Geophysical Survey Report dated 27 May 2015 (Revision 1).pdf

Geophysical Survey Report Guardian Angel Operation Facility Davis-Monthan AFB Tucson, Arizona

Prepared For:

Thelen Associates, Inc.

1398 Cox Avenue Erlanger, Kentucky 41018-1002

Prepared By:

Prism GeoImaging, Inc.

11057 Allisonville Rd., #144 Fishers, Indiana 46038

Prism Project Number:

01.015.006.r1

Date:

May 27, 2015

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

May 27, 2015

Paul S. Larsen Senior Vice President Thelen Associates, Inc.

1398 Cox Avenue Erlanger, Kentucky 41018-1002

Re: Geophysical Investigation Report Guardian Angel Operation Facility Davis-Monthan AFB Tucson, Arizona Prism Project Number: 01.015.006.r1

Dear Mr. Larsen, In accordance with my proposal dated February 24, 2015, Prism GeoImaging, Inc. (Prism) is pleased to present Thelen Associates, Inc. (Thelen) with this letter report documenting the geophysical investigation at the above-referenced project site (the “Site”). My documentation of this project is included in the following sections.

Introduction

Thelen is providing geotechnical services to support the design of the Guardian Angel Operation Facility and all associated pavements and structures at Davis-Monthan AFB in Tucson, Arizona. It has been requested by the Louisville District, Corps of Engineers that a geophysical investigation be completed as part of the geotechnical services package. The stated goals of the geophysical investigation are to "identify the locations of subsurface anomalies that may be caused by the presence of buried waste material (both metallic and non-metallic), uncontrolled fill, changes in shallow subsurface conditions, old building foundations, and existing and abandoned utilities.” The area of investigation comprises a total of approximately 10.8 acres, consisting of generally flat terrain with partial vegetation cover that was removed prior to geophysical data collection (see Figure 1).

Scope of Work and Geophysical Methodology

The scope of work for this investigation includes time-domain electromagnetic (TDEM) metal detection mapping, and electromagnetic induction terrain conductivity mapping. A summary of these methods is as follows:

Time-Domain Electromagnetic Metal Detection TDEM geophysical surveys are commonly used to map the locations of metal objects such as underground storage tanks (USTs), buried drums, relict utilities and infrastructure, former building foundations, construction and industrial debris, and in some situations unexploded ordnance (UXO).

The instrument used for this work is an EM61-MK2 manufactured by Geonics Ltd. in Mississauga, Ontario, Canada. The EM61-MK2 is a high-sensitivity, high-resolution, time-domain metal detector offering significant advancements in target characterization and sensitivity over the time-honored design of the original EM61. It consists of two vertically separated 1-meter by 0.5-meter coaxial coils. The EM61-MK2 takes readings from the bottom coil (designated as channel three) and an additional reading from the top coil (top channel). The top and bottom coil readings are then subtracted to selectively filter out the effect from near-surface metal objects (designated as the channel difference calculation).

The channel three reading is considered to be a measure of all metal within the detection limits of the instrument, while the channel difference calculation is a measure of predominantly deeper metal only.

The depth of detection for the EM61-MK2 is dependent on target characteristics, according to examples given by the manufacturer a 4” steel pipe is detectable to a depth of approximately 7 feet and a single 55 gallon steel drum is detectable to a depth of approximately 10 feet, the manufacturer additionally states that single objects buried in excess of 10-13 feet are generally undetectable. EM61-MK2 anomalies are generally consistent in character from site to site, independent of the environment. For a metal object buried at 2 to 4 feet in depth, the magnitude of the channel three anomaly is generally in the upper 100's to near 1000 millivolts and the channel difference value is generally in the low to mid 100's millivolts. Large metal objects close to the surface (e.g.

reinforced concrete, manholes) cause too great of an instrument reading to be filtered out, so the anomalies from such features will remain on the channel difference map.

Electromagnetic Induction Terrain Conductivity Mapping

Electrical conductivity is one of the most widely varying physical properties of natural materials. Certain minerals, such as native metals and graphite, conduct electricity via the passage of electrons; however, electronic conduction is generally very rare in the subsurface. Most minerals and rocks are insulators, and electrical current preferentially travels through the water-filled pores in soils and rocks by the passage of the free ions in pore waters (i.e., ionic conduction). It thus follows that degree of saturation, interconnected porosity, and water chemistry (i.e., total dissolved solids) are the major controlling variables of the conductivity of soils and rocks. In general, electrical conductivity directly varies with changes in these parameters. Fine-grained sediments, particularly clay-rich sediments, are excellent conductors of electricity, often much better than fresh water found in the pores of sand and gravel.

Conductivity geophysical surveys are often used for locating and mapping the extent of buried waste, fill material, and landfilled areas by providing indications of soil type based on the electrical conductivity. Typically, coarse materials (sand, gravel, non-reinforced concrete rubble, etc.) are the least conductive, whereas silt, clay, ash, cinders, wood, paper and other fine grained, moist materials are conductive to the highest degree of non-metallic materials. Conductivity geophysical surveys are also commonly used to locate potential cave and sinkhole features. Open voids in bedrock have very low electrical conductivity relative to the surrounding rock. Sinkhole features are typically much more conductive than competent rock due to the soil materials that wash into the sink feature.

There is no unique direct conversion from conductivity values to lithology. However, based on site knowledge, geometric shapes and relationships of various anomalies, and the observed ranges of resistivity values, reasonable geologic interpretations can be made.

Electromagnetic induction conductivity instruments require no direct ground contact and therefore are well-suited to rapid scanning of very large areas, although affording limited information on the vertical distribution of anomalies. The instrument used for this work is an EM31, an industry-standard electromagnetic conductivity meter manufactured by Geonics Ltd. in Mississauga, Ontario, Canada. The EM31 operates by inducing electrical current flow in the subsurface by generating an electromagnetic field through a transmitter coil; a receiver coil at the other end of the instrument is used to measure the subsurface current flow. The instrument then converts the transmitter output and receiver input values into apparent conductivity and magnetic susceptibility measurements.

Subsurface materials at a depth of 4.8 feet yield the maximum contribution to EM31 readings, the effective maximum depth of exploration for the instrument is approximately 18 feet.

Data Collection

EM61-MK2 data were collected using a differentially-corrected GPS receiver to record the instrument location in real time (see Figure 2). After the data were collected they were downloaded to a computer for subsequent processing. The EM61-MK2 data were processed with Surfer v12 to create a channel three map (see Figure 3) and a channel difference map (see Figure 4). The channel three map shows all metal within the detection limits of the instrument; the channel difference map shows predominantly deeper metal only.

EM31 data were collected using a differentially-corrected GPS receiver to record the instrument location in real time (see Figure 5). After the data were collected they were downloaded to a computer for subsequent processing. The EM31 data were processed with Surfer v12 to create a terrain conductivity map (see Figure 6) and a magnetic susceptibility map (see Figure 7).

Results

On the EM61 maps, colors in the range of green on up to burgundy indicate the presence of metallic objects. The channel three map (Figure 3) shows a number of relatively small metal objects scattered about the Site. Most of these features are filtered out by the channel differencing calculation, indicating that they are shallow in nature. What remains on the channel difference map are two anomalies of unknown origin (see Figure 4).

The EM31 conductivity map (Figure 6) shows the electrical conductivity of subsurface materials. Normal conductivity range for sandy/gravelly soils is approximately 2-20 mS/m, and normal range for silty/clayey soils is approximately 10-80 mS/m. For this Site, the orange to cyan colors on the EM31 conductivity map are interpreted as normal soil values. Above these values (blue to black) and below (red to white) are anomalous.

The conductivity data indicate that the soil in the western portion of the study area is higher conductivity than the soil in the eastern portion. Additionally the conductivity data show some linear anomalies that are consistent with utility lines, and a very high conductivity anomaly of unknown origin in the southeastern corner of the Site.

The EM31 magnetic susceptibility map (Figure 7) shows the location of metallic objects;

anomalies on this map can be either positive (red) or negative (blue). Strong anomalies (either positive or negative) on the magnetic susceptibility map are generally indicative of ferrous metal. The magnetic susceptibility map shows several relatively small scattered metal objects, and two larger anomalies of unknown origin near the center of the Site.

Interpretations

Buried Debris Buried metallic waste materials (such as demolition debris) typically produce EM61 channel difference anomalies of at least 200-300 mV (bright green to orange on the Figure 4 channel difference map). There is very little geophysical evidence that metallic debris materials were systematically buried at this Site, however there are two anomalies on the channel difference map that are consistent with small accumulations of buried metallic waste (denoted on Figure 4 with black oval outlines).

Building Foundations, Floor Slabs Building foundations and floor slabs are usually detectable on EM61 maps because such structures are often reinforced and/or contain other metal objects such as fasteners, conduit, and steel pipe. In the event that building foundations or floor slabs do not contain any detectable metal it is still possible to locate these structures with the EM31 as long as they are found within the optimal detection depth of the EM31 (approximately 3-18 feet).

As an example, an un-reinforced concrete slab buried a few inches below the surface would be undetectable with the EM61, and difficult to detect with the EM31 which is tuned to preferentially characterize the subsurface at a greater depth interval. Many times there is stronger secondary evidence of old building foundations/slabs (e.g. utility lines that terminate unexpectedly, scattered shallow metal objects remaining from the demolition activities, etc.). Building foundation and floor slab anomalies typically reflect the shape or outline of the former building.

No anomalies indicative of building foundations or floor slabs are noted on the EM61 maps or the EM31 maps (Figures 3, 4, 6, and 7). Therefore there is very little geophysical evidence for building foundations or floor slabs at the Site.

Existing and Abandoned Utilities Underground utilities (relict or active) are typically evident on EM61 maps as elongated linear anomalies if the utility lines are constructed of ferrous metal. EM31 anomalies from utilities are similarly elongated and linear, but can be either very high or very low in conductivity, in either case usually far beyond the range of geologic materials. Utilities are generally more evident on EM31 maps than EM61 maps because the EM31 is a more sensitive instrument and can often detect both ferrous and non-ferrous materials as well as utility trench backfill materials. Also the EM31 magnetic susceptibility (in-phase) readings can show additional anomalies that sometimes do not appear in the conductivity readings.

The EM31 conductivity map from this Site shows a few utility anomalies trending across the investigation area (denoted with dashed lines on Figure 6). Some of these anomalies coincide with known utility lines, however it is unknown which of the utility lines evident on the conductivity map may be active and which may be abandoned.

Fill Materials Non-metallic fill materials typically produce either high or low conductivity EM31 anomalies (e.g. wood, ash, cinders, or clayey soils as high conductivity anomalies; and sand/gravel soils, or brick/concrete rubble as low conductivity anomalies). The very high conductivity anomaly in the southeastern corner of the Site (denoted with solid outline on Figure 6) is consistent with non-metallic fill material.

Results Summary

The results and interpretations of this investigation are presented on Figure 8 and summarized as follows:

1. There is very little geophysical evidence for widespread systematic burial of metallic debris at this Site, however there is scattered surficial metallic debris and two small anomalies of deeper metallic debris.

2. There is very little geophysical evidence for buried building foundations or floor slabs.

3. A few possible utility anomalies are evident on the EM31 conductivity map. It is unknown which of these anomalies may be active or abandoned.

4. There is geophysical evidence for emplacement of fill materials in one area that is near the southeast corner of the Site.

Limitations

This geophysical survey was intended primarily to locate areas of buried debris, old building foundations and floor slabs, utilities, fill materials, and other subsurface features that would impact planned construction activities. Subsurface features that are difficult to detect and would be of concern to project stakeholders (e.g. plastic utility lines, buried wires, non-reinforced concrete rubble etc.) may have gone undetected by this investigation and may not be detectable by any geophysical investigation. Areas obscured by features such as buildings, subsurface utility lines, or other structures, vehicles, waste storage containers, either physically or electromagnetically, or areas that are specifically covered with reinforced concrete, may conceal additional objects of interest that are unknown at this time.

The enclosed maps are considered to be of sufficient accuracy and precision to provide positional data for further investigation activities. However the Site features presented on the base maps are for informational purposes only and no representation is made as to the accuracy or completeness of this information. The enclosed maps, while they may indicate locations of utilities, are not to be taken as a map of utility locations and are not a substitute for a private utility locate.

Closing

Prism GeoImaging, Inc. appreciates the opportunity to provide Thelen with this geophysical survey, and I look forward to working with you on future projects. If you should have any questions regarding this project, please do not hesitate to contact me at jvanderlaan@prismgeo.com or 317-379-5796.

Sincerely, Prism GeoImaging, Inc.

John Vanderlaan, LPG, PG President / Geophysicist

Attachments: Figure 1. Site Layout and Area of Investigation Figure 2. EM61-MK2 Data Coverage Figure 3. EM61-MK2 Channel 3 Map Figure 4. EM61-MK2 Channel Difference Map Figure 5. EM31 Data Coverage Figure 6. EM31 Apparent Conductivity Map Figure 7. EM31 Magnetic Susceptibility Map Figure 8. Results Summary Map mailto:jvanderlaan@prismgeo.com

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Guardian Angel Operation Facility Davis-Monthan AFB Prism Project No. 01-015-006

Geophysical Investigation Area

Site Layout And Area of Investigation

Figure 1

Prism GeoImaging, Inc.

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

LEGEND

UTM Zone 12N, Datum WGS84, Meters© 2015, Prism GeoImaging, Inc.

Scale in Feet

0 50 100 150 200 250 300

1" = 120'

Notice: This drawing/computer file is the property of Prism GeoImaging, Inc. as an instrument of professional service. Any modification or reuse of this document without written permission from Prism GeoImaging, Inc. is prohibited. Any person or entity using these documents for any purpose other than the project for which they were originally intended, with or without permission from Prism GeoImaging, Inc., by their use agrees to indemnify and hold harmless Prism GeoImaging, Inc.

from any loss, including, but not limited to attorney's fees occurring from their use.

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Guardian Angel Operation Facility Davis-Monthan AFB Prism Project No. 01-015-006

EM61-MK2 Data Coverage Figure 2

Prism GeoImaging, Inc.

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

LEGEND

UTM Zone 12N, Datum WGS84, Meters© 2015, Prism GeoImaging, Inc.

Scale in Feet

0 50 100 150 200 250 300

1" = 120'

Notice: This drawing/computer file is the property of Prism GeoImaging, Inc. as an instrument of professional service. Any modification or reuse of this document without written permission from Prism GeoImaging, Inc. is prohibited. Any person or entity using these documents for any purpose other than the project for which they were originally intended, with or without permission from Prism GeoImaging, Manhole Cover Culvert

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Guardian Angel Operation Facility Davis-Monthan AFB Prism Project No. 01-015-006

Instrument Response

(mV) Background

(non-m etallic) response

M etal O bject Response

-910

EM61-MK2 Channel 3 Map All Metal Within Detection Limits

Figure 3

Prism GeoImaging, Inc.

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

LEGEND

UTM Zone 12N, Datum WGS84, Meters© 2015, Prism GeoImaging, Inc.

Scale in Feet

0 50 100 150 200 250 300

1" = 120'

Notice: This drawing/computer file is the property of Prism GeoImaging, Inc. as an instrument of professional service. Any modification or reuse of this document without written permission from Prism GeoImaging, Inc. is prohibited. Any person or entity using these documents for any purpose other than the project for which they were originally intended, with or without permission from Prism GeoImaging, 512,280

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Metal Anomaly -unknown metallic feature

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Instrument Response

(mV)

M etal O bject Response

EM61 Channel Difference Map Predominantly Deeper Metal Only

Figure 4

Prism GeoImaging, Inc.

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

LEGEND

UTM Zone 12N, Datum WGS84, Meters© 2015, Prism GeoImaging, Inc.

Scale in Feet

0 50 100 150 200 250 300

1" = 120'

Notice: This drawing/computer file is the property of Prism GeoImaging, Inc. as an instrument of professional service. Any modification or reuse of this document without written permission from Prism GeoImaging, Inc. is prohibited. Any person or entity using these documents for any purpose other than the project for which they were originally intended, with or without permission from Prism GeoImaging, 512,280

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EM31 Data Coverage Figure 5

Prism GeoImaging, Inc.

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

LEGEND

UTM Zone 12N, Datum WGS84, Meters© 2015, Prism GeoImaging, Inc.

Scale in Feet

0 50 100 150 200 250 300

1" = 120'

Notice: This drawing/computer file is the property of Prism GeoImaging, Inc. as an instrument of professional service. Any modification or reuse of this document without written permission from Prism GeoImaging, Inc. is prohibited. Any person or entity using these documents for any purpose other than the project for which they were originally intended, with or without permission from Prism GeoImaging, Unknown Anomaly

Manhole Cover Culvert

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Linear Anomaly -interpreted utility/relict utility line

Increasing C lay and/or S oil M oisture Increasing S and/G ravel and/or D ecreasing S oil M oisture

Interference R eadings Interference R eadings

Typical S oil C onductivity

Conductivity (mS/m)

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EM31 Apparent Conductivity Map Figure 6

Prism GeoImaging, Inc.

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

LEGEND

UTM Zone 12N, Datum WGS84, Meters© 2015, Prism GeoImaging, Inc.

Scale in Feet

0 50 100 150 200 250 300

1" = 120'

Notice: This drawing/computer file is the property of Prism GeoImaging, Inc. as an instrument of professional service. Any modification or reuse of this document without written permission from Prism GeoImaging, Inc. is prohibited. Any person or entity using these documents for any purpose other than the project for which they were originally intended, with or without permission from Prism GeoImaging, Manhole Cover Culvert

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Ferrous M etal Ferrous M etal

Magnetic Susceptibility Anomaly -unknown metallic feature

EM31 Magnetic Susceptibility Map Figure 7

Prism GeoImaging, Inc.

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

LEGEND

UTM Zone 12N, Datum WGS84, Meters© 2015, Prism GeoImaging, Inc.

Scale in Feet

0 50 100 150 200 250 300

1" = 120'

Notice: This drawing/computer file is the property of Prism GeoImaging, Inc. as an instrument of professional service. Any modification or reuse of this document without written permission from Prism GeoImaging, Inc. is prohibited. Any person or entity using these documents for any purpose other than the project for which they were originally intended, with or without permission from Prism GeoImaging, Unknown Anomaly

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Linear Anomaly -interpreted utility/relict utility line

Metal Anomaly -unknown metallic feature

Results Summary Figure 8

Prism GeoImaging, Inc.

11057 Allisonville Road, #144 Fishers, Indiana 46038-2331 www.prismgeo.com

LEGEND

UTM Zone 12N, Datum WGS84, Meters© 2015, Prism GeoImaging, Inc.

Scale in Feet

0 50 100 150 200 250 300

1" = 120'

Notice: This drawing/computer file is the property of Prism GeoImaging, Inc. as an instrument of professional service. Any modification or reuse of this document without written permission from Prism GeoImaging, Inc. is prohibited. Any person or entity using these documents for any purpose other than the project for which they were originally intended, with or without permission from Prism GeoImaging,