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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

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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.

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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

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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

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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.

https://marshallislands.llnl.gov/

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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: [email protected]

Olson Engineering Job No. 4230A, July 3rd, 2013

mailto:[email protected]

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.


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.


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.


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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.


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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


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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.


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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.


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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.


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


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.


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.


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


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.


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.


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).


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.


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”.


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.


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.


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.


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


+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


+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%


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.


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

.


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.


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


400 Hz Antenna Data

ß

APPENDIX B: IMPACT ECHO RESULTS TABLES

Í

Olson Job No. 4230A Runit Dome Nondestructive Evaluation B

Olson Job #4230A Runit Dome Investigation B1

Olson Job #4230A Runit Dome Investigation C

APPENDIX C: SPECTRAL ANALYSIS OF SURFACE

WAVES RESULTS TABLES

Olson Job #4230A Runit Dome Investigation

C1


C2

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_55 F21* Sound 16.8 Labeled as F21 should be F19






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_72 E25 Questionable 16.8

SW_73 E27 Questionable 18

SW_74 E29 Sound 18



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_83 C11 Sound 18




SW_87 C19 Sound 19.2






C2

File # Test Location

(in)



SW_94 C33 Questionable 13.2






SW_100 SW_101

C45 C47

Sound Sound

14.4 Not Apparent in Data

SW_102 A1 Sound Not Apparent in Data





SW_107 A11 Sound 21.6


SW_109 A15 Sound 20.4


SW_111 A19 Sound 16.8


SW_113 A23 Sound 20.4

SW_114 A25 Sound 20.4



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_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_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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RUNIT PROJECT: DATA REPORT

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