U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2004-5208

Prepared in cooperation with the

U.S. Army Corps of Engineers, Kansas City District

Surface Geophysical Investigation of the Areal and Vertical 

Extent of Metallic Waste at the Former Tyson Valley Powder 

Farm near Eureka, Missouri, Spring 2004

Surface Geophysical Investigation of 

the Areal and Vertical Extent of Metallic 

Waste at the Former Tyson Valley Powder 

Farm near Eureka, Missouri, Spring 2004

By Lyndsay B. Ball, Wade H. Kress, Eric D. Anderson, Andrew P. Teeple, 

James W. Ferguson, and Charles R. Colbert

Prepared in cooperation with the 

U.S. Army Corps of Engineers, Kansas City District

Scientific Investigations Report 2004–5208

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.
iii

Contents

Abstract .......................................................................................................................................................... 1

Introduction ................................................................................................................................................... 1

Purpose and Scope ............................................................................................................................. 2

Site Description .................................................................................................................................... 2

AOC 3 .......................................................................................................................................... 2

AOC 7 .......................................................................................................................................... 2

AOC 10 .......................................................................................................................................... 2

Previous Investigations ...................................................................................................................... 2

AOC 3 .......................................................................................................................................... 2

AOC 7 .......................................................................................................................................... 4

AOC 10 .......................................................................................................................................... 4

Hydrogeology ....................................................................................................................................... 4

Acknowledgments ............................................................................................................................... 4

Methods ......................................................................................................................................................... 4

Electromagnetic Methods .................................................................................................................. 5

Magnetic Methods .............................................................................................................................. 5

Two-Dimensional Direct-Current Resistivity ................................................................................... 6

Time-Domain Induced Polarization ................................................................................................... 7

Forward Modeling of Resistivity Data .............................................................................................. 7

Areal Extent of Anomalies ........................................................................................................................... 7

AOC 3 ................................................................................................................................................... 8

Zone 1 .......................................................................................................................................... 8

Zone 2 .......................................................................................................................................... 8

AOC 7 ................................................................................................................................................. 14

Zone 3 ........................................................................................................................................ 14

Zone 4 ........................................................................................................................................ 14

Zone 5 ........................................................................................................................................ 14

Zone 6 ........................................................................................................................................ 14

Zone 7 ........................................................................................................................................ 14

AOC 10 ................................................................................................................................................. 23

Zone 8 ........................................................................................................................................ 23

Zone 9 ........................................................................................................................................ 23

Zones 10, 11 and 12 ................................................................................................................... 23

Vertical Extent of Anomalies .................................................................................................................... 28

Forward Model Data ......................................................................................................................... 34

Interpretation of Resistivity Data .................................................................................................... 40

Line 1 ........................................................................................................................................ 40

Line 2 ........................................................................................................................................ 40

Line 3 ........................................................................................................................................ 40

Line 4 ........................................................................................................................................ 40

Line 5 ........................................................................................................................................ 40
iv

Excavation of Selected Anomalies to Assess Accuracy of Geophysical Surveys ................. 43

AOC 3 ........................................................................................................................................ 43

AOC 7 ........................................................................................................................................ 43

Summary and Conclusions ........................................................................................................................ 45

Selected References .................................................................................................................................. 45

Appendix 1. Georeferenced locations within AOC 3 (table 1-1), AOC 7 (table 1-2), and 

AOC 10 (table 1-3) ......................................................................................................................... 48

Appendix 2-1. Graphs representing the total percent frequency of occurrence for specific 

data values at AOC 3 for A, total apparent electrical conductivity; B, magnetic 

susceptibility at 2,070 Hz; and C, vertical gradient. ................................................................. 53

Appendix 2-2. Graphs representing the total percent frequency of occurrence for specific 

data values at AOC 7 for A, magnetic susceptibility at 2,070 Hz; and B, vertical 

gradient. .......................................................................................................................................... 54

Appendix 2-3. Graphs representing the total percent frequency of occurrence for specific 

data values at AOC 10 for A, magnetic susceptibility at 2070 Hz; and B, vertical 

gradient. .......................................................................................................................................... 54

Appendix 3. Environmental noise tests on A, April 21, 2004 and B, April 22, 2004. ...................... 55

Appendix 4. Table showing coordinates of zone boundaries. ......................................................... 56

Figures

1. Map showing location of the areas of concern (AOCs), former Tyson Valley Powder 

Farm near St. Louis, Missouri .................................................................................................... 3

2. Diagrams showing results of the electromagnetic and magnetic survey at AOC 3 

showing A, total apparent electrical conductivity; B, magnetic susceptibility 

at 2,070 Hz; and (C) vertical gradient ........................................................................................ 9

3. Site map of AOC 3 showing anomalous zones ..................................................................... 12

4. Photographs of surface metal at AOC 3 including exposures of small arms waste 

in the stream channel looking A, northward downstream and B, at the west bank 

near mark 40, line -12 ................................................................................................................ 13

5–6. Diagrams showing—

 5. Results of the electromagnetic survey at A and B, AOC 7 and C and D, AOC 10 

 comparing the in-phase response of the 60 Hz monitoring frequency to the 

 total apparent electrical conductivity ............................................................................. 17

 6. Results of the electromagnetic and magnetic survey at AOC 7 showing 

A, magnetic susceptibility at 2,070 Hz; and B, vertical gradient ................................. 19

7. A1 and A2, photographs of surficial metal in AOC 7 looking south between mark -40, line 

117 to mark -29, line 102 showing 1-inch diameter metal cable and scrap metal, and 

B1 and B2, photographs of barbed wire and small arms waste near mark -55, line 51 ....... 21

8. Site map of AOC 7 showing anomalous zones ..................................................................... 22

9. Diagrams showing results of the electromagnetic and magnetic survey at AOC 10 

showing A, magnetic susceptibility at 2,070 Hz; and B, vertical gradient ........................ 24

10. Photographs of surficial scrap metal in AOC 10 between mark -80, line 108 to 

mark -70, line 90 ......................................................................................................................... 26

11. Site map of AOC 10 showing anomalous zones ................................................................... 27
v

12. Field data of survey line 1 in AOC 3. Sections showing inverted two-dimensional, 

direct-current resistivity data using A, a dipole-dipole array, B, a Wenner-Schlumberger array, and C, inverted time-domain induced polarization data using a dipoledipole array ................................................................................................................................. 29

13–16. Sections showing A, inverted two-dimensional, direct-current resistivity data using a 

Wenner-Schlumberger array, and B, inverted time-domain induced polarization data 

using a dipole-dipole array—

 13. Survey line 2 in AOC 3 ..................................................................................................... 30

 14. Survey line 3 in AOC 3 ..................................................................................................... 31

 15. Survey line 4 in AOC 7 ...................................................................................................... 32

 16. Survey line 5 in AOC 7 ...................................................................................................... 33

17. Survey line 1, AOC 3. Sections showing A, forward model, and inverted model 

resistivity data using B, a dipole-dipole array and C, a Wenner-Schlumberger 

array from the forward model .................................................................................................. 35

18–21. Sections showing A, forward model, and B, inverted model resistivity data using a 

Wenner-Schlumberger array from the forward model—

 18. Survey line 2, AOC 3 ......................................................................................................... 36

 19. Survey line 3, AOC 3 ......................................................................................................... 37

 20. Survey line 4, AOC 7 ......................................................................................................... 38

 21. Survey line 5, AOC 7 ......................................................................................................... 39

22. Section showing interpretation of inverted field resistivity, inverted model 

resistivity, and forward model sections from survey line 1, AOC 3 ................................... 41

23. Section showing interpretation of inverted field resistivity, inverted model 

resistivity, and forward model sections from survey line 2, AOC 3 ................................... 41

24. Section showing interpretation of inverted field resistivity, inverted model 

resistivity, and forward model sections from survey line 3, AOC 3 ................................... 42

25. Section showing interpretation of inverted field resistivity, inverted model 

resistivity, and forward model sections from survey line 4, AOC 7 ................................... 42

26. Section showing interpretation of inverted field resistivity, inverted model 

resistivity, and forward model sections from survey line 5, AOC 7 ................................... 42

27. Photographs taken during excavation activities at A, AOC 3, showing the 

remains of a 55-gallon drum in E-3, and B, AOC 7, showing small arms waste 

found in E-8 (May 2004) ............................................................................................................ 44
vi

Conversion Factors, Abbreviations, and Datums

Multiply By To obtain

Length

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Area

hectare (ha) 0.003861 square mile (mi2)

Volume

liter (L) 2.113 pint (pt) 

liter (L) 1.057 quart (qt)

cubic meter (m3) 0.2642 gallon (gal)

liter (L) 0.9464 cubic inch (in3)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.

Abbreviations used in this report

2D-DC resistivity two-dimensional direct-current resistivity

AOC area of concern

EM electromagnetic

EMI electromagnetic induction

Hz hertz

kHz kilohertz

m meter

mS/m millisiemens per meter

mV/V millivolt per volt

nT nanotesla

ppm parts per million

RTK GPS real-time kinematic global positioning system

time-domain IP time-domain induced polarization

TRC Tyson Research Center

TVPF Tyson Valley Powder Farm
Surface Geophysical Investigation of the Areal and 

Vertical Extent of Metallic Waste at the Former Tyson 

Valley Powder Farm near Eureka, Missouri, Spring 2004

By Lyndsay B. Ball1, Wade H. Kress1, Eric D. Anderson2, Andrew P. Teeple1, James W. Ferguson3, and 

Charles R. Colbert3

tered distribution of the small arms waste, in addition to the 

mixing of both types of debris in the subsurface.

Electromagnetic and magnetic data showed some zones 

of concentrated anomalies, while there was a general scattering of small anomalies throughout the site. Inverted resistivity 

sections, as well as induced polarization sections, showed the 

debris to have a maximum depth of approximately 1 to 

2 meters below the surface.

Introduction

The former Tyson Valley Powder Farm (TVPF) was 

owned and operated by the U.S. Army from 1941–47, and 

again from 1951–61. The former TVPF was used primarily as 

a storage facility for the production of small arms ammunition, 

although munitions testing and disposal took place on the site 

as well (Kring and Bailey, 2001). During U.S. Army operation, shell casings, munitions, munitions components, storage 

drums, and miscellaneous metallic materials were disposed of 

throughout the property. During the second phase of operation in the 1950’s, the site also was used for the storage of 

artillery rounds and chemicals used in tracers and incendiary 

devices (Francis Zigmund and C.R. Colbert, U.S. Army Corps 

of Engineers, oral commun., 2004). However, little historical 

information exists describing disposal practices during U.S. 

Army operation.

A remedial investigation (RI) conducted by the U.S. 

Army Corps of Engineers (USACE) has identified several 

areas of concern (AOCs) for potential soil and water contamination within the former TVPF. Soil samples from AOCs 3, 7, 

and 10 revealed relatively elevated concentrations of various trace elements, including mercury and arsenic. Surface 

exposures of shell casings were present in AOCs 3 and 7, as 

well as storage drums and miscellaneous scrap metal in AOC 

10; however, the spatial extent and depth of these items in the 

subsurface were unknown. Surface geophysical techniques 

provide a quick, inexpensive, and non-intrusive means of 

collecting data in the subsurface environment. By applying 

electromagnetic (EM), magnetic, two-dimensional direct-curAbstract

The former Tyson Valley Powder Farm near Eureka, Missouri, was used primarily as a storage facility for the production of small arms ammunition during 1941–47 and 1951–61. 

A secondary use of the site was for munitions testing and 

disposal. Surface exposures of small arms waste, characterized 

by brass shell casings and fragments, as well as other miscellaneous scrap metal are remnants of disposal practices that took 

place during U.S. Army operation and can be found throughout the site. Little historical information exists describing 

disposal practices, and more debris is believed to be buried in 

the subsurface. The U.S. Army Corps of Engineers has identified several areas of concern throughout the former Tyson 

Valley Powder Farm. A surface-geophysical investigation was 

performed by the U.S. Geological Survey, in cooperation with 

the U.S. Army Corps of Engineers, to evaluate the areal and 

vertical extent of metallic debris in the subsurface within three 

of these areas of concern.

Electromagnetic and magnetic methods were used to 

locate anomalies indicating relatively large concentrations of 

buried metallic debris within the selected areas of concern. 

Maps were created identifying twelve anomalous zones in the 

three areas of concern, and three of these zones were selected 

for further investigation. The extent and depth of the anomalies within these zones were explored using two-dimensional 

direct-current resistivity methods. Resistivity and time-domain 

induced polarization data were compared to the anomalous 

locations of the electromagnetic and magnetic surveys.

The geophysical methods selected for this study were 

useful in determining the areal and vertical extent of metallic 

waste within the former Tyson Valley Powder Farm. However, 

electromagnetic and magnetic methods were not able to differentiate magnetic scrap metal from non-magnetic metallic 

small arms waste, most likely due to the small size and scat1

U.S. Geological Survey, Lincoln, Nebraska.

2

U.S. Geological Survey, Lakewood, Colorado.

3

U.S. Army Corps of Engineers, Kansas City District, Kansas City, 

Missouri.
rent resistivity (2D-DC resistivity), and time-domain induced 

polarization (time-domain IP) methods, the extent and depth 

of anomalies in the signals potentially resulting from buried 

metallic objects can be characterized. The U.S. Geological 

Survey (USGS), in cooperation with the USACE, investigated 

AOC 3, AOC 7, and AOC 10 for subsurface metallic debris 

using surface geophysical methods. The results of this study 

will aid the USACE, Kansas City District, in performing 

removal of metallic debris under the Defense Environmental 

Restoration Program and in identifying potential locations for 

ground-water monitoring wells.

Purpose and Scope

This report describes the results of EM and magnetic geophysical surveys used in AOCs 3, 7, and 10 with the purpose 

of defining the areal extent of buried small arms ammunition 

waste and scrap metal. Selected anomalies identified by the 

EM and magnetic surveys were characterized vertically with 

2D-DC resistivity and time-domain IP methods. The results 

of excavation activities are also presented, in which some 

selected anomalies were excavated to assess the accuracy of 

the geophysical surveys.

Site Description

The former TVPF site is in St. Louis County, Missouri. 

The site is approximately 32 kilometers southwest of the City 

of St. Louis and 5 kilometers northeast of the City of Eureka. 

The site occupies approximately 1,060 hectares and is divided 

into three areas: Tyson Research Center (TRC), Lone Elk 

County Park, and West Tyson County Park (Kring and Bailey, 

2001) (fig. 1).

AOCs 3, 7, and 10 lie within the TRC property, which is 

currently (2004) owned and operated by Washington University at St. Louis as a biological field station. The property 

is approximately 796 hectares in size and is bounded on the 

north by the Burlington Northern Railroad and the Meramec 

River. Interstate 44 is the southern property boundary. The east 

and west boundaries of the TRC are Lone Elk Park and West 

Tyson County Park, respectively (Ellis Environmental Group, 

2003) (fig. 1).

AOC 3 

AOC 3, the Popping Kettle area, covers 0.26 hectare. It is 

near the northeasternmost boundary of the TRC property, and 

is situated on the steeply sloping forested hillside east of the 

Popping Kettle building. A small, somewhat incised ephemeral 

stream flows through the site northward toward the Meramec 

River. This area was primarily used for the demilitarization of 

off-specification and chemically treated .30- and .50-caliber 

ammunition by use of large, heated kettles. Molten primers 

and anvils plus an inorganic slag were placed in 55-gallon 

drums and/or dumped on the ground at AOC 3 (Francis Zigmund and C.R. Colbert, U.S. Army Corps of Engineers, oral 

commun., 2004). Numerous shell casings and rusty drums, 

both partially exposed at the surface and buried, have been 

found along and within the banks of the stream channel. All 

of the drums on the surface containing slag, some of the small 

arms waste in the upper part of the creek bed, and slag piles 

adjacent to the Popping Kettle building were removed during a Time Critical Removal Action (TCRA) performed by 

Anlab Environmental in November 1998 (U.S. Army Corps of 

Engineers, 2001). Small arms waste can still be found in the 

stream channel.

AOC 7

AOC 7, the Low Water Bridge Open Dump Site, is near 

the north edge of the TRC property. AOC 10 is immediately 

north of AOC 7 and forms its northern boundary. The south 

and east boundaries of AOC 7 are bordered by a gravel road. 

Tyson Hollow Creek, an intermittent stream, defines the western boundary. Although the majority of the site is covered by 

deciduous forest, the southeastern part of AOC 7 is open and 

grassy. This site was used as a disposal area for incinerated 

.30- and .50-caliber small arms waste (HydroGeoLogic, 1999). 

AOC 10

AOC 10, the Scrap Metal Open Dump Site, is in a heavily wooded area directly north of AOC 7 and is on a sloping 

hillside. The eastern part of the site is an open field that ends 

at a gravel road. AOC 10 is bounded on the north by a small, 

unnamed intermittent stream and to the west by Tyson Hollow 

Creek. Angle iron, metal cable, metal drum remnants, and 

construction debris are exposed throughout the site and are 

concentrated near Tyson Hollow Creek.

Previous Investigations

AOC 3

 Relatively elevated concentrations of mercury were 

detected in two shell casings and one composite soil sample 

collected from the streambed at AOC 3 in 1996 by the USACE 

(Ellis Environmental Group, 2003). RIs were conducted to 

delineate the nature and extent of contamination within the 

TRC. During the Phase I and II RIs, performed by HydroGeoLogic, Inc., soil samples were collected at multiple locations. 

Sample analytes included volatile organic compounds (VOCs), 

semivolatile organic compounds (SVOCs), target analyte list 

(TAL) contaminants, explosives and cyanide. Antimony, arsenic, barium, copper, lead, and zinc were detected in samples 

collected from the slag disposal area at concentrations at least 

an order of magnitude greater than the background concentration, with some levels exceeding the risk-based concentration 

(RBC) (HydroGeoLogic, 1999).

2 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 1. Location of the areas of concern (AOCs), former Tyson Valley Powder Farm near St. Louis, Missouri.

Introduction 3
AOC 7 

AOC 7 also was investigated under the RIs. Soil and 

ground-water samples were collected during Phase I to evaluate the existence of contamination resulting from site activities. Trace element concentrations detected in the soil samples 

exceeded background concentrations at several locations. 

The explosive 2,4-dinitrotoluene (2,4-DNT) was detected 

in numerous surface-soil samples. Mercury was detected in 

ground-water samples at a concentration slightly above the 

maximum contaminant level (MCL) (HydroGeoLogic, 1999).

Additional soil and sediment samples were collected during the Phase III RI, performed by Ellis Environmental Group, 

to delineate the extent of arsenic contamination. Arsenic was 

detected in surface-soil, subsurface-soil, and streambed-sediment samples at concentrations exceeding both the residential 

and industrial preliminary remediation goal (PRG). Various 

trace elements including arsenic, chromium, lead, manganese, 

and mercury were detected at concentrations exceeding the 

associated MCL (Ellis Environmental Group, 2003).

AOC 10

AOC 10 also was investigated during the Phase III RI. 

Surface- and subsurface-soil samples were analyzed for explosives, VOCs, SVOCs, and arsenic. Arsenic was detected in 

subsurface-soil samples at concentrations exceeding both the 

residential and industrial PRG values. Trichloroethene (TCE) 

was detected in ground water at a concentration exceeding the 

MCL for this constituent (Ellis Environmental Group, 2003).

Hydrogeology

The former TVPF is characterized by steep karst topography. According to Criss (2001), this area is underlain by nearly 

120 meters of carbonates of Paleozoic age above the 

St. Peter Sandstone aquifer. This deep aquifer acts as the 

dominant source of potable water for the TRC as well as 

nearby communities. Karst features include losing streams and 

lakes, springs, caverns, and sinkholes. The nearby Meramec 

River Valley contains unconsolidated deposits of gravel and 

sand that compose a shallow aquifer used by the nearby communities downstream from the TVPF (Criss, 2001).

Tyson Hollow Creek, which acts as the western boundary 

of AOCs 7 and 10, is underlain by approximately 10 meters 

of unconsolidated alluvium that overlies the Ordovician-aged 

Kimmswick Limestone (Criss, 2001). Although the creek is 

intermittent and considered to be a losing stream, groundwater flow allows deeper parts of the creek to remain wet 

throughout much of the year. The channel substrate is dominated by coarse sands to coarse gravel-sized angular chert. The 

unnamed stream passing through AOC 3 is ephemeral and has 

a substrate similar to that of Tyson Hollow Creek.

Soils of the areas of concern generally are well-drained. 

The dominant soil series in AOC 7 and AOC 10 is the Elsah 

Silt Loam, a very deep, well-drained to somewhat excessively 

well-drained entisol that occurs in the flood plain of Tyson 

Valley Hollow (Benham, 1982). The reddish-brown alluvial 

soil tends to be gravelly with few to many rock fragments. The 

Fishpot Urban-Land complex occurs in the far eastern edge of 

AOC 7 and consists of very deep, somewhat poorly-drained 

alluvial silt loams that have been disturbed at least 76 centimeters below the surface (Benham, 1982). Soils in AOC 3 

are classified as the Menfro series. These soils are very deep, 

well-drained residual soils that appear on uplands and backslopes, as well as on terraces of the Missouri and Mississippi 

Rivers and their tributaries. The solum is composed of reddishbrown silty clay loams, with the tendency to become alkaline 

towards the lower horizons (Natural Resource Conservation 

Service, 2004).

Acknowledgments

The authors acknowledge the USACE, Kansas City 

District, for their assistance. Appreciation is also extended 

to the USGS Crustal Imaging and Characterization Team for 

providing guidance and support throughout this study. Special 

thanks are extended to the staff of the Tyson Research Center, 

especially David Larson, David Schilling, and Angelo Oldani, 

for volunteering their time and resources.

Methods

EM and magnetic surveys were performed along an 

established, georeferenced grid in late April 2004. The grids 

consisted of parallel lines 3 meters apart with each line having 

a marked reference position every 5 meters. All distances were 

measured along the land surface following the topographic 

changes. An Ashtech Z-Xtreme real-time kinematic (RTK) 

global positioning system (GPS) was used to georeference the 

grids in the open areas away from the tree canopy, which interfered with satellite reception (app. 1). Grid locations under the 

tree canopy were georeferenced using an automatic level and 

stadia rod where conditions allowed (app. 1). Because of line 

of sight restrictions from trees, brush, and weather limitations, 

all other grid locations were interpolated from georeferenced 

points through a geographic information system (GIS). The 

grids also were referenced to existing points such as power 

poles from overhead utilities, monitoring wells, buildings, and 

existing benchmarks. Locations of exposed surface metal were 

recorded for comparison to geophysical data.

EM and magnetic methods were used at each AOC to 

provide an initial evaluation of the areal extent and location 

of anomalies. These methods, which do not require ground 

contact, can be performed with hand-held instruments, creating a relatively quick, non-intrusive means of surveying the 

subsurface environment for buried metallic objects (Won and 

Keiswetter, 1997). EM and magnetic techniques were applied 

to AOCs 3, 7, and 10 using the dead-reckoning technique, 

4 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
where the lines of the predetermined grid were walked and 

digital marks were inserted into the dataset as the reference 

points every 5 meters were passed. Each digital mark was then 

adjusted to the correct reference position during post-processing and the data between the reference positions were evenly 

spaced.

After processing the results from the initial survey, anomalies common to both methods were identified. The definition 

of an “anomaly” was determined from the histograms of each 

parameter in the results of the survey (app. 2). The majority of 

the values were considered background levels. Values occurring with a frequency in the outer 5 percent of total occurrence 

were classified as anomalies. Zones were delineated around 

spatial groupings of anomalies in AOCs 3, 7, and 10. These 

zones contained the majority of anomalies found; however, 

smaller, isolated anomalies do exist outside of these zones. 

Selected zones were then further explored by 2D-DC resistivity and time-domain IP to characterize the depth and areal 

extent of the various anomalies. Excavation of a few features 

was performed immediately following the resistivity survey to 

compare the occurrence of metallic debris in the subsurface to 

the interpreted geophysical results.

Electromagnetic Methods

EM methods work by means of electromagnetic induction (EMI). A transmitting coil produces an electromagnetic 

field that induces a secondary electromagnetic field in the 

ground, the magnitude of which is dependent on the conductivity of the subsurface. A receiving coil measures the 

magnitude of the induced field and collects raw in-phase and 

quadrature responses. From this raw data, more interpretive 

parameters can be determined, such as magnetic susceptibility and apparent electrical conductivity. Traditional EMI 

sensors are composed of separate transmitting and receiving 

coils connected by cables that require precise changes in coil 

spacing to alter the depth of measurement (skin depth). In 

contrast, frequency-sounding methods use multiple frequencies to alter skin depth, allowing the spacing of the coils to 

be small and fixed. The development of fixed-coil technology 

has led to compact, hand-held sensors that can be operated by 

a single person (Won, 2003). Because these fixed-coil sensors do not demand platforms or carts for stabilization and 

are contained in a single, lightweight unit, this type of EMI 

sensor was ideal for the heavily vegetated, uneven terrain of 

the former TVPF. The EM part of the study was performed 

with the GEM-2, designed by Geophex, Ltd. (Geophex, Ltd., 

2004). The GEM-2 is a hand-held, digital, multi-frequency, 

fixed-coil EMI sensor with a bandwidth of 300 Hertz (Hz) to 

24 kilohertz (kHz).

The GEM-2 was operated in frequency-domain mode, 

in which five frequencies were simultaneously transmitted 

through a digitally synthesized waveform, a method known as 

the pulse-width modulation technique (Won and others, 1996). 

Two base periods, each being 1/30 of a second when 60 Hz is 

selected for utility-related noise, were averaged for each measurement event during the survey. The sensor was operated in 

vertical-dipole configuration. The vertical-dipole configuration 

is typically more responsive to subsurface metallic debris and 

has a greater depth of investigation than the horizontal dipole 

configuration (Powers and others, 1999).

An environmental noise test was performed prior to 

the beginning of the EM survey to aid in the selection of the 

transmitting frequencies (app. 3). This test was conducted 

by holding the GEM-2 stationary and collecting a small 

dataset, approximately 5 seconds in duration. The data were 

then downloaded and examined for noise using WinGEM 

version 1.50, a post-processing software package designed 

by Geophex, Ltd., which communicates with the GEM-2. 

Frequencies with high noise levels were avoided, including 

the 60 Hz frequency associated with overhead power lines. 

The following frequencies were chosen to obtain a variety of 

depths while minimizing harmonic noise: 2,070 Hz, 5,010 Hz, 

9,030 Hz, 13,830 Hz, and 20,010 Hz. Because of the presence 

of overhead powerlines in AOCs 7 and 10, 60 Hz was chosen 

as a monitoring frequency; that is, the GEM-2 did not transmit 

this frequency, but only recorded the response. AOC 7 was 

surveyed on April 21, 2004; AOCs 3 and 10 were surveyed on 

April 22, 2004. The environmental noise test was performed 

on both days. The results of the tests were found to be similar, 

and the same frequencies were used for each AOC (app. 3).

After EM data were collected, approximate local coordinate values were assigned to each measurement event using 

WinGEM. The locations were finalized in a spreadsheet 

based on the positioning of the digital marks in the data. A 

three-dimensional graphics program was used to grid raw 

in-phase and quadrature results for each frequency, as well as 

apparent electrical conductivity and magnetic susceptibility 

extracted from the raw data in WinGEM. The final gridding 

was performed using the minimum curvature method with a 

cell size of 1.25 meters. The grids were displayed by examining the distribution of data values and maximizing the color 

scale throughout the majority of the variations in values while 

minimizing the effect of extreme single-event outliers (app. 2). 

Magnetic Methods

Ground magnetic surveys consist of measurements of the 

total magnetic field intensity along grid lines. One approach to 

ground magnetic surveys uses two sensors. One sensor is used 

to collect the measurements in the grid area while another sensor is used to monitor the time variations in the earth’s magnetic field caused by magnetic storms and diurnal variations. 

Post-processing techniques allow for the removal of the time 

variations in the data collected within the grid area. Thus the 

anomalies produced in the post-processed dataset are, because 

of local variations in the magnetic field, presumably caused 

by subsurface materials (Breiner, 1999). A second approach, 

which is especially effective for shallow, subsurface investigations, is the gradient technique. The gradient technique 

Methods 5
measures the difference in the total magnetic-field intensity 

between two sensors set at a fixed distance apart from each 

other. The anomalies produced by the gradient technique tend 

to resolve composite or complex anomalies into their individual components, creating more clearly defined anomalies than 

the more traditional method described in the first approach 

(Breiner, 1999). When using the gradient technique, it is not 

necessary to monitor and remove the time variations in the 

magnetic field because such changes would affect both sensors 

in the same manner. Therefore the anomalies produced using 

the gradient technique reflect only the magnetic variations in 

the subsurface materials. Because of its effectiveness in shallow investigations and its simplicity, the gradient technique 

was chosen for this study, and data in this report are referred to 

as vertical gradient.

The G-858 portable cesium magnetometer from Geometrics (Geometrics, 2004) was used to collect vertical gradient 

data; the sensors were operated with one directly over the 

other. The G-858 has an operating range from 17,000 nanotesla (nT) to 100,000 nT. The two sensors were spaced 

0.76 meter apart vertically. Both sensors were set to a 

15-degree angle from vertical to maximize the intensity of the 

signal. Data were collected continuously at 1 Hz, or one cycle 

per second, which gives a sensitivity of 0.01 nT for 90 percent 

of the readings. Data were logged using the MagMapper system from Geometrics.

Original binary data were downloaded from the MagMapper system and converted to ASCII data using MagMap 

2000 software provided by Geometrics. Subsequently the data 

were imported into a database. As an aid in the identification 

and removal of data spikes caused by both saturation of the 

sensor over strongly magnetic bodies and sensor orientation, 

the profiles of top sensor, bottom sensor, and vertical gradient were plotted along the y-axis. The data spikes were then 

deleted and a linear interpolation was performed to fill in the 

deleted values. The data were then plotted in a three-dimensional graphics program using minimum curvature gridding 

method with a cell size of 1.25 meters. The vertical gradient 

was displayed by examining the distribution of the data and 

maximizing the color scale within the peak occurring values 

and minimizing the effect of outliers in the appearance of the 

grid (app. 2).

Two-Dimensional Direct-Current Resistivity

Using the dipole-dipole and Wenner-Schlumberger 

arrays (Loke, 2004), direct-current resistivity measurements 

were made by inducing direct current into the ground through 

two current electrodes and measuring the resulting voltage 

between two potential electrodes. The dipole-dipole array is 

very sensitive to horizontal changes in resistivity; however, it 

is relatively insensitive to vertical changes in resistivity, has 

a shallow depth of penetration, and a relatively low signal 

strength. The Wenner-Schlumberger array has moderate resolution in both the horizontal and vertical directions, a deeper 

penetration depth, and has higher signal strength than the 

dipole-dipole array, resulting in a higher signal-to-noise ratio 

(Loke, 2000). Resistance was calculated by dividing the measured voltage by the induced current. The apparent resistivity 

of the subsurface was calculated by multiplying the resistance 

by a geometric factor that is determined by the geometry 

and the spacing of the electrode array (Stanton and others, 

2003). Apparent resistivity field datasets were inverted using 

RES2DINV version 3.52w software (Loke, 2003) to create 

inverted field datasets that provide a much closer approximation of the true resistivity of the subsurface than the raw data 

itself. The inversion process is described by Loke (2004); the 

model referred to in the following quote is referred to as the 

inverted field dataset in this report:

“In geophysical inversion, we seek to find a model 

that gives a response that is similar to the actual 

measured values. The model is an idealized mathematical representation of a section of the earth. 

The model has a set of model parameters that are 

the physical quantities we want to estimate from the 

observed data. The model response is the synthetic 

data that can be calculated from the mathematical 

relationships defining the model for a given set of 

model parameters. All inversion methods essentially 

try to determine a model for the subsurface whose 

response agrees with the measured data subject to 

certain restrictions. In the cell-based method used 

by the RES2DINV and RES3DINV programs, the 

model parameters are the resistivity values of the 

model cells, while the data is the measured apparent 

resistivity values. The mathematical link between 

the model parameters and the model response for the 

2-D and 3-D resistivity models is provided by the 

finite-difference or finite-element methods.”

Resistivity data collection was once a repetitive process 

in which individual 1-D soundings were collected using two 

current and two potential electrodes. The soundings were collected by keeping the center point of the array the same and 

increasing the electrode spacing to obtain information about 

deeper sections of the subsurface. The center point of the 

array was then moved and the process repeated until multiple 

1-D soundings were collected. Recent advances in computers 

and equipment allow the user to set-up multiple electrodes 

in succession (Stanton and others, 2003). The electrodes are 

connected to electrode takeouts built into multi-conductor 

cables and joined by an automatic switching unit. These units 

are designed to perform automatically pre-defined sets of 

resistivity measurements using multiple electrodes to facilitate 

rapid data collection (Stanton and others, 2003). The data at 

the former TVPF site were collected using an IRIS Syscal R1 

Plus Resistivity Meter. Using four electrodes at a time, the unit 

switches among a combination of six sets of multi-core cables 

with twelve electrodes each at 0.5-meter spacing to collect 

multiple points from a single layout.

6 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Time-Domain Induced Polarization

Using the dipole-dipole and Wenner-Schlumberger arrays 

(Loke, 2004), time-domain induced polarization (time-domain 

IP) measurements were made by inducing direct current into 

the ground through two current electrodes and measuring 

the resulting voltage between two potential electrodes, then 

measuring the residual decay voltage in discrete time intervals after the current is switched off. In time-domain IP the 

measured parameter, the chargeability, is given in millivolt per 

volt (mV/V). Time-domain IP data were collected with the 

IRIS Syscal R1 Plus Resistivity Meter. Measured chargeability 

field datasets were inverted using RES2DINV version 3.52w 

software (Loke, 2003) to create inverted field chargeability 

datasets that provide a much closer approximation of the true 

chargeability of the subsurface than the raw field data (Loke, 

2004).

Forward Modeling of Resistivity Data 

The purpose of forward modeling is to approximately 

match the field resistivity data to a possible representation of 

the subsurface resistivity. After examination of the field data, 

forward modeling was used to calculate apparent resistivity 

values from a user-specified two-dimensional grid of rectangular model blocks. The model blocks are grouped into layers 

that correspond to the layers found in the inverted field resistivity data. Following construction, the forward models were 

used to calculate apparent resistivity values. The apparent 

resistivity values were processed using RES2DINV following 

the same procedures used in processing the field resistivity 

data. The forward model was modified through an iterative 

process in order to maximize the correlation to the inverted 

field model. After processing, the inverted model was compared to the inverted field resistivity dataset. A forward model 

solution is reached when the inverted model and inverted field 

resistivity dataset approximately match. The final forward 

model grid was used to provide a detailed non-unique interpretation of the subsurface (Degnan and others, 2001). 

A basic forward model was developed using 

RES2DMOD software version 3.01n (Loke, 2002) by estimating the number of layers identified in the field resistivity data. 

Driller’s logs from wells registered with the Missouri Department of Natural Resources (URL: http://www.dnr.state.mo.us/

geology/geosrv/wellhd/wellhead.htm, accessed May 2004) and 

driller’s logs from previous investigations were compared to 

the layers identified in the field resistivity data and to determine the possible geologic description of each layer within the 

basic model. Although driller’s logs were used for comparison, 

the data were insufficient to create detailed geologic models, 

mostly because the wells within the AOCs were shallower 

than the resistivity sections and the deeper geologic wells 

were not located near the study area. Because of this lack of 

detailed geologic information, the field resistivity data were 

the primary data used in developing the forward model. 

Resistivity values were assigned to each layer based on 

the field resistivity data. Within these layers, resistivity values 

can vary depending on the coarseness and type of sediment. 

Once each layer had a specific value, the model was modified by changing the depth and thickness of the layer. After 

each modification, the forward model was inverted and then 

compared to the inverted field data until they closely resembled each other. After the general size and shape of the layers 

for each survey line were developed, anomalies, which may 

represent metallic objects, were introduced into the forward 

model. The depth, size, and shape of each anomaly was modified within the forward model for each survey line until the 

inverted model produced anomalies similar to its corresponding inverted field resistivity dataset. After modification, the 

final forward model was compared to the driller’s logs to confirm that the solution is in concordance with known geologic 

information.

Areal Extent of Anomalies

The areal extent of anomalies potentially indicating 

areas with a relatively large abundance of metallic debris was 

determined using EM and magnetic techniques. Based on the 

initial data, the vertical gradient was compared to the magnetic 

susceptibility at 2,070 Hz and the total apparent electrical conductivity (EC). At the local scale of this study, it was assumed 

that there was not enough significant geologic variation in the 

near surface to cause notable disparities within each individual 

AOC. As the background geologic response was assumed to 

be relatively constant, background values were not removed 

from the EM data. As a result, all EM parameter values, 

including magnetic susceptibility and total apparent EC, were 

used qualitatively and not as “true” readings.

For the EM results of total apparent EC and magnetic 

susceptibility, anomalies were visualized as hot spots in 

orange and red, representing values with a frequency of occurrence in the upper 5 percent of the total number of readings. 

Background values fall in the blue range, while more subtle 

variations are seen in yellow and green. Anomalies in the 

vertical gradient, a result of the magnetic survey, are defined 

by approximately the upper and lower 5 percent of the total 

number of readings. The remaining 90 percent of the vertical 

gradient data showed little to no gradient. This background 

range is visualized by green, while red and blue represent 

positive and negative gradients, respectively. Anomalies, 

present in both the EM and magnetic results, were grouped 

into zones based on their proximity to one another. Anomalies 

with relatively low intensities, small size, or that were isolated 

were generally not grouped into zones. It is possible that these 

anomalies characterize metallic waste that exists outside of the 

zones.

Metallic waste within the AOCs was assumed to be 

mixed by nature, with both magnetic and nonmagnetic metals 

being present in the same area. Although the magnetometer 

Areal Extent of Anomalies 7
seeks the existing magnetic field of a target, the EMI sensor 

detects electrically conductive, nonmagnetic metals as well as 

magnetic targets (Won and Keiswetter, 1997). Although this 

difference in functionality potentially allows for the differentiation between magnetic and nonmagnetic targets, the results of 

the EM survey did not show unique anomalies that would be 

indicative of conductive, nonmagnetic targets. It is likely that 

isolated, nonmagnetic metals do not exist in concentration, but 

are scattered throughout the AOCs in quantities too small to be 

detected with the GEM-2. Ground-truthing information confirmed that when small arms waste was found, individual nonmagnetic shell casings were found distributed within the soil 

matrix. Because of this, the metallic composition of anomalies 

was not able to be determined through this study.

Electromagnetic and magnetic data showed a scattering 

of anomalies in all three areas of concern. Anomalous zones 

were identified and mapped—zones 1–2 in AOC 3, zones 3–6 

in AOC 7, and zones 7–11 in AOC 10 (app. 4). Grid locations 

are identified by mark and line location. For example, (35,0) 

refers to a point at mark 35 on line 0.

AOC 3

Zone 1

The anomalies in zone 1 appear to be located in a linear 

feature seen most clearly in the magnetic susceptibility as the 

red diagonal feature running south-southeast from about (35, 

0) to (50, -45) (fig. 2B). Based on the EM and magnetic data, 

the anomalies tend to follow the ephemeral stream (fig. 4); 

however, the anomalies began to shift towards the east bank at 

line location -24 and became independent of the stream at line 

location -39 (figs. 2 and 3). Although the northern part of this 

anomaly zone could be attributed to the metal pipe and small 

arms waste located in the ephemeral stream (figs. 3 and 4), the 

anomaly in the east bank is more likely to be buried metallic objects. A visual investigation around the location where 

the anomalies began to shift towards the east bank revealed a 

piece of scrap metal in a small depression at (45,-30). In this 

area the vertical gradient data showed an elongated area of 

closely spaced high and low values, suggesting magnetization 

of metals in the subsurface. These anomalies were considered significant enough to be further investigated by 2D-DC 

resistivity.

Zone 2

The other major anomaly of AOC 3, located at (5, -33) 

and seen in both the magnetic susceptibility and vertical gradient datasets, could not be attributed to exposed surface waste 

(fig. 2B and C). Although this anomaly was much smaller in 

the EC results, a zone was designated around this anomaly 

based on the correlation between the magnetic susceptibility 

and vertical gradient results (fig. 3).

8 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 2. Results of the electromagnetic and magnetic survey at AOC 3 showing A, total apparent electrical conductivity; 

B, magnetic susceptibility at 2,070 Hz; and C, vertical gradient.

A

Areal Extent of Anomalies 9
Figure 2. Continued.

B

10 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 2. Continued.

C

Areal Extent of Anomalies 11
Figure 3. Site map of AOC 3 showing anomalous zones.

12 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
A

Figure 4. Photographs of surface metal at AOC 3 including exposures of small arms waste in the ephemeral stream channel looking 

A, northward downstream, and B, at the west bank near mark 40, line -12.

B

Areal Extent of Anomalies 13
Zone 5

A somewhat linear anomaly running north-south ((-60, 

72) to (–45, 48)) can be seen in all datasets (fig. 6). Although 

part of this zone falls within the powerline corridor (fig. 8), 

the correlation between the vertical gradient and magnetic 

susceptibility, in addition to the multiple surface exposures of 

small arms waste in this area (fig. 7B), caused these features 

to be delineated as a zone. Small arms waste is not expected 

to create a strong response in the vertical gradient, as the concentration of ferrous, or magnetic, materials is small in such 

debris. Because of the strong response shown in fig. 6B, it was 

suspected that more waste may be buried here in addition to 

the surface small arms waste. This anomaly was selected for 

further characterization by 2D-DC resistivity.

Zone 6

A small anomaly occurred in the magnetic susceptibility 

as well as the vertical gradient near (-20, 30) (fig. 6). No surface debris was recorded at this location. The clear response 

from both instruments validated creating a zone for this feature 

(fig. 8).

Zone 7

The magnetic susceptibility of 2,070 Hz shows a band 

of low intensity anomalies starting at (0, 39) and extending 

to (-20, 72) (fig. 6). However, the vertical gradient does not 

show similar anomalies within this area. Data collection in 

this area was impaired by heavy vegetation, steep topography, 

and vehicle traffic on the gravel road that borders AOC 7. 

Although there is the possibility that the anomaly found in 

the magnetic susceptibility was caused by subsurface metals, 

the difficulty experienced during data collection and the lack 

of corresponding anomalies in the vertical gradient results 

in a lower confidence level in delineating zone 7 than the 

other zones within AOC 7. However, the features seen in the 

magnetic susceptibility are strong enough to be classified as 

anomalies and are distributed over an area large enough to 

warrant creating a zone for these features.

AOC 7

An overhead powerline runs roughly north-south in the 

western part of AOC 7 (fig. 8). Because the powerline oversaturates the GEM-2, the EM data surrounding the powerline 

must be ignored. To determine where the effect of the powerline was overpowering, the 60-Hz monitoring frequency was 

examined (fig. 5). The 60-Hz monitoring frequency shows a 

strong response in an area of approximately 10 meters on each 

side of the powerline. The total apparent EC shows a band in 

the same location, indicating the need to mask out this section 

of the AOC. Because of the effect of the powerline on the EM 

data, the magnetometer survey was given the most weight in 

identifying the anomalies, while the EM datasets were used 

for confirmation. 

Anomalies in AOC 7 can be seen in the vertical gradient 

data that are not found to be major disturbances in the EM data 

(fig. 6). It should be noted that many of these vertical gradient 

features occur in the area influenced by the power lines where 

the EM method was compromised. Although large surface 

exposures of metallic debris were catalogued, smaller debris 

such as randomly distributed small arms waste, barbed wire, 

and other scrap metal may have been left undocumented under 

the dense vegetation throughout AOC 7. Such items could 

have caused the scattered features found in the vertical gradient data that were too small to be found with the EM method. 

Zone 3

The largest anomaly occurred at (-40,117) to (-5, 90) 

(fig. 6). This feature appeared in both the magnetic susceptibility and the vertical gradient. This area was documented to 

have multiple metal sheets on the surface, as well as a large 

distribution of 1-inch diameter metal cable (fig. 7). Because 

of the high level of noise caused by the littering of surface 

metal, the EM and magnetic surveys were unable to determine 

if there was more waste buried at this location. Therefore, this 

anomaly was chosen for further investigation with 2D-DC 

resistivity (fig. 8).

Zone 4

Another relatively large anomaly appeared at (-5, 122), 

which was seen in all transmitted EM frequencies and magnetic data (fig. 6). At the surface a concrete “ring” was found, 

approximately 4 meters in diameter. Because of the strong 

response from both the EM and magnetic results, it was 

believed that metal also is present in the subsurface at this 

location, most likely as part of the structural support, such as 

rebar (fig. 8).

14 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 5. Results of the electromagnetic survey at AOC 7 (A and B) and AOC 10 (C and 

D) comparing the in-phase response of the 60 Hz monitoring frequency to the total 

apparent electrical conductivity.

A

Areal Extent of Anomalies 15
Figure 5. Continued.

B

16 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 5. Continued.

C

Areal Extent of Anomalies 17
Figure 5. Continued.

D

18 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
A

Figure 6. Results of the electromagnetic and magnetic survey at AOC 7 showing 

A, magnetic susceptibility at 2,070 Hz; and B, vertical gradient.

Areal Extent of Anomalies 19
B

Figure 6. Continued.

20 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 7. A1 and A2, photographs of surficial metal in AOC 7 looking south between mark -40, line 117 to mark -29, line 102 showing 

1-inch diameter metal cable and scrap metal, and B1 and B2, photographs of barbed wire and small arms waste near mark -55, line 51.

A1 A2

B1 B2

Areal Extent of Anomalies 21
Figure 8. Site map of AOC 7 showing anomalous zones.

22 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
AOC 10

The overhead powerline running through AOC 7 continues into AOC 10, causing a similar oversaturation of the 

GEM-2 within the area of influence (fig. 5). Therefore, the 

vertical gradient data were determined to be the primary 

investigation technique, while the magnetic susceptibility 

was used as a secondary parameter. Like AOC 7, there was 

an abundance of scattered surface metal throughout AOC 10. 

Although large debris was recorded, not all surface metal 

could be located and documented by sight because of the vegetative cover. It is possible that the scattering of surface metal 

throughout AOC 10 caused the spotty high and low vertical 

gradient anomalies.

Zone 8

The most intense anomalies were found at (-80, 108) to 

(-70, 90) (fig. 9). This area was scattered with exposed steel 

drums, sheet metal, and other debris (fig. 10), which are the 

likely cause of these anomalies. The vertical gradient and 

magnetic susceptibility both showed more subtle anomalies 

extending 15 meters to the east. Though this area is within the 

powerline corridor, the agreement between the vertical gradient and magnetic susceptibility make it unlikely that these 

features are merely artifacts of electrical interference. These 

subtle features were grouped with the results of the exposed 

metal to create zone 8 (fig. 11).

Zone 9

The second major anomaly in the vertical gradient data 

was located near (-15, 30) (fig. 9). Scrap metal was catalogued 

on the surface at this location. However, the features shown in 

the vertical gradient and subtly in the magnetic susceptibility 

northward to line 42 may indicate additional buried ferrous 

metal. Another large anomaly at (-20, 51) did not correspond 

to a surface exposure. The correspondence between the vertical gradient and the magnetic susceptibility indicates that this 

location is likely to contain buried metal. Subtle magnetic 

susceptibility features surrounding these larger anomalies from 

line location 12 to 60 correspond to anomalies present in the 

vertical gradient. Because of the correlation, the area between 

(-10, 12) and (-20, 66) was grouped into zone 9.

Zones 10, 11 and 12

Zones 10, 11 and 12 were created around small anomalies 

seen in both the magnetic susceptibility and the vertical gradient. Zone 10 is directly over the gravel road that runs along 

the eastern edge of AOC 10 and can be seen most clearly in 

the magnetic susceptibility at (0,102) (fig. 9). Despite the 

weaker response in the vertical gradient, the anomaly seen in 

the magnetic susceptibility warranted creating a small zone 

for this feature. Zones 11 and 12 were created around subtle 

features seen most clearly in the magnetic susceptibility at 

(-15, 75), and (-35, 111), respectively (fig. 9). Although these 

locations did not have a strong enough response in the EM 

method to qualify as an anomaly, the corresponding features 

in the vertical gradient indicate that metals could be present in 

the subsurface; therefore, a zone was created around each of 

these features.

Areal Extent of Anomalies 23
Figure 9. Results of the electromagnetic and magnetic survey at AOC 10 showing A, magnetic susceptibility at 2,070 Hz; and 

B, vertical gradient.

A

24 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 9. Continued.

B

Areal Extent of Anomalies 25
Figure 10. Photographs of surficial scrap metal in AOC 10 between mark -80, line 108 to mark -70, line 90.

26 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 11. Site map of AOC 10 showing anomalous zones.

Areal Extent of Anomalies 27
Vertical Extent of Anomalies

In addition to determining the areal extent of anomalies 

throughout each AOC, the vertical extents were determined 

for certain anomalies in AOCs 3 and 7. The vertical extents of 

selected anomalies were analyzed by examining the 2D-DC 

resistivity and time-domain IP data. The 2D-DC resistivity 

data were collected using a dipole-dipole and a Wenner-Schlumberger array for Line 1 (fig. 3). Time-domain IP measurements were also collected using the dipole-dipole array at survey line 1 (fig. 12A). The data from each array were inverted 

in the field and analyzed to determine the most effective array 

that would be used to collect data for additional survey lines. 

After reviewing the raw data and inversion results of the 

resistivity data, the Wenner-Schlumberger array (fig. 12B) was 

chosen for the collection of additional survey lines. Both the 

dipole-dipole and the Wenner-Schlumberger arrays produced 

similar results; however, due to the geometry of the array, 

the Wenner-Schlumberger array has a lower signal-to-noise 

ratio, producing the highest quality data for both the raw 

data and the inverted field resistivity datasets. The WennerSchlumberger array was subsequently used to collect 2D-DC 

resistivity and time-domain IP measurements for lines 2 

through 5 (figs. 3 and 8). The results were displayed by plotting two-dimensional sections of the inverted field resistivity 

and inverted time-domain IP data in a gradational color scale 

(figs. 12, 13, 14, 15, and 16). The cooler colors are less resistive, or have a lower chargeability, and the warmer colors are 

more resistive, or have a higher chargeability. Inversion results 

of the resistivity data were displayed using a logarithmic scale 

and the time-domain IP inversion results are displayed using a 

linear scale of chargeability values.

The inversion results of the field resistivity data from 

both the dipole-dipole and Wenner-Schlumberger arrays from 

survey line 1 (fig. 12) and the Wenner-Schlumberger array 

for survey lines 2 and 3 (figs. 13 and 14) were interpreted as 

having a similar 3-unit case whereas lines 4 and 5 (figs. 15 

and 16) were more difficult to interpret because of the noise 

caused by surface and subsurface metallic debris. Line 4 was 

interpreted to have three resistivity units whereas line 5 was 

interpreted to have only two resistivity units. Unit 1 is a high 

resistivity unit (greater than 74 ohm-meters) followed by 

unit 2, a less resistive layer (less than 74 ohm-meters). Survey 

lines 1 through 3 also show a non-continuous high resistivity (greater than 74 ohm-meters) feature near the bottom of 

each section, which is considered to be unit 3. This unit was 

observed but its location was not clearly defined because of 

the reduction in sensitivity near the bottom of the section. 

Sensitivity represents the degree to which a change in the 

resistivity of a section of the subsurface will influence the 

potential measured by the array (Loke, 2000). Alterations 

in the location and properties of unit 3 in the model tend to 

have little effect on the inversion result because the bottom 

and edges of the section in a Wenner-Schlumberger array is 

the least sensitive part of the section. Because of this lower 

sensitivity, the contact surface of unit 3 is considered to be 

more poorly defined than other units. Areas within unit 1 that 

are less than 74 ohm-meters are considered to be anomalies 

and are found in survey lines 1, 2, 4, and 5 (figs. 12, 13, 15, 

and 16).

Sections of the inverted field chargeability data from 

time-domain IP measurements exhibit features throughout 

each section where chargeability increases more than 

12 mV/V in comparison with the surrounding regions. These 

features are considered to be anomalies for survey lines 1 

through 5 (figs.12, 13, 14, 15, and 16). Anomalies occurring 

within lines 1 though 5 are denoted by the display of colors 

representing 12mV/V or greater.

Time-domain IP measurements from survey lines 1, 

2, and 3 showed a more frequent occurrence of anomalies 

than were shown in the field resistivity sections (figs. 12, 13, 

and 14). The lack of low resistivity anomalies shown in the 

resistivity sections of survey lines 1, 2 and 3 could possibly be 

explained by a relatively high concentration of highly resistive 

chert fragments in unit 1, as well as the scattered distribution 

of small arms waste throughout the soil matrix discovered 

during excavation activities. The chert could be acting as an 

insulator, masking the less-resistive inclusions of small arms 

waste. However, a charge could still be induced in the isolated 

small arms waste, causing a greater IP response than the surrounding topsoil and chert fragments.

Survey lines 4 and 5 show large, low resistivity anomalies throughout the resistivity and time-domain IP sections 

(figs. 15 and 16). These low resistivity anomalies could be 

attributed to barbed wire (fig. 7B) found along survey line 4 

and 1-inch diameter metal cable (fig. 7A) found along survey 

line 5. The presence of this surficial metal could have created 

preferential electrical conduits near the surface, causing the 

majority of the current transmitted by the current electrodes 

to reach the potential electrodes without traveling through 

the more resistive subsurface geology. The inversion process 

would have projected these low resistivity, surface-influenced 

readings at false depths, creating large, deep anomalies in the 

subsurface.

28 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 12. Field data of survey line 1 in AOC 3. Sections showing inverted two-dimensional, direct-current resistivity data using 

A, a dipole-dipole array, B, a Wenner-Schlumberger array, and C, inverted time-domain induced polarization data using a 

dipole-dipole array.

A

B

C

Vertical Extent of Anomalies 29
Figure 13. Field data of survey line 2 in AOC 3. Sections showing A, inverted two-dimensional, direct-current resistivity data using a 

Wenner-Schlumberger array, and B, inverted time-domain induced polarization data using a dipole-dipole array.

A

B

30 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 14. Field data of survey line 3 in AOC 3. Sections showing A, inverted two-dimensional, direct-current resistivity data using a 

Wenner-Schlumberger array, and B, inverted time-domain induced polarization data using a dipole-dipole array.

A

B

Vertical Extent of Anomalies 31
Figure 15. Field data of survey line 4 in AOC 7. Sections showing A, inverted two-dimensional, direct-current resistivity data using a 

Wenner-Schlumberger array, and B, inverted time-domain induced polarization data using a dipole-dipole array.

A

B

32 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 16. Field data of survey line 5 in AOC 7. Sections showing A, inverted two-dimensional, direct-current resistivity data using a 

Wenner-Schlumberger array, and B, inverted time-domain induced polarization data using a dipole-dipole array.

A

B

Vertical Extent of Anomalies 33
Forward Model Data

After the field data were examined, forward models were 

created for 2D-DC resistivity survey lines 1 through 5. The 

layers used in forward modeling were assigned resistivity 

values based on the field resistivity dataset and were altered 

according to the results of the model inversion. Geologic 

descriptions were given to each layer based on driller’s logs: 

a resistivity of 250 ohm-meters was used to model the topsoil 

with chert fragments in layer 1, a resistivity of 25 ohm-meters 

was used to model the clay in layer 2, and a resistivity of 

250 ohm-meters was used to model the limestone in layer 3. 

Layer 1 contains areas that range in resistivity, believed to 

result from variations in the abundance of chert fragments 

within the top soil. Therefore, some areas in layer 1 were 

modeled with values less than 250 ohm-meters. Values of 50 

and 100 ohm-meters were used to represent areas of layer 

1 where there was a decrease in resistivity. In survey line 3, 

layer 1 also contained areas where resistivity values increased 

(fig. 14). This area was located along an unnamed ephemeral 

stream (fig. 3) in AOC 3 and was associated with an increase 

in the abundance of gravel and cobble-sized chert, which was 

assigned a resistivity of 750 ohm-meters. Survey line 4 in 

AOC 7, near Tyson Hollow Creek (fig. 8), also had an increase 

in resistivity in layer 1 because of gravel- and cobble-sized 

chert. A value of 1,000 ohm-meters was used in layer 1 to 

indicate the area where resistivity increased, which is also considered to reflect an increase in the abundance of gravel- and 

cobble-sized chert deposits. Low resistivity anomalies in the 

inverted field resistivity data from survey lines 1, 2, and 5 were 

assigned a resistivity of 10 ohm-meters in the forward models 

for each line. Line 4 also contained low resistivity anomalies 

appearing in layer 1; however, to produce an inverted model 

resistivity section that closely corresponded with the inverted 

field resistivity data from line 4, a resistivity of 0.5 ohm-meter 

was used in the modeling of anomalies for survey line 4.

 Line 1 forward model (fig. 17A) was used as the initial 

input model grid for lines 2 through 5. After many iterations, 

a three-layer model consisting of topsoil with chert fragments 

(layer 1), clay (layer 2), and limestone (layer 3) was produced 

for lines 1, 2, 3 and 4 (figs. 17A, 18A, 19A, and 20A). 

A two-layer model consisting of topsoil with chert fragments 

(layer 1) and clay (layer 2) was developed for survey line 5 

in AOC 7 (fig. 21A). A model solution was reached when the 

inversion results of the model (figs. 17C, 18B, 19B, 20B, and 

21B) visually resembled the inversion results from the field 

data (figs. 12B, 13A, 14A, 15A, 16A). 

34 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 17. Survey line 1, AOC 3. Sections showing A, forward model, and inverted model resistivity data using B, a dipole-dipole array 

and C, a Wenner-Schlumberger array from the forward model. , a Wenner-Schlumberger array from the forward model.

A

B

C

Vertical Extent of Anomalies 35
Figure 18. Survey line 2, AOC 3. Sections showing A, forward model, and B, inverted model resistivity data using a Wenner-Schlumberger array from the forward model.

B

A

36 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 19. Survey line 3, AOC 3. Sections showing A, forward model, and B, inverted model resistivity data using a Wenner-Schlumberger array from the forward model.

B

A

Vertical Extent of Anomalies 37
Figure 20. Survey line 4, AOC 7. Sections showing A, forward model, and B, inverted model resistivity data using a Wenner-Schlumberger array from the forward model.

B

A

38 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 21. Survey line 5, AOC 7. Sections showing A, forward model, and B, inverted model resistivity data using a Wenner-Schlumberger array from the forward model.

B

A

Vertical Extent of Anomalies 39
Interpretation of Resistivity Data

Interpretation sections were created for each survey line 

using results from both the field resistivity data and forward 

models. Lines 1 through 3 were interpreted primarily based 

on the field resistivity data, while forward models were used 

as a guideline for interpreting the field data. Because of the 

more complicated nature of the field resistivity data from 

survey lines 4 and 5, interpretations were based more heavily 

on the forward models than the field resistivity data, yielding 

a 3-layer interpretation for line 4 and a 2-layer interpretation 

for line 5. Because of the lower sensitivity of the bottom of the 

Wenner-Schlumberger array, the interpretation section does 

not accurately characterize the surface of layer 3 in any of the 

lines. Because of the remote nature of 2D-DC resistivity and 

the chance for variability in the subsurface, the interpretations 

are non-unique solutions to the field resistivity data (Degnan, 

2001). Although it is possible to develop different interpretations that would also be reasonable solutions to the field resistivity data, the addition of information from driller’s logs and 

excavation trenches makes the following interpreted sections 

likely scenarios.

Line 1

Layer 1 consists of topsoil with chert fragments occurring 

at land surface and ranging down to 144 to 142 meters (m) 

above the North American Vertical Datum of 1988 (NAVD 

88). Clay is represented as layer 2, but the thickness of this 

layer could not be determined because no consistent third 

layer was found to define the lower boundary. Layer 3, 

limestone, is horizontally discontinuous. The contact between 

layers 2 and 3 occurs intermittently between 141 to 142 m in 

elevation in the northwestern part of the section and does not 

appear in the southeastern part of the section. Three anomalies 

were interpreted along the southeastern edge of the section in 

layer 1, extending below the surface to a depth of 1 to 1.5 m 

(fig. 22). This location corresponds to a strong anomaly seen 

clearly in both the magnetic susceptibility and vertical gradient 

at (50, -39) (fig. 2).

Line 2

Layer 1, topsoil with chert fragments, occurs at the land 

surface and ranges down to 144.5 to 142.5 m in elevation. 

Layer 2 represents clay with an interpreted thickness between 

1.5 and 2.5 m. Layer 3, composed of limestone, is divided 

into three sections that are located on the northwestern part 

of the line. There are three anomalies in layer 1 towards the 

southeastern edge of the section at depths of 0 to 1 m (fig. 23). 

The easternmost anomaly corresponds to the location of an 

anomaly in the magnetic susceptibility and total apparent electrical conductivity as well as the vertical gradient, near (50, 

-36) (fig. 2). The remaining two anomalies in the interpretation 

section are contained within the bounds of zone 1 (fig. 3).

 Line 3

Layer 1, topsoil with chert fragments, occurs in the 

upper 1 to 1.5 m of the section. The surface of layer 2, clay, 

was interpreted to be between 142.5 m elevation along the 

southern edge of the section and 141 m elevation along the 

northern edge of the section and to range in thickness from 

2 to 2.5 m. Layer 3 represents limestone extending from the 

bottom of layer 2 to the bottom of the section. The surface of 

the limestone starts at about 140 m in elevation to the south 

and descends discontinuously to about 139 m elevation at the 

location distance of 27 m. No low resistivity anomalies were 

located in the inverted field resistivity (fig. 24). 

Line 4

The resistivity line crossed through surface exposures 

of small arms waste and barbed wire along the entire length 

of the line, which may have created a path for current flow 

generating large, low resistivity anomalies at greater depths 

than may be realistic. However, the forward model would be 

unable to predict this response caused by the surface debris, 

and therefore also reflects the deep anomalies that may be an 

artifact of surficial debris.

Topsoil and chert fragments (layer 1) were interpreted to 

be as thin as 0.5 m near the southern edge of the section and 

as thick as 2.5 m along the northern edge of the section. A 

layer of chert gravel and cobble, ranging from less than 0.25 m 

to about 1.0 meters thick, is interpreted to cut continuously 

through layer 1. Layer 2 (clay) ranges in elevation from about 

131 m along the southern edge of the section to about 129 m 

at the northern edge of the section. Limestone (layer 3) ranges 

in elevation from about 128.5 m along the southern edge of 

the section to about 129.5 m at location distance 15 m then 

decreases in elevation to about 129 m at the southern edge of 

the section (fig. 25). Seven interpreted low resistivity anomalies of varying length occurred within layers 1 and 2, possibly 

resulting from the barbed wire found near the surface.

Line 5

Layer 1, composed of topsoil with chert fragments, is 

found from an elevation of about 130 m to land surface. The 

second layer, interpreted to be clay, extends below the bottom 

of the section to an unknown depth. Several low resistivity 

anomalies were located in layer 1 of the inverted field resistivity data. These anomalies were modeled in layer 1 (topsoil 

with chert fragments) of the forward model for survey line 

5. Forward modeling results were used to approximate the 

depth and size of these anomalies (fig. 26). The interpretation 

section of resistivity data from line 5 shows a scattering of 

low resistivity anomalies in the eastern part of the section to 

a depth of about 1.5 m below the surface. The time-domain 

IP data supports this depth and distribution. It is likely that 

the surficial waste extends into the subsurface about 1.5 m in 

zone 3 (fig. 8) at this location.

40 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Figure 22. Section showing interpretation of inverted field resistivity, inverted model resistivity, and forward model sections from 

survey line 1, AOC 3.

Figure 23. Section showing interpretation of inverted field resistivity, inverted model resistivity, and forward model sections from 

survey line 2, AOC 3.

Vertical Extent of Anomalies 41
Figure 25. Section showing interpretation of inverted field resistivity, inverted model resistivity, and forward model sections from 

survey line 4, AOC 7.

Figure 26. Section showing interpretation of inverted field resistivity, inverted model resistivity, and forward model sections from 

survey line 5, AOC 7.

Figure 24. Section showing interpretation of inverted field resistivity, inverted model resistivity, and forward model sections from 

survey line 3, AOC 3.

42 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Excavation of Selected Anomalies to Assess 

Accuracy of Geophysical Surveys

Excavation was performed at AOCs 3 and 7 to explore 

selected anomalies and suspicious surface debris and to assess 

the accuracy of the geophysical surveys. A total of nine locations were excavated during two events (trips) in AOCs 3 (E-1, 

E-2, E-3; fig. 3) and 7 (E-4 through E-8; fig. 8). Excavated soil 

was segregated by depth and placed on a tarp. Waste characterization was performed twice by the USACE, which consisted 

of filling a bucket with excavated soil and then determining 

the weight and volume of soil and small arms waste. A tractormounted backhoe was used to excavate the selected areas.

AOC 3

Trench 1 (E-1), oriented approximately east to west, 

(fig. 3) was completed to a depth of 0.6 m at AOC 3 near the 

east bank of the ephemeral stream. This location was chosen 

because of the scattering of small arms waste visible in the 

substrate of the stream channel. Small arms waste was found 

scattered throughout a brown silty clay soil matrix with chert 

fragments to a depth of approximately 0.3 m. A soil sample 

was collected at a depth of approximately 0.1 to 0.15 m, in 

the same zone as the small arms waste. The sample contained 

approximately 1 volumetric percent small arms waste. No 

anomalies were found in this location by any geophysical 

method used in this study, most likely because of the noncontinuous scattering of a small quantity of metallic waste.

The second (E-2) and third (E-3) trenches were positioned to further investigate the southernmost anomaly found 

in zone 1 in the EM and magnetic results near (50, -42) 

(fig. 2), as well as in survey line 1 of the 2D-DC resistivity and 

time-domain surveys (fig. 12). E-2 (fig. 3) was excavated to 

about 1 m below land surface. No metallic debris was found 

at this location. After re-examination of the field data from 

the EM and magnetic surveys, excavation was repositioned 

to E-3. During excavation of E-3, a flattened 55-gallon drum 

was removed from approximately 0.3 m below land surface (fig. 27A). This drum was most likely the cause of the 

anomaly seen in figure 2.

Vertical Extent of Anomalies 43

AOC 7

Five trenches were completed at AOC 7. The first trench, 

E-4 (fig. 8), was approximately 0.8 m deep and opened generally in a west to east direction beginning in the streambed near 

the southwest corner of AOC 7 near grid location (-35, 12). A 

metal post was removed from the alluvium, which consisted 

of silt and chert fragments. Although vertical gradient data 

showed an anomaly at this location, the EM data did not show 

a similar feature. This discrepancy was likely caused by the 

powerline’s influence over the GEM-2 within the powerline 

corridor, while the magnetometer was still able to successfully 

locate metallic debris.

The second trench, E-5 (fig. 8), was opened near grid 

location (-50, 81) in the east bank of Tyson Hollow Creek in 

a north to south direction and extended to a depth of approximately 0.3 m. This site was chosen because of a scattering of 

small arms waste on the surface and because grass had failed 

to grow at this location although the majority of the site was 

heavily vegetated. The EM and magnetic techniques did not 

show any anomalies in this location. The soil consisted of silty 

clay with chert fragments, and small arms waste appeared to 

extend to a depth of approximately 0.08 to 0.10 m. Although 

small arms waste was found at the surface, there was no indication that this deposit extended into the subsurface in high 

concentrations. Therefore, it is reasonable that no anomalies 

were found using these specific geophysical methods. 

E-6, E-7, and E-8 were the third, fourth, and fifth 

trenches (fig. 8) and were east of the stream bank where small 

arms waste was exposed at the surface (fig. 7B) and EM, magnetic, 2D-DC resistivity, and time-domain IP data exhibited 

anomalies (figs. 6 and 15). E-6 was opened near grid location 

(-55, 51), generally in a west to east direction to a depth of 

approximately 0.9 m. Small arms waste appeared to extend to 

a depth of approximately 0.4 to 0.5 m. E-7 was excavated near 

grid location (-55, 69), generally in a north to south direction 

to a depth of approximately 0.6 m. Small arms waste was contained within the first 0.1 m. Barbed wire was located in the 

vicinity of E-6 and E-7 (fig. 7B). E-8 was excavated near grid 

location (-55, 54) to a depth of almost 1 m. Small arms waste 

(fig. 27B) was found within the upper 0.5 m in this trench.
A

B

Figure 27. Photographs taken during excavation activities at A, AOC 3, showing the remains of a 55-gallon drum in E-3, and B, AOC 7, 

showing small arms waste found in E-8. (May 2004).

44 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Summary and Conclusions

The former Tyson Valley Powder Farm near Eureka, 

Missouri, was used primarily as a storage facility for the 

production of small arms ammunition at the nearby St. Louis 

Ordnance Plant during 1941–47 and 1951–61, although munitions testing and disposal took place on site as well. During 

U.S. Army activity at the site, shell casings, munitions, munitions components, storage drums, and miscellaneous metallic 

materials were disposed of throughout the property, remnants 

of which can still be seen on the surface and are believed 

to continue into the subsurface. However, little historical 

information exists describing disposal practices. Three areas 

of concern (AOC 3, AOC 7, and AOC 10), previously identified by the U.S. Army Corps of Engineers, were selected in 

spring 2004 for investigation by the U.S. Geological Survey, 

in cooperation with the U.S. Army Corps of Engineers, using 

four surface geophysical methods. 

Electromagnetic and magnetic methods were used to 

determine the subsurface areal extent of metallic anomalies. 

Results from these methods were used to create maps identifying zones of anomalies within each of the areas of concern. 

Several zones were then selected for further investigation 

using two-dimensional direct-current resistivity and timedomain induced polarization (IP) methods to characterize the 

vertical extent of the anomalies in the selected zones. Using 

an inversion process, sections of the subsurface were developed from the data and were compared to anomaly locations 

from the electromagnetic and magnetic surveys. Excavations 

were made at selected locations to check the results of the four 

geophysical methods. The geophysical methods selected for 

use in this study were useful in determining the areal and vertical extent of metallic waste within the former Tyson Valley 

Powder Farm. However, electromagnetic and magnetic methods were not able to differentiate magnetic scrap metal from 

non-magnetic metallic small arms waste, most likely because 

of the small size and scattered distribution of the small arms 

waste, in addition to the mixing of both types of debris within 

the subsurface.

Electromagnetic and magnetic data showed a scattering 

of anomalies in all three areas of concern. Anomalous zones 

were identified and mapped—zones 1–2 in AOC 3, zones 3–7 

in AOC 7, and zones 8–12 in AOC 10. Zones 1, 3, and 5 were 

selected for further investigation concerning the vertical extent 

of the anomalies.

In zone 1 (AOC 3), sections developed from the resistivity data along survey lines 1 and 2 indicated the presence of 

anomalies in layer 1 (topsoil with chert fragments). Sections 

from the time-domain IP measurements for survey lines 1, 2, 

and 3 showed a greater occurrence of anomalies in layer 1 and 

extending into layer 2. The lack of low resistivity anomalies 

shown in the resistivity section could possibly be explained 

by the high concentration of highly resistive chert fragments 

in layer 1. The chert could have been acting as an insulator, 

masking the less-resistive inclusions of small arms waste. 

However, once the small arms waste was “charged” using 

the time-domain IP method, it showed a greater response 

compared to the surrounding topsoil and chert fragments. 

Excavations showed buried scrap metal and scattered small 

arms waste in zone 1, and did not indicate the presence of any 

high-density continuous small arms waste deposits. Based on 

all of the results, anomalies in AOC 3 were believed to be a 

scattering of a variety of metallic waste that extends from the 

surface to a depth of approximately 1 meter, possibly as deep 

as 1.5 meters.

In zone 3 (AOC 7), resistivity line 5 crossed zone 3 

through surface debris including 1-inch diameter metal cable 

and sheet metal. The field resistivity section for line 5 showed 

a scattering of low resistivity anomalies in the eastern part of 

the section to a depth of approximately 1.5 meters below the 

surface. The time-domain IP section confirmed this depth and 

distribution. Visual reconnaissance showed the metal cable 

entering the ground in multiple locations. The scattered surface metal likely extends into the ground to a depth of approximately 1.5 meters, possibly to 2 meters, below the surface.

Zone 5 (AOC 7) was bisected lengthwise by resistivity line 4 and crossed through multiple surface exposures of 

shell casings and barbed wire. The resistivity section showed 

anomalies extending to a maximum of 1.5 meters below the 

surface. Excavations along the resistivity line showed small 

arms waste present in the soil to an approximate depth of 

0.5 meter below the land surface, although the interpretation of 

resistivity data indicates anomalies extend to a greater depth. 

Barbed wire along the survey line may have created a path for 

current flow, causing low resistivity anomalies to extend below 

their actual depths.

Selected References

Benham, K.E., 1982, Soil survey of St. Louis County and 

St. Louis City, Missouri: Washington, D.C., U.S. Department of Agriculture—Soil Conservation Service: U.S. 

Government Printing Office, Washington, DC. 

Breiner, Sheldon, 1999, Applications manual for portable 

magnetometers: San Jose, California, Geometrics, accessed 

April 2004 at URL http://www.geometrics.com/

Criss, R.E., 2001, Hydrogeology of Tyson Research Center, 

Lone Elk County Park, and West Tyson County Park, eastern Missouri, Tyson Valley (ex) Army Powder Storage Farm 

site file: U.S. Environmental Protection Agency, Region 7, 

58 p.; also at http://www.biology.wustl.edu/tyson/geology.

html (accessed April 2004).

Degnan, J.R., Moore, R.B., and Mack, T.J., 2001, Geophysical 

investigations of well fields to characterize fractured-bedrock aquifers in southern New Hampshire: U.S. Geological 

Survey Water-Resources Investigations Report 01-4183, 

54 p.

Selected References 45
Ellis Environmental Group, 2003, Draft Phase I, II, III Remedial investigation and risk assessment report, former Tyson 

Valley Powder Farm, Eureka, Missouri: Newberry, Florida, 

Prepared for the U.S. Army Corps of Engineers by Ellis 

Environmental Group, September 2003.

Geometrics, 2004, G-858 magnetometer flyer: San Jose, California, Geometrics, accessed May 2004 at URL http://www.

geometrics.com/

Geophex, Ltd., 2004, GEM-2 flyer: Raleigh, North Carolina, 

Geophex, Ltd., accessed May 2004 at URL http://www.

geophex.com/

Huang, H., and Won, I.J., 2000, Conductivity and susceptibility mapping using broadband electromagnetic sensors: 

Journal of Environmental and Engineering Geophysics, v. 5, 

no. 4, p. 31-41.

HydroGeoLogic, 1999, Final data summary report, Phase II 

remedial investigation, Tyson Valley Powder Farm, Eureka, 

Missouri: Overland, Kansas, HydroGeoLogic, Inc., March 

1999.

Kring, Debbie, and Bailey, D., 2001, Tyson Valley (ex.) Army 

Powder Storage Farm, St. Louis, Missouri: U.S. Environmental Protection Agency Region 7 Fact Sheet, 2 p.

Loke, M.H., 2000, Electrical imaging surveys for environmental and engineering studies—a practical guide to 2D and 3D 

surveys: Penang, Malaysia, M.H. Loke, accessed September 

2000 at URL http://www.agiusa.com/literature.shtml

Loke, M.H., 2002, RES2DMOD version 3.01—Rapid 2D 

resistivity forward modeling using the finite-difference and 

finite element methods: accessed October 1, 2003, at URL 

http://www.geoelectrical.com

Loke, M.H., 2003, RES2DINV version 3.52w—Rapid 2D 

resistivity and IP inversion using the least-squares method: 

Geoelectrical Imaging 2-D and 3-D—Geotomo Software, 

125 p., accessed August 10, 2003, at URL http://www.

geoelectrical.com

Loke, M.H., 2004, Tutorial—2-D and 3-D electrical imaging 

surveys: Geotomo Software, 12 p., accessed July 23, 2004, 

at URL http://www.geoelectrical.com

Natural Resource Conservation Service, 2004, Official soil 

descriptions: accessed May 17, 2004 at URL http://soils.

usda.gov/technical/classification/osd/index.html

Powers, C.J., Wilson, Joanna, Haeni, F.P., and Johnson, C.D., 

1999, Surface-geophysical characterization of the University of Connecticut landfill, Storrs, Connecticut: U.S. 

Geological Survey Water-Resources Investigations Report 

99-4211, 34 p.

Stanton, G.P., Kress, W.H., Hobza, C.M., and Czarneci, 

J.B., 2003, Possible extent and depth of salt contamination 

in ground water using geophysical techniques, Red River 

aluminum site, Stamps, Arkansas, April 2003: U.S. Geological Survey Water-Resources Investigations Report 03-4292, 

p. 5-19.

U.S. Army Corps of Engineers, 2001, Scope of work for .30- 

and .50-caliber shell casing disposal, AOC 3, Former Tyson 

Valley Powder Farm: U.S. Army Corps of Engineers, 

Kansas City District, 8 May 2001.

Won, I.J., 2003, Small frequency-domain electromagnetic 

induction sensor—How in the world does a small broad- —How in the world does a small broadband EMI sensor with little or no source-receiver separation 

work?: The Leading Edge, April issue, p. 320-322.

Won, I.J., and Keiswetter, D.A., 1997, Comparison of magnetic and electromagnetic data for underground structures: 

Journal of Environmental and Engineering Geophysics: v. 2, 

no. 2, p. 115-126.

Won, I.J., Keiswetter, D.A., Fields, G.R.A, and Sutton, L.C., 

1996, GEM-2—A new multifrequency electromagnetic sensor: Journal of Environmental and Engineering Geophysics, 

v. 1, no. 2, 129-138 p.

46 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri
Appendixes 1 through 4
48 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri

Appendix 1. Georeferenced locations within AOC 3 (table 1-1), 

AOC 7 (table 1-2), and AOC 10 (table 1-3).

Table 1-1. Georeferenced locations within AOC 3.

[All units are in meters; Coordinate System: Universal Transverse Mercater Zone 15, North American Datum of 1983, elevation is in meters above the North 

American Vertical Datum of 1988; N/A, not applicable]

Line Location Mark Location Northing Easting Elevation Point Description

-3 0 4268411.411 713528.494 148.4161 Grid point

-3 50 4268390.604 713572.594 143.2731 Grid point

-6 0 4268408.512 713528.3998 148.4859 Grid point

-6 50 4268387.45 713572.3893 143.4366 Grid point

-9 0 4268405.665 713528.0822 148.8196 Grid point

-9 50 4268384.548 713572.0385 143.5966 Grid point

-9 50 4268384.371 713572.008 143.6951 Grid point

-12 0 4268402.793 713527.7922 149.0879 Grid point

-12 45 4268383.553 713566.8536 143.343 Grid point

-12 50 4268381.361 713571.5122 143.7705 Grid point

-15 0 4268399.895 713527.6211 149.4011 Grid point

-15 45 4268380.56 713566.238 145.263 Grid point

-15 50 4268378.161 713570.9369 143.9991 Grid point

-18 0 4268397.395 713527.5124 149.9289 Grid point

-18 45 4268377.685 713566.0703 143.8356 Grid point

-18 45 4268377.665 713566.0809 143.8836 Grid point

-18 50 4268374.814 713570.7857 144.2181 Grid point

-21 0 4268395.016 713527.1923 150.2409 Grid point

-21 45 4268374.495 713565.5861 144.011 Grid point

-21 50 4268372.08 713570.0079 144.2701 Grid point

-24 0 4268391.641 713526.7689 150.3229 Grid point

-24 50 4268369.602 713569.6751 144.3631 Grid point

-27 0 4268388.601 713526.5006 150.3344 Grid point

-27 50 4268365.958 713569.3766 144.6166 Grid point

-30 0 4268385.615 713526.1987 150.2949 Grid point

-30 50 4268363.21 713569.1842 144.8636 Grid point

-33 0 4268382.923 713525.9751 150.3119 Grid point

-33 50 4268360.027 713568.8431 144.9671 Grid point

-36 0 4268379.637 713525.6574 150.3314 Grid point

-36 50 4268358.04 713567.8629 145.0996 Grid point
Appendix 1 49

Line Location Mark Location Northing Easting Elevation Point Description

-39 0 4268376.6 713525.3768 150.3339 Grid point

-42 0 4268373.677 713524.9511 150.1584 Grid point

-45 0 4268370.824 713524.8305 150.2249 Grid point

-48 0 4268367.634 713524.561 150.4749 Grid point

N/A N/A 4268401.216 713570.7704 142.8616 Monitoring Well: MW3

N/A N/A 4268395.697 713521.4441 150.6224 Northwest corner of the Popping Kettle 

building 

N/A N/A 4268395.16 713570.5174 143.0901 Yellow benchmark disk: RANDAPLS2579

Table 1-2. Georeferenced locations within AOC 7.

[All units are in meters; Coordinate System: Universal Transverse Mercater Zone 15, North American Datum of 1983, elevation is in meters above the North 

American Vertical Datum of 1988; N/A, not applicable]

Mark Location Line Location Northing Easting Elevation Point Description

0 0 4267928.137 712809.2012 135.95 Grid point

0 -25 4267929.988 712784.4486 134.38 Grid point

0 -25 4267929.965 712784.764 134.36 Grid point

3 0 4267932.789 712808.7444 133.88 Grid point

3 -25 4267932.849 712784.8756 134.42 Grid point

6 0 4267935.804 712809.295 133.71 Grid point

6 -25 4267935.908 712785.3969 134.52 Grid point

9 0 4267936.653 712810.5884 135.29 Grid point

9 0 4268061.566 712803.2501 134.42 Grid point

9 -25 4267938.81 712785.8075 134.42 Grid point

12 0 4267939.601 712811.0294 134.99 Grid point

12 -30 4267942.002 712781.357 133.46 Grid point

15 0 4267942.792 712811.4596 135.11 Grid point

15 -30 4267945.147 712781.7472 133.30 Grid point

18 0 4267945.728 712811.8017 134.90 Grid point

18 -30 4267948.131 712782.1512 133.16 Grid point

21 0 4267948.657 712812.2523 134.66 Grid point

21 -30 4267950.94 712782.6141 133.05 Grid point

24 0 4267951.648 712812.7039 134.43 Grid point

24 -30 4267954.042 712783.0265 133.01 Grid point

27 0 4267954.658 712813.0066 134.38 Grid point

27 -35 4267957.195 712778.4306 132.48 Grid point

Table 1-1. Georeferenced locations within AOC 3.—Continued
50 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri

Mark Location Line Location Northing Easting Elevation Point Description

30 0 4267957.627 712813.4741 134.37 Grid point

30 -35 4267960.497 712778.7926 132.45 Grid point

33 0 4267960.612 712813.8225 134.43 Grid point

33 -35 4267963.107 712779.0301 132.32 Grid point

36 0 4267963.598 712814.2095 134.38 Grid point

36 -40 4267966.208 712774.7161 132.35 Grid point

39 0 4267966.37 712814.5616 134.34 Grid point

39 -40 4267969.336 712774.8814 132.31 Grid point

42 0 4267969.572 712814.9288 134.29 Grid point

42 -40 4267972.52 712775.316 132.13 Grid point

45 0 4267972.965 712815.3445 134.83 Grid point

45 -40 4267975.205 712775.7193 132.17 Grid point

48 -40 4267978.272 712776.4123 132.53 Grid point

51 -40 4267980.428 712776.7662 132.67 Grid point

54 0 4267980.992 712816.8908 135.00 Grid point

54 -45 4267983.524 712772.6194 132.67 Grid point

57 -45 4267986.666 712772.9462 132.54 Grid point

60 -45 4267990.015 712773.4244 132.29 Grid point

63 -45 4267992.336 712773.8831 132.02 Grid point

66 -45 4267995.254 712774.3551 131.80 Grid point

69 -45 4267998.001 712774.6861 131.58 Grid point

72 -45 4268001.03 712775.3072 131.86 Grid point

111 0 4268037.658 712824.3585 134.96 Grid point

114 0 4268040.628 712824.7071 134.83 Grid point

114 0 4268040.892 712824.746 134.86 Grid point

114 -5 4268040.956 712819.9719 134.79 Grid point

117 0 4268043.589 712825.2137 134.76 Grid point

117 -5 4268043.628 712820.2921 134.76 Grid point

120 0 4268046.475 712825.5124 134.75 Grid point

120 -5 4268046.532 712820.7092 134.93 Grid point

123 0 4268049.451 712826.0076 134.75 Grid point

123 -5 4268049.645 712821.0606 134.80 Grid point

123 -40 4268050.684 712786.2554 132.70 Grid point

N/A N/A 4267890.814 712786.2602 135.07 Power pole: PP364779

N/A N/A 4267923.064 712829.4296 136.50 Power pole: PP364780

N/A N/A 4267942.26 712782.726 133.49 Power pole: PP364790

Table 1-2. Georeferenced locations within AOC 7.—Continued
Appendix 1 51

Table 1-3. Georeferenced locations within AOC10.

[All units are in meters; Coordinate System: Universal Transverse Mercater Zone 15, North American Datum of 1983, elevation is in meters above the North 

American Vertical Datum of 1988; N/A, not applicable]

Line Location Mark Location Northing Easting Elevation Point Description

0 0 4268052.919 712801.9002 134.54 Grid point

0 -15 4268053.402 712787.1048 133.65 Grid point

9 0 4268061.64 712803.2616 134.42 Grid point

9 -20 4268062.441 712783.741 132.53 Grid point

27 0 4268079.493 712805.8849 134.15 Grid point

36 0 4268088.361 712807.1011 134.10 Grid point

42 0 4268094.338 712807.6285 133.90 Grid point

45 0 4268097.325 712807.942 133.73 Grid point

48 0 4268100.268 712808.3141 133.67 Grid point

51 0 4268103.282 712808.6508 133.61 Grid point

54 0 4268106.277 712809.0405 133.70 Grid point

54 -5 4268106.699 712804.142 133.64 Grid point

57 0 4268109.198 712809.3741 133.73 Grid point

57 -5 4268109.636 712804.4055 133.74 Grid point

60 0 4268112.174 712809.7435 133.65 Grid point

60 -5 4268112.489 712804.8566 133.70 Grid point

63 0 4268115.12 712810.134 133.65 Grid point

63 -10 4268115.486 712800.2782 133.70 Grid point

66 0 4268118.116 712810.4866 133.64 Grid point

66 -15 4268118.839 712795.6781 133.69 Grid point

69 0 4268121.182 712810.9077 133.54 Grid point

69 -15 4268121.83 712796.1919 133.61 Grid point

72 0 4268124.062 712811.3565 133.51 Grid point

72 -15 4268124.829 712796.5147 133.43 Grid point

75 0 4268127.052 712811.7302 133.45 Grid point

75 -15 4268127.731 712796.8367 133.36 Grid point

78 0 4268130.043 712812.2016 133.47 Grid point

78 -20 4268130.996 712792.4007 133.36 Grid point

81 0 4268132.94 712812.5533 133.49 Grid point

81 0 4268132.976 712812.6697 133.47 Grid point

81 -25 4268134.265 712787.7501 133.48 Grid point

84 0 4268135.926 712812.9699 133.53 Grid point

84 -25 4268137.166 712788.1385 133.45 Grid point
52 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri

Line Location Mark Location Northing Easting Elevation Point Description

87 0 4268138.955 712813.4883 133.57 Grid point

87 -25 4268140.127 712788.6337 133.39 Grid point

90 -25 4268143.117 712788.9688 133.39 Grid point

93 -25 4268146.107 712789.3261 133.41 Grid point

96 -30 4268149.417 712784.7857 133.33 Grid point

99 -35 4268152.599 712780.102 133.27 Grid point

102 -35 4268155.528 712780.4485 133.30 Grid point

105 -35 4268159.628 712780.9841 133.32 Grid point

108 -35 4268162.788 712781.5416 133.39 Grid point

111 -25 4268164.785 712791.7136 133.16 Grid point

111 -35 4268165.39 712781.7606 133.38 Grid point

114 -30 4268168.19 712787.1629 133.28 Grid point

114 -40 4268169.024 712777.2493 133.08 Grid point

Table 1-3. Georeferenced locations within AOC10.—Continued
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Appendix 2 53

Appendix 2-1. Graphs representing the total percent frequency of occurrence 

for specific data values at AOC 3 for A, total apparent electrical conductivity; 

B, magnetic susceptibility at 2,070 Hz; and , magnetic susceptibility at 2,070 Hz; and C, vertical gradient. , vertical gradient.

A

B

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54 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri

Appendix 2-2. Graphs representing the total percent frequency of occurrence 

for specific data values at AOC 7 for A, magnetic susceptibility at 2,070 Hz; and 

B, vertical gradient. , vertical gradient.

Appendix 2-3. Graphs representing the total percent frequency of occurrence 

for specific data values at AOC 10 for A, magnetic susceptibility at 2070 Hz; and 

B, vertical gradient. , vertical gradient.

A B

A B
Appendix 2 55

Appendix 3. Environmental noise tests on A, April 21, 2004 and B, April 22, , April 22,

2004. The y-axis represents the amplitude of the received signal; the 

x-axis represents the specific frequencies at which the signal occurred. Single 

spikes at 2,030Hz; 5,010Hz; 9,030Hz; 13,830Hz; and 20,010Hz are the result of the 

programmed transmission frequencies of the GEM-2 and are not associated with 

environmental noise.

A

B
56 Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri

Appendix 4. Table showing coordinates of zone boundaries.

[All units are in meters; Coordinate System: Universal Transverse Mercator Zone 15, North American Datum of 1983]

Zone Easting Northing

1 713562 4268350

1 713572 4268350

1 713574 4268360

1 713566 4268400

1 713553 4268400

2 713528 4268380

2 713535 4268390

2 713536 4268380

2 713529 4268390

3 712817 4268000

3 712806 4268000

3 712799 4268020

3 712787 4268030

3 712783 4268050

3 712791 4268050

3 712812 4268040

3 712822 4268020

4 712824 4268040

4 712818 4268040

4 712818 4268050

4 712825 4268050

5 712766 4267980

5 712760 4267980

5 712769 4268020

5 712771 4268000

5 712761 4268000

6 712796 4267960

6 712800 4267960

6 712795 4267960

6 712792 4267960

Zone Easting Northing

7 712808 4267970

7 712805 4267980

7 712796 4267990

7 712797 4268000

7 712807 4268000

7 712817 4267990

7 712815 4267970

8 712730 4268140

8 712728 4268150

8 712746 4268170

8 712760 4268150

8 712747 4268130

9 712796 4268060

9 712805 4268080

9 712803 4268100

9 712786 4268120

9 712776 4268100

9 712780 4268080

10 712798 4268120

10 712803 4268130

10 712799 4268130

10 712792 4268130

11 712812 4268150

11 712814 4268160

11 712811 4268150

11 712815 4268150

12 712791 4268160

12 712776 4268160

12 712778 4268170

12 712792 4268170

Ball and others—Surface Geophysical Investigation of Metallic Waste, Former Tyson Valley Powder Farm, Eureka, Missouri—Scientific Investigations Report 2004—5208