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.
                                       13

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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.
                                      14

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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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