This document describes a scenario to test models of the transport of radioactive contaminants from soil to surface water. It focuses on the wash-off of Cesium-137 and Strontium-90 from two experimental plots near Chernobyl following rainfall. One plot was subjected to heavy rain, the other to snowmelt. The scenario provides data on the initial radionuclide deposition, soil characteristics, and time-varying precipitation. It requests predictions of the vertical distribution of radionuclide forms in the soil, radionuclide concentrations in runoff water, and total radionuclide amounts removed from the soil by runoff. Measured data are available for model validation.

1. A.V.Konoplev,*A.A.Bulg水ov,*V.
Yu.V.Shvell(in,十
Abstract-The "Wash-ofP' scenario is designed to test models
concerned with the movement of trace contaminants from
terrestrial sources to bodies of water, specifically the contam.
ination of surface water by wash-off of radionuclides initially
deposited onto soils. Particular emphasis is placed on chemical
speciation and on the geochemical and geophysical processes
affecting transfer of contaminants from soil to water. The
scenario gives descriptions of two experimental plots near the
Chernobyl power plant, one using heavy rain and one using
snow melt, together with characteristics of the initial aerial
deposition of the radionuclides and data on topography, soil
type and characteristics, and time-varying precipitation. Pre-
dictions are requested for (1) the vertical distribution of
concentrations of exchangeable and nonexchangeable forms of
137Cs and eosr in the soil of the experimental plots, (2)
concentrations of 137Cs
and eosr in runoff water from the
experimental plots, and (3) total amounts of 137Cs
and eosr
removed by runoff from the experimental plots. Test data
(field measurements) are available for all endpoints.
Health Phys. 70(1):8-12; 1996
Key words: Chernobyl; environmental transport; contamina-
tion, environmental; 137Cs
INTRODUCTION
Ttre "WASg-oFF' scenario is the first of a set of three
model-testing scenarios developed by the Post Chernobyl
Data Working Group of 'BIOMOVS II (Biospheric
Model Validation Study, Phase II). Information on par-
ticipating in the test exercises or obtaining the test data
for individual test scenarios is provided in an accompa-
nying article (Hoffman et al. 1996).
This scenario offers an excellent opportunity to test
models concerned with the movement of trace contami-
ン 増錨ンDive,Oak Ridge,TN 37830
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Copyright ⑥ 1996 Hcalth Physics SOciety
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al exeikonoplev @ gma il,com
EXPERIMENTAL
E. Popov,x O. F. Popov,T A. V. Scherbak,t
and F. O. Hoffman+
nants from terrestrial sources to water bodies. The
particular objective is to take account of chemical spe-
ciation, its effects on the transfer of contamination from
soil to water, and the geochemical and geophysical
processes that affect such transfer. Although the present
scenario deals with the contamination of water subse-
quent to aerial deposition of radionuclides following the
Chernobyl accident, the processes underlying the sce-
nario may be adapted to many sources of contanrination
of surface and ground water.
Surface water runoff from contaminated land is one
of the main processes responsible for the contamination
of water bodies. Therefore it is very important to have a
reliable model for prediction of the contamination of
surface water by natural runoff. The large area of land
contaminated by the Chernobyl accident has become a
continuing source of radionuclides entering natural wa-
ters and the aquatic ecosystem. This has provided a
unique opportunity to develop a data base suitable for
testing the predictive capability of mathematical models
to assess radionuclide wash-off into rivers and lakes from
soils contaminated by the deposition of fuel particles.
Overall, the scenario will provide the following
oppoftunities: (1) to evaluate the movement of contami-
nants from soil to water; (2) to calculate the attenuation
and migration of contaminants in soil over different time
scales; and (3) to increase understanding of contaminant
transport at the process level.
The scenario examines the wash-off of eosr and
tttcs from two experimental plots established in the
vicinity of the Chernobyl reactor. Later phases of the
scenario development will extend the calculations to
account for wash-off on larger spatial scales, including
the flood plain of the Pripyat River, which provides input
to the Kiev reservoir, and then the whole Dnieper River
basin, starting with the watershed processes and includ-
ing consequent transpolt processes in the rirrer itself.
A distinguishing feature of radioactive contamina-
tion due to a nuclear accident is the chemical speciation
of the radionuclides present in atmospheric fallout and
deposited on the soil. When the Chernobyl accident
occurred, nuclear fuel debris (UO2 + UO.), including
8
Paper一
酌IODEL TESTING USING C]
I.WASH‐OFF OF9°Sr AND 137cs FRO酌質TWO
PLOTS ESTABLISHED IN THE VICINITY OF
THE CHERNOBYL REACTOR

2. Wash― off of 9° Sr and 137cs● A V ItoNOPLEV ET AL
fission products, was released into the environment.
Some of the radionuclides were also deposited onto the
ground as aerosol particles that had been formed in the
atmosphere due to condensation. These parlicles varied
in size, chemical composition, and behavior in the
environment.
Fuel particles have a radionuclide composition sim-
ilar to that of inadiated fuel, but with varying proportions
of highly mobile and volatile decay products. The fuel
particles are of very low solubility in water and hence do
not participate in exchange processes between soil and
soil-water solutions or in plant contamination via root
uptake from soil. However, as the fuel particles slowly
degrade, mobile fission products may be released. The
degradation rate of the particles is dependent on the size
and chemical composition of the particles; these are a
function of the distance from the Chernobyl Nuclear
Power Plant (NPP). The time scale of the particle
degradation varies from 1 to 10 y for different points in
the 30-km zone around the nuclear power plant (Kono-
plev and Bulgakov 1992; Konoplev et al. 1993),
In terms of predicting the migration of 137Cs
and
'"Sr in soil-water systems, it is reasonable to identify the
following chemical forms: (1) dissolved cations (Az); Q)
exchangeable forms (Ar.), including radionuclides ab-
sorbed onto soil or bottom sediments by ion-exchange
mechanisms; and (3) non-exchangeable forms, including
radionuclides of nuclear fuel particles (Ar) and fixed
radionuclides on mineral or organic components of soil
or bottom sediments (A.). Over the course of time,
Fig. 1. Schematic representation of the transformation processes of
radionuclide chemical species. The chemical forms are represented
as follows: Ar, radionuclides of nuclear fuel particles (non-
exchangeable); Ar, dissolved cations; Ar., exchangeable forms,
including radionuclides absorbed onto soil or bottom sediments by
ion exchange mechanisms; and A., non-exchangeable radionu-
clides fixed on mineral or organic components of soil or bottom
sediments. K is the constant for the ion-exchange equilibrium, and
is the rate constant for the process at issue (ij). The chemical
forms may be considered in units of either mass or activity. The
units of the ion-exchange equilibrium constant K will depend on
the choice of concentration units for A, and Ar". Radioactive
decay has been omitted from the diagram because the time scale of
the wash-off process being studied here is considerably smaller
than the halfJives for the radionuclides in question.
Table 1. Soil characteristics of the experimental plots.
Characteristic PIot HR Plot SM
General description
Effective water-holding capacity of
the 0-10 cm layer of sotl, Vo
Hydraulic conductivity' (velocity
of downward percolation of
water in the soil profile), mm
mtn -
Cation exchange capacity (CEC) of
the upper 1 cm of soil, meq g-r
dry weight
Alluvial acid sod Cultlvatcd sod
podzollc soll
45± 6 30± 3
034± 007 031 ± 003
015± 002 007± 001
'Hydraulic conductivity was calculated as the difference between rainfall
intensity (mm min 1) and runoff intensity (mm min-r) during special
experiments using artificial rain on I-m2 plots.
radionuclide chemical species undergo transformation
processes (Fig. 1). The rate of migration processes is
sensitive to the chemical speciation of the radionuclides
in soil and other environmental media. A fraction A,
moves into the dissolved state with retardation occurring
through ion-exchange interaction with the solid phase.
The solid-phase species .A.1, A2", and A. move only with
the particles in which they are incorporated.
EXPERIMENTAL DETAILS
Two experimental plots were constructed in areas
contaminated by dry deposition resulting from the Cher-
nobyl accident. Deposition (>957o) occurred between 26
April and 10 May 1986. The contamination of the plots
was determined by taking randomly selected soil sam-
ples; each sample was 180 cm' in arca and 10 cm in
depth. Runoff samples were collected in plastic bottles
and filtered with a 0.45 p,m filter. The "'Cs content in
soil samples, filters, and water samples was determined
through gamma spectrometry without preconcentrations
using a Canberras gamma counter with a semiconductor
detector (Makhonkb et al. 1985). The eosr content was
determined with a radiochemical analysis that used
carbonates of precipitation (Sereda and Shulepko 1966).
Al1 samples were processed at the Institute of Experi-
mental Meteorology, SPA "Typhoon," in Obninsk, Rus-
sia.
INPUT INFORMATION
Experimental plot for runoff following heavy rain
(plot HR) ^
The 625-m" experimental plot is located 7 km from
the Chernobyl Nuclear Power Plant, 0.6 km from the
village of Benevka on the oxbow of the Pripyat River. It
is defined on three sides by dikes and on the lower part
by a collection chute. The plot size is 25 m X 25 m; the
mean grade of the slope is 5Vo. The total aerial contam-
'uanberra lndustfles,
Connecticut 06450.
Inc.. 800 Research Parkway, Meriden.

3. 10 Health physics
ination in the experim.e^ntal plot was determined to be 1.4
t 0.1 MBq m 'of '"Cs and 1.8 -f 0.4 MBq m-2 of
"Sr 1* standard deviation (SD)1. Descriptions oithe soil
and plot HR are given in Tables I, 2, and 3. The
vegetation on the experimental plot consisted primarily
of mixed grasses. The predominant wild plant species
included Achillea millefolium, Ae godpodium pada[raria,
Carex vulgaris, C. nigra, C. flacca, C. pilosa, Comarum
p alustre, D e schamp sia caespito sa, F ilip endula ulmaria,
Leuc anthemum v ul g ar e, M e lampy rum ne mo r o s um, M en -
tha arvensis, Myosotis palustris, Pedicularis palustris,
P oly g onum li s to rta, P olytric hum c ommLlne, Ranunculus
repens, Trifulium repens, Veronica chamaedrus, and
Vaccinium myrtillus.
Table 2. Soil descriptions for the experimental plots.
Soil layer Depth (cm) pH
January 1996, Volume 70, Number 1
Intense artificial rain was used to simulate the
formation of natural surface runoff on the two experi-
mental plots. This was done for two main reasons. First,
there was an urgent need at the time to predict the
contamination of water bodies due to runoff caused by
rainfall, flooding, and snow melt from areas of contam-
inated soil. However, there was a lack of rainfall durins
the period immediately after the accident, and it was no-t
possible to wait until there was natural surface runoff.
Second, in the 30-km zone there is poor surface runoff
formation; the mean annual runoff coefficient is -ISVo.
The observations were carried out during an exper-
iment conducted on 14 October 1986. The aftificial
heavy rain was applied by pointing a fire hose up in the
air and letting the water come down. A second artificial
rainfall application was used to test the dependence of
radionuclide wash-off on initial conditions (i.e.. before
the first rainfall application, the soil was dry; before the
second application it was wet). A hydrograph of the
runoff dynamics is given in Fig. 2. Chnacteristics of the
artificial rain applications are given in Table 4. The
chemical composition of the artificial rain is not repre-
sentative of the actual rain in the region, in that the
arlificial rain contained more dissolved salts than actual
rain would have contained. The intensitv of the artificial
rain was representative of actual rain that can cause
surface runoff. The applicability of data obtained with
artificial rain to actual environmental conditions has been
discussed by Bulgakov and Konoplev (1992) and Bulga-
kov et al. (1992).
E-xperimental plot for runoff from snow melt (plot
SM)
The 1,000-m2 experimental plot is located on a
north-facing slope near the town of Chernobyl. It is
defined on three sides by dikes and on the lowei part by
a collection chute. The plot size is 50 m X 20 m; the
mean grade of the slope is 47o. The total aerial contam-
ination in the experimental plot was determined to be 4g0
+- 155 kBq m-' of "'Cs and 270 'r 48 kBq m-2 of eoSr
(* SD). The observations were carried out in winter and
Humus
content
(Vo) Soil type
Plot HR
Root zone
Al Horizon
B Homzon
0-8 51 8-12 sandy loam
8 to 15-20 46-48 4-6 sandy loalll
15-20 to 40-50 46 1-2 sandy loal13
Plot SMI
Root zone
Plowld lay研
B Holttzon
一
一
一
5.8 4-5 sandy loam
5.8 1-1.5 sandy loam
5.0-5.2 0.3-0.8 loamy sand-
sand
Table 3. Characteristics of plot HR.
Characteristic Value
Water table depth (m)
Standing water depth during
artificial rain appl icatior.
(mm)
Measured natural plecipitation at
runoff plot during 1986 (mm)
May
June
July
August
September
October
Biomass density
wet weight (g - ')
dry weight (g m-')
Vertical distribution of soil density
in experimental plot HR
Layer (cm)
Voiumetric density (g cm-3 dry
weight)
Porosity (Eo, cm3/cm3)
Chemical forms of radionuclides
in the soil of plo{ HR prior to
artificial rain application
Radionuclide
Mobile fomu (7o)
Non-exchangeable form (7o)
0.5-5
(yearly average, 1.5)
5-10
20.5(cstmatcd)
39.5
195
601
44.6
264
510± 200
130± 40
0-5 5-10
ｒと
一Ｅ
Ｅ
Ｅ
び
中軍
ｃ
鳩
︼
100
495
9°
Sr
149
426
137cs
0 10 20 00 40 50 60 70 80 90
Hme,lnnin
Fig.2.Hydrograph of thc runoff dyna■ lics For plot i=R.
Ｊ
ｌ。
u
Amount in solution and exfacted in 1 N ammonium aeetate solution.

4. Table 4. Characteristics of the artificial rain applied to plot HR.
Characteristic Valuc
Wash― ofC of 9° Sr alld 137cs● A V KoNOPLEV ET AL
Table 5. Characteristics of plot SM.
Characteristic Value
pH
Ionic composition of water (mg L-t)
c*+
K+
Na+
Mg"
HCO3-
Start of rain application
Duration (nin)
Rain amount (mm)
Rainfall intensity (mm min-')
Soil moisture content before rain
(Vo, gH2O g-r soil wet weight)
72
55
5
17
12
170
16:29 17:22
Soil density (0*10 cm)
Soil porosity (0-10 cm)
Snow storage in the snow melt
period
Depth of freezing (January and
February)
pH of snow water
Cation composition of snow water
(mg L-t)
c**
K+
Na*
NHo*
Mg'*
155 g cm 3位 y、veight
375%(cm3 pcr Cm3)
2351111n
60-100 cm
53
15
1.3
19
14
4.4
16
218
137
spring in the snow melt period of 1988 (March). A
hydrograph of the runoff dynamics is given in Fig. 3,
Descriptions of the soil and of the snow water are given
in Tables I,2, 5, 6,7, 8, and 9.
ASSESSMENT TASKS
Predictions for experimental plot HR
Midpoint. Calculate the vertical distribution of the
total amounts (Bq g-' dry weight) qld the percentage of
exchangeable forms of "'Cs and ""Sr in soil immedi-
ately prior to rain application on 14 October 1986.
Include the 957o confidence intervals about the best
estimates of the mean concentrations. Suggested soil
layers are 0-0.5 cm, 0.5-1.0 cm, 1.0-2.0 cm,2.0-3.0
cm. 3.0-5.0 cm. and 5.0-10.0 cm.
Endpoints.
1. Calculate the total concentrations (Bq L*1; of 137Cs
and eosr in surface runoff during the experiment,
18 19 20 21 22 23 24 25 26 27
date and iime,March 1988
Fig。 3.Hydl・ograph of thc mnoff dynamics for plot SM.
Table 6. Chemical forms of the radionuclides deposited with
atmospheric fallout.^
Radionuclide
WIobilc folib
%
Non-exchangeable
fonn 7o
9°
Sr
137cs
a Samplcs wctt talcen dおly ttom fallout collcctors begl■ ning on 26 April
1986,consげ vcd by a spccial lncthod and storcd Tllc chcmical foms、 vere
deterlmned in the laboratory duttng 1988 Sal■lplcs、 vere dded and storcd
in scalcd contalners to e■ sure dlat the chellllcal forms measured、 verc thc
samc as、 vtte depOsited Thc valucs arc intcgrated estmates bascd on the
total actvity rcccivcd by tlc plot over the entre tmc of initial deposition
b AInount in soluion and exttactcd、 vith ammonium acetate
Table 7.Chelnical radionuclidc forms in thc soll of plot SM at thc
cnd ofthc cxpcimcnt(5 Ap五 11988).
Radlo■uclldc
Moblle forma
%
Non-exchangeable
forlr' Vo
9°
Sr
137cs
' Water-soiuble * exchangeable,
together with the percentages in dissolved and partic-
ulate (i.e., associated with suspended particles) forms.
Include the 95Vo confidence intervals about the best
estimates of the mean concentrations.
2. Calculate the amounts (Bq) of t37Cs
and eosr lost
from the HR experimental plot in the 24 h since
application began. Include the 957o confidence inter-
vals about the best estimates of the mean values.
Predictions for experimental plot SM
Midpoint. Calculate the verlical distribution of total
amounts (Bq g-' dry weight) and the percentage of
exchangeable forms of "'Cs and "St in soil as of 15
March 1988. Include Ihe 957o confidence intervals about
the best estimates of the mean concentrations. Suggested
soil layers are 0-0.5 cm, 0.5-1.0 cm, 1.0-2.0 cm,
2.0-3.0 cm, 3.0-5.0 cm, and 5.0*10.0 cm.
ｒ ｂ
一
、ぁ
〓
の
Ｃ
Ｏ
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Ｌ
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Ｏ
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、

5. 12 Health Physics
Table 8. Air and soil temperature for plot SM during the snow
melt period of 1988.
Air temperature, 'C
Soil temperature
(0-2 cm), 'C
■me ■me
March
1988 9:00 15:00 21:00 9,00 15,00 21:00
January 1996, Volume 70, Number 1
Acknowledgmenrs-This scenario was developed by A. V. Konoplev
(Institute of Experimental Meteorology, SPA "Typhoon," Obninsk, Rus-
sia) and F. O. Hoffman (SENES Oak Ridge, U.S.A.) on the basis of
experiments carried out in the 30-km zone of the Chernobyl Nuclear Power
Plant by scientists from the Institute of Experimental Meteorology, SPA
"Typhoon," Obninsk, Russia, and the Ukainian Hydrometeorological
Institute, Kiev, Ukraine. We are grateful to SENES Oak Ridge, Inc., and
personally to K. M. Thiessen and J. S. Hammonds for very helpful
comments and valuable help in preparation of this manuscript for publi-
cation.
REFERENCES
Bulgakov, A. A.; Konoplev, A. V. The role of chemical
speciations of radionuclides in soils in their transfer to
surface runoff. In: Proceedings of the Interxational Sympo-
sium on Radioecology, Chemical Speciation-Hot Parti-
cles. Znojmo: Society of Czechoslovak Radioecologists
12-16 October; 1992: 17 20.
Bulgakov. A. A.;_Konoplev, A. V.; Popov, V. E. Prediction
of '"Sr and "'Cs behavior in soil-water system after the
Chernobyl accident. In: Ecological and geophysical aspects
of nuclear accidents. Moscow: Gidrometeoizdat', 1992:
2l-42 (in Russian).
Hoffman, F. O.; Thiessen, K. M.;Watkins, B. Opportunities for
the testing of environmental transport models using data
obtained following the Chernobyl accident. Health Phys.
70:5-7; 1996.
Konoplev, A. V.; Bulgakov, A. A. Behavior of the Chernobyl-
origin hot particles in the environment. In: Proceedings of
the International Symposium on Radioecology, Chemical
Speciation-Hot Particles. Znojmo: Society of Czechoslo-
vak Radioecologists 12-16 October, 1992: 56-60.
Konoplev, A. V.; Viktorova, N. V.; Virchenko, E. P., Popov,
V. E.; Bulgakov, A. A.; Desmet, G. M. Influence of
agricultural countefineasures on the ratio of different chem-
ical forms ofradionuclides in soil and soil solution. Science
Total Environ. 137:147-162; 1993.
Makhonko, K. P.; Silantiev, A. N.; Shkuratova, L G. Monitor-
ing of environmental radioactivity in the vicinity of nuclear
power plants. Moscow: Gidrometeoizdat; 1985 (in Rus-
sian).
Sereda, G. A.; Shulepko, Z. S. Methods of determination of
radioactivity of the environment. Vol. 2. Moscow: Gidrom-
eteoizdat; 1966 (in Russian).
■ ■
Date
15
16
17
18
19
20
21
22
23
24
25a
-65
-36
37
2.3
-25
-25
-4.6
10
19
2.1
08
13
04
118
41
15
29
4.4
25
45
4.4
75
-1,7
05
1.0
-08
-20
-0.5
-05
03
11
16
2.5
-06 -37
3.9 -2.8
69 13
0.5 0.3
-14 -07
14 -10
-2.1 -2.2
14 0
28 11
39 1
46 0
a Rtlnoff ceased after 25 MIarch 1988.
Table 9.Variations in attnosphcdc prccipitaton at plot SM during
tllc s■ o■7 1nelt poビ lod of MIttch 1988.
Date 15■ 21 22 23 24 25 26 27 28-31
Precipitation, mm
Endpoints
1. Calculate the total concentrations (Bq L-i; of 137Cs
and eosr in surface runoff at the following time
periods, together with the percentages in dissolved
and particulate (i.e., associated with suspended parti-
cles) forms:
a) at peak flow for 18 March 1988,20 March 1988,
and24 March 1988; and
b) at the minimum flow on the night of 20 - 2I
March 1988.
Include Ihe 957o confidence intervals about the best
estimates of the mean concentrations.
2. Calculate the total amounts (Bq) of t3tcs and eosr
lost from the experimental plot as of 31 March 1988.
Include the 957o confidence intervals about the best
estimates of the mean values.