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LLNL-TR-810290
RUNIT PROJECT: DATA
REPORT
Non-destructive Testing and
Evaluation Investigation of Runit
Island Containment Structure
Terry Hamilton
March 2020
Disclaimer
This document was prepared as an account of work sponsored by an agency of the United States
government. Neither the United States government nor Lawrence Livermore National Security, LLC,
nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or
responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or
process disclosed, or represents that its use would not infringe privately owned rights. Reference herein
to any specific commercial product, process, or service by trade name, trademark, manufacturer, or
otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the
United States government or Lawrence Livermore National Security, LLC. The views and opinions of
authors expressed herein do not necessarily state or reflect those of the United States government or
Lawrence Livermore National Security, LLC, and shall not be used for advertising or product
endorsement purposes.
Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC,
for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-
07NA27344.
LLNL-TR-810290
RUNIT PROJECT: DATA REPORT
Non-destructive Testing and Evaluation Investigation
of the Cactus Crater Containment Structure on Runit
Island, Enewetak Atoll
Terry Hamilton
Lawrence Livermore National Laboratory
PO Box 808
Livermore, CA 94550
USA
March 2020
ii
Table of Contents
1.0 PROLOGUE …………………………………………………………………1
2.0 FIELD INVESTIGATION OVERVIEW ………………………………… 3
3.0 SUMMARY RESULTS AND CONCLUSIONS ………………………… 5
4.0 REFERENCES ………………...……………...…………………………… 5
Figure 1. Map of the Marshall Islands ……….……………...…………….….. 2
Figure 2. A Google map image showing a contour-plot overlay of the
relative thickness of the concrete cap covering Runit Dome (based on
Impact Echo (IE) measurements with the thinnest areas around the middle
of the dome represented in a darker bluish, purple shade) [compiled from
data collected by Olson Engineering, Inc., Visual Survey, May 2013] …...…. 7
Appendix A: NON-DESTRUCTIVE TESTING AND EVALUATION
INVESTIGATION RUNIT DOME, RUNIT ISLAND, Olson Engineering Inc,
Contractor Report, Job No. 4230A
1
1.0 PROLOGUE
Enewetak Atoll is a former U.S. atmospheric nuclear test site located in the Marshall Islands about
4000 kms west of Hawaii in the NW Pacific Ocean (Fig. 1). The people of Enewetak returned to
their ancestral homeland in 1980 following an extensive cleanup and rehabilitation program (DNA,
1981). At the time of cleanup, more than 86,000 cubic meters of contaminated soil and debris were
encapsulated in concrete inside an unlined nuclear test crater (Cactus Crater) on the north end of
Runit Island. The mound of encapsulated waste was subsequently covered over by a non-load
bearing concrete cap to help protect the waste pile below from natural erosion.
Public Law (P.L.) 112–149 Insular Areas Act of 2011 was developed to provide U.S. legislative
authority outside of Compact of Free Association (COFA) and the U.S Department of Energy
(DOE) Marshall Islands Program to develop a site-specific monitoring program and reporting on
the status of the Cactus Crater containment structure. The requirements of the Insular Areas Act
of 2011 directed the Secretary to periodically conduct a visual study of the exterior concrete and
perform radiochemical analyses of the groundwater surrounding and in the structure. The
Secretary was also directed to submit to Congress a report describing the results of each visual
survey and the radiochemical analysis; and “a determination on whether the surveys and analyses
indicate any significant change in the health risks to the people of Enewetak from the contaminants
within the Cactus Crater containment structure.”
Historical studies have generally been dismissive about possible hazards associated with leakage
of radioactive waste from the contaminant structure. This conclusion was drawn from a simple
argument that the amount of fallout contamination encapsulated in the contaminant structure is
dwarfed by the quantity of radioactive debris deposited in bottom sediments of the lagoon during
the nuclear testing program (Noshkin and Robison, 1997). The fallout contamination contained in
lagoon sediments subsequently formed a reservoir and source-term for redistribution and
assimilation of fallout radionuclides across the lagoon and into the marine food chain. It was
inferred by the authors that the continuous remobilization of sedimentary sources of contamination
into the water column would dominant any likely contribution from leakage of radioactive
contamination from the containment structure even under an instantaneous release scenario. Such
2
Fig 1. Map of the Marshall Islands.
3
arguments have failed to alleviate the concerns of the people of Enewetak and its leadership, and
under a cooperative effort led to the formulization of the Insular Act of 2011. This P.L. provided
a mandate under the auspices of the U.S. Department of Energy (DOE), together with U.S.
Department of Interior (DOI) as the prime funding agency, to provide a site-specific assessment
of the radiological risks and potential health impacts posed by leakage of radioactive waste from
the Cactus Crater containment structure.
An initial visual survey of the Cactus Crater containment structure was completed in 2013 in
support of the Insular Areas Act of 2011 (Hamilton, 2013). Photographs were taken and visual
descriptions given for 357 external concrete panels and the top cap segment of the containment
structure. Supplemental data and information were also reported on subgrade nondestructive tests
performed by an independent contractor with experience applying nondestructive test methods to
similar structures. The nondestructive testing (NDT) investigation was conducted in conjunction
with the 2013 visual survey with knowledge of the potential future need to drill and establish
groundwater monitoring boreholes on and around the site. Our strategic vision was to ultimately
develop a site monitoring program that meet requirements established under the Insular Areas Act
of 2011 in a scientifically defensible and meaningful manner The visual survey report contained
additional recommendations to include options for maintenance and further testing of the exterior
concrete in support of proposed drilling operation (Hamilton, 2013). These recommendations have
since been executed (Hamilton, 2020) and significant progress made towards devising a work plan
to drill and install groundwater monitoring boreholes inside and around the Cactus Crater
containment structure (Hamilton, 2018). Statements reported by Hamilton (2013) on the condition
of the exterior concrete in the initial visual survey report were based on data and conclusions drawn
from the NDT investigation. This report provides full disclosure of the results of the
NDT investigation and condition assessment of the structure as conducted by Olson Engineering,
Inc., (Wheat Bridge, CO, Job No. 4230A). The work weas facilitated through a subcontract
award issued by LLNL to Pacific Operations International Inc. (POII).
2.0 FIELD INVESTIGATION OVERVIEW
The NDT investigation and condition assessment of the Cactus Crater containment structure on
Runit Island was performed by an independent contractor during May-June of 2013 [Olson
Engineering, Inc, Wheat Ridge, CO]. The investigation was performed under an agreement with
4
Pacific Operations International, Inc. (POII) through a subcontract award from the Lawrence
Livermore National Laboratory (LLNL).
Testing was performed to evaluate the presence of sub-grade support of the exterior concrete cap
and determine the concrete thickness and overall condition. The nondestructive testing (NDT)
techniques utilized during the investigation included Ground Penetrating Radar (GPR) for sub-
grade evaluation, Impact Echo (IE) for concrete thickness and condition, and Spectral Analysis of
Surface Waves (SASW) for concrete condition. Every concrete segment including the top cap of
the containment structure was investigated using GPR and IE. The SASW was performed on a
limited number of panels as a supporting test as time allowed. The analysis, discussion and
recommendations put forward are based on the data acquired during the investigation and previous
experience of the contractor in applying nondestructive test methods to similar structures.
As reported by Olson Engineering, the GPR test method was used to determine the
support condition of concrete slabs on grade and to identify significant air or water filled voids
or other reflective anomalies in the concrete. The GPR testing was performed with two
separate radar antennae of different frequencies (400 MHz and 200 MHz). The 400 MHz
antenna has a lower penetration depth but better resolution than the 200 MHz antenna. The GPR
testing was performed in circular scans around the dome. Scans with the 400 MHz antenna were
performed at 1.54-m (5-foot) intervals down-slope from the apex of the containment structure.
Scans using the 200 MHz antenna were performed at 3.08-m (10-foot) intervals. Appropriately
7000 linear meters (22,717 linear feet) of concrete was scanned using the 400 MHz antenna and
3600 linear meters (11,645 linear feet) scanned using the 200 MHz antenna.
The IE test method was used to measure the thickness of the concrete cap. The IE test method is
sensitive to anomalies parallel to the test surface and can be used to identify concrete degradation
such as near surface de-laminations as well as internal concrete anomalies such as cracks and voids,
and honeycombed concrete. The IE testing was performed on a grid basis with 5 test points in each
of the 357 concrete panels, and an additional 42 test points around the apex of the containment
structure. The 5-point tests were taken in each of the corners and near the center of the concrete
panels. The SASW test method is used to measure the shear wave velocity versus depth profile of
a layered system. As such, it can be used to locate voids and degraded areas in concrete as well as
to assess the overall concrete condition. The SASW testing was performed at the center of selected
5
panels dispersed across the containment structure. A total of 138 SASW tests were performed
during the survey.
3.0 SUMMARY RESULTS AND CONCLUSIONS
Background information, a description and test results of the GPR, IE and SASW test methods
as reported by Olson Engineering are given in Appendix A.
The results of the subgrade nondestructive tests show very few (< 0.6%) voided or poorly
supported regions. Other questionable zones identified from the 200 MHz antenna matched poorly
with results of questionable zones from the 400 MHz antenna, indicating that these reflections may
be due to small changes in the supporting material rather than necessarily being a true indication
of voids or poor support. Conclusions drawn from then NDT results indicate that the concrete cap
covering the containment structure is structurally sound and is shown to be sitting in intimate
contact with the mounded debris pile below. The integrity of the concrete cap and underlying
support material provide confidence that the structure is not in any immediate danger of collapse
or failure.
The IE and SASW test results from the nondestructive investigation indicate that most of the
concrete is in “Sound” structural condition. Visible cracks were readily identified in many concrete
panels; however, where the concrete appears “Sound” it is generally of good condition.
The IE test results also shows that the concrete thickness is highly variable across the containment
structure. These results are presented in the schematic shown in Fig. 2. However, the averaged
measured thickness of the concrete cap of 43 ± 7 cm is very close to the design thickness of 45 cm
(18 inches). Segments around ring rows near the base and apex of the containment structure (ring
rows A, B, I, J, and K) have typical readings greater than the average cap thickness. The thinnest
concrete cap segments appear in the middle rows, especially within ring row D, E and F.
4.0 REFERENCES
DNA (1981). The Radiological Cleanup of Enewetak Atoll, Defense Nuclear Agency (DNA),
Washington D.C.
Hamilton T.F. (2020a). Runit Project: Data Report – Exterior Concrete Core Test Results,
Lawrence Livermore National Laboratory, LLNL-TR-810020.
6
Hamilton T.F. (2020b). Web based mosaic and interactive showing results of a drone visual
survey of the exterior concrete of the Cactus Crater containment structure on Runit Island,
Enewetak Atoll. https://marshallislands.llnl.gov/, Lawrence Livermore National Laboratory
(under construction).
Hamilton, T.F. (2018). Drilling, sampling, and installation of groundwater monitoring wells on
Runit Island, Enewetak Atoll, Republic of the Marshall Islands, Request for Proposal (RFP)
Background Documentation, Statement of Work – Revision 2, Lawrence Livermore National
Laboratory, LLNL-MI-786060
Hamilton T.F. (2013). A Visual Description of the Concrete Exterior of the Cactus Crater
Containment Structure, Lawrence Livermore National Laboratory, LLNL-TR-648143.
Noshkin V.E. and W. L Robison (1997). Assessment of a Radioactive Waste Disposal Site at
Enewetak Atoll. Health Physics, 73(1), 234-247.
7
Fig. 2. A Google map image showing a contour-plot overlay of the relative thickness of the concrete cap covering Runit Dome (based
on Impact Echo (IE) measurements with the thinnest areas around the middle of the dome represented in a darker bluish, purple
shade; thickest panel segments appear in green-yellow) [compiled from data collected by Olson Engineering, Inc., Visual Survey,
May 2013] (after Hamilton, 2013).
Appendix A
NON-DESTRUCTIVE TESTING AND
EVALUATION INVESTIGATION RUNIT
DOME, RUNIT ISLAND
Olson Engineering
Job No. 4230A
3 July 2013
Published with permission Olson Engineering
NON-DESTRUCTIVE TESTING AND EVALUATION INVESTIGATION RUNIT
DOME, RUNIT ISLAND
ENEWETAK ATOLL, MARSHALL ISLANDS
Prepared for:
Pacific Operations International, Inc
P.O. Box 894248 Mililani, HI 96789
Attn: Mr. Lance Yamaguchi Phone:
808.497.9590
E-mail: LYamaguchi@IOSHawaii.org
Olson Engineering Job No. 4230A, July 3rd, 2013
Olson Job No. 4230A
Runit Dome Nondestructive Evaluation
i ii
Table of Contents
Section 1.0 EXECUTIVE SUMMARY ................................................................................ 1
Section 2.0 PROJECT BACKGROUND AND FIELD INVESTIGATION OVERVIEW 4
Section 3. NONDESTRUCTIVE TEST (NDT) METHOD DESCRIPTIONS ..................... 10
3.0 GROUND PENETRATING RADAR (GPR) TEST METHOD ................................. 10
3.1 IMPACT ECHO (IE) TEST METHOD ..................................................................... 12
3.2 SPECTRAL ANALYSIS OF SURFACE WAVES (SASW) TEST METHOD .......... 13
Section 4. NONDESTRUCTIVE EVALUATION RESULTS .............................................. 16
4.0 GROUND PENETRATING RADAR TEST RESULTS ............................................ 16
4.1 IMPACT ECHO TEST RESULTS ............................................................................ 24
4.2 SPECTRAL ANALYSIS OF SURFACE WAVES TEST RESULTS ........................ 27
Section 5.0 CLOSURE ....................................................................................................... 30
Attached Appendices:
Appendix A: Ground Penetrating Radar Results Tables
Appendix B: Impact Echo Results Tables
Appendix C: Spectral Analysis of Surface Waves Results Tables
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 1
1.0 EXECUTIVE SUMMARY
Olson Engineering, Inc. conducted a nondestructive testing (NDT) investigation to
evaluate the Runit Dome on Runit Island, in the Enewetak Atoll in the Marshall Islands from May
29th – June 3rd, 2013. Testing was performed to evaluate the presence of sub-grade support of the
concrete as well as the concrete thickness and overall condition. The nondestructive testing
techniques (NDT) utilized during the investigation included: Ground Penetrating Radar (GPR) for
sub-grade evaluation, Impact Echo (IE) for concrete thickness and condition, and Spectral Analysis
of Surface Waves (SASW) for concrete condition. The Runit Dome consists of 357 individual
panels as well as a circular “donut” panel at the dome apex. The dome is approximately 190 feet
(measured down-slope) in radius. Every panel as well as the donut section was investigated using
GPR and IE. The SASW was performed on a limited number of panels as a supporting test as time
allowed. This report includes background information, descriptions of the GPR, IE and SASW test
methods, as well as the GPR, IE and SASW test results. The analysis, discussion, and
recommendations are based on the data acquired during the investigation and our previous
experience applying nondestructive test methods to similar structures.
Test Methods:
The GPR test method can be used to determine the support condition of concrete slabs on
grade, namely identify significant air or water filled voids immediately beneath the concrete. The
GPR method can also identify the location of “reflectors” or objects with notably different electrical
properties within a medium. The IE test method is used to measure the concrete thickness of walls
and slabs. The IE test method is sensitive to anomalies parallel to the test surface and can be used to
identify concrete degradation such as near surface de-laminations as well as internal concrete
anomalies such as cracks, voids, and honeycombed concrete. The SASW test method is used to
measure the shear wave velocity versus depth profile of a layered system. As such, it can be used to
locate voids and degraded areas in concrete as well as the overall concrete condition. See Section
3.0 for further details.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 2
Test Layout:
The GPR testing was performed with two separate radar antennae of different frequencies,
400 MHz, and 200 MHz. The 400 MHz antenna has a lower penetration depth but better resolution
than the 200 MHz antenna. The GPR testing was performed in circular scans around the dome.
Scans with the 400 MHz antenna were performed at 5-foot intervals down- slope from the dome’s
apex, while the scans with the 200 MHz antenna were performed at 10-foot intervals. The start and
stop location of each scan was at a joint between panels and was recorded. In total, 22,717 linear
feet were scanned using the 400 MHz antenna and 11,645 linear feet were scanned using the 200
MHz antenna.
The IE testing was performed on a grid basis with 5 test points in each of the 357 panels
and an additional 42 test points in the donut area for a total of 1827 IE test points. The 5 test points
per panel were performed near the panel’s 4 corners and near the center of the panel.
The SASW testing was performed at the center of selected panels dispersed across the
entire dome area. A total of 138 SASW tests were performed as a supporting method to evaluate
the concrete condition.
See Section 2.0 for further details.
Results Overview:
The GPR analysis indicates that of the 22,717 linear feet scanned with the 400 MHz antenna,
only two areas consisting of 12.9 linear feet (0.06 %) is suspected to be poorly supported or “Voided”.
These two suspect voids exist at panels A42 and A45 at the 180 feet from the apex mark. Only 192.8
linear feet (0.85 %) was considered “Questionable” which may have a minor void or loose material
under the slab. The “Questionable” areas may also be due to changes in the support material. Similar
results were observed with the 200 MHz antenna, no areas were indicated as “Voided” during the
analysis and only 128 linear feet (1.10 %) were noted as “Questionable”. The two sets of GPR data were
analyzed blindly; therefore, the results of one set of testing did not influence the other analysis. The
“Questionable” zones from the 200 MHz antenna match poorly to the “Questionable” zones from the
400 MHz antenna, indicating that these reflections may be due to small changes in the supporting
material and are less likely a true indication of a minor void or poor support.
The IE and SASW test results from the nondestructive investigation indicate that most of the
concrete is of “Sound” structural condition. There were some cracks in some panels visually
apparent; however, where the concrete appears “Sound” it is generally of good condition.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 3
The IE also shows that the concrete thickness is widely variable across the dome. The
concrete thickness, which was designed to be nominally 18 inches thick, varies at the extremes from
9.7 – 28.4 inches. The average thickness is 17.3 inches with a standard deviation of 2.88 (Coefficient
of Variation of 16.6%). The Panels near the bottom and top of the dome, Rows A, B, I, J, and K and
the donut have many readings greater than the nominal thickness. The panel rows in the middle,
particularly D, E, and F have many readings less than the nominal design thickness. See Section 4.0
for further details.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation
4
2.0 PROJECT BACKGROUND AND FIELD INVESTIGATION OVERVIEW
The nondestructive evaluation (NDE) investigation and condition assessment of the Runit
Dome on Runit Island, in the Enewetak Atoll in the Marshal Islands was performed between May
29th – June 3rd, 2013 by Mr. Patrick Miller and Mr. Scott Leathers, Senior Project Engineer and
Staff Engineer of Olson Engineering respectively. The investigation was performed with
assistance from IOS personnel as well as on-site labor.
The construction of the Runit Dome was completed in 1979. The Runit Dome is comprised
of 357 concrete panels as well as a circular cap, “donut” at the dome apex. The concrete was made
using imported cement, local coral rock as aggregate and seawater, creating a unique concrete
composition. There is no reinforcing steel within the concrete. The concrete panels are not
connected using dowel bars or other means. The concrete panels vary in size, with smaller panels
near the apex and larger panels near the bottom of the dome. The concrete panels are trapezoidal
in shape and arranged in circular rows around the dome. The concrete panels have a design
thickness of 18 inches. Each panel is numbered (engraved in the panel corner in wet concrete) with
a letter and a number, where the letter indicates the row increasing up from the bottom of the dome
and the number indicates the panel number in a circular manner. The panel numbers do not
consistently start at the same orientation among all rows. Also, there are several instances of
numbers that have been skipped or duplicate numbers. Table I below lists the panel numbers of
each row and any errors in sequencing.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation
5
Table I: Number of Panels per Row and Sequencing Errors
Figure 1 below presents a photograph of the dome surface showing several typical
concrete panels note that the debris near the bottom of the photograph was removed prior to
testing.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation
6
Figure 1: Photograph of Runit Dome showing the dome surface and typical panel layout.
The GPR testing was performed using a GSSI SIR-3000 acquisition unit with GSSI 400 MHz
and 200 MHz antennae. The GPR testing was performed in circular scans around the dome at
measured intervals down-slope from the dome apex. Scans were measured down-slope from the
center of the concrete square at the dome’s apex. Scanning with the 400 MHz antenna was
performed at 5’ intervals down-slope from the apex while the scanning with the 200 MHz
antenna was performed at 10’ intervals. The difference in spacing compliments the difference in
antennas; the 200 MHz antenna is roughly 10 times the physical size of the 400 MHz antenna,
has a lower resolution and a deeper penetration. Therefore the 200 MHz antenna is used to look
for large anomalies or reflectors and was thus used at a coarser spacing. All scans were
performed in the clockwise direction. The start and stop locations of each scan relative to the
permanent joints between panels were recorded to ensure that the GPR study could be easily
Olson Job No. 4230A Runit Dome Nondestructive Evaluation
7
Figure 2: Photograph of Scott Leathers performing GPR Testing with the 400 MHz antenna.
Figure 3: Photograph of Scott Leathers performing GPR Testing with the 200 MHz antenna.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation
8
The IE and SASW tests were performed using an Olson Instruments Freedom Data PC with
an IE-1 test head and a SASW test bar, respectively. The IE-1 test head and SASW bar utilize Olson
Instrument’s piezoelectric displacement transducers to measure the vibration of the concrete surface
due to nearby impacts. The spacing between the SASW transducers was set to 14.2 inches (36
cm). The distance between transducers affects the assessment depth of the SASW test method. A
small metal impact hammer (4 oz) was used as the seismic energy source for both the SASW and IE
testing.
The IE testing was performed at five locations per concrete panel. These five locations
include near each of the four corners as well as the panel center. Figure 4 shows a sketch of the IE
test layout. This test layout was consistent on all 357 panels. The distance from the panel corner
varied depending upon the overall panel size; on the smaller panels (Rows K, J and I) the corner
tests were approximately 1’ in from each edge, on the medium size panels (Rows H, G, F, and E)
the corner tests were approximately 2’ in from each edge, and on the bottom rows with the largest
panels (Rows D, C, B, and A) the corner tests were approximately 3’ in from each edge. All SASW
testing was performed at the approximate center of the tested panel. Both the IE and SASW
equipment performs better on relatively smooth concrete, therefore the test locations were typically
on the smoothest area near the intended test point. Figures 5 and 6 present photographs of IE and
SASW testing.
Figure 4: Sketch of IE Test Locations on Each Panel, these test locations referred to in results tables.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation
9
Figure 5: Photograph of Patrick Miller performing IE testing on the Runit Dome.
Figure 6: Photograph of Patrick Miller performing SASW testing on the Runit Dome.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 10
3.0 NONDESTRUCTIVE TEST (NDT) METHOD DESCRIPTIONS
The GPR, IE and SASW nondestructive test methods are discussed below in Sections 3.1
– Section 3.3, respectively.
3.1 GROUND PENETRATING RADAR (GPR) TEST METHOD
The GPR method involves moving an antenna across a test surface while periodically sending
pulsed waveforms from the antenna and recording the received echoes, as sketched in Figure 7.
Pulses are sent out from the Geophysical Survey Systems Inc., SIR-3000 computer driving the
antenna at the design center frequency of the antenna, in this case 400 or 200 MegaHertz (MHz).
These electromagnetic wave pulses propagate through the material directly under the antenna, with
some energy reflected back whenever the wave encounters a change in electrical impedance, such
as at a rebar or other steel embedment or water/air-filled void space. The antenna then receives
these echoes, which are amplified and filtered in the GPR computer, and then digitized and stored.
A distance wheel records scan distance across the test surface and embedded features can be located
as a given distance from the scan start position. For repetitive scanning, a standard survey is
designed and adhered to as field conditions allow, minimizing mistakes and maximizing data
quality.
The scans for this investigation were
created from pulses sent out at lateral intervals
of 24 pulses per foot (2 pulses per inch). The
resulting raw data is in the form of echo
amplitude versus time. By inputting the
dielectric constant, which defines the material
velocity, and by estimating the signal zero
point, the echo time data can be converted to
echo depth. The following equations explain
this conversion:
VEM = c / 0r0.5 Equation 1
Figure 7: Typical GPR Field Setup
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 11
D = (VEM * T) / 2 Equation 2
where VEM is the material electromagnetic velocity, c is the speed of light (in air) 0r is the
material relative dielectric constant, D is depth, and T is the two-way radar pulse travel time. A
typical concrete relative dielectric constant of 0r = 6.0 was used for the concrete in this
investigation based on previous GPR investigations. The scans are then plotted as waterfall plots
of all of the individual data traces collected, with the lightness or darkness (or color) of each point
in the plot being set by the amplitude and polarity (positive or negative) of the data at a given depth
in each trace. See Section 4.1 for example GPR data from the Runit Dome including varying
conditions.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 12
3.2 IMPACT ECHO (IE) TEST METHOD
The IE method involves hitting the concrete surface with a small impactor or hammer and
identifying the reflected wave energy with a displacement or accelerometer receiver mounted on
the surface near the impact point. A simplified diagram of the method is presented in Figure 8. The
resulting displacement response of the receiver is recorded. The resonant echoes are usually not
apparent in the time domain. The resonant echoes are more easily identified in the frequency
domain. Consequently, the time domain test data are processed with a Fast Fourier Transform
(FFT) which allows identification of frequency peaks (echoes). The displacement spectrum of the
receiver is used to determine the resonant peaks. If the thickness of a slab is known, the
compression wave velocity (VP) can be determined by the following equation:
VP = 2*d*f/β (1)
where d = slab thickness, f = resonant frequency peak. The above equation is modified by a β
(Beta) factor of 0.96 for walls and slabs. By using a calibration point to back calculate the velocity
at a single test location, the user can apply the calibrated velocity along with the measured
frequency resonance to calculate the concrete thickness at additional test locations.
Figure 8: Impact Echo (IE) test diagram.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 13
Figure 9: Spectral Analysis of Surface Waves (SASW) test set-up diagram.
Surface wave (also termed Rayleigh; R-wave) velocity varies with frequency in a layered
system with differing velocities. This variation in velocity with frequency is termed dispersion.
A plot of surface wave velocity versus wavelength is called a dispersion curve.
3.3 SPECTRAL ANALYSIS OF SURFACE WAVES (SASW) TEST METHOD
The SASW method is based upon measuring surface waves propagating in layered elastic
media and is illustrated in Figure 9. The ratio of surface wave velocity to shear wave velocity
varies with Poisson's ratio. However, reasonable estimates of Poisson's ratio and mass density for
concrete and other materials can normally be made. Knowledge of the shear wave velocity
combined with reasonable estimates of mass density of the material layers allows calculation of
shear moduli for low-strain amplitudes
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 14
The SASW tests and analyses are generally performed in three phases: (1) collection of
data in situ; (2) construction of an experimental dispersion curve from the field data; and (3) forward
modeling of the theoretical dispersion curve, if desired, to match theoretical and experimental
curves so that a shear wave velocity versus depth profile can be constructed.
Wavelength (λ), frequency (f), and wave velocity (Vr), are related as follows:
Vr = f*λ (2)
Surface wave dispersion can be expressed in terms of a plot of surface wave velocity versus
wavelength. This type of plot is used in this report.
The SASW field tests for this investigation were conducted with an Olson Instruments
Freedom Data PC test system in concert with our SASW bar testing system. An Olson Instruments
Freedom Data PC computer with a data acquisition card was used to digitize the analog receiver
outputs and record the signals for spectral (frequency) analyses. The phase information of the
transfer function (cross power spectrum) between the two receivers for each frequency was the
key spectral measurement. All field data was recorded on the computer hard drive for later
analysis.
The experimental dispersion curve is developed from the phase data for a given site by
knowing the phase (φ) at a given frequency (f) and then calculating the travel time (t) between
receivers of that frequency/wavelength by:
t = φ / 360*f (3)
Surface wave velocity (Vr) is obtained by dividing the receiver spacing (X) by the travel time at
a frequency:
Vr = X / t (4)
The wavelength (λ) is related to the velocity and frequency as shown in equation 2.
By repeating the above procedure for any given frequency, the surface wave velocity
corresponding to a given wavelength is evaluated, and the dispersion curve is determined. The
phase data was viewed on the PC data acquisition system in the field to ensure that acceptable data
was being collected. The phase data were then returned to our office for further processing. The
phase of the cross-power spectrum (transfer function) between the two receivers and the coherence
function are used in creating the dispersion curves.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 15
After masking of the phase record pair from the data set for each test location, an
experimental field dispersion curve is developed that is a plot of surface wave velocity versus
wavelength, which relates to the depth of the material being assessed. These dispersion curve plots
are the basis of the analysis and are used to determine the concrete’s overall condition, the average
surface wave velocity of the concrete and any areas or zones throughout the depth of the structure
that indicate varying conditions.
4.0 NONDESTRUCTIVE EVALUATION RESULTS
The Nondestructive Evaluation (NDE) testing results from the GPR, IE and SASW testing are
described below.
4.1 GROUND PENETRATING RADAR TEST RESULTS
As noted above the Runit Dome concrete was a unique mix design utilizing local coral rock as
aggregate and seawater along with imported cement. The seawater is of the most concern, as this
would drastically increase the salinity of the concrete which in-turn effects the electrical properties
of the material. These electrical properties are key to the effectiveness of the GPR test method.
Therefore, early in the testing preliminary scans were preformed crossing the dome to look for
embedded objects beneath the concrete to ensure that the GPR signal was fully penetrating through
the concrete. These preliminary scans did indeed show that the GPR unit was penetrating through
the concrete; therefore, the testing was performed as originally proposed and planned.
The primary objective of the GPR investigation was to determine the existence and locations of
any significant voids which may exist immediately beneath the concrete. The GPR signature from
such locations typically shows a high-amplitude (bright white and dark black stripes) repeating
signal beginning at the bottom of the concrete and continuing downward to the maximum depth
of the scan. This signal occurs when the radar waves encounter the drastic electrical difference
between concrete and air (or water in the case of water filled voids). The signal repeats as the radar
signal becomes “trapped” in the void and creates multiple echoes, so the signal does not penetrate
beyond a void. In contrast, the supporting material beneath the concrete dome is thought to be
partially cemented soil, which would have very similar electrical properties to the concrete itself,
therefore, very little or no reflection from the bottom of the concrete is expected. Figures 10 and
11 below show examples of “Sound” condition support (no Voids or Questionable areas) from the
400 and 200 MHz antennas.
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Olson Job No. 4230A Runit Dome Nondestructive Evaluation 17
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As noted above, there were areas with numerous reflections from objects (likely metal)
below the concrete slab. When analyzing the 400 MHz data the major (strongest reflections or
clusters of reflections) were noted in the analysis table presented in Appendix A. Figure 12 and 13
show example data from the 400 and 200 MHz antenna of embedded objects creating reflections in
the GPR data. Note that the reflections are typically parabolic in shape indicating that the object is
located at the center of the parabola and of some finite width (not a planar reflection such as a layer
void).
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Olson Job No. 4230A Runit Dome Nondestructive Evaluation 20
The majority of the GPR data showed no indication of void, however there were some areas
that had notably stronger slab bottom reflections and multiple stronger reflections at depth. These
reflections are much less severe than those typically associated with void conditions, however because
they were notably different than surrounding areas they were designated as “Questionable” and may
warrant further investigation in the future. Figures 14 and 15 show example “Questionable” areas
from the 400 and 200 MHz antenna.
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Olson Job No. 4230A Runit Dome Nondestructive Evaluation 22
Only two areas where noted as “Voided”. Both areas were observed in the 400 MHz antenna
data but not observed in adjacent 400 MHz scans, or nearby 200 MHz scans. Figure 16 presents an
example of one of the areas noted as “Voided” from the 400 MHz antenna.
Figure 16: Example 400 MHz GPR data showing a “Voided” area, File 172
Note: the blue lines indicate Joint Locations.
Appendix A presents tables detailing the GPR analysis. The GPR analysis indicates that of the
22,717 linear feet scanned with the 400 MHz antenna, only two areas consisting of 12.9 linear feet (0.06
%) is suspected to be poorly supported or “Voided”. These two suspected voids exist at panels A42 and
A45 at the 180 feet from the apex mark. These suspected voids were not observed (also not considered
“Questionable” in adjacent scans at 175’ and 185’ from the dome apex. Only 192.8 linear feet (0.85 %)
was considered “Questionable” which may have a minor void or loose material under the slab. The
“Questionable” areas may also be due to changes in the electrical properties of the supporting material.
It is also worth noting that nearly half of the “Questionable” areas noted were at or adjacent to joints
between panes. These joints could influence the data in several ways; first the joint could provide access
to rainwater which could be undermining support, second the more from the joint also changes the
electrical properties of the soil, thus making the area look “Questionable”.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 23
The ‘Questionable’ areas were also much more common in rows D – I, where there were also notably
more “Major Reflectors” and other minor object embedment’s which make the data more challenging
to interpret.
Similar results were observed with the 200 MHz antenna; no areas were indicated as ‘Voided’
during the analysis and only 128 linear feet (1.10 %) were noted as ‘Questionable’. The ‘Questionable’
areas are again concentrated near the middle rows of the dome (D – F) where more embedment’s are
observed. The two sets of GPR data were analyzed blindly; therefore, the results of one set of testing
did not influence the other analysis. The ‘Questionable’ zones from the 200 MHz antenna match poorly
to the ‘Questionable’ zones from the 400 MHz antenna, the lack of agreement indicates that these
reflections may be due to small changes in the supporting material and are less likely a true indication
of a minor void.
Overall, the GPR data indicates that the Runit Dome has only a handful of locations, likely a
fraction of a percent of the total area, with possible isolated voids. There are many reflections of objects
buried in the soil-cement beneath the dome concrete, concentrated in rows D – F.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 24
4.2 IMPACT ECHO TEST RESULTS
The IE testing was performed on a grid basis with 5 test points in each of the 357 panels
and an additional 42 test points in the donut area for a total of 1827 IE test points. The velocity
(12,000 ft/sec) used in the thickness calculation was determined based upon a calibration
performed at a core-hole through the dome at a water-well site. The design thickness of the
concrete is 18 inches. The IE results were broken into 7 different categories:
- More than 30 % over the design thickness (+30% Plus)
- Between 20 – 30 % over the design thickness (+20-30%)
- Between 10 – 20 % over the design thickness (+10-20%)
- Within ±10 % of the design thickness (Sound)
- Between 10 – 20 % below the design thickness (-10-20%)
- Between 20 – 30 % below the design thickness (-20-30%)
- And more than 30 % below the design thickness (-30 % Plus)
Figure 17 presents example IE data showing the time domain displacement vibration as
well as the resonant frequency of the concrete which is used along with the velocity to calculate
the concrete thickness. The detailed, tabulated IE results are presented in Appendix B. The IE
results are statistically summarized in Tables II – IV below.
The IE results indicate that the concrete thickness is widely variable across the dome. The
concrete thickness varies at the extremes from 9.7 – 28.4 inches. The average thickness is 17.3
inches with a standard deviation of 2.88 (Coefficient of Variation of 16.6%). The Panels near the
bottom and top of the dome, Rows A, B, I, J, and K and the donut have many readings greater than
the nominal thickness. The panel rows in the middle, particularly D, E, and F have many readings
less than the nominal design thickness. The IE also indicates that the concrete is in overall good
condition with very few indications of internal anomalies and no indications of near surface
delamination.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 25
Figure 17: Example IE Data, File 653: Top plot shows time domain displacement vibration while the lower plot shows the frequency spectrum of the measured vibration and a clear resonant frequency of 5078 Hz
resulting in a calculated thickness of 14.2 inches.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 26
Table II: Statistical Summary of Impact Echo Results by Panel Row
Panel Row A B C D E F G H I J K Donut
Minimum (in) 14.2 10.7 10.8 9.7 12.1 11.5 12.5 13.4 14.5 12.7 13.9 12.5
Maximum (in) 28.4 25.4 23 22.3 25.4 18 24.6 27.3 22.3 26.3 23.8 22.3
Average (in) 20.1 18.7 17.0 14.9 15.7 14.7 17.0 16.2 18.0 18.0 18.4 18.2
St. Dev: 2.34 2.55 2.70 2.01 1.74 1.31 2.39 1.70 1.82 2.90 1.95 1.59
COV: 11.6% 13.6% 15.9% 13.5% 11.1% 8.9% 14.0% 10.5% 10.1% 16.1% 10.6% 8.7%
Table III: Number of IE Test Locations in Each Condition Category by Panel Row
Panel Row A B C D E F G H I J K Donut
+30% Plus 24 8 0 0 1 0 2 1 0 3 1 0
+20-30% 61 36 12 1 1 0 4 0 3 7 3 1
+10-20% 77 49 22 2 2 0 9 1 12 6 13 5
Sound 127 132 115 46 59 17 65 42 51 39 42 33
-10-20% 10 34 48 70 83 78 24 50 14 10 9 2
-20-30% 1 7 31 58 31 44 15 6 0 10 2 0
-30% Plus 0 4 12 23 3 11 1 0 0 0 0 1
Total 300 270 240 200 180 150 120 100 80 75 70 42
# 0f Panels 60 54 48 40 36 30 24 20 16 15 14 NA
Table IV: Percentage of IE Test Locations in Each Condition Category by Panel Row
Panel Row A B C D E F G H I J K Donut
+30% Plus 8.0% 3.0% 0.0% 0.0% 0.6% 0.0% 1.7% 1.0% 0.0% 4.0% 1.4% 0.0%
+20-30% 20.3% 13.3% 5.0% 0.5% 0.6% 0.0% 3.3% 0.0% 3.8% 9.3% 4.3% 2.4%
+10-20% 25.7% 18.1% 9.2% 1.0% 1.1% 0.0% 7.5% 1.0% 15.0% 8.0% 18.6% 11.9%
Sound 42.3% 48.9% 47.9% 23.0% 32.8% 11.3% 54.2% 42.0% 63.8% 52.0% 60.0% 78.6%
-10-20% 3.3% 12.6% 20.0% 35.0% 46.1% 52.0% 20.0% 50.0% 17.5% 13.3% 12.9% 4.8%
-20-30% 0.3% 2.6% 12.9% 29.0% 17.2% 29.3% 12.5% 6.0% 0.0% 13.3% 2.9% 0.0%
-30% Plus 0.0% 1.5% 5.0% 11.5% 1.7% 7.3% 0.8% 0.0% 0.0% 0.0% 0.0% 2.4%
Total Sound+ 96.3% 83.3% 62.1% 24.5% 35.0% 11.3% 66.7% 44.0% 82.5% 73.3% 84.3% 92.9%
Total Thin 3.7% 16.7% 37.9% 75.5% 65.0% 88.7% 33.3% 56.0% 17.5% 26.7% 15.7% 7.1%
Total 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 27
4.3 SPECTRAL ANALYSIS OF SURFACE WAVES TEST RESULTS
The Spectral Analysis of Surface Waves (SASW) test method was performed on a point
by point basis as described in Section 2. The test method utilizes a pair of sensors to measure the
movement of an induced surface wave through the structure. The SASW method detects the
variation in surface wave velocity (related to low strain modulus) with respect to depth in the
structure. A sound concrete condition should have a consistent surface wave velocity of 5,000 –
8,000 ft/sec (typical of structural concrete) throughout the cross section. A weaker area of concrete
will have a lower velocity, or a drop in velocity may be observed if only a portion of the section is
weaker. The SASW testing is sensitive to anomalies perpendicular to the test surface. Small
dispersed areas of low velocity are less likely to be observed with the SASW test method. See
Section 3.3 for a detailed test method description.
The SASW data was analyzed by determining the phase shift between the two measured
signals and developing a dispersion curve. An “Exponential Decay” window is applied to the raw
time domain signals to include only the first surface (Rayleigh) wave arrival in the analysis.
Glitches in the phase plot (which correspond to poor coherence) as well as very high and very low
frequencies are removed from the analysis through a masking procedure. The “masked-out” areas
are observed in the wrapped phase plot as grey areas. The masking procedure ignores those
frequencies without applying any additional processing that may affect the data. The shallowest
depth for which velocities are calculated corresponds to the highest frequency considered in the
analysis. Figure 18 below is an example SASW data set from Runit Dome showing the windowed
time domain data, the coherence between the two measured outputs and the masked phase
spectrum. The phase difference between the two measured signals is related to the surface wave
velocity of the material while the frequency or wavelength relates to the depth of the material being
assessed.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 28
Coherence Plot
Phase Data
Data Removed
by Masking
Figure 18: Example SASW data from the Runit Dome, File 3, typical result.
From the phase data a surface wave velocity profile with respect to wavelength (which is
roughly related to depth) can be calculated. It is this velocity profile that is used to determine the
average surface wave velocity throughout the structure and to observe any significant low velocity
zones. The SASW data presented in Figure 18 produce the example dispersion curve presented in
Figure 19. The concrete at this location has a consistent velocity between 6,500 and
7,500 ft/sec from approximately 0.2 ft to 1.9 feet and is considered of “Excellent” condition.
The velocity drop at a depth of ~1.9 feet corresponds to the backside of the concrete.. corresponds
Windowed time
domain data
.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 29
Figure 19: Example SASW dispersion curve from File SW_3, Excellent Condition,
Concrete thickness ~1.9 feet.
In areas of “Questionable” or “Poor” concrete the resulting velocity of the dispersion curve
is considerably lower. The condition of the concrete based upon the SASW velocity was put into
three categories. Test locations with an average velocity greater than 5,000 ft/sec were noted at
“Sound”, locations between 3,500 – 5,500 ft/sec or with notable drops in velocity within the
concrete were noted as “Questionable”, and test locations with an average velocity less than 3,500
ft/sec were noted as “Poor”. Table V provides a summary of the SASW results. A detailed table
of results can be found in Appendix C.
Table V: Summary of Spectral Analysis of Surface Wave Test Results
Condition Count Percentage
Sound 130 94.2%
Questionable 8 5.8%
Poor 0 0.0%
Total 138 100.0%
In general, the SASW testing supports the findings from the IE testing and indicates that most of the
concrete is of “Sound” condition with velocities typical of structural concrete.
Olson Job No. 4230A Runit Dome Nondestructive Evaluation 30
5.0 CLOSURE
The field portion of this investigation was performed in accordance with generally accepted
testing procedures. If additional information is developed that is pertinent to the findings of this
investigation or we can provide any additional information, please contact our office.
Respectfully submitted,
OLSON ENGINEERING, INC.
Patrick K. Miller, P.E.
Sr. Project Engineer
Dennis A. Sack, P.E.
Associate Engineer, Sr. Vice President
(1 copy emailed, 2 copies mailed)
Olson Job No. 4230A Runit Dome Nondestructive Evaluation A
APPENDIX A: GROUND PENETRATING RADAR RESULTS TABLES
Olson Job No. 4230A Runit Dome Investigation A1
400 MHz Antenna Data
Olson Job No. 4230A Runit Dome Investigation A2
400 MHz Antenna Data
Olson Job No. 4230A Runit Dome Investigation A3
400 MHz Antenna Data
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400 Hz Antenna Data
ß
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APPENDIX B: IMPACT ECHO RESULTS TABLES
Í
Olson Job No. 4230A Runit Dome Nondestructive Evaluation B
Olson Job #4230A Runit Dome Investigation B1
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Olson Job #4230A Runit Dome Investigation C
APPENDIX C: SPECTRAL ANALYSIS OF SURFACE
WAVES RESULTS TABLES
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Concrete Approximate Concrete
File # Test Location Condition
Thickness
Notes
(in)
SW_43 G25 Sound Not Apparent in Data
SW_44 G27 Sound 16.8
SW_45 G29 Questionable 20.4
SW_46 F1 Sound 19.2
SW_47 F3 Sound 15.6
SW_48 F5 Questionable 12
SW_49 F7 Questionable 13.2
SW_50 F9 Sound Not Apparent in Data
SW_51 F11 Sound Not Apparent in Data
SW_52 F13 Sound 16.8
SW_53 F15 Sound 16.8
SW_54 F17 Sound 15.6
SW_55 F21* Sound 16.8 Labeled as F21 should be F19
SW_56 F21 Sound 15.6
SW_57 F23 Sound 15.6
SW_58 F25 Sound 16.8
SW_59 F27 Sound 16.8
SW_60 F29 Sound 16.8
SW_61 E1 Sound 16.8
SW_62 E3 Sound 16.8
SW_63 E5 Sound 15.6
SW_64 E7 Sound 14.4
SW_65 E11 Sound 18 Skipped E9
SW_66 E13 Sound 20.4
SW_67 E15 Sound 15.6
SW_68 E17 Sound 16.8
SW_69 E19 Sound 15.6
SW_70 E21 Sound 15.6
SW_71 E23 Sound 15.6
SW_72 E25 Questionable 16.8
SW_73 E27 Questionable 18
SW_74 E29 Sound 18
SW_75 E31 Sound 15.6
SW_76 E33 Sound 15.6
SW_77 E35 Sound 18
SW_78 C1 Sound 15.6
SW_79 C3 Sound 16.8
SW_80 C5 Sound 20.4
SW_81 C7 Sound Not Apparent in Data
SW_82 C9 Sound Not Apparent in Data
SW_83 C11 Sound 18
SW_84 C13 Sound Not Apparent in Data
SW_85 C15 Sound Not Apparent in Data
SW_86 C17 Sound Not Apparent in Data
SW_87 C19 Sound 19.2
SW_88 C21 Sound 16.8
SW_89 C23 Sound 14.4
SW_90 C25 Sound Not Apparent in Data
SW_91 C27 Sound Not Apparent in Data
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File # Test Location
(in)
SW_92 C29 Sound 20.4
SW_93 C31 Sound Not Apparent in Data
SW_94 C33 Questionable 13.2
SW_95 C35 Sound 16.8
SW_96 C37 Sound 15.6
SW_97 C39 Sound 19.2
SW_98 C41 Sound 15.6
SW_99 C43 Sound 15.6
SW_100 SW_101
C45 C47
Sound Sound
14.4 Not Apparent in Data
SW_102 A1 Sound Not Apparent in Data
SW_103 A3 Sound Not Apparent in Data
SW_104 A5 Sound Not Apparent in Data
SW_105 A7 Sound Not Apparent in Data
SW_106 A9 Sound Not Apparent in Data
SW_107 A11 Sound 21.6
SW_108 A13 Sound Not Apparent in Data
SW_109 A15 Sound 20.4
SW_110 A17 Sound Not Apparent in Data
SW_111 A19 Sound 16.8
SW_112 A21 Sound Not Apparent in Data
SW_113 A23 Sound 20.4
SW_114 A25 Sound 20.4
SW_115 A27 Sound Not Apparent in Data
SW_116 A29 Sound Not Apparent in Data
SW_117 A31 Sound 22.8
SW_118 A33 Sound 20.4
SW_119 A35 Sound 20.4
SW_120 A37 Sound 24
SW_121 A39 Sound 22.8
SW_122 A41 Sound Not Apparent in Data
SW_123 A43 Sound 20.4
SW_124 A45 Sound 21.6
SW_125 A47 Sound 21.6
SW_126 A49 Sound 20.4
SW_127 A51 Sound 22.8
SW_128 A53 Questionable 20.4
SW_129 A55 Sound Not Apparent in Data
SW_130 A57 Sound 20.4
SW_131 A59 Sound 20.4
130 Sound 94.2% 8 Questionable 5.8% 0 Poor 0.0% 138 Total 100.0%
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