EPA/600/R-12/068 | December 2012 | www.epa.gov/ord
United States
Environmental Protection
Agency
Water Wash Down of
Radiological Dispersal
Device (RDD) Material on
Urban Surfaces: Effect of
Washing Conditions on
Cs Removal Efficacy
Office of Research and Development
National Homeland Security Research Center
-------
Notice
The U.S. Environmental Protection Agency (EPA), through its Office of Research and
Development's National Homeland Security Research Center, directed the research described
herein under Contracts EP-C-00-027 with Arcadis G&M. This project was funded and managed
by the U.S. Environmental Protection Agency through its Office of Research and Development
and Chemical, Biological, Radiological and Nuclear Research and Technology Initiative (CRTI)
through Environment Canada. It has been reviewed by the Agency but does not necessarily
reflect the Agency's views. No official endorsement should be inferred. EPA does not endorse
the purchase or sale of any commercial products or services.
Questions concerning this document or its application should be addressed to:
Sang Don Lee
U.S. Environmental Protection Agency
Office of Research and Development
National Homeland Security Research Center
109 T.W. Alexander Dr. (MD E343-06)
Research Triangle Park, NC 27711
Phone: (919)541-4531
Fax (919)541-0496
lee. sangdon@epa. gov
-------
Contents
Notice ii
Contents iii
Figures iv
Tables v
Acronyms and Abbreviations vi
Executive Summary vii
1.0 Introduction 1
2.0 Materials and Methods 3
Test Overview 3
Building Materials 3
Coupon RH conditioning 4
Cesium Particle Deposition 5
Firehose System 7
Wash Down Conditions 8
Wash down duration 8
Water pressure 8
Wash angle 9
Wash pattern 9
Test Matrix 10
Analysis of Wash Down Rinsates 10
Removal Efficacy 12
3.0 Quality Assurance/Quality Control 13
4.0 Results 14
Cs Removal Efficacy 14
Wash Down Duration 14
Water Pressure 15
Wash Angle 17
Wash Pattern 18
5.0 Discussion 20
Appendix 22
References 25
in
-------
Figures
Figure 1. Illustration of particle deposition onto a small coupon 6
Figure 2 Illustration of particle deposition onto a large coupon 6
Figure 3. Simulated Firehose System 8
Figure 4. Water wash down with 45 angle to coupon surface 9
Figure 5. Water wash down test patterns 9
Figure 6. Cs removal efficacy as a function of total applied water volume 16
Figure 7. Comparison of average Cs removal efficacy at wash angles 45 and 90 degrees 18
Figure 8 Average Cs removal efficacy at different wash pattern: top to bottom wash (TB) and
bottom to top wash (BT) for concrete (C) and brick (B) samples 19
IV
-------
Tables
Table 1. Building material description and source 4
Table 2. Test Matrix for Simulated Firehose 10
TableS. Operating conditions for ELAN 6000 11
Table 4. Effect of material types on wash efficacy 14
Table 5. Average Cs removal efficacy as a function of wash duration 14
Table 6. Student's t- test results for the effectiveness of wash duration on Cs removal efficacy 15
Table 7. Effect of water volume on Cs removal efficacy 17
-------
Acronyms and Abbreviations
A
amu
Ce
Co
Cs
CsCl
DI
EPA
ft
Ge
GPM
He
ICP-MS
In
L
Li
mA
Mg
mg
min
mL
Mpc
Mr
NHSRC
Pb
ppm
psi
QA
QC
RDD
Rh
RH
rms
Sc
sec
Tb
U
V
ampere(s)
atomic mass unit(s)
Cerium
Cobalt
Cesium
Cesium Chloride
Deionized
U.S. Environmental Protection Agency
foot
Gallium
Gallon per minute
Helium
Inductively Coupled Plasma - Mass Spectrometry
Indium
liter(s)
Lithium
milliampere(s)
Magnesium
milligram(s)
microgram(s)
microliter
minute(s)
milliliter(s)
Average Cs amount (dg) from positive controls
Average Cs amount (dg) in replicate rinsate samples
National Homeland Security Research Center
Lead
Parts per million
Pounds per square inch
Quality Assurance
Quality Control
Radiological Dispersal Device
Rhodium
Relative Humidity
root mean square
Scandium
second(s)
Terbium
Uranium
volt(s)
VI
-------
Executive Summary
The U.S. Environmental Protection Agency
(EPA) holds responsibilities associated with
homeland security events: EPA is the
primary federal agency responsible for
decontamination following a chemical,
biological, and/or radiological (CBR) attack.
The EPA's Homeland Security Research
Program (HSRP) was established to conduct
research and deliver scientific products that
improve the capability of the Agency to
carry out these responsibilities. As part of
this program, the EPA's National Homeland
Security Research Center (NHSRC) carries
out performance tests on homeland security
technologies. This current study
investigated the impact of water wash down
conditions to decontaminate urban surfaces
contaminated with cesium (Cs). The
contaminated surfaces were prepared and
maintained at constant relative humidity
(RH) and washed in a chamber simulating
the delivery of water from a fire hose.
Various water wash down conditions (e.g.,
duration, water pressure, angle, and pattern)
were evaluated for their efficacy at
removing Cs from the test coupon surfaces.
This removal was determined by the
measurement of the amount of Cs in the
water rinsate samples of a function of each
individual wash condition.
Experimental Procedures. Coupons were
pre-conditioned at 33% RH at 21 ± 3 °C for
five weeks before being dosed with
nonradioactive cesium chloride (CsCl). The
CsCl particles were deposited as aerosols
onto the pre-conditioned urban surfaces of
the test coupons using CsCl-methanol
solution. Twenty-four hours after
contamination, the coupons were
decontaminated using a simulated wash
down by water from a fire hose. The
contaminated coupons were washed under
various wash conditions: wash duration (5,
15, and 20 seconds), water nozzle pressure
(40, 80, 120, and 160 pounds per square
inch (psi)), wash angle (45 and 90 degrees),
wash patterns (from bottom to top and from
top to bottom). To trace the amount of
decontamination resulting from these wash
down tests, the rinsate from each wash down
was collected and analyzed for amount of Cs
using Inductively Coupled Plasma Mass
Spectrometry (ICP-MS).
Results. Various conditions of water wash
down using a simulated fire hose chamber
were tested to investigate the impact of
water wash on Cs removal from three
different urban surfaces. Overall (asphalt,
brick, and concrete coupons combined),
there was a statistically significant
(Student's f-test, p=0.0098) effect of
washing duration. The five second time
period exhibited a consistent lower efficacy
than the 20 second time period. There was
no statistically significant effect of the wash
angle among asphalt samples, but the 45
angle gave lower efficacy than the 90 angle
among brick (p=0.0595) and concrete
samples (p=0.0350). Water volume was
found to have a significant positive effect on
efficacy among asphalt (p=0.0080) and
concrete samples (p=0.0325). The
effectiveness of Cs removal increased with
higher water pressure per applied water
volume for asphalt and concrete samples but
not for brick samples. Wash pattern tests
were conducted with the brick and concrete
coupons. The results showed no difference
in Cs removal efficacy for the two different
patterns tested.
Vll
-------
1.0 Introduction
An explosive radiological dispersal device
(RDD), also called a dirty bomb, is the
combination of a conventional explosive
device with radioactive materials that can be
obtained from industrial, commercial,
medical, or research applications.l An RDD
attack can impact a society in various ways,
including creation of casualties, disruption
of the economy, and potentially desertion of
the contaminated area.2"5 Fast and cost-
effective decontamination strategies are
critical to minimize the social and economic
damage resulting from an RDD event.
One of the major processes for remediation
of the radioactively contaminated surfaces is
wash-off via water application. Weather
phenomena such as rain also play a
significant role in the remediation process.
Numerous studies have been conducted to
assess the impact of water exposure on
contaminated surfaces resulting from
nuclear accidents.6"9 These studies have
demonstrated the removal of radionuclides
from various types of surfaces via rain run-
off and water wash-off after the Chernobyl
accident. The study by Roed6 showed that
the first rain run-off from the contaminated
surfaces removed a higher portion of
radioactive contaminants compared to the
subsequent rain or water application on the
same surfaces. In addition, Andersson et al.9
showed that the radioactive contaminant
removal rates by rain or water application
varied depending on the surface type. These
results are consistent with more recent
studies completed by the U.S.
Environmental Protection Agency (EPA).
US EPA has conducted a test to investigate
the fate and transport of Cs on urban
surfaces after rain exposure.10 The results
from the study showed that the fate of Cs on
surfaces was dependent upon contaminant
deposition conditions and surface types.
Rain or water application onto porous
surfaces may result in increasing difficulty
with decontamination. The US EPA's rain
study showed extended subsurface
penetration of Cs through porous materials
when the surfaces were exposed to rain.10' n
This subsurface penetration of radionuclides
can increase the difficulty of
decontamination by limiting the mass
transfer of Cs ions to the surface. This
subsurface penetration occurs by wet
deposition of water soluble particles onto
porous surfaces or rain or high RH exposure
of dry deposited water-soluble particles on
porous surfaces. An optimized application
of water may remove radioactive materials
more effectively than weathering itself and
would result in reducing the amount of
subsurface penetration.
The current study investigated the impact of
various water wash down conditions on Cs
removal efficiency from porous surfaces
using a simulated fire hose water delivery
system. In this study, the nonradioactive
CsCl particles were deposited by spraying a
CsCl-methanol solution onto the test
surfaces. This method kept particles closer
to the surfaces and in the form of CsCl
compared to the particles from a CsCl-water
solution; this is because most of the
methanol in the droplets evaporates before
the droplets touch the surface (compared to
the water-based solution). The study
focused on the assessment of various
conditions of water wash down parameters
including wash down duration, water
pressure, wash angle, and wash patterns.
Nonradioactive CsCl particles were chosen
as an RDD surrogate materials. Three
-------
materials (asphalt, brick, and concrete) were parameters influencing the effectiveness of
selected as the urban surface materials to be water wash down methods on urban surfaces
used as test substrates in this study. The contaminated through a release from an
results of this study provide insight into RDD.
-------
2.0 Materials and Methods
Test Overview
The amounts of deposited cesium removed
from urban surfaces via water wash down
were studied under specific conditions of
water application. Wash down conditions
included wash down duration, water
pressure, wash angle, and wash patterns.
Three different building materials were
contaminated with Cs particles via
aerosolization, and the contaminated
surfaces were washed simulating water
delivery from a firehose. The wash down
rinsate samples were collected and analyzed
for the amounts of Cs that were removed
from the surface.
Test coupons were prepared and
contaminated at the EPA facility located in
Research Triangle Park, NC. Test coupons
were conditioned at a constant 33% RH for
five weeks before contamination. The
coupons were then dosed (contaminated)
with Cs and conditioned at 33% RH for 24
hours before wash down. All coupons were
washed in a chamber in which a wash down
using a firehose was simulated. This
simulation is based on the use of a reduced
distance and small surface area with less
water delivered through the use of a
conventional garden hose-type nozzle that
sprays water to a smaller coupon area while
maintaining the same pressure on the surface
(normalized to material surface area) as
observed in a realistic fire hose water wash
down application. The Cs amounts from the
collected wash down rinsates were analyzed
using Inductively Coupled Plasma with
Mass Spectrometry (ICP-MS).
Building Materials
Three different building materials were used
in this study and the material information is
described in Table 1. Coupons (3.0 cm x 3.0
cm x 3.0 cm (W x L x H)) for the wash
down duration, water pressure, and wash
angle tests were prepared using a diamond
saw with distilled water as the lubrication
fluid. For the wash pattern test, larger
concrete and brick coupons (12.5 cm x 10.0
cm x 2.5 cm (W x L x H)) were used. Each
coupon was inspected visually to find any
defects, cracks, or stains. Coupons with any
defects discovered by visual inspection were
discarded.
-------
Table 1. Building material description and source.
Material
Brick
Concrete
Asphalt
Description
Red, fine-grained
Cement with sand
aggregate (prepared
within six months of
tests and not weathered)
Laboratory Pressed
Asphalt
(prepared within two
years of tests and not
weathered)
Locality
Made from NC red
Triassic clay
Concrete premix
(QUIKRETE® Atlanta,
GA)
NC
Source
Triangle B. Company,
Durham, NC
Home Depot, NC
NC Department of
Transportation
Freshly cut coupons were stored and soaked
in deionized water overnight (at least 12
hours). These coupons were dried in an
oven at 80 °C at negative pressure (-10" Hg)
for 24 hours. Coupon dimensions and
weight were recorded. Five sides of each
coupon were sealed with water-impermeable
sealant (Stonelok™ E3, Richard James
Specialty Chemicals Corp., Hastings on
Hudson, NY). The top surface remained
unsealed for deposition of the Cs. The
sample identification and the top face
designation were marked on the two
opposite sides of each coupon.
Coupon RH conditioning
Coupons were placed into a chamber that
was held at 33% RH for at least five weeks
before surface contamination. The coupons
were stored in RH-controlled chambers and
were opened only when coupons needed to
be added or taken out. The contaminated
coupons were washed down using a water
delivery system simulating a firehose
washdown after 24 hours of contamination.
Coupons were stored in the same 33% RH
chamber during the 24 hours after
contamination. RH and temperature in the
constant RH chambers were monitored and
recorded every 10 minutes throughout the
test periods using a temperature/RH data
logger (HOBO U10-003, Onset Computer
Corporation, Pocasset, MA). Triplicate
coupons were prepared for each water wash
down testing condition. After a wash down,
coupons were dried in laboratory air for 24
hours and then stored in the 33% RH
chamber.
Prior to particle deposition, the top surfaces
of the larger coupons (12.5 cm x 10.0 cm)
were thoroughly cleaned with a 2550 psi/2.3
gallons per minute (GPM) pressure washer
(Troy-Bilt Gas Pressure Washer, Lowe's,
Durham, NC) to remove any loose pieces of
building materials. After cleaning, the large
coupons were dried in laboratory air for at
least five weeks. After deposition, large
coupons were stored in laboratory air (23 ±
2 °C and 40 ± 2% RH) for 24 hours before
the wash down test.
-------
Cesium Particle Deposition
A Cs-containing methanol solution was
deposited onto coupons using a metered
syringe (MicroSprayer® Aerosolizer, Model
1A-1C and FMJ-250 High Pressure Syringe,
Penn-Century, Inc., Windmoor, PA). The
deposition liquid volume was 25 microliters
(EX) per coupon with 200 parts per million
(ppm) of CsCl (99.99%, Fisher Scientific,
Pittsburgh, PA) solution. For small coupons,
the deposition chamber was designed to
center a coupon on the bottom of the
chamber and to slide the syringe needle to
spray aerosols as shown in Figure 1 through
a centered hole in the top lid. This
procedure yields a nominal 3.7 microgram
(jig) deposition of CsCl onto a 3 cm x 3 cm
coupon surface.
Four different locations were contaminated
on the large coupons using the deposition
apparatus shown in Figure 2. Each
deposition volume was 25 d and contained
200 ppm of CsCl solution. The large
coupon was contaminated with
approximately 15 jig of CsCl per coupon.
Four of the coupon sides were covered with
painter's tape to prevent the potential
deposition of CsCl on the sides, and this
tape was removed after deposition.
The deposition amount was calibrated
(positive control) by depositing CsCl
solutions onto clean polyethylene plastic
sheets held at the same distance from the tip
of the syringe and with the same surface
dimensions as the building test coupons. The
five positive control samples for Cs were
transferred to clean 50 mL tubes for
individual extraction. The tubes were filled
with 5% ultrapure OPTIMA HNO3 (Sigma-
Aldrich, St. Louis, MO) in deionized water
until the solution covered the plastic surface
entirely. The plastic sheets were extracted
by sonication for 20 minutes. After removal
of the coupon, the tubes were filled up to 50
mL with 1% nitric acid solution and
analyzed by ICP-MS.
-------
Coupon
Figure 1. Illustration of particle deposition onto a small coupon
Figure 2. Illustration of particle deposition onto a large coupon
-------
Firehose System
All coupons were washed in a chamber
using a simulated firehose water delivery
system. Water delivered from a firehose as
used for washing down building surfaces
was simulated based on an experiment
performed at a Durham, NC, Highway Fire
station. A force transducer that was used to
measure the pressure showed that water
from a 50 psi, 2.4 cm diameter smooth bore
tip firehose nozzle held 30 feet (ft) from the
target generated a 1.6 psi pressure on an 8"
diameter target surface with a -6.5 inch
water jet diameter. This information was
used as the initial guide for this study. The
nozzle, target dimensions, and distance from
nozzle to the target were scaled down in the
experimental setup to mimic the 1.6 psi
pressure at the target surface. A Plexiglas
chamber (90 cm x 90 cm x 90 cm) was built
and is shown in Figure 2. The nozzle was
fixed in the center of a chamber side, and the
coupon holder was positioned on the
opposite side of the nozzle. The distance
between the nozzle and the coupon surface
was kept constant as 23" for all test
conditions. The chamber top was designed
to be able to open and close for cleaning the
inside of the chamber after each test. The
chamber bottom was slanted slightly to
collect the rinsate water. A force transducer
was located on the back of a coupon in the
coupon holder to measure the applied
pressure by the water jet emitted from the
nozzle. The nozzle and water pressure were
adjusted to create a water jet with the same
cross section as the small coupon surface
area (3 cm x 3 cm) at the point of impact
and with a 1.6 psi pressure on the surface. A
water pressure of 120 psi was required to
generate this pressure at the coupon surface.
The water pressure was monitored using an
inline pressure gauge (Watermaster 200 PSI
Pressure Gauge, 91130, Orbit, Bountiful,
UT) to ensure reproducible wash down
conditions. Deionized water was used for
the simulated firehose test and the water was
applied for a specified time. The rinsate
water was collected in plastic containers
(Cubitainer, Fisher Scientific, Pittsburgh,
PA) located under the bottom drain. The
rinsate containers were weighed pre- and
post-experiment to measure the amount of
water used during each wash down test.
After the wash down, the coupons were
removed from the chamber coupon holder
and the chamber walls were cleaned and
dried before the next test. The rinsate
collecting containers were thoroughly
cleaned with Triton-X (Fisher Scientific,
Pittsburgh, PA) solution and deionized water
prior to each test.
-------
m-
Force transducer
Figure 3. Simulated Firehose System
Wash Down Conditions
Wash down duration
The coupons were washed for three different
durations: 5, 15, and 20 ± 1 seconds. For
the wash down duration tests, the other wash
down conditions were 120 psi water
pressure and a 90 degree angle between
water jet direction and exposed coupon
surface. Water from the hose nozzle
covered the entire coupon surface. The
collected rinsate volume for the 5-, 15- and
20-second washes was collected into one-
gallon Cubitainers. The bottom of the
chamber was capped prior to washing and
the volume of rinsate collected was split into
two samples. The rinsates were analyzed for
Cs amount to determine whether the
decontamination efficacy was dependent on
the wash down duration.
Water pressure
Four different water pressures were applied
to the coupons from the same distance and
for the same duration. The applied nozzle
water pressures were 40, 80, 120, and 160 ±
5 psi. Pressure was adjusted by changing
the nozzle orifice size and also varying
supply water pressure while keeping the
same size orifice in the nozzle. The rinsates
from various water pressure tests were
analyzed for Cs amount to determine the
dependence of water pressure on the
decontamination efficacy. For these tests,
the wash duration was 20 seconds and wash
angle was 90 degrees. The pressures applied
to the coupons during wash down were
monitored using a pressure transducer (S
Beam Load Cell, LCCA-100, Omega,
Stamford, CT) attached to the coupon holder.
-------
Wash angle
The previous wash down tests were
conducted with a 90 degree angle between
the water jet direction and the coupon
surface. The water application angle was
adjusted to 45 degree as shown in Figure 4.
The other conditions during this test were
120 psi water pressure for 20 seconds.
Figure 4. Water wash down with 45 angle to coupon surface
Wash pattern
Two different wash patterns were tested
with 12.5 cm x 10.0 cm x 2.5 cm (W X L x
H) coupons. The two different patterns are
shown in Figure 5. One pattern (Figure 5(a))
involves washing from bottom to the top,
and the other pattern was the opposite (from
top to bottom) as shown in Figure 5(b). The
wash down angle was 90 degrees and the
start
water pressure was 120 psi for 20 seconds.
The rinsates were analyzed for the effect of
wash pattern on decontamination efficacy.
This test was conducted with concrete and
brick coupons only, as these surfaces are
often used as vertical surfaces. Asphalt
surface was not tested since it is usually
used for horizontal surfaces.
start
Figure 5. Water wash down test patterns
-------
Test Matrix
The coupon test matrix is shown in Table 2.
Three replicate samples were prepared for
each surface material. As shown in Table 2,
a total of three blank coupons were prepared
for all three surface materials. Blank
coupons were the coupons without Cs
deposition. These blank coupons were
conditioned at 33% RH, and after wash
down they were placed back in the 33% RH
chamber. These three blank coupons were
washed down and the rinsates were collected
for baseline cesium concentration
determination.
Table 2. Test Matrix for Simulated Firehose
Substrate
Concrete
Brick
Asphalt
Wash
Duration
9
9
9
Water
Pressure
9
9
9
Wash
Angle
3
O
O
Wash
Pattern
6
6
0
Small
Blanks
3
O
O
Large
Blanks
3
O
0
Positive controls were created by depositing
cesium particles on a clean cut Ziploc®
surface using the same conditions as the
coupon deposition. A total of five positive
control samples were prepared before
deposition of Cs onto the building material
test coupons, and the extracted solution was
analyzed by ICP-MS using EPA Method
200.8.13 A total of five positive controls for
large coupons were also prepared using
clean cut Ziploc® surfaces, and cesium
particles were deposited in the same manner
as for the test coupons. Sets of positive
controls were prepared for each of the test
parameters. The extracted solution was
analyzed using ICP-MS.
Analysis of Wash Down Rinsates
The rinsate samples in the plastic containers
were transferred to three 50 mL clean vials
and the rest of the rinsate samples were
discarded. The samples were stored in a
refrigerator until they were analyzed.
Before analysis, the rinsate samples were
filtered using a syringe filter, and 5 mL of
each sample was transferred to a clean 15
mL tube labeled with the sample
identification. The rinsate samples from the
wash down tests were analyzed for Cs using
EPA Method 200.8. A model ELAN 6000
ICP-MS (Perkin Elmer, Waltham, MA) was
used for Cs analysis. The operating
conditions of the ICP-MS are summarized in
Table3.
A 10 jiL aliquot of internal standard
reference solution was dispensed into every
sample vial before analysis. The internal
standard solution contained 100 mg/L of
various elements (Ge, In, Li, Sc and Tb).
Rinsates for the blank samples were also
collected and processed in the same manner
as the test coupons prior to analysis using
EPA Method 200.8. All containers used for
dilution, extraction, and analysis were
cleaned using 1% Triton X-100 (Fisher
Scientific, Pittsburgh, PA) solution in
deionized (DI) water followed by multiple
rinses with DI water and dried in a Class
100 clean bench for 24 hours.
10
-------
Table 3. Operating conditions for ELAN 6000
Parameters Values
Rf power
Carrier Gas Flow Rate
Lens Voltage
Analog Stage Voltage
Pulse Stage Voltage
Discriminator
Threshold
AC Rod Offset
Integration Time
Scanning Time
Replicates
Sweeps
Sample Uptake Rate
Plate Voltage
Plate Current
Grid Current
Filament Voltage
Dwell Time per atomic
mass unit (AMU)
Resolution
1200 Watts
0.87 liters (L)/min
9 Volts (V)
-2600 V
1850V
70 mV
-8V
2000 sec
4.120 minutes
3
20
~0.10mL/min
3347V DC
0.50 A DC
94 milliamperes (mA) DC
6.18V root mean square
100 min
He(3.016amu)=2089
Mg(23.985amu)=2065
Rh (102.905 amu)= 1998
Ce (139.905 amu)= 1995
Pb(207.977amu)=2113
U (238.050 amu)= 2223
11
-------
Removal Efficacy
The efficacy of a firehose wash down was compared to the Cs amount in the positive
assessed by determining the amount of Cs in control rinsate. Removal efficacy of Cs
the water wash rinsate samples. The Cs from the coupon material was calculated as
amount in the rinsate water samples was the ratio of Mr and Mpc:
Removal Efficacy (%) = Mr/ Mpc x 100
where Mr is the average Cs amount (jig) in replicate rinsate samples, and Mpc is the average Cs
amount (jig) from five positive controls.
12
-------
4.0 Quality Assurance/Quality Control
QA/QC procedures were performed
according to the quality assurance project
plan for this test (available upon request).
All equipment (balance), monitoring devices
(e.g., pressure gauge, relative humidity,
temperature) and an analyzer (ICP-MS) used
at the time of evaluation were verified as
being within calibration. QC samples
generated during testing included use of
positive control coupons, blank coupons,
and wash down water samples. The average
recoveries for the Cs positive controls were
between 70% and 120%. The relative
standard deviation of Cs amounts from
positive control recovery results were less
than 14%. The analysis results of blank
coupon rinsate samples showed the Cs
amount to be below the minimum
quantification limit (< 0.025 |ig/L) for all
three materials. The clean deionized water
before wash down application was analyzed
for Cs and the results showed that Cs
amounts were below minimum
quantification limit (< 0.025 |ig/L).
13
-------
5.0 Results
Cs Removal Efficacy
Cs removal efficacy results are listed in
Tables 4 for asphalt, brick, and concrete
materials, respectively. The complete data
are listed in the Appendix. Overall, there
was an effect of the variation of the material
(p < 0.0001). Asphalt samples resulted in
higher decontamination efficacy values than
brick samples (p < 0.0001) with a mean
difference of 28% or concrete samples (p <
0.0001) with a mean difference of 21%.
There was no statistically significant
difference between brick and concrete
samples (p=0.1549). Analysis of variance
(ANOVA) and student's t-tests were
conducted using statistical software (SAS
version 9.2, SAS Institute, Cary, NC).
Table 4. Effect of material types on wash efficacy
Paired Comparison
Overall
Asphalt vs. Brick
Asphalt vs. Concrete
Brick vs. Concrete
Method
ANOVA
t-test
t-test
t-test
p-value
<.0001
<.0001
<.0001
0.1549
Mean difference
Not applicable
Asphalt > Brick, 28%
Asphalt > Concrete, 21%
Not sig. diff, 5%
Sample size
102
30 vs. 36
30 vs. 36
36 vs. 36
Wash Down Duration
The average Cs removal efficacy results as a
function of wash duration is shown in Table
5. The coupons were washed in the
simulated fire hose test chamber under the
following conditions: water pressure 120 psi
and wash angle 90 degrees. The error
ranges in Table 5 are one standard deviation
of triplicate sample results.
Table 5. Average Cs removal efficacy as a function of wash duration
Duration
(sec)
5
15
20
Asphalt
50 ± 7%
61 ± 9%
71 ± 5%
Brick
34 ± 19%
43 ± 26%
46 ± 8%
Concrete
31 ±8%
42 ± 14%
55 ± 7%
The data in Table 5 show gradual increase of
average Cs removal efficacy with increased
wash duration for all three materials. The
positive correlations between removal
efficacy and wash duration were statistically
tested. Student's ^-tests for each material
were conducted using statistical software
(SAS version 9.2, SAS Institute, Cary, NC).
The results are listed in Table 6. Initially,
the statistical tests were conducted with 5%
significance, and many test resulted in
significance at the 5 or 10% confidence
level. To identify the potentially significant
wash conditions, two test statistical
significances are indicated by asterisks on
the p values: ** for 5% and * for 10%
significance. The results show that there
was an effect of duration of decontamination
within asphalt samples. For asphalt, the five
second duration yielded lower efficacy
14
-------
values than either a 15 second duration (p =
0.0855) or a 20 second duration (p = 0.0067),
and a 15 second duration yielded lower
efficacy values than a 20 second duration (p
= 0.0926). For concrete, there was also an
effect of duration, with the 5 second
duration yielding lower efficacy values than
a 20 second duration (p = 0.0166), but there
were no statistically significant results
between 5 and 15 and 15 and 20 seconds.
Brick samples showed no statistically
significant duration effect for all three
durations.
Table 6. Student's t- test results for the effectiveness of wash duration
on Cs removal efficacy
Testing
p-Value Mean Difference
Sample
Size
Asphalt
5 sec vs. 15 sec
5 sec vs. 20 sec
15 sec vs. 20
sec
0.0855*
0.0067*'
0.0670*
5<15, 11%
5 < 20, 21%
15 < 20, 8%
3 vs. 3
3 vs. 3
3 vs. 3
Brick
5 sec vs. 15 sec
5 sec vs. 20 sec
15 sec vs. 20
sec
0.5664
0.4672
0.8709
Not sig. diff, 9%
Not sig. diff, 11%
Not sig. diff, 2%
3 vs. 3
3 vs. 3
3 vs. 3
Concrete
5 sec vs. 15 sec °-1862. Not sig. diff, 11% 3 vs. 3
5 sec vs. 20 sec 0.0166** 5 < 20, 25% 3 vs. 3
15 sec vs. 20
sec 0.1222 Not sig. diff, 13% 3 vs. 3
:* for 5% and * for 10% significance
Water Pressure
The average Cs removal efficacy as a
function of wash pressure was tested, and
the results are plotted versus the total water
volume applied to the coupons (Figure 6).
This water volume per unit time represents
the water pressure applied to the coupon
surface. The coupons were washed in the
simulated firehose test chamber under the
following conditions: wash duration 20
seconds and wash angle 90 degree. Each
test was executed in triplicate. Some tests
were conducted by restricting the nozzle
orifice so that the total applied water volume
per coupon surface area was less with the
higher water pressure. This lower coverage
of water on the coupon surfaces was
observed with 160 psi tests; the surface
coverage was approximately 60 to 70% by
visual inspection. Other tests were
conducted by adjusting the input water
pressure and keeping the same orifice size in
the nozzle. Because the total applied
duration is fixed at 20 seconds, the efficacy
data were plotted as a function of total
applied water volume. As seen in Figure 6,
there is a clear tendency of increased
efficacy with increased water volume for
asphalt. However, the plots for brick and
concrete samples are not clear for exhibiting
this trend.
15
-------
(A) Asphalt
°n
Ov
^ 70 -
5> 60 -
^
.a 5o
^ 40
•a
§ 30 -
1 20 -
u 10
0
*^
» * *
• •
• • *
*'
1 '
0 2468
Water volume (L)
(B) Brick
60
8 50 -
§ 40 -
(C
- 30 -
1 2° "
« 10 -
U
0 -
c
. .
1
• B
' • •
•
12468
Water volume (L)
(C) Concrete
70
^ 60 -
% 50
u
S 40
-------
A linear regression analysis (SAS, version
9.2, SAS Institute, Gary, NC) for the Cs
removal efficacy as a function of water
volume was conducted for each material,
and the results are listed in Table 7 with the
test significance indicated by asterisks on
the p-values: ** 5% and * 10%. Water
volume was found to have a statistically
significant positive effect on efficacy within
"Asphalt" (p = 0.0080) and "Concrete" (p =
0.0325). However, there was no significant
effect of water volume (pressure) within
"Brick". The slope was higher with the
asphalt samples than the concrete samples.
Table 7. Effect of water volume on Cs removal efficacy
Material
Asphalt
Brick
Concrete
p-Value
0.0080"
0.7255
0.0325"
Slope
(%/L)
4.04
0.50
2.93
95%
Confidence
Interval
(1.18,6.90)
(-2.46,3.48)
(0.27,5.59)
Sample
Size
21
21
21
Test significance: 5%.
Wash Angle
The average Cs removal efficacies from
washing at 45 degree and 90 degree angles
are shown in Figure 7. The error ranges in
Figure 7 are one standard deviation for
triplicate sample results. The coupons were
washed in the simulated firehose test
chamber under the following conditions:
water pressure 120 psi for 20 seconds. A
paired t-test (SAS, version 9.2, SAS Institute,
Gary, NC) was used to compare average Cs
removal efficacy for 45 and 90 degree wash
down tests. The test results showed that
there was no statistically significant effect of
wash angle within asphalt sample sets
(p=0.3329), but the 45° angle gave lower
efficacy than the 90° angle with brick (p =
0.0595) and concrete sample sets (p =
0.0350). The mean difference of efficacies
from 45 and 90 degree wash down were 13
and 18% for brick and concrete sample sets,
respectively.
17
-------
45 degree
90 degree
10
Asphalt Brick Concrete
Figure 7. Comparison of average Cs removal efficacy at wash angles 45 and 90 degrees
Wash Pattern
The Cs removal efficacy was studied using
two different wash patterns with large (5" x
4" x 1") coupons. The coupons were
washed in the simulated firehose test
chamber under the following conditions:
water pressure 120 psi for 20 seconds at 90
degree wash angle. The coupons were
washed in two different patterns: from
bottom to top or from top to bottom. The
wash pattern tests were used to evaluate the
potential impact of pattern on vertical
surface wash down efficiency. The results
from the testing of brick and concrete
samples are shown in Figure 8. A paired t-
test was used to compare the average Cs
removal efficacies for two different wash
patterns. Brick (two sample t-tesl, t = -1.2, 4
degrees of freedom, p=0.14) and concrete
samples (two sample Mest, t = 0.42, 4
degrees of freedom, p=0.35) showed no
statistical difference in their mean Cs
removal efficacies for the two different wash
patterns. The removal efficacy results from
wash pattern tests were less than the small
coupon tests. This is because wash pattern
tests were conducted with coupons that were
-10 times larger than the ones used in the
other tests; this resulted in wash water
volume per unit area that was 10 times less
than for the small coupons.
18
-------
C-TB
C-BT
B-TB
B-BT
Figure 8 Average Cs removal efficacy at different wash pattern: top to bottom wash (TB)
and bottom to top wash (BT) for concrete (C) and brick (B) samples
19
-------
6.0 Discussion
Different wash conditions for removal of Cs
from three different urban surfaces using a
simulated fire hose water delivery system
were evaluated. Nonradioactive CsCl
particles were aerosolized from a CsCl
solution (dissolved in methanol) onto three
different materials, asphalt, brick, and
concrete. The tested parameters included
wash duration, water pressure, wash angle,
and wash pattern. The test results were
analyzed to determine whether the variations
in the wash down conditions have an impact
on Cs removal efficacy.
The removal efficacies improved by
increasing the wash duration (from 5
seconds to 20 seconds) from 50% to 70% for
the asphalt samples, 34% to 43% for the
brick samples and 31% to 55% for the
concrete samples. Longer wash duration
from three different wash duration tests
showed a statistically significant increase in
Cs removal efficacy for the asphalt samples
with increase of wash duration. The
concrete samples showed statistically
significant increase for 20 seconds
compared to 5 seconds, but the results for
brick samples were not statistically
significant for all three durations. The
longest wash duration in this test was 20
seconds. Increasing the wash duration
further may increase the effectiveness.
However, increased water duration also
increases the volume of water applied,
which is one of the most important factors in
the logistical requirements for this type of
decontamination. In terms of the removal
amount as a function of applied water
volume, the five-second test showed the
highest efficacy among three test durations
for all three materials. The amount removed
with the 5 second wash down was more than
50% of the total amount removed with a 20
second wash down.
For the water pressure test, Cs removal
efficacies were measured as a function of
water volume with fixed duration (20 sec).
This water volume per unit time represents
the water pressure applied to the coupon
surface. Applied water volume and Cs
removal efficacies were statistically tested
for their correlations. Because some tests
(tests with 160 psi) restricted the water
nozzle orifice for pressure control, the water
stream diameter decreased with increasing
water pressure. As a result, the reduced
water stream diameter may have resulted in
less removal efficacy due to reduced coupon
surface coverage. The impact of the stream
diameter might be minimal because the Cs
contamination is concentrated on the coupon
center and the visual inspection during wash
down confirmed that the water stream
coverage area was centered and
approximately 60 to 70% of the entire
coupon surface. The results in Table 7
showed that the effectiveness of Cs removal
increased with higher water pressure per
applied water volume for asphalt and
concrete samples, but not for brick samples.
The study results imply that Cs is
dominantly removed by water wash down
from the test surface without physical
removal of surface material itself. If the
water pressure increases (e.g. by use of a
pressure washer), the Cs removal efficacy
may increase due to removal of surface
material which Cs is binded.
Two different wash angles (45 and 90
degree) were tested for the impact on Cs
removal efficacy with three materials
(asphalt, brick, and concrete). The statistical
analysis showed higher efficacy with 90
20
-------
degree than 45 degree wash angles for the
brick and concrete samples. The difference
in average removal efficacy for the two
different angles was approximately 15% and
21% for the brick and concrete samples,
respectively. This result is related to the
water pressure amount applied directly to
the coupon surface. The angled water
application reduced the applied pressure to a
coupon surface. The pressure transducer
read the pressure level at the 45 degree wash
angle as approximately 32% of the pressure
at the 90 degree wash angle. As seen in the
water pressure test results, the reduced water
pressure on coupon surfaces resulted in the
low removal efficacy at the 45 degree wash
angle. For asphalt coupons, the statistical
results showed that the Cs removal
difference from these two different wash
angles was not significant. This asphalt
coupon result does not follow the results
from the water pressure tests. It is uncertain
why asphalt samples did not show the higher
removal efficacy with 90 degree wash angle.
Wash patterns were studied for impact on
removal efficacy for the brick and concrete
samples. The wash patterns evaluated were
moving the hose from bottom to top and
from top to bottom of a coupon. The
removal efficacies from two different
patterns were tested statistically, and the
results showed no effects on Cs removal for
both materials. This result could be an
artifact of using the small coupons, and this
explanation needs to be confirmed with
operational scale tests.
The current study was conducted as an
exploratory test to probe any potential
improvement on Cs removal efficacy from
porous urban surfaces by adjusting water
wash down conditions. The study
demonstrated the effect of water wash down
conditions on efficacy of Cs removal from
porous urban surfaces. The Cs removal
efficacy showed a positive correlation with
wash duration and water pressure for the
asphalt and concrete samples. The 90
degree wash angle was more effective than
the 45 degree wash angle for the brick and
concrete samples. Wash patterns (bottom to
top and top to bottom) did not affect Cs
removal efficacy for the materials tested.
These findings are applicable only to the
condition where Cs particles have limited
penetration into porous surfaces. If Cs
particles have penetrated into the subsurface
via high RH or rain exposure prior to a
water wash down, then the improvement by
adjusting wash conditions may be reduced.
21
-------
Appendix
Table A-l. Test conditions and efficacy results for asphalt coupons
Sample ID
Al
A2
A3
A4
A5
A6
A7
A8
A9
A10
All
A12
A13
A14
A15
A16
A17
A18
A22
A23
A24
A25
A26
A27
A28
A29
A30
A19
A20
A21
Wash
Duration (sec)
5
5
5
15
15
15
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
Nozzle
Pressure
(psi)
120
120
120
120
120
120
120
120
120
40
40
40
80
80
80
160
160
160
40
40
40
80
80
80
140
140
140
120
120
120
Applied
Water
Volume (L)
1
1
1
5
5
5
6
6
6
7
7
7
6
6
6
4
4
4
2
2
2
3
3
3
6
6
6
6
6
6
Wash
Angle
(degree)
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
45
45
45
Wash
Pattern
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
Wash
Area (cm2)
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
Removal
Efficacy (%)
45
58
48
60
54
69
67
76
70
53
60
58
60
66
58
64
58
65
46
53
35
47
40
37
48
71
47
66
64
72
22
-------
Table A-2. Test conditions and efficacy results for brick coupons
Sample ID
Bl
B2
B3
B4
B5
B6
B7
B8
B9
BIO
Bll
B12
B13
B14
B15
B16
B17
B18
B28
B29
B30
B31
B32
B33
B34
B35
B36
B19
B20
B21
B22
B23
B24
B25
B26
B27
Wash
Duration (sec)
5
5
5
15
15
15
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
Nozzle
Pressure (psi)
120
120
120
120
120
120
120
120
120
40
40
40
80
80
80
160
160
160
40
40
40
80
80
80
140
140
140
120
120
120
120
120
120
120
120
120
Applied
Water
Volume (L)
2
2
2
5
5
5
6
6
6
7
7
7
3
6
6
6
4
4
2
2
2
3
3
3
6
6
6
6
6
6
7
7
7
7
7
7
Wash Angle
(degree)
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
45
45
45
90
90
90
90
90
90
Wash
Pattern
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
TB
TB
TB
BT
BT
BT
Wash Area
(cm2)
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
129
129
129
129
129
129
Removal
Efficacy (%)
54
31
19
27
32
72
38
48
52
32
32
30
14
22
28
48
24
39
28
30
29
52
45
43
26
39
33
36
35
27
11
9
11
16
11
11
23
-------
Table A-3. Test conditions and efficacy results for concrete coupons
Sample
ID
Cl
C2
C3
C4
C5
C6
C7
C8
C9
CIO
Cll
C12
C13
C14
C15
C16
C17
CIS
C28
C29
C30
C31
C32
C33
C34
C35
C36
C19
C20
C21
C22
C23
C24
C25
C26
C27
Wash
Duration (sec)
5
5
5
15
15
15
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
Nozzle
Pressure (psi)
120
120
120
120
120
120
120
120
120
40
40
40
80
80
80
160
160
160
40
40
40
80
80
80
140
140
140
120
120
120
120
120
120
120
120
120
Applied
Water
Volume (L)
1
1
2
5
5
5
6
6
6
7
7
7
6
6
6
4
4
4
2
2
2
3
3
3
6
6
6
6
6
6
7
7
7
7
7
7
Wash Angle
(degree)
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
45
45
45
90
90
90
90
90
90
Wash
Pattern
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
TB
TB
TB
BT
BT
BT
Wash Area
(cm2)
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
129
129
129
129
129
129
Removal
Efficacy (%)
29
24
39
51
28
47
62
56
48
48
41
38
45
38
45
30
40
38
21
48
46
18
35
33
39
37
34
45
33
34
17
24
18
13
20
22
24
-------
References
1 Gonzalez, A.J. (2003) Security of radioactive sources: threats and answers. In International Conference
on Security of Radioactive Sources, pp.33-58. Vienna, Austria: International Atomic Energy Agency.
NRC (May 2007) Backgrounder on Dirty Bombs: U.S. Nuclear Regulatory Commission.
3 Zimmerman, P.D. and Loeb, C. (2004) Dirty Bombs: The threat revisited. Defense Horizons, pp.1-11.
4 Karam, P.A. (2005) Radiological terrorism. Hum Ecol Risk Assess, 11, 501-523.
5 Rosoff, H. and von Winterfeldt, D. (2007) A risk and economic analysis of dirty bomb attacks on
the ports of Los Angeles and long beach. Risk Ana/27, 533-546.
6 Roed, J. (1987). Run-off from the weathering of roof material following the Chernobyl accident.
Radiation Protection Dosimetry, 21 (1/3), 59-63.
7 Roed, J. (1988). The Distribution on Trees of Dry Deposited material from the Chernobyl
Accident. Paper NKA/AKTU-245 988)2, presented at the Joint CEC/OECD (NEA) Workshop on
Recent Advances in Reactor Accident Consequence Assessment, Rome, Italy, 25-30 January 1988.
8 Karlberg, O. (1988). Weathering and Migration of Chernobyl Fallout in Sweden. Studsvik, Sweden,
Report NP 216 EA.
9 Andersson, K.G., J. Roed, and C.L. Fogh. (2002b). Weathering of radio caesium contaminationon
urban streets, walls and roofs. Journal of Environmental Radioactivity, 62, 49-60.
10 U.S. Environmental Protection Agency (U.S. EPA). 2012. Fate of Radiological Dispersal Device
(RDD) Material on Urban Surfaces: Impact of Rain on Removal of Cesium, Washington, D.C.,
EPA/600/R/12/569.
11 U.S. Environmental Protection Agency (U.S. EPA). 2010. Radiological Dispersal Device Outdoor
Simulation Test: Fate of Cs on Limestone, Washington, D.C., EPA/600/X/10/005 (FOUO).
12 Gusarov, A., IPicheva, N., Konoplev, A., Lee, S.D., Maslova, K., Popov, V., and Stepina, I. (2011)
Fate and Transport of radiocesium in urban building materials. International Conference on
Radioecology & Environmental Radioactivity: Environment & Nuclear Renaissance 46(6), S265-
S269.
13 U.S. Environmental Protection Agency (U.S. EPA). 1994. Determination of Trace Elements in
Waters and Wastes by Inductively Coupled Plasma-Mass Spectrometry, Washington, D.C. Method
200.8 revision 5.4.
25
-------
United States
Environmental Protection
Agency
PRESORTED STANDARD
POSTAGE & FEES PAID
EPA
PERMIT NO. G-35
Office of Research and Development (8101R)
Washington, DC 20460
Official Business
Penalty for Private Use
$300
------- |