detail, quality assurance, and accurate data collection was paramount
to the successful conclusion of this project.
-------
TABLE OF CONTENTS
Page No.
List of Tables vii
List of Figures viii
Abstract 1
1. Introduction 3
2. Butte Description 7
History 7
Geography 7
Climate 7
Geology 7
3. Evaluation of Phosphate Slag Use 10
4. Radon/Radon Progeny Measurements 16
Selection of Homes for Measurement 16
Indoor Measurement of Radon and Radon Progeny 17
Measurement of Indoor Radon Progeny 17
Short-Term Sampling 17
Long-Term Sampling 17
Measurement of Indoor Radon 18
Short-Term Sampling 18
Long-Term Sampling 18
Factors Affecting Radon and Radon Progeny
Concentrations in Structures 18
Use of Indoor Measurements to Identify
Geographical Areas Impacted by Elevated
Indoor Radon Concentrations 19
5. Radon Source Assessment 21
Summary 21
Ambient Measurements 21
Soil Sampling and Analysis 31
Measurement of Radon Progeny (Working Levels)
in Structures 31
Silver Bow Homes 43
Skyway Park 43
Radon Soil Gas Measurements 43
Localized Measurements of Radon Soil Gas
Concentrations 56
Silver Bow Homes 57
Skyway Park 57
Walkerville 61
West Junior High School 61
Yellow Jacket Vein 64
Gold Street 64
Henry Street 64
Radon Exhalation Measurements 64
-------
Page No.
Dissolved Radon in Water 70
Radon Measurements in Underground Sewers 70
Radon in Natural Gas Supplies 70
6. Conclusions 73
Radon Sources 73
Phosphate Slag 73
Outside Air 73
Soil 73
Surface Geology 73
Other Measurements 74
Summary 74
References 75
-------
TABLES
Page No.
Table 3-1 Radioactivity in Phosphate Slag Produced
from Ore Mined in Montana and in Idaho 10
Table 3-2 Comparative Radon Exhalation Measurements
Performed on 25 cm Depths of Phosphate Ore,
Phosphate Slag, and Decomposed Granite Soils
from Butte 13
Table 4-1 Indoor Radon Progeny Grab Sample Measurements
in Butte (1979-1982) 19
Table 4-2 Average Annual Concentrations of Radon Progeny
in Homes Measured With Radon Progeny Integrating
Sampling Units 20
Table 5-1 Radioactivity in Soil Samples From Butte 35
Table 5-2 Radon Soil Gas Measurements in Butte, 1980-1981 52
Table 5-3 Comparative Radon Exhalation Measurements of
Butte Area Rock and Soil Samples 69
Table 5-4 Dissolved Radon Concentrations in Water Sources
in the Butte Area 71
Table 5-5 Radon Concentrations in Butte Underground Sewers 72
vii
-------
FIGURES
Page No.
Figure 1-1
Fiqure 2-1
Figure 3-1
Figure 5-1
Figure 5-2
Figure 5-3
Figure 5-4
Figure 5-5
Figure 5-6
Figure 5-7
Figure 5-8
Figure 5-9
Figure 5-10
Figure 5-11
Figure 5-12
Figure 5-13
Naturally Occurring Radionuclides 4
Prominent Faults, Veins, and Rock Types
of Butte 9
Uranium-238 Decay Series 11
City Map of Butte Showing Locations
of Reference Streets 22
Reference Streets and Outside Air
Monitoring Station Locations 23
Ambient Radon Concentrations, Hebgen Park
Monitoring Station, August 8 - September 4,
1980 25
Ambient Radon Concentrations, Hebgen Park
Monitoring Station, January 21 - January 27,
1981 26
Ambient Radon Concentrations, Hebgen Park
Monitoring Station, April 1 - April 7, 1981 27
Ambient Radon Concentrations, Hebgen Park
Monitoring Station, July 9 - July 15, 1981 28
Average Weekly Ambient Radon Concentrations,
Hebgen Park Monitoring Station, August, 1980 -
August, 1981 29
Average Monthly Ambient Radon Concentrations,
Hebgen Park Monitoring Station, August, 1980 -
August, 1981 30
Average Weekly Outside Radon Concentrations,
Hornet Street Monitoring Station, February,
1982 - January, 1983 32
Average Monthly Outside Radon Concentrations,
Hornet Street Monitoring Station, February,
1982 - January, 1983 33
Soil Sampling Locations 34
Northwest Butte Surface Geology 40
Veins and Fractures in Northwest Butte Geology 41
viii
-------
Page No.
Figure 5-14 Butte Geology/Indoor Radon Progeny Concen-
trations (WL) in Individual Structures 42
Figure 5-15 Three Hundred Foot Aggregate Average of Indoor
Radon Progeny Concentrations (WL) in Butte 44
Figure 5-16 Three Hundred Foot Aggregate Average of Indoor
Radon Progeny Concentrations (WL) in N.W. Butte 45
Figure 5-17 Indoor Radon Progeny Measurements (WL) - Silver
Bow Homes 46
Figure 5-18 Indoor Radon Progeny Measurements (WL) -
Skyway Park 47
Figure 5-19 Alpha Track Detector in PVC Sleeve Assembly 49
Figure 5-20 Butte Radon Soil Gas Measurement Sites 50
Figure 5-21 Radon Soil Gas Measurement Sites in N.W.
Butte 51
Figure 5-22 Radon Soil Gas Concentrations (pCi/1) -
Silver Bow Homes 58
Figure 5-23 Radon Soil Gas Concentrations (pCi/1) at
Measurement Sites Traversing Mineralized
Veins - Silver Bow Homes 59
Figure 5-24 Radon Soil Gas Concentrations (pCi/1) -
Skyway Park 60
Figure 5-25 Radon Soil Gas Concentrations (pCi/1) in
Aplite - Walkerville 62
Figure 5-26 Radon Soil Gas Concentrations (pCi/1) in
Aplite - West Junior High School 63
Figure 5-27 Radon Soil Gas Concentrations (pCi/1) at
Measurement Points Traversing the Yellow
Jacket Vein 65
Figure 5-28 Radon Soil Gas Concentrations (pCi/1) at
Measurement Sites Traversing Mineralized
Veins - Gold and Jackson Streets 66
Figure 5-29 Radon Soil Gas Concentrations (pCi/1) at
Measurement Sites Traversing Mineralized
Veins - Henry and Antimony Streets 67
Figure 5-30 Rock and Soil Collection Sites for Radon
Exhalation Tests 68
ix
-------
ABSTRACT
In 1978, DHES began investigating the potential sources of radon
(radon-222) which contribute to the elevated ambient and indoor
concentrations of radon and its decay products in Butte, Montana.
During the early stages of the investigation, efforts were directed
toward the evaluation of phosphate slag which has been used extensively
for paving and graveling and building materials in the Butte area. The
phosphate slag proved not to be a significant source of radon.
In July, 1980, DHES contracted with the EPA to further investigate
the potential sources of radon in Butte. Under the agreement with EPA,
surface geological constituents, air, water and natural gas supplies,
and building materials were investigated as potential radon sources.
Butte Geology
The northern part of Butte is located on a hill interlaced with
geological fractures and richly mineralized veins. Extensive mining of
gold, silver, copper, manganese and other metals has been conducted on
the Butte hill during the past hundred years. The most prevalent rock
type in the area, commonly known as "Butte granite", is technically
quartz monzonite. Aplite and alaskite dikes are prevalent in the quartz
monzonite. Rhyolite, which is of volcanic origin, is found in the most
northwestern part of the city. Alluvium is the prevalent geology in the
southern portions of the city. The alluvium is predominantly sand and
gravel that resulted from the erosion of the surrounding hills so that
in gross composition it is nearly the same as the quartz monzonite,
rhyolite, and aplite.
Geological Constituents
Soil samples were collected throughout the Butte area and analyzed
for radium (radium-226) content. The radium content of the samples
ranged from 0.7 to 3.2 picocuries per gram (pCi/gm) with a mean of 1.84
pCi/gm.
Alpha track detectors were used to measure radon soil gas
concentrations during both summer and winter months. The average radon
soil gas concentration measured during summer months was 1082 picocuries
per liter (pCi/1), whereas the average winter concentration was 1407
pCi/1. While radon soil gas concentrations of less than 100 pCi/1 were
measured, concentrations in excess of 5000 pCi/1 were not uncommon. The
highest radon soil gas concentrations were associated with measurement
sites located over major fractures and mineralized veins. The lowest
concentrations were measured in rhyolite. At many measurement sites it
was impossible to determine if the underlying rock was quartz monzonite
or aplite or if the alluvial cover was of sufficient depth to prevent
the upward migration of radon to the detector location. Consequently,
it was impossible to determine radon soil gas concentration differences
resulting from these different formations.
Radon exhalation tests were performed on 25 cm depths of quartz
monzonite, aplite, alluvium, and mineralized vein samples. The highest
1
-------
radon exhalation rates were from mineralized vein material which
averaged 2139 picocuries per square meter per minute (pCi/m2/min).
Aplite samples showed exhalation rates (713 pCi/m2/min. average) that
are about three times the exhalation rates from quartz monzonite (237
pCi/m2/min. average) and alluvium (226 pCi/m2/min. average).
Air
Radon concentrations in ambient air were monitored at the Hebgen
Park station, using radon gas monitors that provided hourly data
printouts, from August 1980 through August 1981. Monthly average
ambient radon concentrations ranged from a high of about 3 pCi/1 to a
low of less than 0.25 pCi/1. The highest concentrations were observed
between August and November. Concentrations diminished through the
winter months and reached a low in May and June.
Outdoor air (not considered ambient because of the location of the
intake) was monitored at the Hornet Street station from February 1982
through January 1983. Outdoor radon concentrations at this location
averaged 3.25 pCi/1 for the entire monitoring period.
Water Supplies
The Butte municipal water supply system is fed by surface water
sources. Of these sources, the highest dissolved radon content measured
was 69 pCi/1, thus eliminating water supplies as a suspect radon source.
Natural Gas
The radon content of natural gas in Butte averaged 14 pCi/1. This
low concentration eliminated natural gas as a suspect source.
Building Materials
Radon exhalation tests were performed on numerous building
materials. Building materials proved not to be a significant radon
source in Butte.
Following the investigation of potential radon sources in Butte, it
was concluded that ambient air, soils and surface geology all contribute
to Butte's radon problem.
It is believed that homes constructed over major factures or
mineralized veins are the most severely impacted. Aplite and quartz
monzonite also contribute to the problem, but to a lesser extent.
Ambient air is probably a major source of indoor radon in structures
having low concentrations.
-------
1. INTRODUCTION
Many mineral deposits contain uranium and thorium as natural
constituents. When these naturally-occurring radionuclides and their
radioactive decay products (see Figure 1-1) are underground, they
normally present no significant impact to man except for the possibility
of leaching into groundwaters. These naturally-occurring radionuclides
become a concern when there is an insufficient layer of overburden to
provide adequate gamma radiation shielding or to prevent the occurrence
of abnormal radon entry into structures built on these locations. In
some instances, the occurrence of insufficient layers of protective
overburden is a natural phenomenon. In other instances, the mining and
processing of mineral deposits removes, the protective overburden and
redistributes the radioactivity. Distribution of these natural-
ly-occurring radioactive materials can increase the public exposure to
ionizing radiation.
Studies performed by DHES have confirmed that the Butte, Montana
vicinity has high levels of gamma radiation resulting from both natural
phenomena and the redistribution of natural radioactivity from mining
and smelting operations. Also, a large number of structures in the
Butte vicinity have exhibited significantly elevated concentrations of
the radioactive gas radon-222 (radon) and its particulate decay products
(radon progeny).
An elemental phosphorus smelter is located approximately seven
miles west of Butte. In early 1977, DHES suspected that slag, which is
produced as a byproduct at this smelter, was elevated in content of
natural radioactivity. Slag samples were sent to the EPA Las Vegas
Facility for analysis. As suspected, the EPA Laboratory reports
revealed the slag to be elevated in uranium and radium-226 content.
During the period between the fall of 1977 and the spring of 1978,
DHES learned that phosphate slag had been used extensively throughout
the Butte area for construction purposes. Since the 1950's, slag had
been used for ballast in railroad beds, for road and highway
construction, for graveling roads, for building construction and for
aggregate in asphalt surfacing materials.
EPA sent a van equipped with a large collimated gamma scintillation
detector and a pressurized ion chamber to Butte in April, 1978. This
van was used to identify locations in Butte having elevated gamma
radiation levels. Data accumulated through the use of this van assisted
DHES in locating numerous homes constructed with building materials
containing phosphate slag.
It was suspected that the decaying radium present in concrete
blocks containing phosphate slag could cause elevated radon and radon
progeny concentrations in structures constructed of these materials. In
April, 1978, DHES obtained from the EPA's Las Vegas Facility several
Radon Progeny Integrating Sampling Unit (RPISU) instruments to measure
radon progeny concentrations, and soon after began monitoring homes
containing phosphate slag building materials. Numerous Butte homes were
-------
URANIUM - 238 DECAY SERIES
THORIUM - 232 DECAY SERIES
238
U
4. Si 10* y;.
a
234
Th
24 da.
234
Pa
6.76 hr.
if
/»
234
U
2.5*10' yr
4
o.Y
230
Th
a»104vr.
a.Y
226
Ra
1620 yr.
a.Y
222
Rn
3. 8 da
o.y
218
Po
3min.
a
214
Pb
27 min.
214 210
Po Po
16x10' tec 138 da
^ ,,.,.,. *
214 A a-y 21° /B «y
Bi '*•* Bi '* °-y
197mln. Sda.
* f
/B.y 210 /fi.1 206
/* P6 / Pb
19.4yr. Stable
FIGURE 1-1
NATURALLY OCCURRING RADIONUCLIDES
-------
found to have radon progeny concentrations sufficiently elevated to
constitute a potential health risk.
Following this discovery, then Governor Thomas Judge was advised of
the Butte area radiation problems and associated health risks. The
Governor responded by supporting a program to determine the magnitude of
the radiation problem, assess health risks and initiate necessary
measures to protect the health and safety of the exposed people .
Through the Governor's efforts, funds to initiate this program were made
available July 1, 1978.
Many Butte homes having elevated radon progeny concentrations were
identified by the fall of 1978, and it was determined that phosphate
slag had been used extensively in the Butte and Anaconda areas for the
paving and graveling of streets, parking lots, and playgrounds. Copper
and manganese slags in the Butte and Anaconda areas were also found to
be elevated in radioactivity, although to a lesser extent than the
phosphate slag. For these reasons, DHES requested that the 1979 State
Legislature fund a study to determine the extent of these radiation
sources and, if necessary, initiate controls concerning the use of these
materials. The legislature provided DHES with $100,000 to conduct this
study during the 1980-1981 biennium.
By early 1979, it was apparent that the source of indoor radon was
not clear-cut. Some Butte structures did not contain phosphate slag,
but were sampled to determine background levels. Of these structures, a
number were found to have higher radon progeny concentrations than
structures containing phosphate slag. It was determined that
construction-related use of phosphate slag was not a principal radon
source and that other sources would require investigation. It was
determined that the radiation hazard associated with phosphate slag was
primarily gamma radiation, and that the slag was not responsible for the
elevated radon levels in Butte. Therefore, it was necessary to alter
the direction of the study.
Numerous potential sources became suspect. There have been
extensive disturbances to the surface and subsurface geology in the
Butte area due to underground and surface mining. It was suspected that
this mining activity in conjunction with the subsidence it creates and
the presence of natural geologic fault zones could be causing a higher
radon flux than would occur in an undisturbed location.
A study that, originally appeared to be straightforward became more
complex. During the original study it was envisioned that approximately
150 homes constructed with phosphate slag building materials would have
to be investigated. The re-directed study required the investigation of
several thousand homes.
Additional staff were needed to expand the scope of the Butte
Radiation Study. In July, 1979, DHES made application to the EPA Office
of Radiation Programs for a grant to enable DHES to expand the scope of
the study during fiscal years 1980 and 1981. EPA awarded DHES a
contract for $81,804 to acquire data and information concerning the
radon and radon progeny levels in Butte. The scope of the work
-------
specified in the EPA/DHES contract consisted of two main tasks. The
principal task was to perform measurements of radon and radon progeny
inside and outside structures. The measurements were to be directed
toward identifying, to the extent possible, the source of elevated radon
concentrations inside structures and in the community. A second task
was to emplace approximately 200 alpha-track detectors in the soil on a
grid basis in the Butte area to determine radon soil-gas concentrations.
The EPA and DHES agreed to keep the plan flexible in order to provide
for additional work and re-direction as data was acquired.
-------
2. BUTTE DESCRIPTION
History
Butte originated in 1864 as a gold mining camp following a placer
strike. Later, underground silver mining led to the discovery of large
deposits of copper and other metals, giving it the title of "the richest
hill on earth." More than two hundred mines have operated in the Butte
area during the past hundred years. These mines have honeycombed the
Butte hill with shafts and tunnels and have littered the surface with
mine wastes. During Butte's early years, nine smelters and numerous
stamp mills were in operation. Subsidence resulting from underground
mining is an ongoing phenomenon as the hill area continues to settle and
shift.
The emphasis of mining operations in Butte shifted from underground
to open pit mining in 1955 when The Anaconda Company began stripping
overburden from the Berkeley Pit. In 1975 underground mining in Butte
was discontinued.
The Anaconda Company was acquired by the Atlantic Richfield Company
in the late 1970's. The Atlantic Richfield Company continued the
Berkeley Pit operations until July, 1982, when mining in the pit ended.
In early 1983, the Atlantic Richfield Company announced thart its Butte
mining operations would terminate on July 1, 1983.
Geography
Butte is a city with a population of approximately 25,000 people,
and is situated on the west side of the Continental Divide in
southwestern Montana. The city is sited on the north end of a high
mountain valley which is surrounded, except to the west, by mountains.
Butte has been called the "Mile High City" because its entire area is at
least one mile above sea level. The Butte Airport which is located in
the valley to the south of Butte has an elevation of 5540 feet.
Climate
Severe seasonal temperature extremes are encountered in the Butte
area. The annual mean temperature is 38.8°F (3.8°C) with extremes
ranging from near -40°F (-40°C) to over 90°F (32°C). There are
periods, especially during winter when the Butte area is subjected to
severe atmospheric temperature inversions. During these times
atmospheric pollutants are trapped in the valley bowl.
Geology
Butte lies within the Boulder Batholith, a mass of granitic rock
that congealed from a molten liquid mass about 70 million years ago.
The batholith is from 10-15 kilometers thick. As the liquid rock
cooled, certain chemical elements became preferentially separated and as
a result, different rock types were formed. The most prevalent type in
the area, commonly termed the "Butte granite", is technically quartz
-------
monzonite. Within the quartz monzonite are further effects of
segregation. When the quartz monzonite solidified, aplite and alaskite
dikes were still liquid or semi-liquid and were injected into cracks and
fissures. Depending on the rate at which the injections cooled, aplite
or alaskite resulted. Both rock types have approximately the same
chemical composition, but different textures—individual grains
(minerals) comprising alaskite grew to a larger size than those in
aplite bodies. Another rock type commonly found in the northwest part
of Butte is rhyolite. This rock also was molten, but was formed in a
volcanic environment, either on the surface of the earth or in the neck
of a volcano.
During the time the Boulder Batholith was created and cooled, the
earth's crust was subjected to stresses coming from outside the
immediate area. In addition, stress fields were established within the
body as a result of cooling and solidification processes. Effects of
these stresses are seen as breaks in the rocks (faults and fissures).
The faults vary in size from a fraction of an inch thick to tens of feet
thick and from simple tensional openings to much more complex structures
with hundreds of feet of both horizontal and vertical movement. Because
of their open nature, some of the faults of the Butte area provided a
plumbing system for hot fluids that gave rise to many mineral deposits.
In this case, veins formed along the faults and fissures. The more
prominent faults, veins and rock types of Butte are shown in Figure 2-1.
Although a multitude of separate veins exist at Butte, collectively they
are regarded as a single deposit. Chemical zoning along particular
veins both horizontally and vertically is duplicated in all of the veins
so that the district as a whole exhibits zoning from a copper-rich
central core to a silver-rich peripheral band.
From an areal viewpoint the most prevalent geologic unit in Butte
is the alluvium along the flood plain of Silver Bow Creek and in the
basin. This material is predominantly sand and gravel and resulted from
the erosion of the surrounding hills so that in gross composition it is
nearly the same as the quartz monzonite, rhyolite and aplite.
The Butte mineral deposit is a world class deposit. According to
Meyer and others (1968) the Butte district produced 3.3 x 10 tons of
ore from 1880 to 1964. From this ore more than 16 billion pounds of
copper have been produced, greater than 4 billion pounds of zinc, 3
billion pounds of manganese, more than 600 million ounces of silver and
in excess of two and a half million ounces of gold. Additionally, lead,
cadmium, bismuth, arsenic, selenium and tellurium have been produced.
In order to extract these metals, the area was opened by more than 40
miles of vertical shafts and literally thousands of miles of tunnels and
other underground passageways. The latest mining resulted in the
excavation of the Berkeley pit, an open pit mine within the town proper
and two smaller pits on the eastern fringe of the residential area.
8
-------
/IT. CON SHAFT
KELLEY SH
STEWARD *
FIGURE 2-1
PROMINENT FAULTS, VEINS, AND
ROCK TYPES OF BUTTE
-------
3. EVALUATION OF PHOSPHATE SLAG USE
Elevated radioactivity,-in phosphate rock was noted as early as
1908. According to Habashi uranium normally occurs in phosphate rock
in concentrations^ranging between 100 and 200 parts per million (ppm).
Andrews and Bibb report that concentrations observed in the United
States range from 8 to 399 ppm, with the highest concentrations being
found in ore from South Carolina and the lowest in Tennessee ore. The
radioactivity in phosphate rock is due almost exclusively to uranium and
its decay products (see Figure 3-1).
An elemental phosphorus smelter operated by the Stauffer Chemical
Company is sited approximately seven miles west of Butte. Phosphorus
smelting at this plant began in the early 1950's. During its first
decade of operation, the plant processed ore from an underground mine in
the Maiden Rock area, which is about 25 miles south of the smelter.
Mining at Maiden Rock was discontinued in the 1960's. The ore processed
since that time has been shipped by rail from a mine-site located near
Soda Springs, Idaho.
In early 1977, the DHES obtained samples of slag produced as a
by-product from the smelting operation. The samples were sent to the
EPA Las Vegas Facility for analyses. The results of the laboratory
analyses for the slag from Montana mined ore and Idaho ore are in Table
3-1.
Montana Slag
TABLE 3-1
RADIOACTIVITY IN PHOSPHATE SLAG PRODUCED
FROM ORE MINED IN MONTANA AND IN IDAHO
Nuclide
226Ra
238,,a
235U
234U
23°Th
1'1
Idaho Slag
226
238
235,
234
230!
232
Ra
U
U
|U
Th
Th
pCi/gm 2 sigma
28.0
21.0
1.3
20.0
20.0
0.9
4.7
4.6
4.6
0.77± 0.19
48.0 ± 1.2
41.0 ± 6.2
2.4 ± 1.6
40.0 ± 6.3
35.0 ± 7.4
0.5 ± 0.22
10
-------
ATOMIC WGT.
ELEMENT
ATOMIC NO.
HALF-LIFE
FIGURE 3-1
URANIUM-238 DECAY SERIES
11
-------
As shown in Table 3-1, the radioactivity contained in the Idaho
slag is nearly twice that of Montana slag.
Following the receipt of the EPA laboratory report, ONES initiated
an investigation to determine the off-site uses of the phosphate slag.
It was learned that slag had been used extensively throughout the Butte
area for construction purposes.
Since the 1950's phosphate slag has been used for ballast on
railroad beds, road and highway construction, graveling and for asphalt
aggregates. Also, a company produced concrete blocks and pre-stressed
concrete beams and slabs during the late 1950's, using phosphate slag
for aggregate. These concrete products were used in the construction of
homes, schools, hospitals and commercial buildings.
The EPA's Las Vegas Facility sent a van, fitted with a Pressurized
Ion Chamber (PIC) and a collimated Nal (Tl) detector coupled to a
multichannel analyzer, to Butte in April, 1978. Two EPA radiation
specialists accompanied the van. Data accumulated through use of this
van assisted in locating numerous homes containing phosphate slag
building materials.
The occupants of each home containing slag were contacted and, with
their permission, gamma radiation and radon progeny measurements were
made. Similar measurements were also made in a number of homes that did
not contain phosphate slag (non-slag homes).
Radon Progeny Integrating Sampling Units (RPISUs) loaned to DHES by
the EPA Las Vegas Facility were used to measure indoor radon progeny
concentrations. A RPISLJ was installed in a home for a period of one
week and then the detector head was removed and sent to Las Vegas for
analysis. The minimum time of data acquisition when using the RPISU
approached one month because of the time requirements for sampling,
transportation, readout and reporting.
After several months of sampling , it was apparent there was no
difference in radon progeny concentrations between slag homes and
non-slag homes.
Two Radon Gas Monitors (RGMs) were acquired in early 1979. These
instruments enabled the direct measurement of radon. Using these RGMs,
radon exhalation tests were performed on samples of phosphate ore,
phosphate slag and decomposed granite soils from the Butte area.
Radon exhalation measurements were performed by placing a sample 25
cm deep in an air-tight cylindrical container having an Inside diameter
of 28 cm and a 35 cm depth. Air from the container was drawn Into the
RGM and recirculated back to the container in a closed-loop design. The
rate of increase of the radon concentration in the air space above the
sample and in the RGM scintillation cell was measured and the radon
exhalation rate calculated. As the 25 cm sample depth does not
constitute a diffusion path length for radon in the samples tested, the
data derived are valid only for comparative purposes.
12
-------
Data from the comparative radon exhalation measurements are shown
in Table 3-2.
TABLE 3-2
COMPARATIVE RADON EXHALATION MEASUREMENTS
PERFORMED ON 25 CM DEPTHS OF PHOSPHATE ORE,
PHOSPHATE-SLAG, AND DECOMPOSED GRANITE SOILS
FROM BUTTE
Radon Exhalation Rate
Material (pCi/m /min.)
Stauffer Phosphate Ore (Idaho) 3822
Stauffer Crushed (3/4") Slag (Idaho) 18
Concrete Block (Phosphate Slag) 30
Butte Decomposed Granite Soils 100 - 1000
Monsanto Phosphate Ore (Idaho)* 3402
Monsanto Uncrushed Slag (Idaho)* 18
Monsanto Crushed (3/4") Slag (Idaho)* 30
*The Monsanto Corporation provided samples from their Pocatello,
Idaho, phosphate smelting plant to enable DHES to conduct
comparative measurements.
An evaluation of Table 3-2 shows that phosphate slag exhales less
than 1 percent of the radon that is exhaled by the phosphate ore. The
radium-226 content of the slag and the ore is essentially the same. The
smelting of the ore apparently creates a matrix that inhibits the
exhalation of radon. Table 3-2 also shows that phosphate slag exhales
less radoji than do native soils from the Butte area. In 1982, Andrews
and Bibb reported results of radon flux measurements performed on
phosphate ore, slag and soil at the Stauffer plant site. Their data
concur with the DHES findings.
Elevated gamma radiation was found in building materials containing
phosphate slag. A Pressurized Ion Chamber (PIC) was used to measure
gamma radiation levels in approximately 90 homes partially constructed
with concrete blocks containing phosphate slag and 12 homes not
containing phosphate slag. A comparison between gamma radiation levels
in slag homes and non-slag homes proved difficult. Due to the
variability of the mineralized soils in the Butte area, gamma radiation
measurements made at one meter above the ground ranged from a low of 15
jjR/hr to about 30 jjR/hr. The number and the placement of the concrete
blocks varied from structure to structure. Some homes had foundations
totally constructed of slag blocks. Other homes had only a shower stall
or one or two basement walls constructed of the blocks. No home was
identified where slag blocks were used in construction above the
basement level.
The average gamma radiation level was 19.6 jjR/hr on the main floor
of slag homes and 37.1 pR/hr in the basement. In non-slag homes gamma
radiation levels averaged 15.5 /jR/hr on the main floor and 20.7 jjR/hr in
13
-------
the basement. All measurements were made at a distance of 1 meter above
the floor.
The results indicate that use of the slag blocks for foundation
construction elevates the gamma radiation level in basements by an
average of 16 to 17^iR/hr and by about 4 to 5 /jR/hr on the main floor.
Measurements made in three schools, where additions were
constructed with phosphate slag beams in the ceilings, showed gamma
radiation levels averaging 35.7 /jR/hr in the slag additions and 15.9
/jR/hr in the older parts of the buildings where slag building materials
were not used . In these structures, the presence of phosphate slag
appeared to increase the gamma radiation level by approximately 20
/jR/hr. The presence of phosphate slag thus increases the gamma
radiation dose to a school child exposed 6 hours per day, 180 days per
year, by about 21 milliroentgens per year.
The determination of ambient gamma radiation attributable to use of
phosphate slag for paving and other surfacing in Butte is difficult
because of the many variables involved. Natural radiation levels vary
by as much as 15/jR/hr. Most of the phosphate slag used for surfacing
came from smelted Montana ore. Recently, slag produced by smelting
Idaho ore has been used. Also, the depth of slag used in streets and
for surfacing differs from project to project.
Street measurements of gamma radiation levels were made in Butte,
Anaconda and Helena to determine background radiation levels.
Measurements in Anaconda average 15juR/hr; Helena, 13juR/hr; and Butte,
19juR/hr in areas where no phosphate slag was present.
Radiation levels at one meter above Butte streets paved with
Montana slag average 28 juR/hr; whereas, the radiation levels above
streets paved with Idaho slag averaged approximately 45 jjR/hr. Some
measurements as high as 50 juR/hr were recorded on streets paved with
Idaho slag. Numerous streets which were originally paved using Montana
slag have been repaved using Idaho slag. Radiation measurements on
these streets generally range between 30 and 40juR/hr.
Most streets, alleys, parking lots and some school grounds are
paved or graveled with phosphate slag. It is estimated that
approximately one-fourth to one-third of the populated area of Butte is
covered with phosphate slag or phosphate slag bearing materials.
Because of the variability in natural background radiation levels,
and in radiation levels measured in areas covered with phosphate slag,
it was not possible to measure the overall radiation exposure
attributable to the phosphate slag used in Butte. However, it has been
estimated that the use of phosphate slag in Butte may have elevated the
average radiation exposure rate within the city by as much as 10/iR/hr.
The use of phosphate slag for graveling creates another potential
health risk. Phosphate slag is rapidly pulverized by traffic. During
dry periods, roads graveled with phosphate slag become extremely dusty.
Individuals driving on, or living near, these roads are exposed to high
14
-------
concentrations of slag dust. Because of the elevated content of natural
radioactivity contained in the phosphate slag (see Table 3-1), and
particularly because of the radium-226 and thorium-230 content,
phosphate slag should not be used for road gravel. When inhaled or
ingested, if soluble, radium and thorium metabolize to the bone and
increase the risk of bone tumors and leukemia.
The potential for contaminating ground and surface water by
radioactivity leached from phosphate slag was investigated. Samples of
phosphate slag were crushed into powder and placed in beakers containing
water having pH values ran'ging between 5 and 9. Each sample was
periodically agitated, then filtered after a period of 24 hours. One
hundred ml of filtrate from each sample was dried in a planchette and
counted for gross alpha and gross beta activity. Nothing above normal
background levels was detected in any of the samples, indicating that
phosphate slag was insoluble in water under most environmental
conditions. As this was a short-term test, the potential for long-term
chemical and solubility changes was not determined.
From the evaluation of data concerning use of phosphate slag for
building and construction purposes, it is concluded that:
1. Phosphate slag should not be used as an ingredient when
building structures for human occupancy. Such use elevates
gamma radiation exposure rates and results in unnecessary
radiation exposure to occupants.
2. Phosphate slag should not be used for road or area graveling.
The slag is readily pulverized and produces dust elevated in
radium-226, thorium-230 and other nuc-lides in the uranium-238
decay series. This potential hazard should be further studied.
3. Phosphate slag can be used for some purposes without
significant risk to the public health. However, any use of
phosphate slag should be strictly controlled. Some uses which
may be acceptable on a case-by-case basis are construction of
highways, airport runways, bridges, culverts and other
underground pipe and for railroad ballast.
The use of phosphate slag should be limited to projects where
no significant human exposure to increased gamma radiation
levels will occur. Control measures should be implemented to
prevent the use of slag for unacceptable purposes.
4. Human exposure to radon and radon progeny is not a health risk
that is associated with use of phosphate slag for building and
construction purposes since radon exhalation from phosphate
slag is relatively insignificant. Radon exhalation rates from
the slag are lower than those normally expected from native
soils in the Butte area.
15
-------
4. RADON/RADON PROGENY MEASUREMENTS
Selection of Homes for Measurement
Initially, homes containing phosphate slag building materials were
the subject of investigation. Radon progeny measurements were made in
these homes and other, non-slag homes using RPISUs. Equipment for
making short-term "grab" sample (less than 10 minute) measurements was
also acquired. Soon after this equipment was obtained, it was learned
that the most severely impacted area of Butte was the northwest section.
The first indication of elevated radon concentrations in northwest Butte
occurred when a home on Waukesha Street, which contained phosphate
building blocks, was found to have radon progeny concentrations in
excess of 0.25 Working Levels (WL). Comparing measurements from other
homes containing phosphate slag building materials, it was apparent that
the phosphate slag was not responsible for this high radon progeny
concentration.
Following the discovery of the elevated levels of radon progeny in
the Waukesha Street home, measurement activities were intensified to
determine the boundaries of the impacted area. Occupants were contacted
on a house-to-house basis and were asked for permission to measure radon
progeny concentrations. The people were generally cooperative, with
only about a ten percent rejection rate.
The radiation study received considerable publicity from the news
media. Consequently, many local homeowners became aware of the
potential health risks and requested that radon progeny concentrations
be measured in their homes. DHES performed measurements in each home
where the measurement was requested.
In 1979, the U. S. Department of Housing and Urban Development
(HUD) initiated a requirement that all HUD-subsidized housing be
measured to determine radon progeny concentrations. At the same time,
HUD's Federal Housing Administration (FHA) instituted a requirement that
radon progeny concentrations had to be determined for all FHA-insured
home loans. Following the initiation of HUD's measurement requirements,
DHES entered into a contract with HUD to perform these measurements in
HUD-subsidized housing.
After DHES acquired grab sampling equipment, all homes studied were
initially measured using the grab sample method. Radon and radon
progeny concentrations in structures are subject to significant
variability. Because of this, RPISUs were installed in homes measuring
0.03 WL or higher to obtain long-term integrated measurements.
Long-term measurements were also performed in numerous homes where the
measurement was requested by the occupants.
In summary, structures chosen for grab sample measurement of radon
progeny were selected because:
1. The homes contained phosphate slag building materials.
16
-------
2. The homes were located in areas known to be elevated in indoor
radon concentrations.
3. Individuals requested sampling of their homes because of health
concerns.
4. The sampling was required by HUD or FHA.
Structures selected for long-term integrated measurement were, for
the most part, homes in which grab samples showed elevated radon progeny
concentrations.
Because of the selection criteria, structures chosen for both
short-term and long-term measurements constitute a biased sample. Data
obtained from these measurements should not be extrapolated for a
city-wide average.
Indoor Measurement of Radon and Radon Progeny
Radon and radon progeny concentrations were determined by using both
short-term and long-term sampling techniques. There are inherent
advantages and disadvantages to each technique. Because of this, the
purpose of measurement and data needs were carefully evaluated prior to
beginning each phase of the study and determining which measurement
technique would be used.
Measurement of Indoor Radon Progeny
Short-term sampling
The grab sample method for measuring radon progeny concentrations
was used to obtain rapid measurements in many homes. This technique
enabled the screening of large numbers of homes and apartments to
determine which areas of the city were most severely affected.
Most screening by grab sampling was done during cold weather when
it could be assured that doors and windows were closed. When homes were
measured during warm periods, occupants were contacted in advance and
asked to close all doors and windows for a period of at least eight
hours prior to sampling. For HUD and FHA sampling, the occupant was
requested to sign a statement that the house had not been ventilated for
a period of at least three hours prior to measurement. No actual
ventilation rate measurements were made.
Grab sampling provides a reasonably accurate measurement of the
radon progeny concentration present at the time of sampling; however,
extrapolation of short-term data to estimate long-term averages is
subject to considerable error because of the daily and seasonal
fluctuations in radon and radon progeny concentrations.
Long-term sampling
Long-term measurement of indoor radon progeny was used to estimate
average concentrations for a period of one year. Throughout the study
17
-------
RPISUs, loaned by the EPA Las Vegas Facility, were used to obtain
integrated measurements of radon progeny concentrations.
In most homes, the RPISUs were used for a period of one week every
three-months for a year. This sampling schedule was established to
enable the collection of one week's data during each season of the year.
The four week's data were equally weighted and averaged to estimate the
"Annual Average Concentration."
Measurement of Indoor Radon
Short-term sampling
Short-term measurements of indoor radon concentrations were made
using Eberline 500-ml scintillation cells . This measurement device
provides an accurate assessment of the indoor radon concentration at the
specific time of sample collection. Most radon grab samples were
collected simultaneously with radon progeny grab samples. This enabled
the calculation of the percentage equilibrium of the radon progeny with
the parent radon-222.
Long-term sampling
Few long-term measurements of indoor radon concentrations were done
during the study. DHES acquired two Eberline Radon Gas Monitors (Model
RGM-1) in early 1980. These were the only integrating radon monitors
available during most of the study, and were mainly used for ambient
monitoring, radon exhalation and radon flux measurements.
Factors Affecting Radon and Radon Progeny Concentrations in Structures
Concentrations of indoor radon and its progeny are subject to
variation. Factors that affect structure ventilation rates and those
that affect radon soil gas concentrations in soils adjacent to
structures are probably responsible for most of the fluctuations.
It is believed that radon soil gas concentrations near a structure
can be elevated by the installation of adjacent concrete or asphalt
slabs, driveways or sidewalks. These appurtenances create a capping
effect that inhibits the exhalation of radon from the soil. This
capping increases radon soil gas concentrations and can elevate the
radon concentration within the structure itself.
Naturally-occurring phenomena that affect radon exhalation from the
soil adjacent to structures can also change concentrations of Indoor
radon. Some examples of these phenomena are changes in soil moisture
and the ground frost during winter.
Factors affecting structure air change rates are open doors and
windows, wind speed and traffic in and out of the building. In
structures that have combustion-type heating systems, the combustion air
demands of the heating system can significantly affect the air exchange
rate.
18
-------
Radon progeny concentrations are also affected by ventilation
changes and by conditions that alter the plateout of the progeny. The
plate-out of radon progeny is affected by airborne nuclei
concentrations, humidity, air motion, home furnishing types, the number
of occupants and even the living habits of the occupants themselves.
Use of Indoor Measurements to Identify Geographical Areas Impacted by
Elevated Indoor Radon Concentrations'
During the period between early 1979 and mid-1981, emphasis was
placed on research to determine the geographical areas of Butte most
severely affected by elevated indoor radon concentrations. Initial
screening of neighborhoods was conducted by the grab sample method.
Homes were sampled only when the occupants provided assurance that the
house had not been ventilated for at least three hours. Through
September, 1981, 2884 grab samples had been collected in homes to
determine radon progeny concentrations. Through December, 1982, the
total increased to 3099 grab samples. These measurements were
distributed in housing units as shown in Table 4-1. Many homes showing
elevated radon progeny concentrations were sampled more than once to
substantiate the measurements.
TABLE 4-1
INDOOR RADON PROGENY GRAB SAMPLE MEASUREMENTS
IN BUTTE (1979 - 1982)
Working Level
Less than 0.010
0.010 - 0.019
0.020 - 0.049
0.050 - 0.100
Greater than 0.100
Total Samples
Total Housing Units*
1102
426
187
43
13
1771
*A single family house or living unit in a multifamily
structure is defined as a "housing unit".
Integrated radon progeny measurements were completed in 254 housing
units with the use of RPISUs. The average annual concentrations in
homes measured with RPISUs are shown in Table 4-2.
19
-------
TABLE 4-2
v
AVERAGE ANNUAL CONCENTRATIONS OR RADON PROGENY IN HOUSING UNITS
MEASURED WITH RADON PROGENY INTEGRATING SAMPLING UNITS
Main Floor Basement
Working Level Measurements Measurements
Less than 0.010 58 9
0.010 - 0.019 39 12
0.020 - 0.050 76 16
Greater than 0.050 37 7
Total Housing Units Measured 210 44
20
-------
5. RADON SOURCE ASSESSMENT
Summary
The objective of this study was to identify, to the extent
possible, the source or sources of the elevated radon in structures in
Butte and the Butte vicinity.
Tasks performed in the radon source assessment were:
1. the measurement of radon and radon progeny in ambient air;
2. analysis of soil for radioactivity content;
3. measurement of radon/radon progeny concentrations
in structures;
4. measurement of radon soil gas concentrations;
5. investigation of possible interrelationships between
radon concentrations in structures, radon soil-
gas concentrations and the surface geology;
6. measurement of dissolved radon concentrations in
water supplies, and
7. evaluation of miscellaneous other potential sources
of radon in structures.
Through an agreement with the U. S. Bureau of Mines (BOM), Spokane
Research Center, acquired data were digitized and programmed into the
BOM computer along with the coordinates of a Butte city map and
available geological information. The BOM computer enabled the
graphical display and evaluation of data. Numerous figures in this
section were produced by the BOM computer system.
Figure 5-1 shows a city map of Butte with reference streets
emphasized. The reference streets are identified by name in Figure 5-2.
Reference streets shown in Figures 5-1 and 5-2 are used in most figures
in this section to orient measurement sites. The grid markings shown in
Figures 5-1 and 5-2 were established by the Anaconda Company for land
survey purposes. The Anaconda grid was used by DHES and BOM to plot
measurement sites and data points.
Ambient Measurements
In August, 1980, an ambient radon monitoring station was
established at Hebgen Park (see Figure 5-2, location A). Hebgen Park is
situated two blocks east of Arizona Street and one block north of Front
Street. An Eberli'ne Radon Gas Monitor, Model RGM-1, with an air intake
located approximately 6 feet above ground level, was used to measure the
ambient radon concentrations and was programmed to provide an hourly
21
-------
_ 138800
_ 132500
_ 128500
SCflLE 1"
BOUNDflRY
ERST - 145000.00 o
WEST - 119000.00 L
136500 _
132SDO _
128900 _
12CDO _
120600 _
4000. '
BOUNDflRY
4DCO NORTH - 139500.00
SOUTH = 112500.00
FEET
FIGURE 5-1
CITY MAP OF BUTTE SHOWING
LOCATIONS OF REFERENCE STREETS
22
-------
-133900
-138500
_ 13«00
-130500
-118500
120600 -
laeoo _
Elizabeth WaJ2i
130600 _
,116800 _
SCRLE 1" - 4000. '
BOUNDRRY BOUNDRRY
ERST - 145000.00 o «BO NORTH - 139500.00
WEST - 119000.00 I I SOUTH - 112500.00
FEET
FIGURE 5-2
REFERENCE STREETS
AND OUTSIDE AIR MONITORING STATION LOCATIONS
23
-------
printout of measurement data. Ambient radon measurements were collected
almost continuously at the Hebgen Park Station between August, 1980, and
August, 1981, with the exception of October, 1980. In October, the
radon gas monitor was removed for maintenance and quality assurance
tests.
The Butte area is subject to severe atmospheric thermal inversions
that often trap atmospheric pollutants, including radon, in the Butte
Basin during certain periods of the day. The inversion periods follow a
diurnal pattern with the highest concentrations of radon occurring at
approximately 6:00 a.m. and the lowest concentrations at about 6:00 p.m.
The pattern of diurnal thermal inversions occurs throughout the year,
but is frequently interrupted by winds and storms. The radon
concentrations shown in Figures 5-3 through 5-6 are seasonally selected
examples based on three-hour averages to show the effect of the diurnal
thermal inversions on the ambient radon concentrations at the Hebgen
Park monitoring station.
Figure 5-7 shows ambient radon concentrations averaged weekly and
Figure 5-8 shows average monthly ambient radon concentrations at the
Hebgen Park Monitoring Station for the period August, 1980 through
August, 1981. It is interesting to note that average ambient radon
concentrations ranged from a high of about 3 pCi/1 to a low of less than
0.25 pCi/1. The highest concentrations were observed between August and
November. Concentrations diminished through the winter months and
reached a low in May and June.
Measurements of soil moisture were not made, but it is believed
that the soil moisture content is probably responsible for the differing
ambient radon concentations seen in Figures 5-7 and 5-8. In the winter
months, the soil in the Butte area freezes to a depth of several feet.
DHES believes that the frozen soil produces a capping effect that
inhibits radon exhalation. Radon soil gas measurements made in the
alluvium at a depth of 30 inches showed a radon soil gas concentration
in winter months 69 percent higher than in summer months.
The spring of 1981 was unusually wet in western Montana.
Precipitation in Butte during the months of April, May and June totaled
7.62 inches. The ambient radon concentrations for May and June, when
the soil was heavy with water, were the lowest of the year. These
measurements also indicate that an inverse relationship most likely
exists between soil moisture content and the soil radon flux.
In February, 1982, an outside radon and radon progeny monitoring
station was established at 933 Hornet Street (see Figure 5-2, location
B). This station is situated in the first block west of Excelsior
Street, one block north of Empire Street. The Hornet Street monitoring
site is in the area of the city exhibiting the highest radon soil gas
concentrations and the highest density of homes affected by elevated
radon concentrations.
Unlike the Hebgen Park station, the air intake for the Radon Gas
Monitor at the Hornet Street station was located about one foot above
the ground and between two houses that are spaced by only six feet. The
24
-------
0)
s.
0)
0»
•r^
3
0
o
!» £
O1 Q.
as
94
24
IS
12 1B 24 § T2 1*8 2*4 6 12 18 24 6 T2 T8 24 6 12 1*8 24 6 12 1B 24 § 12 1B 24
8-28-80 8-29 8-30 9-1 9-2 9-3 9-4
FIGURE 5-3
AMBIENT RADON CONCENTRATIONS
HEBGEN PARK MONITORING STATION, AUGUST 8 - SEPTEMBER 4, 1980
-------
JL5
o
U
ro
0.6
0.0
24 6 12 18 24 6 12 18 24 6 12 18 24 6,12 18 24 6,12 18 24 6,12 18 24 6 , 12 18 24
1-21-81 1-22 1-23 1-24 1~25 1-26 1-27
FIGURE 5-4
AMBIENT RADON CONCENTRATIONS
HEBGEN PARK MONITORING STATION, JANUARY 21 - JANUARY 27, 1981
-------
-------
0)
•p
0£
0)
•I—
3
O
8
00
0,3
o.o
24 6 12 18 24 6 12 18 24 6 12 18 24 6 12 18 24 6 12 18 24 6 12 18 24 6 12 18 24
7-9-81 710 7-11 7-12 7-13 7-14 7-15
FIGURE 5-6
AMBIENT RADON CONCENTRATIONS
HEB6EN PARK MONITORING STATION, JULY 9 - JULY 15, 1981
-------
25.
-------
0)
o.
CO
OJ
•r-
3
U
O
U
FIGURE 5-8
AVERAGE MONTHLY AMBIENT RADON CONCENTRATIONS
HEBGEN PARK MONITORING STATION, AUGUST, 1980 - AUGUST, 1981
-------
location of the air intake probably accounts, at least partially, for
the high outside radon measurements at the Hornet Street station.
Outside radon concentrations measured at the Hornet Street station
averaged 3.25 pCi/1 for the period February, 1982, through January,
1983. This average was substantially higher than the Hebgen Park
station average of 0.98 pCi/1 for the period August, 1980, through July,
1981.
The weekly average outside radon concentrations measured at the
Hornet Street Station are shown in Figure 5-9. The average monthly
measurements are presented in Figure 5-10. As seen in Figure 5-10, the
monthly average outside radon concentrations at the Hornet Street
Station ranged from a low of 1.47 pCi/1 in February, 1982, to a high of
5.86 pCi/1 in August, 1982.
The outside radon concentrations measured at the Hornet Street
Station are higher than normally expected. Worldwide, ambient ragon
measurements normally vary from less than 0.1 pCi/1 to about 1 pCi/1 .
A RPISU was used at the Hornet Street station to monitor outside
radon progeny concentrations. The average outside radon progeny
concentration for the period February, 1982, through January, T983, was
0.0031 WL. The outside radon progeny/radon equilibrium averaged about
10 percent for the period. The equilibrium from November through
February averaged 17.5 percent. The equilibrium during the remaining
months averaged 7 percent.
Soil Sampling and Analysis
Twenty-six soil samples were collected at selected sites ranging
from Walkerville on the north to the airport on the south. These
sampling site locations are shown in Figure 5-11. With the exception of
Sample No. 7 which was collected at a soil depth of 10-15 cm, all soil
samples were collected from the top 5 cm of soil. The soil samples were
analyzed at the EPA's Las Vegas Facility for U-234, U-235, U-238,
Th-230, Th-232, and Ra-226 content. The data for these 26 soil samples
are shown in Table 5-1.
The normal Radium-226 qontent of soils ranges from about 0.4 to 1.3
picocuries per gram of soil . The Ra-226 content in the samples shown
in Table 5-1 averages 1.58 ± 0.59 picocuries per gram of soil with a
range of 0.7 to 3.2 picocuries per gram. The Ra-226 content of soil in
sections of the city experiencing elevated indoor radon concentrations
does not differ substantially from concentrations in areas experiencing
little or no problem.
Measurement of Radon Progeny Concentrations (WL) in Structures
Radon progeny concentrations measuring 0.02 WL or greater are found
in structures scattered throughout the Butte area. The majority of the
severely affected structures are in the northwest section of the city
roughly bounded by Excelsior Street on the east and Park Street on the
south.
31
-------
co 3
ro o
o
u
1SL
O.O
iFeblMar I Apr JMay I Jun[ Jul | Aug[Sept[ Oct (Nov | Dec [ Jan|
FIGURE 5-9
AVERAGE WEEKLY OUTSIDE RADON CONCENTRATIONS
HORNET STREET MONITORING STATION, FEBRUARY, 1982 - JANUARY, 1983
-------
-------
_ 132900
_ 12BSDD
_12€DD
_ 120SOD
_1183DD
Elizabeth! Warren
<8i'
BOUNDRRY
EflST - 145000.00 o
SCnLE 1" - 4000. '
BOUNDflRY
coo NORTH - 139500.00
WEST - 119000.00 L
FEET
FIGURE 5-11
SOIL SAMPLING SITE LOCATIONS
SOUTH - 112500.00
34
-------
TABLE 5-1
RADIOACTIVITY IN SOIL SAMPLES FROM BUTTE
Sample No.
1 Walkerville-Sunview Terrace
2 Walkerville-Missoula Gulch
3 Western at Waukesha
4 Amherst at Sheridan
5 Keokuk at Continental
6 Foothills East Ridge
Analysis
234U
235U
238U
232TH
230TH
226RA
234U
238U
235U
232TH
230TH
226RA
235U
234U
238U
232TH
230TH
226RA
238U
234U
235U
232TH
230TH
226RA
234U
238U
235U
232TH
230TH
226RA
235U
234U
238U
232TH
230TH
226RA
Result
1.3EOO
3.4E-02
1.4EOO
2.1EOO
1.3EOO
1.7EOO
1.4EOO
1.3EOO
4.4E-02
1.8EOO
1.5EOO
2.2EOO
4.1E-02
7.5E-01
7.7E-01
6.4E-01
7.7E-01
l.OEOO
2.0EOO
1.9EOO
5.9E-02
2.9EOO
1.8EOO
1.4EOO
2.5EOO
2.6EOO
l.OE-01
8.2EOO
3.2EOO
3.0EOO
<2.7E-02
l.OEOO
l.OEOO
1.9EOO
1.1EOO
1.3EOO
2 Siqma*
1.2E-01
1.9E-02
1.3E-01
2.9E-01
2.0E-01
2.3E-01
1.3E-01
1.2E-01
2.1E-02
2.5E-01
2.1E-01
2.6E-01
2.1E-02
9.0E-02
9.2E-02
2.3E-01
2.7E-01
1.8E-01
1.6E-01
1.6E-01
2.4E-02
4.6E-01
3.0E-01
2.1E-01
1.9E-01
1.9E-01
3.2E-02
1.2EOO
5.1E-01
3.0E-01
1.1E-01
1.1E-01
2.7E-01
1.7E-01
2.0E-01
Units
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
35
-------
Sample No.
7 Foothills East Ridge
8 Quincy at Banks
9 Greenl ane
10 Lowell at Warren
11 Wynne at Garfield
12 Butte Ranger Station
13 Shelly at Hill
Analysis
234U
238U
235U
232TH
230TH
226RA
235U
234U
238U
232TH
230TH
226RA
238U
234U
235U
232TH
230TH
226RA
235U
234U
238U
230TH
232TH
226RA
234U
238U
235U
230TH
232TH
226RA
235U
234U
238U
230TH
232TH
226RA
238U
234U
235U
230TH
232TH
226RA
Result
1.2EOO
1.3EOO
4.9E-02
2.4EOO
1.4EOO
1.4EOO
<3.6E-02
1.6EOO
1.4EOO
3.0EOO
1.6EOO
3.2EOO
7.0E-01
7.5E-01
<2.9E-02
1.5EOO
7.0E-01
9.6E-01
4.3E-02
1.4EQO
1.3EOO
1.5EOO
2.3EOO
1.8EOO
l.OEOO
l.OEOO
3.5E-02
1.1EOO
1.9EOO
1.3EOO
4.0E-02
1.1EOO
1.1EOO
1.4EOO
2.1EOO
1.6EOO
1.5EOO
1.5EOO
5.2E-02
1.3EOO
1.7EOO
2.0EOO
2 Siqma*
1.1E-01
1.2E-01
2.2E-02
3.8E-01
2.5E-01
2.1E-01
1.6E-01
1.5E-01
3.8E-01
2.2E-01
3.1E-01
8.9E-02
9.2E-02
2.1E-01
1.4E-01
1.8E-01
2.1E-02
1.3E-01
1.3E-01
2.3E-01
3.3E-01
2.4E-01
1.1E-01
1.1E-01
1.9E-02
1.9E-01
2.9E-01
2.1E-01
2.2E-02
1.2E-01
1.2E-01
2.1E-01
3.1E-01
2.3E-01
1.3E-01
1.3E-01
2.2E-02
4.6E-01
4.7E-01
2.5E-01
Units
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
36
-------
Sample No.
Analysis
Result
2 Sigma* Units
14 Colusa at Hobson
15 Cobban at Lexington
16 Warren at A Street
17 Mass at Majors
18 Cobban at Porter
19 Lafayette at Grand
20 Silverbow at Carolina
235U
234U
238U
230TH
232TH
226RA
234U
238U
235U
230TH
232TH
226RA
235U
234U
238U
230TH
232TH
226RA
234U
238U
235U
230TH
232TH
226RA
235U
234U
238U
230TH
232TH
226 RA
234U
238U
235U
230TH
232TH
226RA
235U
234U
238U
230TH
232TH
226RA
4.8E-02
1.3EOO
1.4EOO
1.2EOO
2.7EOO
1.7EOO
1.7EOO
1.7EOO
6.2E-02
1.5EOO
3.8EOO
1.4EOO.
5.6E-02
1.3EOO
1.3EOO
1.4EOO
1.9EOO
1.8EOO
1.4EOO
1.3EOO
5.1E-02
1.5EOO
1.9EOO
2.0EOO
5.5E-02
1.5EOO
1.5EOO
1.6EOO
2.5EOO
2.2EOO
2.0EOO
1.9EOO
5.9E-02
1.9EOO
2.0EOO
2.6EOO
8.7E-02
2.4EOO
2.3EOO
2.1EOO
2.3EOO
2.0EOO
2.3E-02
1.3E-01
1.3E-01
2.6E-01
4.0E-01
2.3E-01
1.5E-01
1.5E-01
2.5E-02
1.9E-01
3.4E-01
2.1E-01
2.4E-02
1.3E-01
1.2E-01
1.3E-01
1.5E-01
2.4E-01
1.3E-01
1.2E-01
2.3E-02
1.7E-01
1.9E-01
2.5E-01
2.5E-02
1.4E-01
1.4E-01
2.1E-01
2.7E-01
2.6E-01
1.7E-01
1.6E-01
2.5E-02
1.4E-01
1.4E-01
2.8E-01
2.9E-02
1.8E-01
1.7E-01
1.5E-01
1.6E-01
2.5E-01
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
37
-------
Sample No.
Analysis
Result
2 Sigma* Units
21 Ohio at Davidson
22 1st at California
23 Zinc Street
24 Jackson at Gold
25 Diamond at Girard
26 Sutter Street
238U
234U
235U
230TH
232TH
226RA
235U
234U
238U
230TH
232TH
226RA
238U
234U
232TH
235U
230TH
226RA
232TH
235U
230TH
234U
238U
226RA
232TH
234U
230TH
238U
235U
226RA
232TH
235U
230TH
234U
238U
226 RA
1.2EOO
l.OEOO
<3.1E-02
9.8E-01
1.8EOO
1.8EOO
7.7E-02
2.2EOO
2.1EOO
1.9EOO
l.OEOO
2.2EOO
l.OEOO
l.OEOO
1.5EOO
4.2E-02
1.2EOO
7.0E-01
3.1EOO
5.5E-02
2.0EOO
1.6EOO
1.6EOO
2.3EOO
3.5EOO
1.2EOO
2.0EOO
1.4EOO
4.1E-02
2.3EOO
2.5EOO
4.4E-02
2.1EOO
1.6EOO
1.5EOO
2.0EOO
1.2E-01
1.1E-01
2.9E-01
3.9E-01
2.4E-01
2.9E-02
1.8E-01
1.7E-01
4.6E-01
3.4E-01
2.6E-01
1.1E-01
1.1E-01
1.2E-01
2.1E-02
1.1E-01
1.5E-01
3.6E-01
2.2E-02
2.8E-01
1.3E-01
1.3E-01
2.6E-01
2.3E-01
1.2E-01
1.6E-01
1.3E-01
2.2E-02
2.6E-01
1.8E-01
2.0E-02
1.6E-01
1.3E-01
1.3E-01
2.4E-01
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
PCI/GM
*The number following the "E" is the exponent of ten by which the preceding
number should be multiplied. There is a 95 percent assurance that the true
value lies between the reported value +_ 2 sigma.
38
-------
An intrusive rhyolite plug known as "Big Butte" adjoins the
northwest side of this area. The remainder of the Butte surface geology
consists primarily of quartz monzonite interspersed with aplite dikes
and areas of alluvium. The Butte hill is interspersed with mineralized
veins which have been actively mined for the last hundred years. The
surface geology is highly fractured. The fracturing becomes extreme at
the periphery of Big Butte, and underlies the area of the city most
seriously affected by high indoor radon concentrations.
The surface geology of the Butte hill is shown in Figure 5-12.
Veins and fractures are shown in Figure 5-13. Veins are shown as solid
lines and fractures by dashed lines.
Efforts to correlate specific geologic types with indoor radon
measurements and with radon soil gas concentrations were only partly
successful. No home investigated that was built over rhyolite had
indoor radon progeny concentrations exceeding 0.02 WL. Radon soil gas
measurements in rhyolite were low. Six radon soil gas measurements (see
Figure 5-21, sampling sites numbers 54, 55, 92, 108, 116 and 117) in
rhyolite averaged 80 pCi/1 during summer months as compared to an
average of 1082 pCi/1 for the Butte area as a whole.
In an area west of Excelsior Street and particularly between
Lewisohn Street on the south and Zarelda Street on the north, dramatic
changes were noted in indoor radon progeny concentrations as
measurements progressed from structures built over rhyolite to
structures built over aplite and quartz monzonite. In some instances
measurements changed from- less than 0.02 WL to over 0.1 WL in less than
one city block.
Most of the homes that measured in excess of 0.10 working levels
were in the northern section of the city west of Excelsior Street (see
Figure 5-14). The surface geology in this area is primarily quartz
monzonite with some outcroppings of aplite,,is severely fractured and
interlaced with mineralized veins. McClernan believes that the severe
fracturing in this area resulted when the rhyolite plug forming Big
Butte was thrust upward through the underlying quartz monzonite basement
rock.
Radon soil gas measurements in this area are high and fluctuate
erratically with location as do indoor measurements of radon and radon
progeny. The rock type upon which structures are built is not totally
responsible for the elevated indoor radon concentrations. Measurements
of radon soil gas concentrations over mineralized veins and over major
fractures show radon levels considerably higher than those measured in
the surrounding rock.
The elevated radioactivity content of mineralized veins is easily
demonstrated by a portable gamma scintillometer. The gamma radiation,
levels of some veins- are an order of magnitude higher than the gamma
measurements of surrounding rocks.
It is believed that many structures having high concentrations of
indoor radon are built over mineralized veins or over fractures which
39
-------
.'••.•.•'.I ALLUVIUM
APLITE
I I QUARTZ MONZONITE
RHYOLITE
BOUNDRRY
ERST - 131625.00
WEST - 121900.00
SCRLE 1"
I
FEET
FIGURE 5-12
NORTHWEST BUTTE SURFACE GEOLOGY
1500. '
BOUNDRRY
ism NORTH - 139700.00
SOUTH - 129400.00
40
-------
SCRLE 1" - 1500. '
BOUNDRRY BOUNDRRY
ERST - 131625.00 o isoo NORTH - 139700.00
WEST - 121900.00 I I SOUTH - 129400.00
FEET
FIGURE 5-13
VEINS AND FRACTURES IN
NORTHWEST BUTTE GEOLOGY
41
-------
X-'.-'.l ALLUVIUM
APLITE
I I QUARTZ MONZONITE
RHYOLITE
scflLE i
BOUNDflRY
ERST - 127450.00 o
WEST - 122400.00
NORTH - 137200.00
SOUTH - 131750.00
FEET
FIGURE 5-14
8/8/79-1/31/83
800. '
+ BELOW .01
aoo A .01 TO .01999
| O.02 TO .04999
X .05 TO .09999
• .10 (OR RBOVE)
BUTTE GEOLOGY/INDOOR RADON PROGENY CONCENTRATIONS
IN INDIVIDUAL STRUCTURES
42
-------
act as conduits for transporting radon to the structure. This theory
would also account for the erratic soil gas measurements in fractured
areas and areas interlaced by veins.
Structures having radon progeny concentrations exceeding 0.02 WL
are distributed throughout the city. Figures 5-15 and 5-16 show the
aggregate average of all indoor radon progeny measurements based upon a
300 foot grid.
Besides the northwest section of the city, two other areas have a
relatively high density of structures with indoor radon progeny
concentrations that exceed 0.02 WL. A community housing project known
as Silver Bow Homes is in one of these areas. Silver Bow Homes consists
of 19 two-story apartment buildings, and is on the east side of Arizona
Street between Park and Front Streets. Skyway Park is in the second
area. Skyway Park is located on the south side of the city just north
of the airport, between Harrison Avenue and Continental Drive. Except
for a multi-family housing project known as Town and Country Apartments,
the Skyway Park addition consists primarily of single-family housing.
Silver Bow Homes
In September, 1979, HUD initiated a requirement that all subsidized
housing units in Butte must have radon progeny concentrations of 0.02 WL
or less. Under contract with HUD, DHES measured each apartment in the
Silver Bow Homes complex, with results as shown in Figure 5-17.
Fifty-seven of the 225 apartments in the Silver Bow Homes complex
exceeded the 0.02 WL criteria established by HUD. In 1980, HUD provided
funds to Silver Bow Homes to remediate the radon problem.
In 1982, the remediation of Silver Bow Homes was accomplished by
sealing penetrations between the crawl spaces and the apartments. The
undersides of the floors were sprayed with one and one-half inches of
closed-cell polyurethane foam and passive ventilation stacks were
installed from the crawl space through the roof of each structure.
After remediation, each apartment which originally measured in
excess of 0.02 WL was remeasured. All apartments were found to meet the
HUD criterion.
Skyway Park
The surface geology in Skyway Park is alluvium estimated to be
approximately one hundred feet deep. Because of the deep alluvium, it
was not anticipated that structures in this area would be troubled by
indoor radon; however, measurements of radon progeny concentrations in
some Skyway Park structures were surprisingly high. These measurements
are shown in Figure 5-18.
Radon Soil Gas Measurements
Soil gas measurement sites were located throughout the Butte area
on a one-half mile grid. In northwest Butte additional sampling sites
were established on a sub-grid of one city block.
43
-------
1358DO _
131500 _
127900 _.
1239DD _
119900 _
SCflLE 1"
BOUNDnRY
EflST - 149000.00
WEST - 119000.00
NORTH - 139500.00
SOUTH - 111500.00
FEET
FIGURE 5-15
8/8/79-1/1/85
4000 '
+ BELOW .01
4000 A .01 TO .01999
J O .02 TO .04999
X.05 TO .09999
.10 (OR flBOVE)
THREE HUNDRED FOOT AGGREGATE AVERAGE OF INDOOR RADON PROGENY
CONCENTRATIONS (WL) IN BUTTE
44
-------
_ 139*0
_ 138800
-135400
-133800
138*30 _
136800 _
135CO _
0
A O •
A A + A O
A A + + +
A O A A Park
O +
+ A A A A A
+ A A +
BOUNDflRY
ERST
NEST
NORTH
SOUTH
131390.00
121900.00
139700-00
129400.00
8/8/79-1/1/83
SCflLE 1" - 1500. '
+ BELOW .01
o isoo A .01 TO .01999
| J O.02 TO .04999
X .05 TO .09999
• .10 (OR flBOVE)
FEET
FIGURE 5-16
THREE HUNDRED FOOT AGGREGATE AVERAGE
_ CONCENTRATIONS (HI) IN
OF INDOOR RADON PROGENY
N.W. BUTTE _
45
-------
8/8/79-1/31/83
SCRLE I1
150. '
BOUNDRRY
ERST - 129880.00 o
WEST - 128920.00 L
FEET
+ BELOW .01
iso A .01 TO .01999
O .02 TO .04999
X .05 TO .09999
• .10 (OR RBOVE3
J
NORTH - 131500.00
SOUTH - 130500.00
FIGURE 5-17
INDOOR RADON PROGENY MEASUREMENTS (ML) - SILVER BOW HOMES
46
-------
-116100
-119800
-115103
-114800
-114100
115900 _
115100 _
1HBOO _
114100 _
8/8/79-1/31/83
SCflLE 1" - 500. '
BOUNDRRY
ERST - 140800.00
WEST - 137500.00
NORTH - 116800.00
SOUTH - 113600.00
FEET
+ BELOW .01
A .01 TO .01999
O .02 TO .04999
X.05 TO .09999
• .10 (OR RBOVE)
FIGURE 5-18
INDOOR RADON PROGENY MEASUREMENTS (WL) - SKYWAY PARK
47
-------
Alpha track detectors were used for measurement of radon soil gas
concentrations. The alpha-track detector is a plastic chip which, after
processing, shows tracks (damaged areas) where the detector was struck
by alpha particles. The tracks are counted under magnification. The
number of tracks in a given area is proportional to the concentration of
radon to which the detector was exposed and to the time of exposure.
The alpha-track detectors were placed in plastic cups, with the
tops covered by a thin membrane (thoron filter) that prevents the
penetration of thoron (radon-220) but allows the entry of radon
(radon-222).
Precautions were taken during the placement of the alpha-track
detectors. For the safety of personnel and to assure that underground
utilities would not be damaged while digging holes, utility companies
were given maps showing proposed measurement site locations. Utilities
included were electric, natural gas, telephone and cable television.
After a review by the companies, two sites had to be relocated a few
feet to avoid lines.
When alpha-track detectors are used for uranium exploration, the
location of the detector is generally marked with a flag. There was
concern that the detectors would be removed by vandals or curiosity
seekers if the locations of the detectors were visibly marked in a
populated area. To simplify recovery and to prevent theft, the
alpha-track detectors were placed at a soil depth of 30 inches in a
4-inch PVC sleeve. A string was attached to the detector cup to lower
it into the sleeve. An ample length of string was attached to the
detector cup to allow the string to extend through the top of the
sleeve. A pipe cap was then placed on the sleeve. The sleeves were cut
at a length of 26 inches to provide for a detector depth of 30 inches
with a 4-inch soil cover over the pipe cap. An iron washer was placed
on top of the pipe cap prior to covering the cap with soil.
The location of each detector was carefully logged with reference to
readily identifiable landmarks. For recovery, a metal detector was used
to locate each sleeve. Only 3 out of more than 400 detectors which were
emplaced were lost. These detectors were lost because road grading
excavations had removed the iron washer or possibly even the sleeve and
detector.
Figure 5-19 shows the alpha-track detector placed in the PVC sleeve
assembly. Figure 5-20 shows the locations where alpha-track detectors
were placed throughout Butte on a one-half mile grid. Figure 5-21 shows
the locations where alpha-track detectors were placed in northwest Butte
on a grid of one city block.
Alpha-track detectors were emplaced from July through October,
1980, and again from October, 1980, through April, -1981, to obtain
measurements in both the summer and winter seasons. The radon soil gas
concentration measured at each site during each sampling period is shown
in Table 5-2. In Table 5-2 there is an uncertainty of the stated
concentrations 1n pCi/1. It is believed that the relative
intercomparisons between values are more valid.
48
-------
Alpha track
detector
Cup
4" PVC pipe
(26" long)
Itylon filament tape
Thoron filter
Filter holder
FIGURE 5-19
ALPHA TRACK DETECTOR IN PVC SLEEVE ASSEMBLY
49
-------
_ 138880
_133400
_ 128120
-122B4D
_ 117580
-112260
4-10 +11
46 45
133400 _
128120 _
123940 _
117SBO _
11280 _
(IE 11/24/80-11/24/80)
SCflLE 1" - 5280. '
BOUNDflRY BOUNDflRY
ERST - 149000.00 o saeo NORTH - 141500.00
WEST
116000.00
FEET
FIGURE 5-20
BUTTE RADON SOIL GAS MEASUREMENT SITES
J SOUTH - 107000.00
50
-------
_13BTOO
_ 136000
-135300
_ 133900
+92
+1
+1
+1
+142
+140
+139 +1381-137 +13S
+128
+129 +130
+127
+118H19
+126 +125
481 +90
i i
+120 +121
+117 +116 +115 +114
+109 +110 +lLUgfll2
+108 +107 +106 +105
+101 +102 +103 +104
+100+99+98+97
+93+94+95+96
+99 "I8 +37
I
5
133800 _
133300 _
SCflLE 1" - 700. '
BOUNDflRY
EflST - 126325.00
WEST - 121875.00
I
BOUNDflRY
TOO NORTH - 137150.00
SOUTH - 132500.00
FEET
FIGURE 5-21
RADON SOIL GAS MEASUREMENT SITES IN N.W, RUTTE
51
-------
TABLE 5-2
RADON SOIL GAS MEASUREMENTS
IN B.UTTE, 1980-1981
July, 1980 - October, 1980
December, 1980 - April, 1981
Measurement Site pCi/1 pCi/1
001
002
003
004
005
006
007
008
009
010
Oil
012
013
014
015
016
017
018
019
020
021
022
023
024
025
026
027
028
029
030
031
032
033
034
035
036
037
038
039
040
Harrison-5 Mile
So. End Warren
500 Ft. West No. 2
Harrison-Legion Lane
Motor View-Warren
West End Motor View
4 Mile View-Utah
4 Mile View-Warren
4 Mile View-Harrison
NW Norm Ch-4 Mile View
4 Mile View-McGuiness
Continental Dr-Fleecer Dr
Blacktail -Rampart
Highland-Meadow Lark
Harrison-Lowell
Lowel 1 -Warren
Lowell -Western
South Montana
Nansen Road-Holmes
Holmes-Warren
Harrison-Holmes
N End Burning Tree
Burl i ngton-Augus ta
Burlington- Interstate
Continental -Edwards
Porter-Edwards
Harrison-115
Hi 11 -Sampson
Lexi ngton-Sampson
Montana-Hanson Rd
Montana-Greenwood
Lexi ngton-Greenwood
Warren-C Street
Ottawa-Massachusetts
Ottawa-Porter
Ottawa-Con ti nental
Conti nental -Gagnon
Porter-George
George-Massachusetts
George-Whi tman
362.35
277.67
131.15
246.95
363.13
263.91
462.35
640.93
404.80
678.64
696.50
434.57
533.98
364.92
387.54
698.48
438.53
825.48
316.70
540.53
192.88
462.35
1083.44
519.89
213.24
999.17
688.45
523.95
385.86
743.28
372.79
278.08
165.64
491.68
584.88
381.80
345.24
980.89
509.74
253.85
757.19
261.34
596.42
709.11
1337.19
999.11
423.62
450.67
869.89
814.29
1277.09
495.75
1338.69
279.38
407.09
1520.50
277.87
470.20
670.05
842.84
201.24
548.34
1628.69
1168.90
1134.34
1123.82
766.21
665.54
1194.45
1106.54
974.69
68.47
1412.22
1718.26
460.09
259.84
574.19
924.82
1332.87
530.37
52
-------
July, 1980 - October, 1980
December, 1980 - April, 1981
Measurement Site pCi/1 pCi/1
041
042
043
044
045
046
047
048
049
050
051
052
053
054
055
056
057
058
059
060
061
062
063
064
065
066
067
068
069
070
071
072
073
074
075
076
077
078
079
080
081
082
083
084
085
086
087
088
089
090
George-Lexington
Montana-Si Iverbow Cr
115-South Big Butte
Excelsior-115
Montana- Iron
3rd- Utah
Ist-Warren
Monroe- Pine
Stuart- Pine
Conti nental -Warren
Mercury-Ohio
Montana-Mercury
Galena-Excelsior
Oredigger Field
Big Butte M
Lewi sohn- Excelsior
Montana-Boa rdman
Bennett
La Platta-Montana
17th-Excelsior
Brown's Gulch Road
W of Ryan's Tower
E of Ryan's Tower
WM Street Walkerville
E of Walkerville
Silver Bow Homes 107
Silver Bow Homes 106
Silver Bow Homes 206
Silver Bow Homes 306
Silver Bow Homes 406
Silver Bow Homes 506
Silver Bow Homes 606
Silver Bow Homes 706
Silver Bow Homes 806
Silver Bow Homes 906
Silver Bow Homes 1006
Silver Bow Homes 1909
Silver Bow Homes 1902
Silver Bow Homes 1107
Silver Bow Homes 1207
Silver Bow Homes 1306
Silver Bow Homes 1407
Silver Bow Homes 1506
Silver Bow Homes 1607
Silver Bow Homes 1707
Silver Bow Homes 1806
Granite-Excelsior"
Granite-Henry
Granite-Emmett
Granite-Western
120.63
264.01
773.74
400.07
1751.59
312.75
237.61
696.57
2290.77
566.60
38.07
74.30
556.73
76.76
176.68
1209.36
2296.86
868.18
566.60
1620.60
960.98
464.63
798.26
558.78
2014.07
361.49
276.19
501.61
521.92
132.82
259.95
233.54
218.11
278.22
371.64
542.23
148.60
605.86
378.66
315.21
452.35
665.22
478.96
245.62
268.20
350.72
760.18
727.41
1022.31
515.52
241.71
802.40
702.66
1593.57
1668.38
813.74
602.91
1706.92
1720.52
1462.09
73.95
201.24
129.72
322.95
112.34
1038.17
1137.91
689.05
963.36
1230.86
1060.84
1634.38
2470.89
734.39
*
371.91
1118.28
2346.41
476.20
469.20
1181.32
754.05
217.81
1106.61
1223.35
334.55
747.04
1410.14
655.98
1029.56
1487.19
2311.39
590.61
653.65
1428.82
348.56
1774.37
1641.29
1420,49
964.22
53
-------
Measurement Site
July, 1980 -
December, 1980
pCi/1
October, 1980
- April, 1981
PCi/1
091
092
093
094
095
096
097
098
099
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
Granite- Prospect
Granite-Ophir
Quartz-Western
Quartz-Emmett
Quartz-Henry
Quartz-Excelsior 18"
Copper- Excel si or
Copper-Henry
Copper-Emmett
Copper-Western
Caledonia-Western 18"
Caledonia-Emmett
Caledonia-Henry
Caledonia-Excelsior
Wool man-Excelsior 14"
Wool man-Henry
Wool man- Emmett
Wool man-Western
Antimony-Western
Antimony- Emmett
Antimony-Henry 15"
Antimony-Excelsior
Lewi sohn- Al abama
Lewisohn-Excelsior
Lewisohn-Henry
Lewi sohn- Emmett 13"
Lewi sohn- Western
Waukesha-Western
Waukesha- Emmett
Waukesha-Henry
Waukesha-Excelsior
Waukesha-Al abama 11"
Empire-Clark
Empire- Alabama
Empire- Excelsior
Empi re-Henry
Kennedy School
Brown's Gulch-Zarelda
Hornet-Henry
Hornet-Excelsior
Hornet-Alabama
Hornet-Pit
Zarel da-Clark East
Zarel da-Clark
Zarel da- Alabama
Zarel da-Excelsior 20"
Zarel da-Henry 21"
Zarel da-Henry
Zarel da-Hornet
End Prospect
178.25
44.61
323.83
526.50
2821.95
315.02
697.23
637.75
249.81
266.55
203.48
210.03
253.94
1649.45
169.18
1057.41
106.40
66.09
414.15
54.85
592.22
867.99
727.85.
1586.80
2271.70
28.75
94.26
211.57
1528.89
1953.01
1624.66
362.56
933.75
920.07
1351.03
4282.26
1073.99
679.51
1857.24
2544.73
1228.42
3554.12
1228.42
186.33
292.61
1490.66
855,75
434.78
10295.22
5472.54
308.32
27.67
270.89
*
2673.46
923.22
2495.23
777.07
459.82
780.64
216.94
294.04
227.70
910.85
424.93
2338.13
69.91
252.80
190.04
40.86
367.56
3837.12
437.49
3478.51
3944.71
158,96
394.45
292.25
5271.57
5250.05
3885.44
2010.44
1504.26"
463.38
1432.97
5706.97
4491.43
723.60
1896.37
3814.15
1076.50
4455.78
2495.23
484.77
862.62
3457.68
3029.93
2709,11
7172.21
6454,99
54
-------
July, 1980 - October, 1980
December, 1980 - April, 1981
Measurement Site pCi/1 pCi/1
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
616 Butte Fire St 20"
Missoula West End
Mlssoula Green Apt.
Missoula White Apt.
Excelsior-Walker 20"
Excelsior- 12th
Excel si or- 14th
Excel sior-15th
Henry- 15th
Henry-l'7th 20"
Excel sior-17th
14th-Clark 20"
llth-Clark 20"
9th-Clark 20"
Missoula-Clark
Clark-6th
Kenwood- Clark
Alabama- Empire 20"
Alabama- Empire
Alabama- Empire
Alabama- Empire
Alabama- Empire 20"
Alabama- Empire 20"
Alabama- Empire 30"
Alabama- Empire 15"
Alabama- Empire
Alabama-Empire
Alabama -Empire
Alabama- Empire 20"
Alabama-Empire
Alabama-Empire
Alabama-Empire
Alabama- Empire
Alabama- Empire
Silver Bow Homes 1904
Silver Bow Homes 1904
Silver Bow Homes 1904
Silver Bow Homes 1904
Silver Bow Homes 1112
Silver Bow Homes 1112
Silver Bow Homes 1112
Silver Bow Homes 1112
1371.56
244.30
2870.91
678.62
630.31
2022.05
1269.82
775.24
625.71
156.66
1469.96
1863.33
1055.89
743.03
683.22
394.75
502.41
1059.78
1839.62
*
1066.44
290.61
679.86
737.62
249.68
1327.09
978.22
1347.61
515.33
1005.58
1015.84
1224.48
2202.70
1522.05
140.92
214.11
239.47
249.13
400.27
240.85
185.64
724.63
7172.21
54.80
3872.99
281.49
1004.09
2402.68
1169.05
720.79
1384.22
92.32
3119.90
989.75
846.30
1047.12
2689.57
591.69
824.79
2920.99
3401.67
1663.85
451.07
1116.62
'843.01
650.74
204.57
3327.72
2699.14
3253.77
2292.42
3031.92
2551.24
4030.24
6285.71
3253.77
232.92
573.09
467.71
691.41
769.06
103.51
84.28
1072.25
Mean 1082.39 1407.2
*Alpha-track detector lost.
55
-------
Gingrich reports that worldwide radon soil gas concentrations
average about 100 pCi/1. According to Gingrich, radon soil gas
concentrations can be expected to vary by a factor of about 2 to 5 from
the 100 pCi/1 value. Gingrich's information is based on data acquired
from more than 300 different surveys in which the alpha-track detectors
were used. According to Gingrich, only 12 of the 300 areas measured had
radon soil gas concentrations averaging above 1000 pCi/1. Butte was one
of the 12 areas.
The average radon soil gas concentration measured during summer
months was 1082 pCi/1. The average radon soil gas concentration
measured in the winter was 1407 pCi/1. The higher winter concentration
was attributed to the capping effect created by the freezing of the top
layers of soil.
The depth to which soil freezes in Butte during the winter exceeds
the depth at which the alpha-track detectors were placed. The
difference between the winter and summer measurements would likely have
been greater if the detectors had been placed below the frost line.
From Table 5-2, it can be seen that radon soil gas concentrations
ranged from lows of less than 100 pCi/1 to a high that exceeded 10,000
pCi./l.
Homes having indoor radon progeny concentrations of 0.02 WL or less
were not considered to have a significant indoor radon problem based on
the U. S. Surgeon General's guidelines for Grand Junction, Colorado, and
the EPA standards for inactive uranium mill sites (10 CFR 192).
Generally, radon progeny concentrations in homes did not exceed 0.02 WL
where radon soil gas concentrations were less than 500 pCi/1. However,
there were exceptions. These exceptions may be due to construction
differences or variations in radon soil gas concentrations between
structure locations and the sites where radon soil gas concentrations
were measured.
As seen in Table 5-2, radon soil gas concentrations frequently
exceed 1000 pCi/1 in northwest Butte where high levels of indoor radon
are found.
There appears to be a sufficient enough relationship between radon
soil gas measurements and indoor radon concentrations to predict that
elevated radon soil gas concentrations may be an indicator of potential
indoor radon problems in Butte.
Localized Measurements of Radon Soil Gas Concentrations
In addition to the grid measurements of radon soil gas, alpha-track
detectors were used to measure radon soil gas concentrations in straight
lines traversing identifiable fractures, mineralized veins, and areas of
specific geologic composition.
56
-------
Silver Bow Homes
At Silver Bow Homes, alpha-track detectors were placed between
apartment buildings at locations shown in Figure 5-22. The values to
the left of the site location (+) are measurements made during the
months of August, September and October, 1981. The values to the right
of the site marker are measurements made between the months of November,
1981 and April, 1982.
At Silver Bow Homes the average radon soil gas concentration in the
summer (362 pCi/1) and in the winter (964 pCi/1) was lower than the
overall average soil gas concentration .for the city during the summer
and winter (1082 pCi/1 and 1407 pCi/1, respectively).
Mineralized veins, shown as solid lines in Figure 5-22, traverse
the Silver Bow complex in an east-west direction. The veins are covered
with soil and are not visible.
Figure 5-23 shows radon soil gas measurement sites traversing two
mineralized veins. Positioning the alpha-track detectors proved
difficult due to the rock encountered while digging in the southernmost
sites shown in Figure 5-23.
Skyway Park
Skyway Park is in the Butte valley where the alluvium is estimated
to range between 80 and 200 feet in depth.
Radon soil gas measurements were made in Skyway Park between
November, 1981, and April, 1982. Difficulty was encountered in
establishing locations where alpha-track detectors could be placed in
this area. The streets in Skyway Park are paved and there are no
alleys. Nearly all the residences have been landscaped. It would have
been desirable to position some alpha-track detectors near homes having
elevated indoor radon concentrations but this was generally not possible
due to the landscaping. With few exceptions, the alpha-track detectors
were placed on vacant lots.
The average radon soil gas measurement in Skyway Park was 666 pCi/1
which is less than half the average radon soil gas concentration
measured in Butte during the winter months, yet still significantly
higher than what Gingrich considers normal. The Skyway Park radon soil
gas measurement sites and data in pCi/1 are shown in Figure 5-24.
Radon and radon progeny concentrations were measured in several
Skyway Park homes by long-term integrating methods; however, most homes
were measured by grab sampling. Of the 56 homes tested in the Skyway
Park area, 22 measured in excess of 0.02 Working Levels.
No mineralized veins, fractures, or unusual geologic features are
found in Skyway Park, and the radon soil gas concentrations are
relatively constant. It is not known if the difference in radon progeny
concentrations between homes in this area is due to structural
57
-------
_ 130BSD
SCflLE 1" - , 150. ' "
BOUNDflRY BOUNDflRY
ERST - 129880.00 o iso NORTH - 131500.00
WEST - 128920.00 I I SOUTH - 130500.00
FEET
FIGURE 5-22
RADON SOIL GAS CONCENTRATIONS (pCi/1) - SILVER BOW HOMES
58
-------
-131385
131385 _
-131340
-131315
605+H10
131340 _
131315 _
131290
4004789
240+103
131290 -
SCRLE 1" - 25. '
BOUNDflRY
EflST - 129550.00
WEST - 129387.00
= Veins
(IE 11/24/80-7/15/82)
25
FEET
FIGURE 5-23
BOUNDflRY
NORTH - 131400.00
SOUTH - 131240.00
•*• = Measurement Location
xxx+yyy = Summer & Winter
Measurement
RADON SOIL GAS CONCENTRATIONS (pCi/1) AT MEASUREMENT SITES
TRAVERSING MINERALIZED VEINS - SILVER ROW HOMES
59
-------
-114100
115100 -
11«00 _
1MIOD -
scniE r - 500. • "
BOUNDflRY BOUNDflRY
ERST - 140800.00 o soo NORTH - 116800.00
WEST - 137500.00 I I SOUTH - 113600.00
+ = Measurement Site
FEET
FIGURE 5-24
RADON SOIL GAS CONCENTRATIONS (pC1/U - SKYWAY PARK
60
-------
differences, differing lifestyles or if there are localized areas having
high soil radium-226 content that were not indicated by the radon soil
gas measurements.
McClernan believes that Skyway Park was marshy or underwater at
one time and that there may be small localized areas having soils with
elevated radium content that may have resulted from either the
precipitation or organic concentration of radium.
Walkerville
Radon, soil gas measurements were made in aplite in the Walkerville
area which is located on the north side of Butte. The measurement site
selected was from about 30 to 200 feet west of Walkerville Drive with
the northernmost sampling point approximately 200 feet south of where
Walkerville Drive curves into Daly Street. Eleven alpha-track detectors
were emplaced in October, 1981, and recovered in April, 1982. The
measurements and locations are shown in Figure 5-25.
The line of alpha-track detectors crossed a major fracture (shown
as a dotted line in Figure 5-25). The radon soil gas measurements at
the two measurement points near the fracture averaged 7171 pCi/1;
whereas, the other nine measurement points averaged 1226 pCi/-l. The
average of the nine measurement points located away from the fracture
compares closely with the overall average for the Butte area during
winter months (1407 pCi/1). v
Fractures in underlying geology are believed to act as conduits for
transporting radon to the surface. The measurements at the two sites
near the fracture support this theory.
The purpose in placing the alpha-track detectors in the aplite was
to determine if the radon soil gas concentrations in the aplite varied
significantly from the concentrations measured in other surface rock and
soil types. When the two measurement points near the fracture are
excluded, the average (1226 pCi/1) compares closely with the overall
radon soil gas concentration average for Butte, but is still nearly
double the average measurement for the Skyway Park area and is about 25%
higher than the average radon soil gas concentration during a comparable
time period at Silver Bow Homes.
West Junior High School
Six measurement points in aplite were established at a site north
of the Interstate 90 on-ramp at a distance of about 200 feet south of
the West Junior High School. The locations of the measurement points
and the radon soil gas measurement data in pCi/1 are shown in Figure
5-26. Fairly consistent concentrations averaging 547 pCi/1 were
measured at five of the six sampling points. The sixth point measured
1766 pCi/1. The anomalous measurement was near a small mineralized
vein.
If the anomalous measurement is discounted, the radon soil gas
measurements at the West Junior High School average only about one-half
61
-------
/ I
+^749
48593 v
+2003
+1428
+1972
+846
+778
+1428
+704
+1137
+741
_137«C
SCflLE 1"
BOUNDflRY
EflST - 125290.000
WEST - 125000.00
— = Fractures
FEET
, (IE 11/24/80-7/15/82)
OLJ»
BOUNDRRY
s&NORTH - 137710.00
J SOUTH - 137370.00
+ = Measurement Site
FIGURE 5-25
RADON SOIL GAS CONCENTRATIONS (pCi/U
IN APLITE - WALKERVILLE
62
-------
-I29B15
West Junior
High School
129915 _
_ims
129215 -
_ 123165
-129115
-129065
SCflLE 1" - 50. ' (IE
BOUNDflRY BOUNDflRY
ERST - 123850.00 o so NORTH - 129350.00
WEST - 123550.00 I I SOUTH - 129015.00
+ = Measurement Site
FEET
FIGURE 5-26
RADON SOIL GAS CONCENTRATIONS (pCi/1) IN APLITE -
WEST JUNIOR HIGH SCHOOL
63
-------
the concentration measured at the Walkerville site. Although no
laboratory analyses were made, it appears that either the radium content
of the aplite varies or that the radon permeability of aplite varies
between the two sites.
Yellow Jacket Vein
Radon soil gas measurements were made on both sides of Alabama
Street between Hornet and Empire Streets, traversing two forks of the
Yellow Jacket Vein. The sampling points and measurement data in pCi/1
are displayed in Figure 5-27. The measurements recorded to the left of
the sampling point (+) are summer measurements and the measurements on
the right side are winter measurements. As seen in Figure 5-27, the
radon soil gas concentrations measured over veins are higher than
measurements which were not over veins.
Gold Street
Radon soil gas measurements were made at a site near Gold and
Jackson Streets. At this site a number of exposed mineralized veins
traverse Jackson Street in an east-northeast direction. Six alpha-track
detectors were placed, traversing the exposed veins as shown in Figure
5-28. The average radon soil gas concentration at this site was 3396
pCi/1, approximately three times the average for the Butte area.
Henry Street
Another series of exposed mineralized veins traverses Henry Street
at its intersection with Antimony Street. As at the Gold Street site,
the veins traverse Henry Street in an east-northeast direction.
The average radon soil gas measurement at the Henry Street site was
4979 pCi/1, about four times the average for the Butte area, with a
range from 1391 to 10591 pCi/1. The mineralized veins (solid lines) and
radon soil gas measurement data for this site are displayed in Figure
5-29.
Radon Exhalation Measurements
Rock and Soil
Rock and soil samples were collected at ten sampling sites located
in and near Butte. The locations of eight of these sampling sites are
shown in Figure 5-30. Sites numbers 9 and 10 are located on Homestake
Pass, eight miles east of Butte where Interstate 90 crosses the
Continental Divide. Comparative radon exhalation measurements were made
using 25 cm sample depths with results as shown in Table 5-3.
As seen in Table 5-3, the highest radon exhalation rates were from
mineralized vein material. The aplite samples showed exhalation rates
that are about three times the exhalation rates from quartz monzonite
and alluvium. From these tests, mineralized vein material and aplite
appear to be the most important sources of radon in the Butte area.
64
-------
-1318*}
1839+34CI
+163
01
Ol
+J
t/1
1224-HOBO
1015 +2551
1005+3031
515+2292-
249+304
Empi re
jjj Street g
j I
1347-K5253
^——
978+2699
(IE 11/31/80-7/15/82)
SCRLE 1" - 50. '
BOUNDflRY BOUNDflRY
EflST - 125300.00 o go NORTH - 135080.00
WEST - 124975.00 L
= Veins
I
FEET
FIGURE 5-27
SOUTH - 134740.00
+ = Measurement Sites
xxx+yyy = Summer & Winter
Measurements
RADON SOIL GAS CONCENTRATIONS (pCi/D AT
MEASUREMENT POINTS TRAVERSING THE YELLOW JACKET VEIN
65
-------
BOUNDflRY
EflST - 126260.00 o
WEST - 126065.00 L
= Veins
SCRLE 1" - 30. • m
BOUNDRRY
30 NORTH - 130400.00
J SOUTH - 130200.00
+ = Measurement Sites
FEET
FIGURE 5-28
RADON SOIL GAS CONCENTRATIONS (pCi/1) AT MEASUREMENT SITES
TRAVERSING MINERALIZED VEINS - GOLD AND JACKSON STREETS
66
-------
Antimony » Street
SCflLE 1" - 25. • CK
BOUNDflRY BOUNDflRY
ERST - 124150.00 o 25 NORTH - 134050.00
WEST - 124000.00 I I SOUTH - 133925.00
FEET
= Veins + = Measurement Sites
FEET
FIGURE 5-29
RADON SOIL GAS CONCENTRATIONS (pCi/1) AT MEASUREMENT SITES
TRAVERSING MINERALIZED VEINS - HENRY AND ANTIMONY STREETS
67
-------
SCflLE 1M- 4000.
BOUNDARY BOUNDflRY
ERST - 145000.00 o coo NORTH - 139500.00
NEST - 119000.00 I I SOUTH - 112500.00
FEET
FIGURE 5-30
ROCK AND SOIL COLLECTION SITES
FOR RADON EXHALATION TESTS
68
-------
TABLE 5-3
COMPARATIVE RADON EXHALATION MEASUREMENTS
OF BUTTE AREA ROCK AND SOIL SAMPLES
Radon Exhalation
Sample No. Sample Location Sample Type Rate (pCi/m /min)
1
2
3
4
5
6
7
8
9
10
Jackson & Gold Sts.
Jackson & Gold Sts.
Antimony & Henry Sts.
Walkerville Drive
Emmett & Missoula Sts.
West Junior High Sch.
Columbus & East
Lake Streets
100 Star Lane
Homestake Lake
Homestake Pass
Aplite
Vein Material
Vein Material
Aplite
Apl i te
Aplite
Alluvium
Alluvium
Quartz Monzonite
Quartz Monzonite
520
1663
2615
727
1001
602
301
151
305
169
Building Materials
Building materials were evaluated to determine if they were a
source of radon in structures. Activated charcoal canisters were
obtained from the EPA Eastern Environmental Radiation Facility (EERF) in
Montgomery, Alabama, to measure radon exhalation rates from these
materials. The following building materials were evaluated:
1. Concrete
2. Conventional concrete blocks
3. Concrete blocks containing slag from smelting operations
4. Bricks (red and white)
5. Gypsum board
6. Plaster
Radon exhalation measurements were performed by making an air-tight
seal between the activated charcoal canister and the material to be
tested using duct tape. The canister was attached to the material being
tested from 48 to 96 hours. During each measurement, additional
canisters were simultaneously placed to measure ambient radon.
Following each measurement, the canisters were sealed to prevent further
radon exposure, and were returned to the EERF for analysis by gamma
spectroscopy.
The ambient radon measurements during each test were higher than
the measurements made with the canisters which were sealed to the
material being evaluated, thus eliminating building materials as suspect
sources.
69
-------
Dissolved Radon in Water
Butte city water supplies originate from surface water sources;
however, these water supplies were measured to determine dissolved radon
content. In addition, springs and private water supplies outside the
city were measured. Liquid scintillation vials were obtained from the
EERF for sample collection. A measured volume of each water sample was
injected into duplicate scintillation vials and returned to the
laboratory for analysis.
Data obtained from analyses of Butte water samples for dissolved
radon content are presented in Table 5-4. As seen in Table 5-4, the
dissolved radon concentrations in the Butte surface water supplies are
so low that they cannot be accurately measured. Groundwater supplies in
the Butte area are elevated in dissolved radon content but not to the
point where they are considered as a significant source of indoor radon.
Radon Measurements in Underground Sewers
It is possible that the entry route of radon into some structures
is through unsealed service entries or through plumbing fixtures having
dry traps or no traps at all. For this reason, measurements of radon
concentrations in underground sewers were made.
Samples were collected by lowering an intake tube through manhole
cover ventilation holes to a depth of six to eight feet and drawing air
from this intake tube through a 500 ml scintillation cell. This method
of sample collection was preferred to removing the manhole cover, since
it prevented abnormal air circulation at the point of sampling.
Measurements were made at 41 locations throughout the city as shown
in Table 5-5. Measurements ranged from lows of less than 1 pCi/1 to a
high of more than 400 pCi/1. Generally the highest radon concentrations
were measured in areas demonstrating high indoor radon concentrations.
The highest measurements were again found in the northwest part of the
city.
Structures have not been evaluated to determine the degree of radon
entry through unsealed service entries or through dry-trapped or
untrapped plumbing fixtures. The radon concentrations measured in
underground sewers does demonstrate the need to evaluate service
entrances as potential routes of radon entry into structures.
Radon In Natural Gas Supplies
The radon content of natural gas was measured to determine if
unvented gas appliances contribute significantly to indoor radon
concentrations. The radon content of natural gas in Butte averaged 14
pCi/1. Thus, the natural gas contribution to indoor radon
concentrations is negligible.
70
-------
TABLE 5-4
DISSOLVED RADON CONCENTRATIONS IN
WATER SOURCES IN THE BUTTE AREA
Sampl e
Sample Location Number
Butte Water Co., 129 W. Galena
(Big Hole River Supply)
Blaine Elementary School
(Moulton Reservoir Supply)
Hawthorne Elementary School
(Basin Creek Reservoir Supply)
Hoeffner's Pump Station
(Anaconda) - 3 wells
(55-70 feet)
Private Residence (Lost Creek)
private well (55 feet)
Private Residence (Roosevelt
Drive), private well (115 feet)
Spring Water from Source
1000 Block between Zarelda
and Lexington Streets
1
2
1
2
1
2
1
2
1
2
1
2
1
2
Dissolved Radon Concentration
(pCi/1 + 2 sigma)*
- 4 +
12 +_
- 6 +
69 +
- 38 +
- 49 +
510 +
464 +
2913 +
2938 +
3346 +
3277 +
4029 +
4110 +
1359%
455%
905%
79%
141%
111%
13%
14%
3%
3%
2%
2%
2%
2%
*There is a 95 percent assurance that the true value lies between the
reported value +. 2 sigma.
71
-------
TABLE 5-5
RADON CONCENTRATIONS IN
BUTTE UNDERGROUND SEWERS
12/10/80
12/11/80
12/18/80
1/14/81
1/16/81
1/15/81
1/16/81
1/15/81
Location
Excelsior & 17th
Excelsior & 15th
Excelsior & llth
Excelsior & Missoula
Thornton between Pine & Walnut
Thornton between Continental & Pine
Stuart between Pine & Walnut
Garfield between Silver Bow & Locust
Blacktail & 4 Mile Vue
Blacktail & 4 Mile Vue
Elizabeth Warren & Bartoletti Prop.
KOA & Kaw
George & Silver Bow Creek
Farragut & Yale (west)
Farragut & Yale (east)
Hill & Evans (SW)
Hill & Evans (east)
Hill & Evans (NW)
Lexington & Majors
Oregon (W) & Silver Bow Creek (N)
US-10 & Hamblin Heights
Excelsior & Woolman (SE)
Excelsior & Woolman (SW)
Caledonia & Excelsior (W)
Emmett & Park
Mercury (S) between Girard & Emmett
Silver & Emmett
Silver between Emmett & Girard
Gold between Emmett & Girard
Platinum between Emmett & Girard
Girard between Platinum & Steele
Waukesha & Emmett
Woolman & Emmett
Galena & Clark
Silver & Colorado
Colorado & Aluminum
Nevada & 1st
Atlantic & 1st
Monroe & Wall
Lafayette & Irene (SE)
Hannibal & Hancock
,7
.4
Radon
(pCi/1)
0.2
0.8
0.4
12.6
0.8
0.3
1.1
2.1
2.6
0.4
1.1
72.0
84.
59.
3.1
4.9
5.9
5,2
105.1
105.0
52.4
110.
283.
403.8
1.5
1.1
16.
12.
22.
1.3
1.9
125.6
10.
20.
167.
219.8
1.0
20.0
7.6
0.8
1.8
.5
.4
.1
.6
,1
.4
.9
,1
72
-------
6. CONCLUSIONS
Radon Sources
Phosphate slag
Phosphate slag produced near Butte by the Stauffer Chemical Company
is elevated in radium-226 content. However, tests have confirmed that
radon exhalation from the slag is not a significant health concern. The
radium content of the slag is essentially the same as that of the
phosphate ore, but the slag exhales less than one percent as much radon
as the ore.
Outside Air
Monthly averages of radon in ambient air ranged from low of about
0.25 pCi/1 at the Hebgen Park Station to a high of 5.86 pCi/1 at the
Hornet Street Station. Ambient air is not responsible for the high
radon and radon progeny concentrations measured in homes; however, when
radon concentrations are high, the contributions from the ambient air
should be considered when measuring indoor radon and radon progeny
concentrations.
The high ambient radon concentrations measured in Butte show the
need to consider ambient radon when standards are developed that relate
to maximum permissible concentrations of indoor radon or radon progeny.
The average outside radon concentration (3.25 pCi/1) measured at the
Hornet Street Station, when drawn into a structure, produces a radon
progeny concentration of 0.010 WL at an equilibrium of 32 percent (the
average integrated measurement equilibrium for the 20 study homes). If
the equilibrium should increase to 45 percent, as measured in some
homes, the ambient contribution to the indoor radon progeny
concentration would be 0.015 WL.
Soil
The radium-226 content of soil in the Butte area ranges from about
one to three picocuries per gram. The radium in the soil undoubtedly
contributes to indoor radon concentrations; however, except for the
Skyway Park area, sources other than soils are thought to be responsible
for the high indoor radon concentrations observed in the Butte area.
Soil is believed to be the most substantial source of radon in Skyway
Park; however Skyway Park is not as severely impacted by elevated indoor
radon concentrations as is northwest Butte.
Surface Geology
Radon soil gas measurements made in rhyolite were generally less
than 100 pCi/1. Indoor radon and radon progeny concentrations measured
in structures built on rhyolite were low. Rhyolite is not considered a
source of Butte's indoor radon problem.
It was difficult to determine the rock types at the radon soil gas
measurement sites; however, radon soil gas measurements in aplite and
73
-------
quartz monzonite appeared to be about the same as the average for Butte
as a whole. Measurements in aplite in Walkerville were about twice the
levels measured in aplite near the West Junior High School. This
measurement difference probably results from the structure of the aplite
because radon exhalation tests on aplite from these locations did not
show a substantial difference.
Radon exhalation measurements made on mineralized vein material,
aplite, quartz monzonite and alluvium show the vein material exhales
substantially more radon than do other rock and soil samples tested.
Tests on aplite indicate that the aplite exhales approximately three
times the radon that is exhaled from quartz monzonite and alluvium.
Fractures and mineralized veins are the surface geology features
believed to be the cause of the most severely elevated indoor radon
concentrations. Radon soil gas measurements over fractures and over
mineralized veins were often five to ten times higher than the average
concentrations measured in the Butte area. Gamma radiation measurements
at mineralized veins also are often an order of magnitude higher than
measurements of surrounding rocks.
Other Measurements
Measurements of radon in natural gas, dissolved radon in water, and
radon exhalation rates from common building materials showed that they
make no significant contribution to the indoor radon concentrations in
Butte.
Summary
Ambient air, soils and surface geology all contribute to the indoor
radon problem in Butte. It is believed that homes constructed over
major fractures or mineralized veins are the most severely affected.
Aplite and quartz monzonite and soils also contribute to the problem,
but to a lesser extent. It is possible that ambient air is a
significant source of indoor radon during certain atmospheric conditions
in structures having no other substantial source of radon.
74
-------
REFERENCES
1. U. S. Environmental Protection Agency. Federal Register. Vol. 44,
No. 128, July 2, 1979.
2. National Oceanic and Atmospheric Administration. Climatological Data,
Annual Summary, Montana, 1980, Volume 83, No. 13.
3. Climatological information compiled by the Montana Bureau of Mines,
1931 to 1981.
4. Meyer, Charles, et.al. "Ore Deposits in Butte, Montana", Ore Deposits
of the United States, 1933-1967, John D. Ridge, ed., American Inst. of
Mm., Met., and Pet. Eng. S., Inc., New York, 1968, pgs. 1373-1416.
5. Habashi, Fathi. Uranium in Phosphate Rock, Special Publication 52,
Montana Bureau of Mines and Geology, Montana College of Mineral Science
and Technology, Butte, Montana, December, 1970.
6. Andrews, V., and T. Bibb. Emissions of Naturally Occurring Radioactivity,
Stauffer Elemental Phosphorus Plant, EPA-520/6-82-019, November, 1982.
7. Lloyd, Larry L. Butte Radiation Study - Background and Current Status,
Report to the 46th Montana Legislature, Montana Department of Health
and Environmental Sciences, Helena, Montana, 1979.
8. National Council on Radiation Protection and Measurements. Natural
Background Radiation in the United States, NCRP Report No. 45, 1975,
Washington, D.C.
9. Eisenbud, Merril. Environmental Radioactivity, McGraw-Hill, New York,
1963.
10. McClernan, HenryG., Ph.D. Montana Bureau of Mines and Geology, Montana
College of Mineral Science and Technology, Butte, Montana, oral communi-
cations, 1982 and 1983.
11. Gingrich, James. Terradex Corporation, Walnut Creek, California, personal
telephone communication, March 15, 1983.
tV U.8. GOVERNMENT PRINTING OFFICE:1«M-4214a / 802
75
------- |