EPA/600/R-12/569 | July 2012 | www.epa.gov/ord
United States
Environmental Protection
Agency
Fate of Radiological
Dispersal Device (RDD)
Material on Urban Surfaces:
Impact of Rain on
Removal of Cesium
Office of Research and Development
National Homeland Security Research Center
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Fate of Radiological Dispersal Device (RDD) Material on Urban
Surfaces: Impact of Rain on Removal of Cesium
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Table of Contents
List of Figures ii
List of Tables iii
Disclaimer iv
Foreword v
Acronyms and Abbreviations vi
Acknowledgments vii
Executive Summary viii
1. I ntroduction 1
2. Materials and Methods 2
2.1 Test Overview 2
2.2 Building Materials 2
2.3 Test Matrix 3
2.4 Cs Deposition 4
2.5 Rain Exposure 5
2.6 Analysis of Rainwater Runoff 6
2.7 Analysis of Coupons 7
2.8 Removal Efficacy (%) 8
3. Quality Assurance/Quality Control (QA/QC) 9
4. Results and Discussion 11
4.1 Rain Characteristics 11
4.2 Rainwater Analysis 12
4.2.1 Cs Subsurface Distribution of Blank Coupons 12
4.2.2 Cs Subsurface Distribution of Positive Controls 14
4.2.3 Cs Removal by Rain 19
5. Discussion 29
6. References 32
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List of Figures
Figure 1. Illustration of particle deposition onto a coupon 5
Figure 2. Containers after rain exposure 6
Figure 3. Rain Volume (ml_) collected. Location of empty containers are marked (X) 11
Figure 4. Background Cs distribution profiles (in ppm) of blank coupons for (a) asphalt, (b) brick,
(c) concrete, (d) granite, and (e) limestone 14
Figure 5. Cs distribution profiles of asphalt positive controls for (a) water solution sample and (b)
methanol solution sample 15
Figure 6. Cs distribution profiles of brick positive controls for (a) water solution sample and (b)
methanol solution sample 16
Figure 7. Cs distribution profiles of concrete positive controls for (a) water solution sample and
(b) methanol solution sample 17
Figure 8. Cs distribution profiles of granite positive controls for (a) water solution sample and (b)
methanol solution sample 18
Figure 9. Cs distribution profiles of limestone positive controls for (a) water solution sample and
(b) methanol solution sample 19
Figure 10. Cesium amounts in rainwater runoff as function of collected rainwater volume for
water (solid) and methanol (open) deposition 20
Figure 11. Cesium amounts in rainwater runoff as function of building material type and
deposition method (H2O: Cs in water; MeOH: Cs in methanol) 22
Figure 12. Brick rain test example samples: (a) water solution sample and (b) methanol solution
sam pie 24
Figure 13. Concrete rain test example samples: (a) water solution sample and (b) methanol
solution sample 25
Figure 14. Limestone rain test example samples: (a) water solution sample and (b) methanol
solution sample 26
Figure 15. Asphalt rain test example samples: (a) water solution sample and (b) methanol
solution sample 27
Figure 16. Granite rain test example samples: (a) water solution sample and (b) methanol
solution sample 28
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List of Tables
Table 1. Building material descriptions and sources 3
Table 2. Test matrix 4
Tables. Operating conditions for ELAN 6000 6
Table 4. Equipment Calibration 9
Table 5. DQIs for Critical Measurements 9
Table 6. Correlation coefficient of rainwater volume and Cs amount in runoff 20
Table 7. Efficacies for removal of cesium by (simulated) rain event 23
Table 8. Pore properties of test surface materials 29
in
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Disclaimer
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 subjected to the Environmental Protection Agency's review and this
document is intended for internal Agency use only. Note that approval does not signify that the contents necessarily
reflect the views of the Agency. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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
IV
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the nation's air, water,
and land resources. Under a mandate of national environmental laws, the Agency strives to formulate and implement
actions leading to a compatible balance between human activities and the ability of natural systems to support and
nurture life. To meet this mandate, the EPA's Office of Research and Development (ORD) provides data and
science support that can be used to solve environmental problems and to build the scientific knowledge base needed
to manage our ecological resources wisely, to understand how pollutants affect our health, and to prevent or reduce
environmental risks.
In September 2002, EPA announced the formation of the National Homeland Security Research Center (NHSRC).
The NHSRC is part of the ORD; NHSRC manages, coordinates, supports, and conducts a variety of research and
technical assistance efforts. These efforts are designed to provide appropriate, affordable, effective, and validated
technologies and methods for addressing risks posed by intentional releases of chemical, biological, and radiological
agents. Research focuses on enhancing our ability to detect, contain, and decontaminate in the event of such releases.
The NHSRC conducts decontamination testing in an effort to provide reliable information regarding the
performance of decontamination approaches. Such testing provides independent, quality assured performance
information that is useful to decision makers in purchasing or applying the tested approaches. Information on the
variety of homeland security technologies and topics that NHSRC research has evaluated can be found at
http ://www. epa. gov/nhsrc.
Jonathan G. Herrmann, Director
National Homeland Security Research Center
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Acronyms and Abbreviations
A: ampere
amu: atomic mass unit
Co: Cobalt
Cs: Cesium
CsCl: Cesium Chloride
DI: deionized
DRDC: Defence Research and Development Canada
EPA: Environmental Protection Agency
Hz: hertz
ICP: Inductively Coupled Plasma
LA: Laser Ablation
LLNL: Lawrence Livermore National Laboratory
mA: Miliampere
MS: Mass Spectrometry
NHSRC: National Homeland Security Research Center
NIST: National Institute of Standards and Technology
NRC: Nuclear Regulatory Council
ORD: Office of Research and Development
PC: Procedural Control
QA/QC: Quality Assurance/Quality Control
ROD: Radiological Dispersal Device
RH:Relative Humidity
Rms: root mean square
RTF: Research Triangle Park
SRM: Standard Reference Material
WIS: Wehrwissenschaftliches Institut fur Schutztechnologien - ABC-Schutz
um: micrometer
uL: microleter
VI
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Acknowledgments
Contributions of the following individuals and organizations to the development of this document are gratefully
acknowledged: Sang Don Lee (EPA) and Lukas Oudejans (EPA) for preparing this document, Defence Research
and Development Canada (DRDC) Ottawa and Wehrwissenschaftliches Institut fur Schutztechnologien - ABC-
Schutz (WIS), Munster, Germany for conducting the rain test, and ARCADIS U.S., Inc. for preparing test coupons
and analyzing rainwater samples.
VII
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Executive Summary
The U.S. Environmental Protection Agency's (EPA's) National Homeland Security Research Center (NHSRC)
helps to protect human health and the environment from adverse impacts of terrorist acts by conducting applied
research leading to enhancement of mitigation and remediation activities. This study investigated the effect of rain
on the fate of cesium (Cs) on urban surfaces. The amount of Cs rinsed by rain from contaminated surfaces was
measured, and the distribution of Cs at and below the surface was characterized.
Experimental Procedures. Five different building materials (asphalt, brick, concrete, granite, and limestone) were
contaminated with Cs liquid particles (using methanol or water solution) via aerosolization, and the contaminated
surfaces were exposed to simulated rain. The rainwater runoffs were analyzed for the Cs amount that was removed
from the surface. The surface coupons were further analyzed to investigate the subsurface profile of Cs.
Results. The Cs test results showed that the removal % varies depending on the material types. The removal %
was in the following order: asphalt > granite > brick ~ concrete ~ limestone. This order is the same irrespective of
the Cs deposition solution (methanol or water). Granite coupons showed a noticeable difference (37 % removal for
Cs in methanol and 14% for Cs in water) in % removal as a function of deposition solution. For Cs tests, the
penetration depth was in the following order: limestone > brick > concrete ~ asphalt ~ granite. The pattern of the
subsurface Cs distribution varied depending on the surface type: uniform distributions for concrete and brick and
highly localized distribution for asphalt, granite, and limestone. The Cs data showed that the pattern and depth of Cs
penetration is closely related to the pore properties of the materials.
Vlll
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1. Introduction
A radiological dispersal device (ROD), 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.1>2 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.3'4'5 Fast and cost-
effective decontamination strategies are critical to
minimize the social and economic damage from RDD
events. The physicochemical behavior of RDD
materials on various surfaces must be understood to
promote the development of efficacious
decontamination technologies and strategies.
A recent study conducted through a collaborative
effort between U.S. Environmental Protection
Agency (EPA) and Lawrence Livermore National
Laboratory (LLNL) demonstrated RDD particle
characteristics on building material surfaces from a
simulated RDD test.6 The results from this study
showed the subsurface penetration of cesium (Cs)
into limestone.7 Other studies conducted by Defence
Research and Development Canada (DRDC, Ottawa)
have shown that a wet application of the water -
soluble contaminant led to lower decontamination
efficiencies when compared to use of a dry non-
soluble contaminant.8 These studies all indicate that
environmental conditions such as humidity and
precipitation may impact the interaction of RDD
contaminants with urban surfaces. To determine an
optimum decontamination strategy, understanding of
the fate of RDD contaminants under the expected
environmental conditions is critical.
The occurrence of rain prior to decontamination of
outdoor building materials can affect the
decontamination process in various ways. Some
portion of RDD contaminants on surfaces may be
washed off by rain, but rain may also accelerate the
penetration of water soluble RDD compounds such as
cesium chloride (CsCl) through porous surfaces.
Subsurface penetration may result in a more difficult
removal of the radioactive contaminants due to the
limited access of decontamination technologies to the
contaminants inside pores. RDD materials may also
establish strong bonds to inner surface sites through
chemical reaction. Information on the impact of rain
on the fate of RDD contamination of surfaces of
various materials can be utilized to optimize
decontamination strategies. To generate this
information, this project investigated the effects of
rain on Cs penetration through common urban
surfaces such as concrete, brick, granite, asphalt, and
limestone. Specifically, this study investigated the
amount of Cs washed off by rain from building
surfaces. The remaining Cs was characterized for its
subsurface penetration. The subsurface penetration
was investigated as a function of two different
surface deposition methods: RDD contamination
placed in methanol or placed in water. Deposition of
Cs ions from methanol solution results in deposition
of Cs particles close to the material surface with less
penetration than deposition of Cs ions from water
solution.
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2. Materials and Methods
2.1 Test Overview
The effect of rain on the fate of Cs on urban surfaces
was investigated. Five different building materials
were contaminated with nonradioactive Cs containing
liquid particles via aerosolization and the
contaminated surfaces were exposed to rain. The
rainwater runoff samples were analyzed for the
amount of the Cs that was removed from the surfaces
in runoff. The surface coupons were analyzed further
to investigate the subsurface profile of the Cs. Test
coupons were prepared and contaminated at the
Environmental Protection Agency (EPA) facility
located at Research Triangle Park (RTF), North
Carolina (NC). After contamination, coupons were
shipped to a rain exposure facility in WIS, Munster,
Germany. The coupons delivered to WIS were
exposed to light rain (~ 2 cm/hr) for 30 min. After
rain exposure, the rainwater samples and test coupons
were shipped back to the EPA facility. Cs in
rainwater samples was analyzed using Inductively
Coupled Plasma with Mass Spectrometry (ICP-MS),
and the potential migration of Cs within the surface
materials was assessed with Laser Ablation (LA)
coupled with ICP-MS.
2.2 Building Materials
Five different building materials were used in this
study and the material information is described in
Table 1. Test coupons [3 cm x 3 cm x 3 cm (W x L x
H)] were prepared using a diamond saw (14"
Brick Xtreme BX3 model 157721, MK Diamond
Products, Inc. Torrance, CA) with distilled water as
the lubrication fluid. Each coupon was inspected
visually to find any defects, cracks, or stains.
Coupons with any defects noticed during visual
inspection were discarded.
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Table 1. Building material descriptions and sources.
Material
Red brick
Limestone
Granite
Concrete
Asphalt
Description
Red, fine-grained
Light-grey, coarse-grained, -75%
skeletal grains, remainder calcite
cement and trace (1%) quartz,
dolomite, pyrite, clay
Pink with dark banding, medium-
coarse texture, biotite
Cement with sand aggregate
Laboratory Pressed Asphalt
Locality
Made from North
Carolina red
Triassic clay
South central
Indiana
Mount Airy, North
Carolina
Concrete premix
(QUIKRETE®
Atlanta, GA)
N/A
Source
Triangle Brick Company Durham,
North Carolina
Cathedral Stone Products Hanover
Park, Maryland
Triangle Brick Company Durham,
North Carolina
Home Depot
Durham, North Carolina
North Carolina Department of
Transportation
Coupons were dried in an oven at 80 °C with slight
negative pressure (~10" Hg) for 24 hours; coupon
dimensions and weight were then 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 surrogate ROD contaminant and
subsequent rain exposure. The sample identification
and the top face designation were marked on two
opposite sides of each coupon. All coupons were
stored in a constant relative humidity (RH) chamber
(33% RH) for four weeks and then removed for Cs
particle deposition. Constant RH was maintained at
33% RH in an airtight container with a slurry mixture
of magnesium chloride (MgC^) and DI water. This
constant RH method is described in ASTM Standard
Method E104-02.9 RH and temperature were
monitored once every hour using a data logger
(HOBO RH/TEMP, Onset Computer Corporation,
Cape Cod, MA) during coupon conditioning.
2.3 Test Matrix
The coupon test matrix for the simulated rain test is
shown in Table 2. Procedural control coupons (not
contaminated, but with rain exposure) consisted of
the five different building materials without Cs
deposition. Simulated rainwater was collected in
clean containers to quantify the amount of Cs. Four
replicate samples were prepared for each surface
material and deposition method. Two coupons for
each material were contaminated with Cs, but were
not exposed to rain. These coupons (positive controls,
PCs) were analyzed for baseline Cs penetration
through the surface of the building material. All test
coupons were prepared and stored under the same
RH and temperature conditions.
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Table 2. Test matrix
Surface
Material
Asphalt
Brick
Concrete
Granite
Limestone
Water
4
4
4
4
4
Cs
Methanol
4
4
4
4
4
Procedural
Control
3
3
3
3
3
PC
2
2
2
2
2
2.4 Cs Deposition
Two different solvents were used to create the
contamination solutions that were deposited onto the
surfaces in this study. Water and methanol solution-
based particles were deposited on the coupons using
a metered syringe (MicroSprayer® Aerosolizer,
Model 1A-1C andFMJ-250 High Pressure Syringe,
Penn-Century, Inc., Wyndmoor, PA). Based on the
manufacturer's information, this metered syringe can
generate a plume of liquid aerosols with a mass mean
diameter of 16-22 um. Water solutions of CsCl
(99.99%, Fisher Scientific, Pittsburgh, PA) create Cs
ions on coupon surfaces with subsurface penetration
due to the capillary suction of the liquid in the case of
porous surfaces. Methanol solutions of Cs when
deposited onto the coupon surfaces create ions in a
manner similar to the water solution. As with the
water solution, the Cs particles are deposited onto the
coupon surfaces, but are expected to penetrate less
into the subsurface due to the higher volatility of
methanol compared to water. Each coupon was
contaminated with the same concentration of CsCl in
water or methanol solution. The deposition liquid
volume was 25 |oL per coupon with 200 ppm of CsCl.
The deposition chamber was designed to center a
coupon on the bottom of the chamber and to slide the
syringe needle to spray aerosols through a centered
hole in the top lid at a fixed distance of 2.3 cm as
shown in Figure 1. Four sides of coupons were
covered with painter's tape (Scotch blue, 3M,
Maplewood, MM) to prevent deposition on the sides.
The tape was removed after deposition.
The deposition amount was calibrated (spike control)
by depositing Cs solutions onto clean polyethylene
plastic sheets (Ziploc, SC Johnson, Racine, WI) held
at the same distance from the tip of the syringe as the
building material coupons and with the same surface
dimensions as the building coupons. The five spike
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 (DI) water
until the solution covered the plastic surface entirely.
Coupons were extracted by sonication for 20 minutes.
After removal of the coupon, the tubes were filled to
50 mL with 1% nitric acid (Optima, Fisher Scientific,
Pittsburgh, PA) solution and analyzed by ICP-MS.
The Cs-deposited coupons were packed in airtight
containers containing dehydrating material (Silica
Gel Desiccant bag, McMaster-Carr, Robbinsville, NJ)
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and shipped to the WIS rain facility in Germany.
Approximately 20 days elapsed from the time of
contamination to the rain test. The RH and
temperature were monitored using a data logger
throughout the shipping period. The data showed that
the range of RH and temperature during this period
were 15 - 20% RH and 10-20 °C, respectively. The
airtight containers were packaged into one parcel,
and one data logger was included in one of the
airtight containers.
Figure 1. Illustration of particle
2.5 Rain Exposure
The coupons were exposed to water from a simulated
rain event for 30 min at the WIS rain facility in
Germany. The average rain rate was set to 20 mm/hr
(with a droplet size of 20-100 |am according to the
measurement by WIS). Each coupon was placed in a
separate plastic container (5 cm diameter x 5.6 cm
height, PCI Scientific, Fairfield, NJ) before exposure
to the rain. The individual coupon and container
were weighed before the rain exposure using a
balance (TE 802 S, Sartorius GMBH, Gottingen,
Germany). The contaminated coupon surfaces in the
containers were positioned ~4 m under the assembly
of nozzles and exposed directly to the simulated rain.
Rainwater runoff (see Figure 2) was collected in a
deposition onto a coupon
container to measure the amount of Cs removed from
the contaminated top surface. The amount of
collected rainwater was determined by measurement
of the difference in weight of the container including
the coupon before and after the rain exposure. After
the rain exposure, the coupons were removed from
the container and dried inside the laboratory for 24
hours. These dried coupons were packed in airtight
containers with dehydrating material and shipped
back to the EPA facility (Research Triangle Park, NC)
for further analysis. The coupons were dried to
minimize additional Cs penetration unrelated to the
rain event. Each rainwater sample was transferred to
three 15 mL airtight polyethylene vials (Fisher
Scientific, Pittsburgh, PA), up to 5 mL per vial, and
shipped to the EPA facility for analysis. The
remaining rainwater was discarded.
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2.6 Analysis of Rainwater Runoff
Prior to analysis, the rainwater samples were filtered
using a syringe filter and 5 mL of each sample was
transferred to a clean 15 mL tube labeled with the
Figure 2. Containers after rain exposure
sample ID. Rainwater samples were analyzed for Cs
using EPA Standard Method 200.8.10 A model
ELAN 6000 ICP-MS (Perkin Elmer, Waltham, MA)
was used for Cs analysis. The operating conditions
for the ICP-MS are summarized in Table 3.
Table 3. Operating conditions for ELAN 6000
Radio frequency (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
1200 Watts
0.87 L/min
9 Volts (V)
-2600 V
1850V
70 mV
-8V
2000 sec
4.12 minutes
3
20
~0.10mL/min
3347V DC
0.50 A DC
6
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Grid Current
Filament Voltage
Dwell Time Per amu
Resolution
94 mA DC
6.18Vrms
100 min
He (3.016 amu)= 2089
Mg (23.985 amu)= 2065
Rh (102.905 amu)= 1998
Ce (139.905)= 1995
Pb (207.977)= 2113
U (238.050)= 2223
Internal standard reference solution (10 |oL) was
dispensed into every sample vial before analysis.
The internal standard solution contained 100 mg/L of
Ge, In, Li, Sc and Tb. Rainwater runoff for the
procedural control coupons was 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 DI water
followed by multiple rinses with DI water and dried
on a Class 100 clean bench for at least 12 hours.
2.7 Analysis of Coupons
After arrival at the EPA facility for analysis, the
coupons were dried in a vacuum oven for 24 hours at
80 °C with slightly negative pressure (~10 inches of
Hg). Dried coupons were cut vertically using a
diamond saw (Model 830036, Barranca Diamond
Products, Torrance, CA) without the use of lubricant
(i.e., water). Freshly-prepared surfaces were cleaned
thoroughly with compressed air to remove residual
particles from the cut surface. The dissected coupons
were stored separately in plastic containers which
contained dehydration materials. These containers
were closed with air-tight lids and shipped to the
University of Texas at Arlington, TX, for LA/ICP-
MS analysis. The RH and temperature were
monitored throughout the coupon transportation and
stored using a sensor (HOBO RH/TEMP, Onset
Computer Corporation, Cape Cod, MA) coupled with
a data logger.
The inner surfaces of coupons were analyzed at the
University of Texas for Cs vertical concentration
profiles using LA/ICP-MS. This analysis mapped the
distribution of trace elements within urban building
materials using laser ablation (193 nm, UP193FX,
New Wave Research, Inc., Fremont, CA) coupled
with ICP-MS (ELAN DRC-e, PerkinElmer, Waltham,
CT). The laser spot size was maintained at 100 |am
with 10 Hz pulse rate, and 30 |j,m/sec scan speed.
The inner surface of a blank coupon (not
contaminated and no rain exposure) of each material
type was analyzed to quantify the background levels
of Cs. Cs concentrations in the blank were averaged
and the quantifiable background of Cs concentration
was set as the sum of three times the standard
deviation of the background Cs concentration and the
average background concentration of Cs. Three lines
were scanned for the standard materials (National
Institute of Standards and Technology (NIST)
Standard Reference Material (SRM) 612 and 614)
before coupon analysis, and these standards were also
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rescanned for every 12 scans of the coupon. A
detailed analysis procedure is described in a joint
report of EPA and LLNL and the references therein.7
The necessary analysis areas for laser ablation were
determined initially by analyzing one of the four test
coupons exposed to rain for each material. The Cs
profiles from LA/ICP-MS analysis of the test
coupons were compared to the Cs profiles from the
blank coupons. The analysis depth for individual
surface materials was established as 2 mm for asphalt,
5 mm for brick, 5 mm for concrete, 2 mm for granite,
and 8 mm for limestone.
2.8 Removal Efficacy (%)
The removal efficacy by the simulated rain was
assessed by determining the amount of Cs in the
rainwater runoff samples. Cs amounts in the
rainwater samples were compared to Cs amounts
from the spike control and the removal efficacy of Cs
from the coupon material was calculated as the ratio
of Mr and Msc:
Removal % = Mr/ Msc x 100
where Mr is the average Cs amount (|ag) in replicate
rainwater samples and Msc is the average Cs amount
(|ag) from five spike controls.
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3. Quality Assurance/Quality Control (QA/QC)
All equipment (balance), monitoring devices (e.g., RH, temperature) and analyzers (LA/ICP-MS and ICP-MS) used
at the time of evaluation were verified as being calibrated (Table 4).
Table 4. Equipment Calibration
Instrument
Frequency
RH sensor
Temperature sensor
Balance
ICP-MS
LA/ICP-MS
Prior to Experiment
Prior to Experiment
Prior to Experiment
Daily when used
Daily when used
Data quality indicators (Table 5) for the critical measurements were used to determine if the collected data met the
quality assurance objectives.
Table 5. DQIs for Critical Measurements
Measurement
Parameter
Cs Concentration Map
Cs concentration
RH
Temperature
Sample Mass
Coupon Conditioning Time
Rain water mass
Measurement
Method
Completeness
%
LA/ICP-MS
ICP-MS
RH probes
100
100
100
Temperature probes 100
Analytical Scale 100
Computer Clock 100
Balance 100
The data quality indicators included Cs concentration
in rainwater, Cs subsurface penetration map,
rainwater weight, RH, temperature, and conditioning
time. All measurements were completed and the
percent completeness was more than 95%, exceeding
the requirements for the percent completeness
indicator for all of the measurement parameters.
QC samples generated during the rain testing
included PC coupons (no deposition, rain exposed)
and rainwater samples (no coupon). The relative
standard deviation for the amount of Cs recovered
from the five spike controls was less than 25%. The
analysis of PC coupon rainwater samples showed a
minimal amount of Cs (less than 0.5% of Msc). The
rainwater sample results showed no quantifiable
amount (<0.025|ag/L) of Cs. The temperature and
RH during transportation from the EPA facility to the
WIS rain facility were 10-20 °C and 15 - 20% RH,
respectively. However, the RH reading inside one of
the four plastic shipping containers (each containing
~30 coupons) was more than 90% when the samples
were shipped from WIS to the EPA facility after the
simulated rain event. This exposure to high RH was
due to the presence of relatively wet coupons in the
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shipping containers following the exposure to rain. coupons are not influenced by high RH because of
Since not all shipping containers were monitored for the high water content within the material. The Cs
the exposure to the RH level, some coupons without penetration depths for positive controls could be
rain exposure may also have experienced this high further into the material due to high RH exposure.
humidity during transportation. The wet test
10
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4. Results and Discussion
4.1 Rain Characteristics
The WIS simulated rain facility uses multiple nozzles
in series at equal distances from each other connected
to parallel water lines to provide a homogeneous rain
volume distribution across the test facility. Figure 3
shows the observed distribution of the collected
rainwater amounts based on the approximate location
of each container on the table as shown in Figure 2.
Ten containers without a coupon inside were
included for accurate measurement of the volume of
rain. Rain water amounts collected in these empty
containers were found to be consistent in volume
with nearby containers containing coupons. This
provides evidence that backsplash of rain to areas
outside the containers containing coupons is
negligible. The usage of multiple nozzles creates an
interference pattern with local maxima and minima in
water volumes collected ranging between 5 mL and
45 mL per container, corresponding to a range in
10-
jy
.a
9-
8-
7-
6-
5-
I
o 4^
.c
| 3-
t 2-
J8 ^
o:
o-
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Raster points Long Axis Table (arb units)
Figure 3. Rain Volume (mL) collected. Location of empty containers are marked (X)
rain rate between 0.23 and 2.32 cm (average of 1.03
cm) for this 30-minute test. Such variation was
unexpected but creates the opportunity to study the
amount of Cs in the runoffs as function of the
collected amount of rainwater. No overflow of
11
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rainwater from individual containers onto the
supporting table was observed after the rain event.
4.2 Rainwater Analysis
Cs concentration results from the ICP-MS analysis
were converted to total amounts of Cs removed from
the surface of the treated coupon using the total
amount of rainwater in each specific container as
determined by the difference in weight of the
container before and after the rain event.
4.2.1 Cs Subsurface Distribution of
Blank Coupons
Blank coupons (not contaminated and no rain
exposure) were analyzed to investigate the
background Cs distribution profile. The inside
surface of a dissected blank coupon of each surface
type was analyzed for the Cs distribution in two
dimensions using LA/ICP-MS. The X-axis (in |j,m)
is the penetration direction and the particle deposited
surface is along the Y-axis (in |am). A limestone
blank coupon (Figure 4(e)) shows a negligible
amount of Cs background (level 0.01 ppm) with a
uniform distribution. This uniform Cs distribution is
also found within the concrete blank coupon (Figure
4(c)) with a Cs background level of 0.77 ppm. The
granite blank coupon (Figure 4(d)) contains high Cs
levels with islands of Cs in multiple locations. The
Cs background level, including these localized high
Cs spots, is 4.42 ppm. The asphalt blank coupon
(Figure 4(a)) contains widely spread higher Cs spots
with the Cs background level is 2.33 ppm. The
highest Cs background level was found for the brick
blank coupon (Figure 4(b)) with a level of 9.41 ppm.
12
-------
5000
4000
3000
2000
1000
5000
4000
3000
2000
1000
5000
4000
3000
2000
1000
1000 2000 3000
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
13
-------
5000
4000
3000
2000 P
1000
5000
4000
3000
2000
1000
1000 2000 3000 4000
5000
6000
7000
Figure 4. Background Cs distribution profiles (in ppm) of blank coupons for (a) asphalt, (b) brick, (c)
concrete, (d) granite, and (e) limestone
4.2.2 Cs Subsurface Distribution of
Positive Controls
Cs-contaminated (but not exposed to rain) coupons
were analyzed to investigate Cs subsurface
penetration after deposition. The inside surface of a
dissected coupon was analyzed for Cs distribution in
two dimensions using LA/ICP-MS. Figures 5
through 9 show the analysis results for positive
control coupons using both water and methanol
solution deposition methods. The penetration
direction is the X-axis and the particle deposited
surface is along the Y-axis. The units of the analyzed
surface area are in |am. Cs distribution profiles for
the asphalt positive control coupons are shown in
Figure 5. High Cs areas were localized close to the
deposition surface for both deposition methods, and
this localized contamination is due to the limited pore
connectivity of asphalt. Cs penetration was deeper
for the water solution coupon (more than 2 mm in
Figure 5(a)) than for the methanol solution (—1.5 mm
in Figure 5(b)).
14
-------
Penetration direction
5000
Cs
ppm
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
I 48
46
44
42
40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
S°
0 500 1000 1500 2000 ° 50° 100° 150° 200°
Figure 5. Cs distribution profiles of asphalt positive controls for (a) water solution sample and (b) methanol
solution sample
Cs distribution profiles of the brick positive control
coupons are shown in Figure 6. The Cs distribution
pattern of a brick coupon was found to be different
from asphalt. Cs in the brick coupon was more
homogeneously distributed across the contaminated
surface of the brick coupon than on the surface of the
asphalt coupon. High Cs concentration was observed
at the deposition surface and the Cs amount
decreased gradually toward the inside of the coupon.
This pattern is similar for both deposition methods
(water versus methanol). Further, Cs penetration was
deeper for a water solution deposition coupon (~2
mm in Figure 6(a)) than a methanol solution (—1.5
mm in Figure 6(b)), and this result was similar to the
asphalt coupons.
15
-------
Penetration direction
Cs
I.
«
*
,4,
— 1$
12(
„(
m
i
ppm
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
I a:
j
I
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Figure 6. Cs distribution profiles of brick positive controls for (a) water solution sample and (b) methanol
solution sample
Cs distribution profiles for the concrete positive
control coupons are shown in Figure 7. Cs in the
concrete coupon was distributed across the deposition
surface with the gradual decrease in amount from the
deposition surface toward the inside of the coupon.
A few areas of concentrated Cs are shown near the
deposition surface, possibly because of irregular pore
characteristics in the mixture of cement and mineral
aggregates. This pattern is similar for both
deposition methods, and Cs penetration depth (~1
mm) was similar for both the water solution coupon
(Figure 7(a)) and the methanol solution (Figure 7(b)).
16
-------
Penetration direction
Cs
i
ppm
500 1000 1500 2000 2500 3000 3500 4000 4500 5000
I
500 1000 1500 2000 2500 3000 3500 4000 4500 5TOO
Figure 7. Cs distribution profiles of concrete positive controls for (a) water solution sample and (b) methanol
solution sample
Cs distribution profiles in the granite positive control
coupons are shown in Figure 8. High Cs distribution
was localized near the deposition surface, and Cs was
less widely distributed across the contaminated
surface than in the brick and concrete coupons.
These areas of localized high Cs are encountered
because of the limited pore connectivity, similar to
the connectivity observed for the asphalt coupons.
Some areas of concentrated Cs can be observed
inside the coupon for both the water solution sample
(a) and the methanol solution sample (b). These
islands of high Cs were also found in the blank
granite coupon. However, it is difficult to
distinguish which islands are due to the surface
contamination (deposition) and which islands are
background Cs. The Cs distribution characteristics
are similar for both deposition methods.
17
-------
Penetration direction
5000
Cs
I 48
46
44
42
40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
10
ppm
5000
4500
4000
3500
3000-
2500
2000-
1500-
1000
500
32
30
28
26
24
22
20
18
16
14
12
8°
I5
\l
0 500 1000 1500 2000 0 500 1000 1500 2000
Figure 8. Cs distribution profiles of granite positive controls for (a) water solution sample and (b) methanol
solution sample
Cs distribution profiles for limestone positive control
coupons are shown in Figure 9. Cs was distributed
widely across the deposition surface and on the inside
of the coupon. Multiple islands of high Cs
concentration were also observed, but these high Cs
concentration islands were not found in the blank
limestone coupon analysis. This particular limestone
contains the clay mineral illite as an inclusion at
about 1 wt% according to the previous RDD study by
EPA.7 This illite inclusion mineral has a high Cs
sorption capability compared to calcite, the major
mineral (> 90 wt %) in limestone. When Cs ions
travel through the subsurface of a limestone coupon,
the Cs ions are more attracted to the illite inclusion
sites, and Cs becomes concentrated at these sites. Cs
penetration was deeper when the contamination was
applied as a water solution (~5 mm in Figure 9(a))
versus as a methanol solution (~2 mm in Figure 9(b)).
18
-------
Penetration direction
3000 4000 5000 6000 7000
Cs
I
c
A
A
f.
I
5.5
5
4.5
4
3.5
3
110
"9
I
1000 2000 3000 4000 5000 6000
ppm
Figure 9. Cs distribution profiles of limestone positive controls for (a) water solution sample and (b) methanol
solution sample
4.2.3 Cs Removal by Rain
The amounts of Cs in the rainwater runoff as
determined by ICP-MS and the rain rate are plotted
as a function of the collected rainwater amount
(shown in Figure 10). The dependence of the Cs
removal upon the rain rate is tested using the
Pearson's product-moment correlation coefficient11
and shown in Table 6. The absolute correlation
coefficients for all water solution samples are higher
than 0.6, and the absolute correlation coefficients for
methanol samples are below 0.5 except for brick
samples (0.99). This result implies that the status of
Cs particles on surfaces (deposited from water and
methanol solutions in this study) may respond
differently to (rain) water application.
19
-------
10
15
20
25
0.45
0.30
0.15
0.00
3.0
2.0
1.0
8-9
0.4
0.3
0.2
0.1
0.0
0.15
0.10
0.05
0..
1.5
1.0
0.5
0.0
- Brick
. Asphalt
r Concrete
r A
~ Limestone
—
-
T
1 Granite o
'- 4
n
m m
* 0-
A _
A A :
A -
V
T
TV V
V T
i . i . i "
/\ ""
o -
*» :
0
10 15 20
Rain rate (mm/hr)
25
Figure 10. Cs amounts in rainwater runoff as function of collected rainwater volume for water (solid) and
methanol (open) deposition
Table 6. Correlation coefficient of rainwater volume and Cs amount in runoff
Sample Type
Brick - water
Brick - methanol
Asphalt - water
# of Samples
4
4
4
Pearson's r
0.78
0.99
0.98
20
-------
Asphalt - methanol
Concrete ~ water
Concrete ~ methanol
Limestone - water
Limestone - methanol
Granite - water
Granite - methanol
4
4
4
4
4
4
4
0.02
0.80
0.16
0.75
0.55
0.60
-0.27
Figure 11 shows the average (four coupons) amount
of Cs detected in the rainwater runoff for the five
building materials and as function of the type of Cs
deposition (use of water versus methanol).
Rainwater runoff from procedural control coupons
contained less than 0.006 (o,g Cs, much less than the
minimum observed amount in the runoffs for any of
the treated coupons. The Cs level in rainwater was
below the minimum quantifiable level of the ICP-MS
instrument. The largest amounts of Cs in the
rainwater runoffs were found for asphalt (water and
methanol solutions during Cs contamination) and
granite samples (methanol solution during Cs
deposition). Table 7 has the calculated removal
efficiencies based on the initial application of 4.6±0.1
(o,g Cs per treated coupon as determined from ICP-
MS analysis of the average spike control amount.
21
-------
Figure 11. Cs amounts in rainwater runoff as function of building material type and deposition method (H2O:
Cs in water; MeOH: Cs in methanol)
Cs removal efficacies by rain increase in the order of
brick ~ concrete ~ limestone < granite < asphalt for
both water and methanol based Cs deposition
methods. Removal efficacies for Cs from brick.
concrete, and limestone are small (< 5%) for both
deposition methods. This low Cs removal by rain is
due to the high water absorption capability of these
porous surface materials. The LMCP-MS results for
brick, concrete, and limestone samples are shown in
Figures 12, 13, and 14, respectively. The Cs
distribution profiles for these surfaces have a pattern
similar to the pattern of the positive control samples
(Figures 6, 7 and 9). For brick (Figure 12), Cs from
the deposition is distributed widely on the surface
and the Cs gradually penetrates across the surface for
both water- and methanol- based Cs solution samples.
The subsurface penetration appears deeper the
subsurface penetration for the positive control
samples shown in Figure 6. For concrete (Figure 13).
samples exposed to rain show similar Cs distribution
patterns and penetration depths when compared to the
positive controls. This limited Cs penetration is due
to the excess of Cs sorption sites which bind the Cs
instead of allowing it to penetrate.
22
-------
Table 7. Efficacies for removal of Cs by (simulated) rain event
Material
Brick
Asphalt
Concrete
Limestone
Granite
Deposition
method
water
methanol
water
methanol
water
methanol
water
methanol
water
methanol
Removal % ± SD (n=4)
5±2
4±4
45 ±17
45 ±5
4±3
5±1
2±1
2±1
14 ±5
37 ±7
23
-------
Penetration direction
ro
to
O
Q.
0»
Cs
1
S5
SO
55
50
45
40
35
30
25
20
15
1 O
SOO 10OO 1 5OO 2OOO 25OO 3OOO 35OO 4OOO 45OO 5OOO
26
.
ppm
500 1000 1500 2000 25OO 3OOO 35OO 4OOO 45OO
Figure 12. Brick rain test example samples: (a) water solution sample and (b) methanol solution sample
24
-------
Penetration direction
Cs
Figure 13. Concrete rain test example samples: (a) water solution sample and (b) methanol solution sample
25
-------
Penetration direction
5000
8000
1000 2000 3000 4000
1000 2000 3000 4000
5000
6000
7000
8000
Cs
2.3
12.1
1.7
1.1
ppm
Figure 14. Limestone rain test example samples: (a) water solution sample and (b) methanol solution sample
26
-------
Penetration direction
5000
5000
ppm
I
0 500 1000 1500 2000 0 500 1000 1500 2000
Figure 15. Asphalt rain test example samples: (a) water solution sample and (b) methanol solution sample
The Cs penetration pattern through asphalt coupons
(Figure 15) after rain could not be discerned from the
positive control asphalt coupons shown in Figure 5.
Rainwater runoff from asphalt samples showed the
highest Cs removal efficacy among the five test
materials. Asphalt coupons are a mixture of mineral
aggregates and binder from crude petroleum. When
the liquid Cs particles are deposited onto the asphalt
coupon surface, the particles on the mineral
aggregate surface area are wetted (and therefore the
Cs penetrates through the pores) via capillary suction
while the other particles on the binder surface area
may not get wetted (therefore the Cs stays on the
surface). When the Cs contaminated asphalt coupons
were exposed to rain, Cs particles on the binder
surfaces might have been washed off more easily
than the Cs on mineral aggregates. This type of
capillary suction did not occur for the other four
surfaces (brick, concrete, granite, and limestone)
because they were composed of 100 % porous
mineral materials.
27
-------
Penetration direction
5000
5000
0
ppm
10.5
10
9.5
9
8.5
8
6.5
6
5.5
5
4.5
4
3.5
3
l"
'
1 0.5
'o
0
0 500 1000 1500 2000 0 500 1000 1500 2000
Figure 16. Granite rain test example samples: (a) water solution sample and (b) methanol solution sample
The Cs penetration pattern through granite coupons
(Figure 16) after rain could not be discerned from the
positive control granite coupons shown in Figure 8.
The rainwater runoff from the granite samples
showed the second highest Cs removal among the
five surface types, possibly because of relatively less
water-permeable surface pore characteristics (low
porosity and pore connectivity) of granite versus the
brick, concrete, or limestone. The deposited liquid
particles on the granite surface might not have
penetrated into the granite as deeply as other porous
surfaces. In addition, because of low water
permeability, the rainwater on the granite surface
flows as runoff rather than being absorbed into the
subsurface. Table 7 shows that the methanol
solution-based Cs deposition on granite samples
showed higher removal efficacy than water solution
samples because the methanol solution Cs particles
penetrated less into the surface than the water
solution particles.
28
-------
5. Discussion
The simulated rain test results for Cs showed that the
removal percentages vary depending on the material
types. The removal percentage was in the following
order: brick ~ concrete ~ limestone < granite <
asphalt. This order is same for both Cs surface
contamination methods. Granite coupons showed a
noticeable difference in removal efficiency (37 % for
methanol and 14% for water) depending on the
deposition method. Also, the subsurface penetration
of Cs was different for all five material types.
Following the simulated rain test, the penetration
depth of Cs into the building material was in the
following order: limestone > brick > concrete ~
asphalt ~ granite. The pattern of the subsurface Cs
distribution was highly diverse depending on the
surface types, ranging from a uniform distribution for
concrete and brick to a highly localized distribution
for asphalt, granite, and limestone. This variation in
Cs fate after the rain exposure can be explained by
the characteristics of the material. The pore
properties of the five materials were measured and
are summarized in Table 8.
Table 8. Pore properties of test surface materials
Material
Asphalt
Brick
Concrete
Granite
Limestone
Porosity a
(%)
2.18
20.28
20.33
1.46
15.30
Imbibition Slope b
0.256
0.497-0.603
0.540-0.706
0.207-0.245
0.534-0.586
Water Sorptivity c
(mm/seclfl)
0.0005
0.13
0.03
0.002
0.06
a Testing according to reference 12.
b Testing according to reference 13.
0 Testing according to reference 14.
Porosity in Table 8 represents the total volume of
water that can be stored within the material.
Concrete can contain more water than any of the
other materials; the lowest porosity is found in
granite. The imbibition slope explains the pore
connectivity. If the slope is close to 0.5, the material
has good pore connectivity.15 However, if the slope
is lower than 0.5, the pores within the material are
not well connected. Materials with good pore
connectivity such as brick, concrete, and limestone
can deliver water and Cs ions into the subsurface
with a uniform spread pattern. However, Cs ions
may be localized (trapped in pores) in asphalt and
granite coupons. Water sorptivity indicates how fast
a material absorbs water. The water sorptivity values
in Table 8 were obtained after the materials were
equilibrated at 86% RH. The table shows that brick
absorbs water fastest and asphalt absorbs water
slowest. When this information is combined, the
brick coupons absorb rainwater faster and absorb a
higher volume than the other materials. Asphalt
absorbs water much slower and absorbs less volume
of water than other materials. Concrete coupons
showed low Cs penetration depth and low Cs
29
-------
removal by rain. This limited penetration depth (~1
mm) is due to the available sorption sites for Cs on
the concrete surface. Asphalt also showed a
penetration depth similar to the concrete, but the
limited penetration within asphalt is due mainly to
the poor pore connectivity and not sorptivity. The Cs
removal by rain from concrete is, therefore, much
lower than Cs removal from asphalt due to the high
water sorptivity on concrete.
The removal of Cs by rain is related closely to these
pore characteristics of the material. At the start of the
rain, the rainwater is mostly absorbed if the materials
are porous until the pores are saturated with rainwater.
The time required to saturate surface pores is closely
related to the water sorptivity shown in Table 8.
Based upon the data in Table 8, the asphalt coupons
are saturated approximately 200 times faster than the
brick coupons. The asphalt coupons are, therefore,
saturated with water at the beginning of the exposure
to the rain. However, for the brick coupons, the rain
water was absorbed into the brick coupons for a
longer period than the asphalt coupons. During this
period of rainwater absorption, Cs on the surface (as
deposited in methanol solution) and subsurface Cs
ions (as deposited in water solution) were pushed
farther into the coupons. The water saturated pores
provide a barrier (film) to the following rain on the
surface and it becomes more difficult for rainwater to
remove Cs ions inside pores due to the limited
exchange of water between surface pores and run-off
rainwater. While the surface is saturated, the
subsurface Cs ions keep being delivered deeper into
the material. This penetration is governed by pore
connectivity and Cs sorptivity. Since asphalt and
granite have poor pore connectivity, the Cs ions
penetrate minimally into the subsurface and can be
removed rather easily by continuous rain when
compared to brick, concrete and limestone coupons.
From these test results, it is clear that it will be more
difficult to remove RDD Cs from some materials
such as brick, concrete, and limestone after rain
exposure than before rain due to subsurface
penetration through the contaminated material. The
test results also show that the Cs removal by rain for
high water sorptivity surface materials (brick,
concrete, and limestone) may not be affected by
deposition type (dry/methanol or wet/water
deposition). However, the dry deposited CsCl
particles on asphalt and granite are expected to be
removed more easily by rain than the wet CsCl
particle deposition.
The study results imply that rain can affect the
contaminated areas in various ways after an RDD
event in the urban environment, especially with a
water-soluble RDD material such as CsCl. Most of
the porous building surfaces such as concrete and
brick may retain RDD material within the surface
material. However, asphalt material may release a
significant amount (less than 50%) of RDD
contamination during a rain event ,and the area can
subsequently be further (potentially widely)
contaminated with RDD Cs-containing rainwater.
For example, if RDD Cs-contaminated rainwater
runoff meets the clean concrete pavement, the
pavement can then be contaminated, and this
contamination could potentially penetrate the
subsurface due to this rainwater exposure.
This test has been conducted with non-radioactive Cs.
The actual RDD contamination may be much less
(—100 to 1000 times lower) than the level used in this
30
-------
study. If the surfaces are contaminated with lower
levels than the test conditions in this study, the
removal percent and penetration pattern may be
different. The effect of time has not been
investigated in this study. Some surfaces may react
with Cs ions as a function of time and the reactions
can increase the binding forces between surfaces and
Cs. The current study showed that rain on RDD Cs-
contaminated surfaces can redistribute the
contaminants over a wide area and increase the
necessary decontamination efforts due to the
subsurface penetration. The decontamination
strategies should consider the potential impact of rain
on a contaminated area. The best option can be to
apply decontamination technologies to a
contaminated area before any meteorological events
that produce water in the atmosphere (including fog,
mist, possibly snow). A systematic method or tool
that aides in the prediction of the fate of water
soluble RDD contamination as a function of
atmospheric precipitation for various surface types
would be helpful in assessing the impact during
remediation.
31
-------
6. References
1 Gonzalez, AJ. (2003) Security of radioactive sources: threats and answers. In International Conference on
Security of Radioactive Sources, 33-58. Vienna, Austria: International Atomic Energy Agency.
2 NRC (May 2007) Backgrounder on Dirty Bombs: U.S. Nuclear Regulatory Commission.
3 Zimmerman, P.D. andLoeb, C. (2004) Dirty bombs: The Threat Revisited. In Defense Horizons, ppl-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 Anal 27, 533-546.
6 Lee, S.D., Snyder, E.G., Willis, R., Fischer, R., Gates-Anderson, D., Sutton, M, Viani, B., Drake, J. and
MacKinney, J. (2010) Radiological Dispersal Device Outdoor Simulation Test: Cesium Chloride Particle
Characteristics. Journal of Hazardous Materials 176, 56-63.
7 Lee, S.D., Snyder, E.G., Oudejans, L., Fischer, R., Gates-Anderson, D. and Sutton, M. Radiological Dispersal
Device Outdoor Simulation Test: Fate of Cs on Limestone. Washington, D.C.: U.S. Environmental Protection
Agency; 2010 January. Internal Report No.: EPA/600/X-10/005.
8 Desrosier, M., Volchek, K., et al. The Radiological Decontamination Laboratory Study. Ottawa
Ontario, Canada. Environmental Canada; 2006. Report No.: EE-180.
9 ASTM International. Standard Test Method E104-02. Standard Practice for Maintaining Constant Relative
Humidity by Means of Aqueous Solutions. West Conshohocken, PA: American Society for Testing and Materials;
2007.
10 U.S. Environmental Protection Agency. Method 200.8. Determination of Trace Elements in
Waters and Wastes by Inductively Coupled Plasma - Mass Spectrometry. 1994.
11 Neter, J., Wasserman, W., Kutner, M.H. 1990. Applied Linear Statistical Model: Regression,
Analysis of Variance, and Experimental Designs. 3r ed. Homewood, Illinois: Irwin, 38-44, 62-
104.
32
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12Klute, A. 1986. Methods of Soil Analysis, Part 1, Physical and Mineralogical Methods, Second
edition. American Society of Agronomy Inc., Soil Society of America, Inc., Madison, WI.
13 Hu, Q., Persoff, P. and Wang, J.S.Y. (2001). Laboratory Measurement of Water Imbibition
into low-Permeability Welded Tuff. Journal of Hydrology, 242(1-2), 64-78.
14 ASTM International. Standard Test Method C1585-04. Standard Test Method for
Measurement of Rate of Absorption of Water by Hydraulic-Cement Concretes. West
Conshohocken, PA: American Society for Testing and Materials; 2004.
15 Ewing, R.P., and Horton, R. (2002) Diffusion in Sparsely Connected Pore Spaces: Temporal
and Spatial Scaling. Water Resources Research, 38(12), 1285-1297.
33
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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
------- |