United States
Environmental Protection
Agency
Office of Radiation Programs
Las Vegas Facility
P.O. Box 1 5027
Las Vegas NV89114
Technical Note
ORP/LVF-81-2
April 1981
Radiation
&EPA
Airborne Radiological
Sampling Of
Mount St. Helens Plumes
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Technical Note
ORP/LVF-81-2
AIRBORNE RADIOLOGICAL SAMPLING
OF MOUNT ST. HELENS PLUMES
Vernon E. Andrews
April 1981
Office of Radiation Programs - Las Vegas Facility
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
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DISCLAIMER
This report has been reviewed by the Office of Radiation Programs - Las
Vegas Facility, U.S. Environmental Protection Agency, and approved for publi-
cation. Mention of trade names or commercial products constitutes neither
endorsement nor recommendation for their use.
11
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PREFACE
The Office of Radiation Programs (ORP) of the U.S. Environmental
Protection Agency (EPA) conducts a national program for evaluating exposure of
humans to ionizing and nonionizing radiation. The goal of this program is to
promote the development of controls necessary to ensure the public health and
safety.
The eruption of the Mount St. Helens volcano constituted an unusual source
of airborne radiation. In order to assess the potential radiation exposure
to the public the EPA performed aerial sampling of the materials released.
Although time, distance, and available funds limited the scope of this
investigation, the results indicate that radioactivity associated with the
eruption was not a threat to public health.
ORP encourages readers of the report to inform the Director, ORP, of any
omissions or errors. Comments or requests for further information are also
invited.
Donald W. Hendricks
Director, Office of Radiation Programs
Las Vegas Facility
iii
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INTRODUCTION
On March 27, 1980 Washington State's Mount St. Helens returned to life
from a 123-year dormancy. New life began as a strong gaseous venting which
carried aloft a large amount of tephra eroded from older deposits in the
mountain. This was followed by frequent eruptions of steam or steam and
tephra interspersed with periods of quiet.
Evidence from other volcanoes has shown that eruptions may release greater
concentrations of naturally occurring radionuclides than those usually found
in the atmosphere. The State of Washington, concerned about possible
radiation exposures to its residents, requested that the Environmental
Protection Agency (EPA) determine the radiological hazard associated with the
eruption. The Office of Radiation Programs-Las Vegas Facility (ORP) was asked
to respond to the request.
An EPA-owned airplane which had been acquired and modified through
Department of Energy (DOE) funding for cloud tracking and sampling in support
of DOE's nuclear testing program was available at the EPA's Environmental
Monitoring Systems Laboratory (EMSL) in Las Vegas. The EMSL made the airplane
available to ORP, and DOE provided the airplane operating funds. The airplane
departed Las Vegas on the morning of April 4, flew a 2-hour sampling mission
during the afternoon, and returned to Las Vegas that evening.
A second mission was requested of EPA following the explosive eruption of
May 18. The aircraft and crew departed Las Vegas at mid-morning on May 19 and
flew a 2-hour sampling mission late that afternoon. The crew flew a final
sampling mission on the morning of May 20.
This report describes the equipment and procedures used to collect and
analyze the samples, and discusses the results in terms of potential effect on
people.
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EQUIPMENT DESCRIPTION
The aircraft used for the Mount St. Helens missions is a twin-turbo-prop
Beechcraft BEST. EPA had converted it to the BEST configuration from a
military C-45 and specially modified it for aerial tracking and sampling. EPA
had equipped the aircraft to collect a variety of gaseous and particulate
samples. Sampling personnel used a remote console in the aircraft cabin to
operate and monitor external, wing-mounted pods.
A pod on one wing collects compressed air samples. The pod contains three
stainless steel bottles, each with a 0.034-m3 volume connected to a distri-
bution manifold. The compressor stage of one of the aircrafts turbine engines
fills the bottles, and limiting orifices control the flow rate. Sampling
rates of 0.0075, 0.0145, and 0.022 cubic meters per minute (m^/min) are
selectable at the console.
A pod on the other wing collects particulate samples using a filter
sampler and an electrostatic precipitator sampler. The filter sampler
simultaneously collects four samples on 10-cm diameter filters. Only one set
of filter samples can be collected per flight. A venturi mass flow meter
measures air flow. Sampling rates for the pod filter sampler are approxi-
mately 0.6 m3/min using Microsorban polystyrene fiber filters and 0.8
m3/miri using glass fiber filters. The electrostatic precipitator sampling
system consists of two tubes. Each tube, 3 feet long by 3 inches in
diameter, has a wire mounted along the tube axis. The wire is electrically
insulated from the tube wall and is maintained at approximately 18 kv negative
with respect to the tube wall. A venturi mass flow meter again measures air
flow. The electrostatic precipitator sampler operates at about 1.3 m3/min
through each tube.
Because the sampling pods are inaccessible during flight, additional
samplers were used in the aircraft cabin to collect several samples during a
mission. Air entering the sample probe at the aircraft nose passed through a
plenum in the cabin. An air sampler using a 7- by 10-inch filter collected
samples from the plenum. Crew members used a second nose probe discharging
into the cabin to collect short term grab samples of air in 30-liter Tedlar
2
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bags. The cabin filter sampler has a flow rate of about 2.5 m^/min with
glass fiber filters and 2.0 m3/min with Microsorban filters.
MISSION DESCRIPTIONS
April 4, 1980
The sampling team reached Mount St. Helens at 1:30 p.m., about 90 minutes
after an earthquake of magnitude 4.5 had occurred. An eruption of gas and
dust lasting for about 45 minutes followed the earthquake. As the team
approached from the west they saw a light brown dust plume extending several
miles to the northwest from near the Goat Rocks region on the northwest slope.
The plume top was at about 3050 meters (10,000 feet) above mean sea level
(MSL). The maximum visible dust density in the plume was at about 2130 meters
(7,000 feet) above MSL. A small cloud of water vapor was observed near the
summit on the east side, but the dust plume was the major visible evidence of
an eruption.
An east-west sampling pattern was flown across the dust plume at the
altitudes and locations shown in Table 1. At each altitude the team collected
cabin filter and bag samples, while the wing pod particulate samplers operated
during the entire mission.
May 19. 1980
The EPA aircraft arrived in Portland, Oregon in the early afternoon of
May 19 and flew a sampling mission from 1500 to 1700 hours.
During the sampling mission the ash plume was observed to be rising to
approximately 3050 m above MSL at the east (downwind) lip of the crater. As
the ash plume moved easterly, the visible top rose slowly. The plume top rise
was estimated to be less than 300 m within the first 50 km from the volcano.
The plume centerline was visually estimated to be at about 2750 m above MSL.
The south edge of the visible plume was fairly well defined along an east-west
line from the crater across the north slope of Mount Adams. Mount Adams lies
approximately 55 km due east of Mount St. Helens. Considerable resuspended
ash from the area north of the volcano and low clouds to the north, combined
with the more diffuse release issuing from the blown-out north face of Mount
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St. Helens, made it difficult to estimate the northern boundary of the ash
plume.
Samples were collected along the south edge of the plume from about 8 to
55 km east of Mount St. Helens. The plume was penetrated at a shallow angle
near the volcano with the east end of a sampling run being 3 to 5 km inside
the plume. Some passes were also made at altitudes as low as 1750 m in the
region south and west of Mount Adams through low-lying clouds of ash drifting
over the area. The sandblasted paint and windshield of a plane which had
flown under the plume earlier in the day persuaded the team to avoid the more
dense portions of the plume.
TABLE 1. APRIL 4 SAMPLING SUMMARY
Time Interval Altitude Number Distance From
(PST) (ft. MSL) of Passes Goat Rocks
1316-1321 7,000 50-80 km south
1323-1328 7,000 15-40 km south
1336-1343 10,000 3 3 km north
1347-1353 9,000 3 3 km north
1357-1420 8,000-7,000 6 3 km north
1423-1445 7,000 7 3 km north
1450-1515 7,000 7 1.5 km north
1316-1515 Alie 26 1.5-3 km north
1316-1515 Alie 26 1.5-3 km north
1520 6,000 15 km south
a. GF = 7- by 10-inch glass fiber filter
b. MS = 7- by 10-inch Microsorban polystyrene fiber filter
c. Set of four 10-cm filters
d. Electrostatic precipitator
Samples Coll
Filter
GF*
MS&
MS
GF
MS
GF
MS
Podc
Precip.d
e. Collected on all sampling passes at 10,000, 9,000, 8,000, and 7,000
f. Ambient samples collected south of Mount St. Helens.
ected
Bag
2
2
2
3
2
2
1
ft.
The wing pod particulate samplers were operated continuously from 1500 to
1700 hours. One cabin filter sample was collected from 1503 to 1555 and
second one was collected from 1600 to 1700 hours. Two of the compressed air
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bottles in the wing pod were filled simultaneously by periodic collections
while inside the plume between 1510 and 1630 hours. Table 2 shows the
collection data for the grab bag samples collected.
TABLE 2. MAY 19 GRAB BAG SAMPLE COLLECTION DATA
Time Location Altitude (m.MSL)
1547-1548 8 km west of Mount Adams 2770
1549-1550 8 km north of Mount Adams 2770
1614-1615 8 km south of Mount Adams 2130
1624-1625 16 km east of Mount St. Helens 1750
1630-1632 9-16 km west of Mount Adams 2130
1638-1640 15-20 km west of Mount Adams 2280
May 20. 1980
By the morning of May 20 the weather had deteriorated with most of the
area under clouds. When the team arrived at the volcano at 0920 hours, a
cloud layer 300 to 400 m thick lay over Mount St. Helens, with the base
slightly below the crater lip. A dense white plume rose through the cloud
layer, topping out at about 300 m above the cloud. As the plume cooled and
the steam dissipated - within 1 km of the downwind crater lip - a tan-colored
ash plume remained. This ash plume descended, then leveled off with the top
at about 2700 m above MSL. Whereas on the 19th the southern plume edge was
about due east from the volcano, passing over the north flank of Mount Adams,
now it passed 15 to 20 km north of Mount Adams. The plume centerline had
shifted from east-northeast to northeast.
Decreased ash density allowed a safe flight through the plume. A series
of passes were made diagonally across the plume on a path southwest to north-
east, between points on the southern edge of the plume about 5 km east of the
east lip of the crater and about 30 km north-east on the north edge. On the
final pass to the southwest the flight path was altered to fly inbound along
the plume centerline to within about 8 km of Mount St. Helens, then counter-
clockwise around the crater on that radius until exiting the ash cloud north
of the mountain. All passes were flown at 2440 to 2650 m above MSL.
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The pod filter sampler was operated continuously during the entire sam-
pling flight from 0933 to 1026 hours. One cabin air filter sample was
collected from 0936 to 0950 and a second was collected from 0951 to 1026. A
compressed air sample was collected intermittently in the bottle remaining in
the wing pod from 0933 to 1053. Four grab bag air samples were collected from
near the plume center, 15 to 20 km from Mount St. Helens, 2440, 2540, 2560,
and 2650 m above MSL.
ANALYSIS OF SAMPLES
The samples were divided among three laboratories for a variety of
analyses. Some of the grab bag and compressed air samples were sent to the
Washington State University Air Resources Laboratory for use in their program
of measuring naturally occurring halocarbons. Some of the particulate filter
samples and one electrostatic precipitator sample were sent to Los Alamos
Scientific Laboratory for particulate sulfate analysis. The remainder of the
samples were analyzed for naturally occurring radioactivity and elemental
abundance at the EPA laboratory in Las Vegas. This report contains the
results of the EPA analyses.
The radioactivity reported for each sample is the net radioactivity plus or
minus twice the standard deviation (2s). The net radioactivity is the gross
sample radioactivity minus counter background, and for filter samples, minus
an average value for the radioactivity content of a blank filter. The stand-
ard deviation is based only on the random variations inherent in radioactivity
counting and is propagated through the various steps to the net result.
Due to the low levels of radioactivity encountered, an occasional sample
is reported with a net negative result. Of course, there is no negative
radioactivity. In these cases, as with all others, the net result must be
considered along with the 2s uncertainty.
April 4. 1980. Samples
Radon in the grab bag samples was removed from the rest of the air using a
combination cryogenic and gas chromatographic technique. The radon plus
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carrier gas was collected in a gas scintillation cell and counted for alpha
activity after allowing several hours for ingrowth of radon progeny. All
radon-222 concentrations were below the lower limits of detection (LLD) of 30
to 40 picocuries per cubic meter (pCi/m3).
The LLD is defined (Harley) as the smallest concentration of radioactive
material sampled that has a 95 percent probability of being validly detected.
.._. 4.66 Sh ,
LLD = 2.22 x E x S ' Where;
4.66 = 2 VTk, where k is the value for the upper percentile
of the standardized normal variate corresponding to the
preselected risk for concluding falsely that activity is
present (a) = 0.05
Sb = standard deviation of the background
2.22 = disintegrations per minute/pCi
E = fractional counting efficiency
S = sample size
Two cabin filter samples and two of the four filters from the pod sampler
were analyzed for radioactive particulates. One cabin sample was collected
on three passes across the dust plume at 2440 m (8,000 feet) MSL and three
passes at 2130 m (7,000 feet) above MSL. The other sample was collected on
seven passes across the plume at 2130 m above MSL. The filters were dissolved
for radiochemical separation and analysis for the elements of interest.
Neither cabin filter sample contained naturally occurring radionuclides
significantly greater than the quantities measured in blank filters. The two
filters from the pod sampler were analyzed independently and the results for
each radionuclide were summed. The calculated concentrations, assuming that
all of the net radioactivity was collected while actually in the plume, are
presented in Table 3.
May 19 - 20. 1980 Samples
Whole air samples from the grab bags and one compressed air bottle from
May 19 were transferred directly into the gas scintillation cells without
concentrating the radon. Table 4 shows the measured concentrations at ambient
conditions of samples collected on both days. Only one sample, collected at
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0944 hours on May 20, had a measured concentration greater than twice the
standard deviation.
TABLE 3. POD FILTER SAMPLE RADIOACTIVITY CONCENTRATIONS APRIL 4, 1980
Radionuclide Concentration (pCi/m3)*
Uranium-234 0.008 ± 0.004
Uranium-238 0.008 ± 0.005
Thorium-230 0.076 ± 0.014
Thorium-232 0.008 ± 0.005
Radium-226 0.059 ± 0.017
Polonium-210 0.008 ± 0.021
* Concentration plus or minus two standard deviations based on counting
statistics only.
The samples collected each day were collected under similar conditions.
Therefore, the average concentration was calculated for each day. The
associated uncertainty is twice the standard error of the mean. An average
concentration of 290 ± 260 pCi/m3 was calculated for May 19. The average
concentration calculated for May 20 was 390 ± 250 pCi/m3.
TABLE 4. RADON-222 CONCENTRATIONS MAY 19 AND 20, 1980
Date & Time
5/19 1547
5/19 1549
5/19 1614
5/19 1624
5/19 1638
5/19 1510-
1630
5/19
5/20 0941
5/20 0944
5/20 0952
5/20 0955
5/20
* Concentration
activity count
Altitude
(m.MSL)
2770
2770
2130,
1750
2290
1750-
2770
2650
2530
2440
2560
plus or minus
or twice the
Location
8 km west of Mount Adams
8 km north of Mount Adams
8 km south of Mount Adams
15 km east of Mount St. Helens
15 km west of Mount Adams
Compressed air; integrated
throughout mission
Average of all samples
30 km NE of Mount St. Helens
15 km NE of Mount St. Helens
15 km NE of Mount St. Helens
15 km NE of Mount St. Helens
Average of all samples
Concentration
(pCi/m3)*
130 ± 530
330 ± 570
500 ± 710
-300 ± 600
620 ± 720
470 ± 650
290 ± 260
410 ± 450
600 ± 510
300 ± 520
240 ± 530
390 ± 250
twice the standard deviation based on radio-
standard error of the mean for averages.
8
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One pod filter sample from each day was analyzed as before for natural
radioactivity. The observed concentrations of radioactivity at ambient
conditions are shown in Table 5. On the whole they did not differ signifi-
cantly between nuclides or between filters for the same nuclide. The one
exception was polonium-210 on the sample collected May 20. The concentration
of 0.039 + 0.019 pCi/m3 is 13 times the mean surface air concentration of
0.003 pCi/m3 (NCRP).
TABLE 5. POD FILTER SAMPLE RADIOACTIVITY CONCENTRATIONS
MAY 19 AND 20, 1980
Concentration (pCi/m3)
Radionuclide May 19 May 20
Uranium-234 0.012 + 0.006 -0.001 + 0.008
Uranium-238 0.009 +. 0.008 -0.003 + 0-006
Thorium-230 0.000+0.003 0.004+0.007
Thorium-232 0.000 + 0.003 -0.001 + 0.005
Polonium-210 0.008 +. 0.010 0.039 ± 0.019
Uranium decay chain average 0.007 +_ 0.005 0.000* +_ 0.003
(average +_ standard error of mean)
* Excluding Polonium-210. Thorium-232 is not a member of the uranium chain.
For comparison, Table 6 shows the concentrations of radioactivity in ash
fallout samples collected by the State of Washington Environmental Radiation
Program and a private citizen. It can be seen that the ash collected on
April 4 exhibited no significant difference between polonium-210 and the other
members of the uranium decay chain. All of the samples collected following
the May 18 and May 25 eruptions were similar to each other, with polonium-210
concentrations about twice the average of the other uranium chain members.
Particulates collected on the electrostatic precipitator May 20 were removed
by washing with deionized water. The particles in the wash water were sent to
LFE Environmental Analysis Laboratories in Richmond, California, for particle
size analysis. LFE resuspended the particles using ultrasonic agitation for
10 minutes. An aliquot was optically sized using a Leitz phase contrast
microscope at 500X magnification. The results are shown in Table 7. The
volume distribution best fits a normal distribution with a mean diameter of
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23.5 micrometers (ym) and standard deviation of 8.5 urn. The number distribu-
tion appears bimodal with 85.6 percent of the particles represented by a log-
normal distribution having a geometric median diameter of 0.65 \im and
geometric standard deviation of 1.54. The other 14.4 percent of the particles
have a geometric median diameter of 3.6 ym a geometric standard deviation of
2.92.
TABLE 6. RADIOACTIVITY CONCENTRATIONS IN ASH FALLOUT
Uranium- Uranium- Thorium- Polonium-
Date Location 238 234 230 210
April 4 North side 0.50+0.21 0.30+0.07 0.36+0.08 <0.36
Mount St. Helens
May 18 Morton, WA 0.39 + 0.11 0.38 + 0.11 0.33 + 0.08 1.0 +'0.2
May 18 Wenatchee, WA 0.47+0.14 0.42+0.13 0.41+0.09 0.78+0.19
May 19 Royal City, WA 0.51 + 0.12 0.43 + 0.12 0.41 + 0.09 0.62 + 0.31
May 19 Boise, ID 0.39 + 0.11 0.54 + 0.13 0.49 +_ 0.12 0.95 + 0.19
May 25 Centralia, WA 0.44 ± 0.11 0.40+0.11 0.44+0.09 1.2 +0.3
10
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TABLE 7. AIRBORNE PARTICLE SIZE ANALYSIS MAY 20, 1980
Size
u
0.3
0.6
0.9
1.2
1.8
2.5
3.5
5.0
7.0
10.0
14.0
20.0
28.2
Range
m
- 0.6
- 0.9
- 1.2
- 1.8
- 2.5
- 3.5
- 5.0
- 7.0
- 10.0
- 14.0
- 20.0
- 28.2
- 39.8
Number of
Particles
669
504
249
116
83
45
28
28
24
23
14
10
3
Numerical
Percent
37.25
28.06
13.86
6.46
4.62
2.51
1.56
1.56
1.34
1.28
0.78 .
0.56
0.17
Cumulative
Numerical %
37.25
65.31
79.18
85.63
90.26
92.76
94.32
95.88
97.22
98.50
99.28
99.83
100.00
Volume
Percent
0.016
0.054
0.073
0.100
0.21
0.31
0.55
1.54
3.76
10.13
17.53
35.68
30.05
Cumulative
Volume %
0.016
0.070
0.143
0.243
0.453
0.763
1.31
2.85
6.61
16.74
34.27
69.95
100.003
Total
1796
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DISCUSSION AND CONCLUSIONS
The aerial samples collected from the dust plume following the small
eruption on April 4 contained low levels of naturally occurring radionuclides.
The isotopic ratios indicate that composition of the airborne dust was similar
to that of crustal rock. The airborne radioactivity was comparable to what
might be found under any severely dusty condition, such as a dust storm. No
evidence was found of enrichment of gaseous or volatile radionuclides -
particularly including radon-222 and polonium-210.
Heavy ash concentrations on May 19 prohibited sampling deep within the
plume. The particulate samples collected along the plume fringes yielded
results similar to those collected on April 4. Radon-222 results may indicate
some elevation above ambient, however, measured concentrations had such large
standard deviations and were so variable that no definite increase can be
inferred.
A less dense plume on May 20 permitted collection of aerial samples while
traversing the plume. The only significant particulate radioactivity measured
was polonium-210. Polonium is the most volatile of the elements, other than
radon, in the uranium series. Polonium-210 is commonly found to be enriched
in particulate emissions from mineral smelting and calcining operations that
have temperatures comparable to that of magma. Because polonium-210 is
released as a vapor and condenses to a particulate, it is usually associated
with the smaller particle sizes (EPA). This association could explain the
difference observed between the polonium-to-uranium chain ratios of the aerial
sample and ash fallout. Possibly, the polonium-210, associated with smaller
particles, remained airborne as the coarse particles fell to earth.
J. S. Fruchter et al. at Battelle's Pacific Northwest Laboratory reported
increasing polonium-210 concentration with decreasing particle size on ash
collected at Moses Lake. They found 41 percent of the polonium-210 was
associated with particles less than 3.5 pro diameter - or with less than one
percent by volume of the particles. The Battelle data also showed that the
polonium-210 concentration in particles greater than 3.5 ym was the same as
12
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what might be expected in normal rock. It follows that almost all of the
excess polonium-210 in the aerial samples at Mount St. Helens was also
associated with the small particles. Therefore, although most of the airborne
particulate mass was too large to be inhaled, most of the polonium-210 was
respirable.
Radon-222 was significantly above the system detection limit in one sample
collected on May 20. That sample was collected at 2530 m above MSL, approxi-
mately even with the crater lip. The average of the four samples from the
20th analyzed for radon-222 is believed to be a reasonable estimate of the
plume concentration at 15 km from Mount St. Helens. This average of 390
pCi/m3 is about 4 times the- average radon-222 concentration of 100 pCi/m3
in the northern hemisphere at ground level (NCRP). The radon-222 levels
measured during the continuous release following the May 18 explosion were too
low to be considered a hazard. They would, however, have raised the airborne
concentrations of radon and its decay products at ground level in the plume.
The short-term exposure of the affected population to the plume from Mount
St. Helens would have resulted in a small increase above the annual radiation
dose due to naturally occurring radioactivity. For most of the radioactive
elements present the additional dose was comparable to that received by being
in a dust storm for several days. In the case of polonium-210 and the radio-
active decay products of radon-222, both of which were released in greater
quantity than the other radionuclides, the radiation doses were probably less
than the dose which would have been received during a month or two of exposure
to those radionuclides under normal background conditions.
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REFERENCES
Fruchter, J.S., et al. Mount St. Helens ash from the May 18, 1980 eruption:
chemical, physical, mineralogical, and biological properties. Science, Vol.
209, pp 1116-1125, Sept. 5, 1980.
Harley, J.H., Editor, HASL Procedures Manual, HASL-300, Health and Safety
Laboratory, U.S. Energy Research and Development Administration, New York,
1972 (with revisions).
National Council on Radiation Protection and Measurements. Environmental
Radiation Measurements. NCRP Report No. 50, 1976. Washington, D.C.
U.S. Environmental Protection Agency, Office of Radiation Programs, Las Vegas,
Nevada. Unpublished data.
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TECHNICAL REPORT DATA
(Pteau read Instructions on the reverse before completing)
1. REPORT NO.
ORP-LVF-81-2
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Airborne Radiological Sampling of Mount St. Helens
Plumes
8. REPORT DATE
April 1981
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Vernon E. Andrews
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME ANO ADDRESS
U.S. Environmental Protection Agency
Office of Radiation Programs-Las Vegas Facility
P.O. Box 18416
Las Vegas, Nevada 89114
10. PROGRAM ELEMENT NO.
11. CONTHACTTGRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT ANO PERIOD COVERED
SAME AS ABOVE
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Particulate and gaseous samples for radiologial analyses were collected
from the plumes created by eruptions of Mount St. Helens. The sampling
aircraft and equipment used are routinely employed in aerial radiological
surveillance at the Nevada Test Site by the Environmental Protection Agency's
Environmental Monitoring Systems Laboratory in Las Vegas, Nevada. An initial
sample set was collected on April 4, 1980, during the period of recurring
minor eruptions. Samples were collected again on May 19 and 20 following the
major eruption of May 18. The Environmental Protection Agency's Office of
Radiation Programs analyzed the samples for uranium and thorium isotopes,
radium-226, lead-210, polonium-210, and radon-222. Other laboratories
analyzed samples to determine particle size distribution and elemental
composition. The only samples containing radioactivity above normal ambient
levels were collected on May 20. Polonium-210 concentrations in the plume,
determined from a sample collected between 5 and 30 km from the crater, were
approximately an order of magnitude above background. Radon-222 concentra-
tions in samples collected from the plume centerline at a distance of 15 km
averaged approximately four times the average surface concentrations. The
small increases in radioactivity would cause no observable adverse health
17.
KEY WORDS ANO DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Natural radioactivity
Volcanic ejecta
Air pollution
0807
1808
1302
18. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
18
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (R*«. 4-77) PREVIOUS EDITION is OBSOLETE
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