S-EPA
United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington, D.C. 20460
EPA/520/6-88-059
October 1988
Radiation
Radon
Around the
L-Bar Uranium
Mill Site
B
y
k
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DISCLAIMER
This report has been reviewed by the staff from the Office of Radiation
Programs, U.S. Environmental Protection Agency, and approved for publication.
The mention of trade names or commerical products does not constitute an
endorsement or recommendation for their use.
ii
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ABSTRACT
Measurements of radon concentrations were made between November 1985 and
November 1986 1n the vicinity of the uranium mill tailings pile of SOHIO L-Bar
site near Seboyeta, New Mexico. The data can be used for exposure and risk
estimates as discussed in the National Emission Standards for Hazardous Air
Pollutants (NESHAP's) for radon-222 emission from licensed uranium mill
tailings. Twenty-two Passive Environmental Radon Monitors (PERM'S) were used
in this investigation. They were placed 400, 600, and 800 meters away from
the centroid of the pile. In addition, a background PERM station was
established 1200 meters to the north and upwind from the centroid of the
tailings. Radon concentrations were determined monthly by analyses of a pair
of thermoluminescent dosimeters (TLD's) located in each PERM. Results of the
data show that radon concentrations decreased with distance from the centroid
of the tailings pile. During the year the average radon concentrations ranged
-3 -3
between 14.9 Bq m and 35.6 Bq m at the 400 m interval, between
-3 -3 3
6.20 Bq m and 18.8 Bq m for 600 m, and at 800 m between 1.80 Bq m
_3
and 9.80 Bq m . The annual net radon concentrations at 600 and 800 meters
3
were less than 18.5 Bq m .
iii
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ACKNONLEDGMENTS
Sample collection 1s always the unglamourous part of any study, but 1n
reality Is the most Important aspect of an Investigation. The authors are
most appreciative and Indebted to those persons who, despite Inclement
weather, collected the samples for analysis. They are Dr. Paul Hahn, Edith
Boyd, Shirley Duran, Robert Lyon, and Roger Shura, who are staff members from
the Office of Radiation Programs at the Las Vegas Facility.
Ne also thank the State of New Mexico, Environmental Improvement
Division, for the support provided at the L-Bar site.
A special acknowledgment 1s accorded to Hayne Bliss, Director of ORP-LVF,
for his strong support in this type of work.
vi
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FIGURES
Number Page
1. Map of locations of the uranium mills in New Mexico 5
2. Map of the locations of the PERM stations at the L-Bar Site ... 8
3. Average net radon concentrations and iso concentration
contours for the first quarter.
(Numbers expressed in Bq m ) 12
4. Average net radon concentrations and iso concentration
contours for the second quarter.
(Numbers expressed in Bq m ) 13
5. Average net radon concentrations and iso concentration
contours for the third quarter.
(Numbers expressed in Bq m ) 14
6. Average net radon concentrations and iso concentration
contours for the fourth quarter.
(Numbers expressed in Bq nf ) 15
7. Average net radon concentrations and iso concentration
contours for the entire study (11/15/86 to 11/10/86).
3
(Numbers expressed in Bq m ) 16
8. Gross monthly average radon concentrations at sampling
locations at the 400 m, 600 m, 800 m, and 1200
meter distances 18
TABLES
Number Page
1. Monthly radon concentration at L-Bar
(November 1985 to November 1986) 10
2. Average annual radon concentration at
L-Bar (Bq m~3) 11
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CONTENTS
PAGE
Disclaimer ii
Abstract 111
List of Figures and Tables v
Acknowledgements vi
Introduction 1
Method 7
Results and Discussion 7
References 19
iv
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INTRODUCTION
The United States Environmental Protection Agency (EPA) on
January 13, 1977 (42 FR 2858) published its response to public comments on the
proposed "Environmental Radiation Protection Standards for Nuclear Power
Operations." It was noted "...that doses resulting from exposure to radon and
its daughters which are discharged from a mill site, or result from material
which has been discharged, are excluded..." from these standards. The EPA on
the same day promulgated standards (42 FR 2860) under Title 40, Code of
Federal Regulations Part 190, Section 190.10 which exempted from control,
radon and its decay products.
On September 30, 1983, the Agency issued standards under the Uranium Mill
Tailings Radiation Control Act (UMTRCA) (40 CFR 192, Subparts D and E) for the
management of tailings at active mills licensed by the Nuclear Regulatory
Commission (NRC) or the States under Title II of the UMTRCA. These standards
do not specifically limit radon-222 emissions until after closure of a
facility; however, they require as low as reasonably achievable (ALARA)
procedures for radon-222 control, and the NRC does consider ALARA procedures
in licensing a mill. When the UMTRCA standards were promulgated, the Agency
stated that it would issue an Advance Notice of Proposed Rulemaking with
respect to control of radon-222 emissions from uranium tailings piles during
the operational period of a uranium mill.
On April 6, 1983, emission radionuclide standards for NRC licensees were
proposed under the Clean Air Act (48 FR 15076, April 6, 1983); however,
uranium fuel-cycle facilities, which included operating uranium mills, were
excluded because these sources are subject to EPA's 40 CFR Part 190 and 192
environmental health radiation standards. During the comment period for the
Clean Air Act standards, it was noted that radon-222 emissions from operating
uranium mills and tailings piles were not subject to any current or proposed
EPA standards, and that such emissions could pose significant risks.
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On October 31, 1984, EPA published an Advance Notice of Proposed
Rulemaking (ANPR) in the Federal Register. 49 FR 43916, for radon-222
emissions from licensed uranium mills. The notice stated that the Agency is
considering emissions standards for licensed uranium mills and solicited
information in the following areas:
- Radon-222 emission rates from uranium mills and associated tailings
piles
- Local and regional impacts due to emissions of radon-222 from uranium
mills and associated tailings piles prior to permanent disposal
- Applicable radon-222 control options and strategies, including work
practices
- Feasibility and cost of radon-222 control options and strategies
- Methods of determining compliance with a work practice type of standard
to control radon-222 emissions
- Impact of radon-222 control on the uranium industry.
Prior to the publishing of this ANPR, the New Mexico Environmental
Improvement Division (NMEID) conducted a 2-year indoor/outdoor radon
concentration monitoring program 1n 1978 to 1980 in the Ambrosia Lake - Grants
mineral belt area (Buhl et al. 1985). Additional sampling was done by the
NMEID between March 1983 and May 1985 (NMEID 84, unpublished data). The NMEID
asked the Office of Radiation Programs-Las Vegas Facility (ORP-LVF) to assist
in surveying for radon 1n the environs of uranium mill sites in this State.
At their request and 1n support of the Clean Air Act the ORP-LVF undertook a
study to measure the Rn-222 concentration in the vicinity of SOHIO L-Bar
uranium mill site.
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Radon 1s released at the mill site during the crushing and grinding of
the ore, as well as the extraction, recovery and concentration stages In which
the "yellowcake" 1s produced. The ore storage area 1s an additional way for
radon to emanate. However, the releases of radon from these sources are small
relative to the tailings (EPA86) and will not be discussed In this report.
Tailings Disposal
With the exception of the uranium extracted during milling, the dry
weight of the tailings represents the total dry weight of the processed ore.
Ore contains only about 0.1 percent uranium; therefore* the tailings consist
of 99.9 percent of the ore, Including all the radioactive decay products. The
tailings discharge 1s composed of three fractions: (1) the sands, which
consist of solids larger than 200 mesh; (2) the slimes, which consist of
solids smaller than 200-mesh; and (3) the liquid solution containing milling
reagents and dissolved ore solids. Dry tailings from an acid leach mill are
typically composed of 20 to 37 percent slimes by weight (NRC80). Tailings are
discharged from the mill as a slurry at an average ratio, by weight, of about
1:1 (solids to liquids) and are sent to an impoundment, where the tailings
settle.
Approximately 10 percent of the uranium-238 and virtually all of the
other radionuclides in the ore are contained in the tailings. Tailings
represent the largest and longest lasting source of radon-222 emissions from
licensed conventional uranium mills because of the large exposed areas and the
significant presence of concentrated radium-226. The fraction containing the
fine slimes makes up the majority of the rad1um-226 in the tailings (up to
80 percent) (NRC80K The sand fraction contains radium-226 concentrations
from 26 to 100 pd/gram (NRC80), and the tailings liquid (raffinate) of 1.7 to
35,000 pC1/liter for radium-226 and 50 to 250,000 pd/liter for thorium-230
(EPA83).
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L-Bar Mill
The SOHIO L-Bar uranium mill is located in the northwestern part of
New Mexico, near Seboyeta in Cibola County. The mill site in an area of hilly
terrain is about 71 km (44 miles) west of Albuquerque and 16 km (10 miles)
north of Laguna, New Mexico. The general location of L-Bar is seen from
Figure 1 of the different mills in New Mexico. Ore is obtained from an
underground mine in the Jackpile sandstone formation. The mill used an
acid-leach process and began operations in 1976, but since May 1981 has been
on standby status (NRC84). The ore processing capacity of the mill is 1500 mt
(1650 tons) per day. Ore reserves are adequate to provide for 10 to 15 years
of operation. The ore grade varies from 0.05 to 0.30 percent ILOg and
averages 0.225 percent (NRC84). Size reduction of the ore is accomplished by
semi autogenous grinding.
Mill tailings are contained in a single tailings impoundment. The L-Bar
tailings dam was one of the last dams permitted in the industry in which the
upstream construction method was used (Jo80). The tailings impoundment is
built above grade with an earthen starter dam to the west that keys into
natural topography on the north and south. A smaller saddle dam is
constructed to the east. Tailings have been discharged to the Impoundment
from a single pipe that was moved along the dam. Coarse sands settled near
the dike with the slimes deposited in the interior area. Hater was decanted
and pumped back to the mill. During operations, the edge of the tailings
solution was maintained about 60 m (200 feet) from the dam crest. A light-
track pressure dozer was used to construct raises with the sand tailings. The
total site area covers 72 ha (180 acres) of which 51.8 ha (128 acres) are
tailings (NRC84). Approximately 11.3 ha (28 acres) of the tailings are
covered with tailings solution (EPA85). The impoundment consists of about
1.5 x 106 mt (1.6 x 106 tons) of tailings (,
reported to contain 500 pCi/g of radium-226 (EPA83).
During operations, ore is stockpiled at the mill on an ore pad and apron
feeder. However, since 1981 when the plant went to a standby status, no ore
has been stored in these areas except for a short supply which hui> been stored
north of the tailings area (NM85).
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SANTA FE
ALBUQUERQUE
s
UE
X
J
ROSWELL
1 Sohio
L-Bar Mill
2 United Nuclear Corp.
Churchrock Mill
3 Anaconda Minerals Co.
Bluewater Mill
4 Kerr-McGee Nuclear Corp.
Quivira Mill
5 Homestake Mining Co.
Homestake Mill
Figure 1. Map of locations of the uranium mills in New Mexico.
5
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The surrounding area is sparsely populated. The results of a 1983
population survey showed no individuals lived within a 3-km (1.9 mi) radius of
the tailings impoundment, while 42 and 129 people resided between 3 and 4-km
(1.9 and 2.5 mi) and between 4 and 5-km (2.5 and 3.1 mi) away from this
impoundment, respectively (PNL84).
Estimating Emissions
Estimates of radon-222 emissions are based on an assumed emission rate
2
that equals the specific flux of 1 pCi radon-222/m s for each pCi
radium-226/g of dry tailings times the dry area (NRC80). It has been assumed
that tailings which are either saturated with or covered by tailings solution
do not emit radon-222. These assumptions were applied to the site-specific
data to estimate emissions.
The L-Bar tailings pile consists of 51.8 ha (128 acres) of which 11.3 ha
(28 acres) are ponded, 22.3 ha (55 acres) wet, and 18.2 ha (45 acres) dry
beach. In the Background Information Document (EPA86), it was estimated that
the release of Rn-222 was between 3-4 kCi/yr.
The dam for the impoundment area of this mill site is constructed from
coarse tailings material. The total tailings surface area is 51.8 ha (128
acres) with an average activity of 500 pCi/g of Ra-226 (EPA83). It was
predicted that 11 kCi/y of Rn-222 is released from a 57 ha (140 acres)
tailings pile that contained 1.9 x 10 mt material lined with natural clay,
and an annual rainfall and evaporation of 8" and 56", respectively (EPA86).
This predicted scenario closely approximates the L-Bar site.
Study Objective
This study was made to determine the concentration of radon-222 in the
vicinity of a licensed uranium mill tailings pile. The data can be used for
exposure and risk estimates as discussed in the National Emission Standards
for Hazardous Air Pollutants (NESHAPs) for radon-222 emission from licensed
iM\iriium mill tailings.
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METHOD
The L-Bar mill site was selected as the study area because of Its small
tailings size (51.8ha) and readily measureable radium activity (500 pC1/g). A
description of the site 1s discussed earlier 1n this report.
Twenty-two Passive Environmental Radon Monitors (PERM'S) (Ge77, Ho84)
were placed 1n the area of the tailings pile of L-Bar (Figure 2). The
sampling design was a circular one with the PERM'S located at distances of
400, 600, and 800 meters away from the centroid of the pile. Five samplers
were located at the 400 meter distance at equal intervals from one another.
Seven samplers were equally spaced at the 600 meters distance and ten samplers
were placed at the 800 meters distance. Thus the samplers were placed
approximately the same arc length from one another. Each PERM was housed in a
protective structure and placed at a height of one-meter above the ground. An
additional pair of PERM'S was used for the background station which was
established 1200 meters to the north and upwind from the centroid of the
tailings. During the period of this study, two extra PERM'S were placed
adjacent to the previously established stations. These additional PERM'S were
for quality assurance (QA). The availability of PERM'S dictated the extent of
the QA program for this study.
Radon concentrations were determined monthly by analyses of a pair of
thermoluminescent dosimeters (TLD) located in each PERM. There were 500 TLD
measurements made during the period of the study from November 1985 to
November 1986. Over 300 soil and tailings samples were taken and gamma
counted primarily for radium-226 activity. The discussion of the analytical
results of the soil and tailings samples will be presented in other reports.
RESULTS AND DISCUSSION
In our discussion, radon and radon-222 are considered synonymous and the
former shall be used whenever concentration values are presented.
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A
N
©
.Site boundary
.Roads
Tailings boundary
©PERM stations
Scale: 1 inch equals approximately 340 ne-ters
Figure 2. Map :* the locations of the PERM stations at the L-Bar site.
8
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The radon concentration values (Bq m ), the distance and the azlmuthal
direction of the Individual sampling location are given In Table 1. The radon
values are for each month of the study which began on 11/15/85 and ended on
11/20/86. The distance and azlmuthal directions of each location were taken
from the centrold of the tailings pile. The annual and net annual averages of
radon values are presented 1n Table 2. At the 1200-meter distance, the annual
average radon value was 11.8 Bq m (0.32 pC1 1 ). The radon value of
3 1
30.0 Bq m (0.81 pC1 1 ) at this sample location during the period of
November 15 to December 17, 1985, 1s unusually high compared to the other
values obtained at this location during the course of the study. This data
point which is greater than 3s (standard deviation) above the average
background value is considered an outlier and is not used in our discussion of
the radon concentrations for the L-Bar site.
The data of net radon concentrations are contour plotted using the
Surface II program and are presented 1n Figures 3 to 7 for the four different
sampling quarters as well as the entire year's study. All contour plots are
in the same direction and scale as Figure 2. Generally, the data 1n all of
these figures indicated higher radon activity in the two sampling locations on
the south end of the tailings pile than at the northern locations at the
400 meter interval. It should be stated that four of the five sampling
stations at the 400 meter distance are on the edge of the tailings; and the
depth of the tailings material ranged from about 6" (15 cm) in the northern
part to about 50' (15 m) 1n the south. Thus this difference in radon values
may be related to a larger volume of tailings resulting 1n a greater emanation
of radon.
Also in these figures, the isoconcentration values of radon show an
elongation toward the northeastern portion of the tailings pile which is
usually the direction of the prevailing diurnal wind. On the other hand, the
elevated radon level in the southwestern direction 1s due to the nocturnal
drainage or gravity flow from the pile to the lower terrain surrounding the
site.
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TABLE 1. MONTHLY RADON CONCENTRATION AT L-BAR (Nov. 1985 - Nov. 1986)
(Bq m-3)
1985
1985-1986
1986
1986
1986
19»6
1986
1986
1986
1986
Location 11/15-12/17 12/17-1/16 1/16-2/19
4/23-5/23 5/23-6/24 6/24-7/25 7/25-8/26 8/26-9/25 9/25-10/26 10/26-11/20
40CTO-E
400ra-SSE
400m-SSW
400ID-NW
400m-N
600m-E
600ro-SE
OTOm-SN
600m--.?.J
600m-v.*
600n*&*r
600ro-.l~
600W-NE
800m-E
800m-SE
800m-SE
800ro-S
800m-SSW
80Cto-WSH
BOOm-W
800m-WNH
800D-W
SOOro-NNE
800m-NE
1200m-NNE
1200nH«E
27.4
40.0
55.1
30.7
36.6
20.7
19.2
26.6
22.2
15.2
25.9
12.2
24.4
10.7
17.4
23.7
20.7
30.0
14.1
23.3
27.4
30.0
14.8
41.4
44.0
49.6
65.9
54.0
36.6
66.6
28.1
57.4
35.5
2U.4
32.2
21.5
44.8
23.7
24.4
33.7
32.2
20.7
22.9
25.5
29.2
16.3
15.9
27.4
40.3
47.0
13.0
20.7
20.0
27.0
21.8
26.6
18.5
16.7
26.3
31.1
24.4
18.5
22.6
13.7
14.1
17.8
16.3
19.2
13.0
10.7
24.8
24.4
23.7
20.0
13.0
14.4
17.4
8.1
12.6
5.6
8.1
17.8
8.5
13.0
4.1
8.9
13.3
13.0
14.1
7.8
14.8
15.5
5.9
7.0
20.4
40.3
41.4
18.1
24.8
16.7
20.0
10.0
31.1
10.4
. 30.0
11.8
4.1
7.0
10.7
15.9
14.4
5.2
8.9
9.6
12.6
6.7
8.9
28.5
15.9
24.1
13.3
13.7
10.7
10.7
11.1
8.5
29.2
11.5
14.1
11.1
13.0
10.0
8.1
10.0
12.6
6.3
5.9
29.2
36.3
12.2
24.1
15.5
25.2
12.2
17.0
15.2
10.4
31.1
12.2
11.8
19.2
15.9
12.6
10.0
9.3
15.9
11.1
14.8
21.8
48.8
74.0
45.5
24.1
17.0
20.0
13.3
26.3
18.1
11.1
28.5
14.1
12.6
9.6
18.9
16.7
'
9.3
15.5
20.4
9.6
27.8
45.1
49.2
23.3
28.5
21.1
19.6
22.6
16.7
12.6
3.7
12.6
13.3
10.7
15.5
18.5
9.3
13.7
27.8
9.3
31.1
56.2
48.8
38.5
37.0
48.8
18.9
31.5
16.7
15.2
11.5
22.9
12.2
14.8
19.6
14.1
15.2
18.9
18.1
18.9
16.7
15.5
22.6
8.5
32.9
54.0
64.8
41.1
14.4
24.8
18.9
21.8
19.2
12.2
12.2
24.1
10.4
19.2
.
11.5
20.4
31.8
24.4
16.3
14.1
13.7
15.9
15.5
39.6
32.9
14.1
34.0
12.2
15.5
27.4
32.9
37.7
23.7
17.0
18.9
26.6
21.5
21.5
13.3
21.5
26.3
21.5
23.3
20.4
15.9
18.5
17.8
13.3
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TABLE 2. ANNUAL AVERAGE RADON CONCENTRATION AT L-BAR (Bq m-3)
Location
400m-E
400m-SSE
400m-SSW
400m-NW
400m-N
600m-E
600m-SE
600m-SW
600m-WSW
600m-NW
600m-NNW
600m-NE
800m-E
800m-SE
800m-S
SOOin-SSW
800m-WSW
800m-W
800m-WNW
800m-NW
800m-NNE
800m-NE
1200m-NNE
Annual
Average
29.6
42.2
.45.1
29.2
26.6
18.9
28.5
17.8
26.6
17.8
13.3
26.6
13.7
22.6
13.3
15.9
21.1
17.8
17.0
13.7
15.5
19.6
11.1
Net Annual
Average
18.5
31.1
34.0
18.1
15.5
7.8
17.4
6.7
15.5
6.7
2.2
15.5
2.6
11.5
2.2
4.8
10.0-
6.7
5.9
2.6
4.4
8.5
Bkgd
11
-------
7.40
4.00
3.20^
11.00
N
1.40
Cf
Scale: 1 inch equals approximately 340 meters
Figure 3. Average net radon concentrations and isoconcentration contours
for the first quarter. (Numbers expressed in Bq m~3)
12
-------
4.70
1.50
6.80
2.20
2.50
8.00
5.70
N
3.80
7.30
10.20
1.40
3.40
Scale: 1 inch equals approximately 340 meters
Figure 4. Average net radon concentrations and isoconcentration contours
for the second quarter. (Numbers expressed in Bq m-3)
13
-------
1.10
0.40
0.00
6.00
3.40
A
N
1.80
7.10
3.70
6.20
1.10
Scale: 1 inch equals approximately 340 meters
Figure 5. Average net radon concentrations and isoconcentration contours
for the third quarter. (Numbers expressed in Bq m-3)
14
-------
1.80
3.90
1.30
A
N
5.80
6.30
11.30
0.00
1.50
6.10
0.00
Scale: 1 inch equals approximately 340 meters
Figure 6. Average net radon concentrations and isoconcentration contours
for the fourth quarter. (Numbers expressed in Bq m-3)
15
-------
4.00
2.40
A
N
1.40
8.60
-w .17.70
0 ' 7.60
2.20
6.50
9.10
1.90
Scale: 1 inch equals approximately 340 meters
Figure 7. Average net radon concentrations and isoconcentration contours
for the entire study (11/15/85 to 11/20/86). (Numbers expressed
in Bq m-3)
16
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In Figure 7, entire year's study, the radon concentrations decreased with
distance from the centrold of the uranium tailings pile. There Is a decrease
In radon activity by about a factor of 2 between the 400 and 600 meter
Interval, about a factor of 4 between the 400 and 800 meter distance, and
about a factor of 2 between the 600 and 800 meter Intervals. During the year
the average radon concentrations at the different sampling distances ranged
betweeen 14.9 Bq m"3 (0.40 pC1 I'1) and 35.6 Bq m"3 (0.96 pCI I'1) at
the 400 m Interval, between 6.20 Bq m"3 (0.17 pC1 I'1) to 18.8 Bq m~3
(0.51 pC1 I"1) for 600 m, and between 1.80 Bq m~3 (0.05 pC1 I"1) and
9.80 Bq m~3 (0.26 pC1 I"1) at 800 meters (Figure 7).
In Figure 8, the average radon concentrations at 400, 600, 800, and
1200 meters are graphically presented for each month of the study, beginning
November 15, 1985 and ending November 20, 1986. The data show the highest
radon activity occurred 1n the first sampling quarter, followed by the third
and fourth quarters which had similar patterns of activity, and the lowest
activity In the second quarter. Also, there 1s a definite decrease of radon
concentration with Increasing distance from the centrold of the tailings pile.
Earlier In our discussion, we stated that most of the PERM stations at
the 400 meter distance were established on the edge of the mill tailings pile,
whereas those at 600 and 800 meters were not near the edge. In fact, several
were located as far away as the perimeter of the site boundary. The net
o
annual radon concentrations as seen in Figure 8 were less than 18.5 Bq m
(0.5 pC1 I"1) at the 600 and 800 meter Intervals.
17
-------
59.2
55.5
51.8
48.1
44.4
40.7
37.0
33.3
Rn-222
Bq/m3
00
25.9
22^
18.5
14.8
11.1
7.4
3.7
0
400m
600m
800m
1200m
_L
_L
JL
_L
_L
11/15-
12/17
1985
1/16-
2/19
1986
3/20-
4/23
1986
1st Quarter
2nd Quarter
5AJ3- 7/25-
6/24 8/26
1986 1986
3rd Quarter
9/25-
10/26
1986
4th Quarter
A
Figure 8. Gross monthly average radon concentrations at sampling locations at
400m, 600m, 800m, and 1200 meter distances.
Annual Net
Annual
Average
11/15/85 to
11/20/86
the
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20
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