GROUND PENETRATING RADAR SURVEY OF PROPOSED ELEVATOR 

SHAFT SITE EXPLORATION (PEPC 47098) IN THE OLD COURTHOUSE AT 

JEFFERSON NATIONAL EXPANSION MEMORIAL, ST. LOUIS, MISSOURI 

Steven L. De Vore

MIDWEST ARCHEOLOGICAL CENTER

ARCHEOLOGICAL REPORT No. 2

United States Department of the Interior

National Park Service

Lincoln, Nebraska

2014

GROUND PENETRATING RADAR SURVEY OF PROPOSED 

ELEVATOR SHAFT SITE EXPLORATION (PEPC 47098) IN 

THE OLD COURTHOUSE AT JEFFERSON NATIONAL 

EXPANSION MEMORIAL, ST. LOUIS, MISSOURI

By

Steven L. De Vore

Dates of field work: June 10-12, 2013

NATIONAL PARK SERVICE

MIDWEST ARCHEOLOGICAL CENTER

ARCHEOLOGICAL REPORT NO. 2

United States Department of the Interior

National Park Service

Lincoln, Nebraska

2014
This report has been reviewed against the criteria contained in 43CFR Part 7, Subpart 

A, Section 7.18 (a) (1) and, upon recommendation of the Midwest Regional Office

and the Midwest Archeological Center, has been classified as

Available

Making the report available meets the criteria of 43CFR Part 7, Subpart A, Section 7.18 

(a) (1).
i

TABLE OF CONTENTS

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

Purpose of archeological work per sow and project 

design.............................................................................................................................1

Geophysical project location ........................................................................................2

Archeological project personnel ..................................................................................3

Environmental description of project area..................................................................3

General description of the geophysical project and 

methods.........................................................................................................................4

Overall research design.........................................................................................4

Culture history and previous work.......................................................................4

Description of investigations................................................................................5

Field methods........................................................................................................6

Ground-penetrating radar survey ................................................................6

Description of geophysical interpretation of 

cultural resources located............................................................................................10

National register evaluation of cultural 

Resources located.........................................................................................................11

National register recommendations with justifications for 

eligible, not eligible, need more information from 

testing, etc ............................................................................................................12

Site integrity and conservation/stabilization/avoidance 

recommendations.................................................................................................12

Effects of project on resources....................................................................................12

Location of artifactual materials and records 

from the work ..............................................................................................................13

References cited ...........................................................................................................15

Summary management recommendations ................................................................23
ii

Figures...........................................................................................................................25
iii

LIST OF FIGURES

Figure 1. Location of the geophysical project at the Old 

Courthouse, Jefferson National Expansion Memorial. ..............................................25

Figure 2. General view of the Old Courthouse. ........................................................26

Figure 3. Drawing of the Old Courthouse expansion projects 

between 1838 and 1852 ..............................................................................................27

Figure 4. View of the Old Courthouse in 1852 with exterior 

entry stairs visible on the south side...........................................................................28

Figure 5. Location of the North and South Transept geophysical 

project areas.................................................................................................................28

Figure 6. General view of the North Transept...........................................................29

Figure 7. General view of the South Transept...........................................................29

Figure 8. Sketchmap of the North Transept geophysical project 

area. .............................................................................................................................30

Figure 9. Sketchmap of the South Transept geophysical project 

area. .............................................................................................................................30

Figure 10. Conducting the ground-penetrating radar survey with 

the GPR cart and 400 MHz antenna in the North Transept geophysical 

project area. .................................................................................................................31

Figure 11. Ground-penetrating radar time slice survey data from 

the North Transept geophysical project area. ............................................................31

Figure 12. Ground-penetrating radar time slice survey data from 

the South Transept geophysical project area. ............................................................32

Figure 13. Image and contour plots of the ground-penetrating radar 

time slice 3 (6-11 ns) survey data from the North Transept geophysical 

project area. .................................................................................................................32

Figure 14. Image and contour plots of the ground-penetrating radar 

time slice 3 (6-11 ns) survey data from the South Transept geophysical 

project area. .................................................................................................................33

Figure 15. Interpretation of ground-penetrating radar data from time 

slice 3 (6-11 ns) from the North Transept geophysical project area..........................33
iv

Figure 16. Interpretation of ground-penetrating radar data from time 

slice 3 (6-11 ns) from the South Transept geophysical project area..........................34
1

ABSTRACT

The ground-penetrating radar survey at the Old Courthouse was conducted 

between June 10 and 12, 2013, at the Jefferson National Expansion Memorial (JEFF) 

in St. Louis, Missouri as part of the Proposed Elevator Shaft Site Exploration project 

(Planning, Environment and Public Comment [PEPC] document number 47098). The 

Midwest Archeological Center provided technical assistance for the ground-penetrating 

radar survey of the two transepts between the rotunda and the North and South wings of 

the Old Courthouse. The geophysical investigations consisted of a ground-penetrating 

radar survey with a GPR cart system and 400 MHz antenna. Overall, the geophysical 

project areas in the two transepts totaled 128 m2 (1,377.82 ft2) or 0.032 ac. The groundpenetrating radar survey resulted in the potential identification of original external 

stairs in both transepts, additional fill to level the floors, and utility lines located under 

the stone floors in both transepts. The removal of the stone floor in the vicinity of the 

proposed elevator shaft site(s) and the excavation of the fill are recommended to meet 

compliance with Section 106 of the National Historic Preservation Act.

PURPOSE OF ARCHEOLOGICAL WORK PER SOW AND 

PROJECT DESIGN

Jefferson National Expansion Memorial (JEFF) is located in downtown St. 

Louis, Missouri, along the Mississippi River. The park consists of the Gateway Arch and 

grounds, the Old Courthouse, and the Luther Ely Smith Square. The Memorial Drive 

and the depressed Interstate Highway 70 separate the Gateway Arch and grounds from 

the Old Courthouse and the Luther Ely Smith Square. The ground-penetrating radar 

survey is located in the North and South transepts of the Old Courthouse (Figure 1).

The Jefferson National Expansion Memorial was established in 1935 under 

Executive Order 7253 by President Franklin D. Roosevelt for “a permanent memorial to 

the men who made possible the territorial expansion of the United States, particularly 

President Thomas Jefferson and his aides, Livingston and Monroe, and the hardy 

hunters, trappers, frontiersmen, and pioneers and others who contributed to the 

territorial expansion and development of the United States” (Brown 1984; BVHA 2013:9; 

Moore 1994; NPS 2009:1-3,A-1/A-2). The park was the first urban park within the NPS 

system located outside Washington, D.C. (Moore 1994). The Old Courthouse is part of 

the Jefferson National Expansion Memorial along with the Luther Ely Smith Square 

on the west side of Memorial Drive and the depressed Interstate 70 (Figure 2). The 

courthouse is bounded on the north by Chestnut Street, on the south by Market Street, 

on the east by 4th Street, and on the west by Broadway in downtown St. Louis. 

The Old Courthouse was an important public gathering space for people traveling 

west. During its lifetime, the Old Courthouse served as the physical and symbolic center 

of St. Louis (BVHA 2013:215-219). It was the site of the historic Dred Scott case (Swain 

2004). Scott, a slave, sued for his freedom from the widow of Dr. John Emerson. The first 

trial verdict in 1847 favored Mrs. Emerson, but, on appeal in 1850, Scott was awarded his 

freedom by the St. Louis Court. His freedom was taken away on appeals to the Missouri 

Supreme Court in 1852 and ultimately, the U.S. Supreme Court in 1857. The 1857 U.S. 
2

Supreme Court decision in the Dred Scott v. Sandford case (Finkelman 1997) resulted 

in the denial of citizenship to persons of color and that slavery in the territories was a 

property right that could not be terminated by legislation (Bryan 1937; BVHA 2013:13-

14; NPS 2009:3-9).

The Old Courthouse was originally built in phases between 1839 and 1862 (BVHA 

2013:23; Lindenbusch 1982). It replaced the original courthouse on the property, which 

was built in 1826 (BVHA 2013:13-36,169-214). The original 1826 courthouse was built to 

replace the several courts that were housed in various buildings in St. Louis. By 1838, 

the original courthouse was too small to meet the demands of the rapidly increasing St. 

Louis population. The cruciform design of the new courthouse with a central rotunda 

included the first courthouse as the east wing (Figure 3). Between 1843 and 1857, the 

north and south entry to the Old Courthouse were located on the exterior of the building 

(Figure 4). They were enclosed with the addition of the North and South wings between 

1857 and 1862. In 1852, the Old Courthouse was expanded with additional wings added 

to the north and south sides, as well as the demolition of the original courthouse. The 

courts vacated the building in 1930. The Old Courthouse was acquired by the National 

Park Service in 1940. Rehabilitation and maintenance of the Old Courthouse by NPS 

from 1940 to the present has maintained the historic appearance of the Old Courthouse 

and provided the public with an interpretive center and community center. Accessibility 

was first addressed in 1987 when an accessibility lift was added to the west portico along 

with portable interior ramps on the first floor for ease of access to the museum galleries. 

A new lift was added in the southwest courtyard in 2007 and replaced in 2012. While 

these lifts provided access to the first floor, the disabled public did not have access to the 

historic second floor courtrooms. The proposed elevator installation in the transepts 

will provide access to the second floor.

The National Park Service’s (NPS) Jefferson National Expansion Memorial 

(JEFF) staff proposed the placement of elevators in the North and South transepts at the 

Old Courthouse to meet accessibility requirements for disabled visitors to the historic 

courthouse under the Americans with Disabilities Act of 1990 (ADA), as amended by 

the ADA Amendments Act of 2008. In order to determine the existence of architectural 

features associated with the original Courthouse, a ground-penetrating radar (GPR) 

survey was proposed. The Midwest Archeological Center (MWAC) provided technical 

assistance to the park for the GPR survey of the two transepts where the original 

exterior stairs to the Courthouse were located. The enclosed transepts connect the 

original courthouse structure to the North and South wing additions and cover the 

original exterior stairs. The work is conducted to meet stipulations of the National 

Historic Preservation Act of 1966 (NHPA), as amended (NPS 2006:35-99), the National 

Environmental Policy Act of 1970 (NEPA), as amended (NPS 2006:101-104), and 

Director’s Order #28 (NPS 1998). 

GEOPHYSICAL PROJECT LOCATION

The geophysical project areas are located on the first floor of the Old Courthouse 

in downtown St. Louis, Missouri (Figure 5). The 19th-century courthouse represents a 

Greek Revival style building with a central rotunda and four wings. The corner stone 
3

for the Old Courthouse is located on the northwest corner of the North Transept. The 

two project areas are located in the North and South transepts. Both rooms are elevated 

above the ground and separate the main part of the courthouse from the newer North 

and South wings. The original exterior stairs have been enclosed in the two transepts. 

The transepts have been filled and covered with stone slab flooring. 

ARCHEOLOGICAL PROJECT PERSONNEL

MWAC archeologist Steven L. De Vore directed and conducted the groundpenetrating radar survey. Historic Architect Al O’Bright, Midwest Regional Office, 

and JEFF Park Historian Bob Moore assisted in the GPR investigations. JEFF Chief 

of Museum Services and Interpretation and NEPA specialist Ann Honious provided 

background material for the project. MWAC Archeologist Timothy Schilling provided 

archeological background on the project for the geophysical investigations.

ENVIRONMENTAL DESCRIPTION OF PROJECT AREA

The Jefferson National Expansion Memorial is located in the Dissected Till 

Plains section of the Central Lowland province of the Interior Plains division (Fenneman 

1938:588-605; Hunt 1967:205211) of the North American continent. The Dissected 

Till Plain section consists of submaturely to maturely dissected till plains. This area is 

located within the Central Mississippi Valley Wooded Slopes, Western Part major land 

resource area of the Central Feed Grains and Livestock land resource region (USDA 

2006:315-316,365-367). The region consists of deeply dissected, loess covered hills 

(USDA 2006:366). Nearly level to very steep uplands are dissected by the tributaries of 

the Mississippi and Missouri rivers. Major streams have numerous stream terraces along 

the broad flood plains in well-defined valleys. Smaller streams have narrow flood plains. 

Broad summits range from nearly level to slightly sloping. Uplands are covered with 

loess. Glacial deposits are underlain by Mississippian, Ordovician, and Pennsylvanian 

bedrock (USDA 2006:366). The area also lies within the Carolinian biotic province (Dice 

1943:16-18). The native vegetation is dominated by deciduous forest vegetation and 

tall-grass prairies. The upland hardwood vegetation includes oak, hickory, and sugar 

maple (Shelford 1963:23-35, 89-114; USDA 2006:367). Elm, cottonwood, river birch, ash, 

silver maple, pin oak, and willow are found on the floodplains. The tall-grass prairies 

are dominated by big bluestem and little bluestem while sedges occur on the lowlands 

in addition to the prairie grasses (Shelford 1963:334-344; UDSA 2006:367). Wildlife 

include white-tailed deer, coyote, gray and red fox, beaver, raccoon, skunk, muskrat, 

opossum, mink, rabbit, squirrels and other small mammals, reptiles, amphibians, fish, 

insects and spiders, songbirds, raptors, waterfowl, turkey, pheasant and quail (Shelford 

1963:23-35,89-114,334-344; USDA 2006:367). The climate is subhumid midcontinental 

with long hot summers and cold winters (Benham 1982:2, 72-73,88-89; Trewartha and 

Horn 1980:297-313; USDA 2006:366). The annual average temperature is 13.06° C with 

a January average temperature of -1.11° C and a July average temperature of 25.94° C 

(Benham 1982:88; Moxom 1941:947; USDA 2006:366). The annual precipitation for 

the county averages 85.88 cm with an annual snowfall of 45.21 cm (Benham 1982:88; 

Moxom 1941:947; USDA 2006:366). Most thunderstorms occur between mid-June and 

early September. The freeze-free period averages 205 days but ranges between 185 days 

and 230 days (Benham 1982:89; USDA 2006:366).
4

Alfisols, Entisols, Inceptisols, and Mollisols dominate the soils of the region 

(Foth and Schafer 1980; USDA 2006:367). The soils have a mesic soil temperature regime 

with an udic or aquic soil moisture regime. The soils are dominated by mixed or smectitic 

mineralogy (USDA 2006:367). The soils range from very shallow to very deep and poorly 

drained to excessively drained. They are loamy, silty, or clayey. The Old Courthouse is 

located within Urban land-Harvester-Fishpot soil association with “[u]rban land and 

nearly level to moderately steep, moderately well drained and somewhat poorly drained, 

deep soils formed in silty fill material, loess, and alluvium; on uplands, terraces, and 

bottom lands” (Bedham 1982:8). The soil mapping unit is identified as Urban land (7B), 

on the upland with 0 to 5 percent slope (Benham 1982:19). The soil mapping unit has 

more than 85% of surface covered with asphalt, concrete, buildings, or other impervious 

materials. The areas have been reshaped by cutting and filling episodes in order to 

produce nearly level surfaces within the urban setting. Cut and fill depths may be as 

shallow as two meters to as deep as ten meters in order to level the original topography 

(Benham 1982:19).

GENERAL DESCRIPTION OF THE GEOPHYSICAL PROJECT 

AND METHODS

The present geophysical inventory project represents the first phase in the 

architectural/archeological exploration of the proposed elevator locations in the North 

and South transepts inside the Old Courthouse in St. Louis, Missouri (De Vore 2013). 

The ground-penetrating radar survey provides a baseline geophysical data set for the 

identification of buried architectural features under the stone slab floor of the two 

transepts at the Old Courthouse. 

Overall Research Design

The overall research design of the geophysical project was to determine the 

presence of the original external stairs in the North and South transepts. The collection 

of GPR profile data follows standard operating procedures used in MWAC GPR projects 

(De Vore 2013).

Culture History and Previous Work

Jefferson National Expansion Memorial lies within the Central Mississippi 

Valley subarea of the Eastern Woodland archeological culture area of North America 

(Wiley 1966:246-341). The geophysical project area is also located within the Middle 

Mississippi Study Unit (Wright 1987a:B-14-1-B-14-13). The prehistoric archeological 

resources in Missouri are divided between the Early Man, Paleo-Indian, Dalton, Archaic, 

Woodland, and Mississippian periods (Chapman 1975, 1980; O’Brien and Wood 1998; 

Wright 1987b:C-1-1-C-10-8). The prehistoric periods are followed by the Protohistoric 

and Historic periods. An archeological and historic overview of the Jefferson National 

Expansion Memorial is provided by Timothy Schilling (2013:2-8). Additional synopsis of 

the regional prehistory and history may be found in LeeDecker et al. 2013:17-49). 
5

Archeological investigations at the Jefferson National Expansion Memorial 

have been sporadic since its initial inception. In 1937, the Architectural Research Unit 

identified 80 potential sites of historic interest including the Old Courthouse, the 

Old Cathedral, and the Manuel Lisa Warehouse (Schilling 2013:8). The Manuel Lisa 

Warehouse or Old Rock House was dismantled in the 1940s but before it was dismantled, 

limited archeological investigations were conducted by Chief Landscape Draftsman 

Henry Rice (Schilling 2013:8). Rice indicated the lack of intact sediments along the 

river. During the late 1950s and early 1960s, NPS Archeologist Zorro Bradley undertook 

archeological investigations to identify and recover historic archeological resources 

before the construction of the arch monument and museum. He also came to the 

conclusion that little if any intact archeological resources were present along the river 

(Schilling 2013:8). The area had been highly disturbed, although, he did find the remains 

of foundations of buildings that had been demolished by NPS. During the construction 

of the Parking Ground at the northwestern corner of the JEFF grounds in 1984, a few 

artifacts were collected during the monitoring of the construction activities (Wells and 

Williams 1985). They suggested that the material was related to the W. H. Bull medicine 

factory at was demolished by NPS in the late 1930s. In 1998, MWAC Archeologist Vergil 

Noble monitored a geotechnical coring project for the construction of the maintenance 

facility. He indicated that the area was covered with deep fill deposits to a depth of at least 

three meters (Noble 1999). During the installation of a utility line across the northwest 

corner of the Old Courthouse lawn in 2007, Noble (2007) documented a late 19thcentury brick sewer. In 2012, geoarcheological coring was conducted in association with 

the CityArchRiver2015 West Entrance project for the proposed new west entrance to 

the JEFF Gateway Arch and grounds (LeeDecker et al. 2012, 2013). Cores were extracted 

from the Gateway Arch grounds and the Luther Ely Smith Square. The geoarcheological 

investigations indicated the presence of deep fill deposits across the project area to a 

depth averaging more than 4.5 meters. The fill sits on top of weathered Pleistocene loess 

deposits predating any human presence in the region. The fill contains brick, concrete, 

and limestone building materials reflecting the 20th-century demolition and reshaping 

of the 19th-century urban landscape. According to LeeDecker et al (2013:64):

The archeological record at JEFF for the most part reflects events that occurred 

either (1) more than 12,000 years ago or (2) more recent than 1937. The record of 

Native American use of the landscape, the early settlement of St. Louis, and the 

vibrant nineteenth-century commercial district appear to have been destroyed. 

Additional synopsis of the previous archeological and cultural resource 

investigations may be found in Schilling (2013) and LeeDecker et al. (2013:8-9, 13-17).

Description of Investigations

Geophysical prospection techniques available for archeological investigations 

consist of a number of techniques that record the various physical properties of the earth, 

typically in the upper couple of meters; however, deeper prospection can be utilized if 

necessary (David 1995). Geophysical techniques are divided between passive and active 

techniques. Passive techniques are primarily ones that measure inherently or naturally 

occurring local or planetary fields created by earth-related processes (Heimmer and 

De Vore 1995:7, 2000:55; Kvamme 2001:356). The primary passive method utilized in 
6

archeology is magnetic surveying. Other passive methods with limited archeological 

applications include self-potential methods, gravity survey techniques, and differential 

thermal analysis. Active techniques transmit an electrical, electromagnetic, or acoustic 

signal into the ground (Heimmer and De Vore 1995:9,2000:58-59; Kvamme 2001:355-

356). The interaction of these signals with buried materials produces alternated return 

signals that are measured by the appropriate geophysical instruments. Changes in the 

transmitted signal of amplitude, frequency, wavelength, and time delay properties may 

also be observable. Active methods applicable to archeological investigations include 

electrical resistivity, electromagnetic conductivity (including ground-conductivity and 

metal detectors), magnetic susceptibility, and ground-penetrating radar. Active acoustic 

techniques, including seismic, sonar, and acoustic sounding, have very limited or specific 

archeological applications.

Field Methods

In order to determine the presence of the original external stair case located 

under the stone floor in the North and South transepts, NPS staff utilized a groundpenetrating radar cart system with a 400 MHz antenna to collect subfloor GPR data. 

In order to collect the GPR profile data, the geophysical project areas in the North 

and South transepts were outlined and marked off with blue painter’s masking tape 

to establish a geophysical project grid on the floor of the two rooms between the 

rotunda and the newer wings. The length and width of the rooms were measured and 

the masking tape was placed on the floor at intervals, which provided the maximum 

coverage with the GPR cart and 400 MHz antenna. Additional strips of tape were placed 

at 0.5-meter intervals along the guide tapes to provide placement of the GPR cart during 

the collection of the profile data. The North Transept measures approximately 17.6 

meters (57 ft, 8 in) east-west by approximately 4.0 meters (13 ft, 1 in) north-south (Figure 

6). The room is also slightly tapered along its length and width. The geophysical grid in 

the North Transept measures 16 meters east-west by 4.0 meters north-south. The South 

Transept measures approximately 17.6 meters (57 ft, 8 in) east-west by approximately 4.0 

meters (13 ft, 1 in) north-south (Figure 7). The room is also slightly tapered along its 

length and width. The geophysical grids in the North and South transepts each measure 

16 meters east-west by 4.0 meters north-south. The geophysical grids in each transept 

paralleled the interior walls of the transepts next to the rotunda with approximately a 

meter offset from the east and west walls. Sketch maps were made of the North (Figure 

8) and South (Figure 9) transepts after the grids were established in each one. The 

geophysical project area within the North Transept measures 64 m2 (688.91 ft2) or 0.016 

ac. The geophysical project area within the South Transept also measures 64 m2 (688.91 

ft2) or 0.016 ac. The total area covered by the ground-penetrating radar survey in both 

transepts total 128 m2 (1,377.82 ft2) or 0.032 ac.

Ground-Penetrating Radar Survey

Instrument Geophysical Survey Systems Inc. (GSSI) TerraSIRch SIR System-3000 

ground-penetrating radar cart system with a 400 megahertz (MHz) antenna (GSSI 2003).

Specifications: SIR 3000: System hardware contains a 512-mb compact flash 

memory card as its internal memory. It accepts industry-standard compact flash 
7

memory cards up to 2 gb. Processor is a 32-bit Intel StrongArm PISC 206 MHz processor 

with enhanced 8.4” TFT display, 800 x 600 resolution, and 64k colors. The processor 

also produces linescan and O-scope displays. The GPR system uses one channel. It also 

uses the GSSI Model 623 survey cart with survey wheel for mounting the antenna and 

control unit. The 400 MHz Model 5103 ground-coupled antenna has a depth of view of 

approximately 4 m assuming a ground dielectric constant of 8 with a range of 50 ns, 512 

samples per scan, 16-bit resolution, 5 gain points, 100 MHz vertical high-pass filter, 800 

MHz vertical low-pass filter, 64 scans per second, and 100 KHz transmit rate.

Survey type: ground-penetrating radar

Operators: Steven De Vore

The ground-penetrating radar (GPR) survey is an active geophysical technique 

that uses pulses of radar energy (i.e., short electromagnetic waves) that are transmitted 

into the ground through the surface transmitting antenna (see Annan 2005:357-438; 

Bevan 1991, 1998:43-57; Clark 2000:118-120, 183-186; Conyers 2004, 2006:131-159, 

2007:329-344; Conyers and Goodman 1997; Davenport 2001:89-103; David 1995:23-27; 

David et al. 2008:28-34; Gaffney and Gater 2003:47-51, 74-76; Gaffney et al. 1991:5-6, 

2002:9-10; Goodman et al. 2007:375-394; Heimmer and DeVore 1995:42-47, 2000:63-

64; Kvamme 2001:363-365, 2003:442-443, 2005:436-438; Lowrie 1997:221-222; Milsom 

and Eriksen 2011:185-209; Mussett and Khan 2000:227-231; Nishimura 2001:547-551; 

Scollar et al. 1990:575-584; Weymouth 1986:370-383; and Witten 2006:214-258 for more 

details on GPR surveys). The radar wave is reflected off buried objects, features, or 

interfaces between soil layers. These reflections result from contrasts in electrical and 

magnetic properties of the buried materials or reflectors. The contrasts are a function 

of the dielectric constant of the materials (Sheriff 1973:51). The depth of the object 

or soil interface is estimated by the time it takes the radar energy to travel from the 

transmitting antenna and for its reflected wave to return to the receiving antenna. The 

depth of penetration of the wave is determined by the frequency of the radar wave. The 

lower the frequency, the deeper the radar energy can penetrate the subsurface; however, 

the resulting resolution, or the ability to distinguish objects, features, and soil changes 

decreases. The low-frequency antennas generate long wavelength radar energy that can 

penetrate several tens of meters under certain conditions, but can only resolve larger 

targets or reflectors. The higher the radar wave frequency, the higher the resulting 

resolution, but the penetration depth decreases. High frequency antennas generate 

much shorter wavelength energy, which may only penetrate a meter into the ground. 

The generated reflections from these high frequency antennas are capable of resolving 

objects or features with maximum dimensions of a few centimeters. A resulting tradeoff 

exists between subsurface resolution and depth penetration: the deeper the penetration 

then the resulting resolution is less, or the higher the resolution then the resulting depth 

penetration is much shallower.

As the radar antenna system (transmitting and receiving antennas) is moved 

along the survey line, a large number of subsurface reflections are collected. The 

various subsurface materials affect the velocity of the radar waves as they travel through 

the ground (Conyers and Goodman 1997:31-40). The rate at which these waves move 

through the ground is affected by the changes in the physical and chemical properties 
8

of the buried materials through which they travel. The greater the contrast in electrical 

and magnetic properties between two materials at the interface results in a stronger 

reflected signal. As the radar pulse travels through the ground, changes in material 

composition or water saturation cause changes in the velocity of the pulse with a portion 

of the energy reflected back to the surface where it is detected by the receiving antenna 

and recorded by ground-penetrating radar unit. The remaining energy continues to 

pass into the subsurface materials where it can be reflected by deeper reflectors until 

the energy finally dissipates with depth. The radar system measures the time it takes the 

radar pulse to travel to a buried reflector and return to the unit. If the velocity of the 

pulse is known, then the distance to the reflector or the depth of the reflector beneath 

the surface can be estimated (Conyers and Lucius 1996).

The success of the survey is dependent on soil and sediment mineralogy, clay 

content, ground moisture, depth of the archeological resource, and surface topography 

and vegetation. The ground-penetrating radar signal can be lost or attenuated (i.e., 

quickly dissipated) in soils that have high moisture content, high electrical conductivity, 

highly magnetic materials, or high clay content. Dry soils and sediments, especially 

those with low clay content, represent the best conditions for energy propagation. A 

ground-penetrating radar survey, with its capability for estimating the depth and shape 

of buried objects, may be an extremely valuable tool in the search for grave shafts and 

trenches. At times, radar cannot profile deep enough or the strata may be so complex as 

to render the trenches, graves, and other types of excavations indistinguishable from the 

surrounding soil profile. 

The TerraSIRch SIR System-3000 survey cart (Figure 10) contained a data-logger 

with a display that allowed the results to be viewed almost immediately after they were 

recorded (GSSI 2003). The SIR 3000 was set to collect GPR data with the 400 MHz 

antenna at an antenna transmission rate of 100 MHz and the distance mode selected 

for use of the survey wheel on the cart. The scan menu was set with 512 samples; 16-bit 

format; 60 ns range or window; a dielectric constant of 8; a scan rate of 100; and 50 scans 

per meter for the project area. In the gain menu, the gain was set to manual with a default 

value of 1. The GPR system was moved around the grid prior to the start of the survey to 

adjust the gain. If a location caused the trace wave to go off the screen, the gain was set to 

auto and then back to manual. The position was set to the manual mode with the offset 

value at the factory default and the surface display option set to zero. The filters were 

left at the default settings. With the setup completed, the run/stop button at the bottom 

of the display screen was selected and the collect mode was initiated. The GPR unit was 

moved across the grid, and at the end of the traverse the next file button was selected 

and data acquisition was halted. The GPR unit was placed at the start of the next line 

before saving the profile. Once the profile data were saved, the GPR unit was ready to 

collect the next profile line. The GPR data were recorded on a 512-mb compact flash 

card and transferred to a laptop computer at the end of the survey of the two transepts. 

The TerraSIRch SIR System-3000 survey cart system (GSSI 2003) operated 

an antenna at a nominal frequency of 400 MHz. The antenna was mounted in a cart 

that recorded the location of the radar unit along the grid line. The GPR profiles were 

collected along 0.5-m traverses beginning in the lower right hand corner of the grid for 

the first traverse oriented to the east. The data were collected in a zigzag or bidirectional 
9

fashion with the surveyor alternating the direction of travel for each traverse across the 

grid. At each survey grid location, the GPR file was identified with an alpha designation: 

the North Transept project area was designated OCHN and the South Transept project 

area was designated OCHS. Sixteen radar profiles were collected across OCHN for a 

linear distance of 98 m. Fourteen radar profiles were collected across OCHS for a 

linear distance of 86 m. Overall, thirty radar profiles were collected in the two transept 

geophysical project areas for a total linear distance of 184 m. 

Ground-penetrating radar surveys generally represent a tradeoff between depth 

of detection and detail. Lower frequency antennas permit detection of features at greater 

depths but they cannot resolve objects or strata that are as small as those detectable by 

higher frequency antennas. Actual maximum depth of detection also depends upon 

the electrical properties of the soil. If one has an open excavation, one can place a steel 

rod in the excavation wall at a known depth and use the observed radar reflection to 

calibrate the radar charts. When it is not possible to place a target at a known depth, one 

can use values from comparable soils. Reasonable estimates of the velocity of the radar 

signal in the site’s soil can be achieved by this method (Conyers and Lucius 1996). Using 

one of the hyperbolas on a radargram profile from the OCHN project area (Goodman 

2012:194-199), the velocity was calculated to be approximately 9.8 cm per nanosecond 

(ns) with a dielectric constant of 10.4. For a time slice between 5 and 15 ns with the 

center at 10 ns (two-way travel time), the approximate depth to the center of the GPR 

slice would be 49 cm. With a time window of 60 ns, the GPR profiles extended to a depth 

of 2.67 m. The signal velocity for the OCHS project area was calculated to be 0.089 m/

ns with a dielectric constant of 11.36 based on the hyperbola matching routine in the 

GPR-SLICE software. The GPR profiles extended to a depth of 2.36 m. 

The GPR radargram profile line data from the two geophysical project areas 

were imported into GPR-SLICE (Goodman 2012) for processing. The first step in 

GPR-SLICE was to create a new survey project for each area using the file name for the 

survey project name (Goodman 2012:16). This step identified the file name and folder 

locations (Goodman 2008:13). The second step was to transfer the raw GPR profile 

data from its original location on the computer hard drive to the GRP-SLICE project 

folder (Goodman 2012:17). The next step was to create the information file (Goodman 

2012-18-21). The information file included the number of profiles collected for the area, 

along with the file identifier name, extension identifier for GSSI radargrams, the profile 

naming increment, the first radargram name, direction of profiling, x and y beginning 

and ending coordinates, units per marker, the time-window opening in nanoseconds, 

samples per scan, the number of scans per meter, and the type of data. The information 

file was edited, if necessary, to correct profile lengths (Goodman 2012:21-26). The 

16-bit GSSI data were then converted to remove extraneous header information, to 

regain the data to enhance the signal, and to remove any DC drift in the profile data. 

Once the conversion process was completed, the next step was to reverse the profile 

data (Goodman 2012:29-31). Since the radargrams were collected in the zigzag mode, 

every half-meter profile line or odd interval needed to be reversed (Goodman 2012:29-

30). The next step was to insert navigation markers into the resampled radargrams 

(Goodman 2012:31-32, 59-67). These markers assign xyz locations to the radargrams 

and to all time-slice images. The next step was to create the time slices of the profile data 

(Conyers and Goodman 1997; Goodman 2012:32-40; Goodman et al. 1995). The time-
10

slice analysis included the search for the 0 ns location of the ground surface reflection, 

setting the number of time slices and determining the slice thickness, setting the cut 

parameters, setting the cuts per mark, and finally conducting the slice, resampling, and 

xyz processing. Once the time-slice data files were created, the next step was to create 

the grid and time-slice data files (Goodman 2012:41-50, 68-88). The gridding process 

interpolated between the xyz data in order to create the time slices and pixel maps. 

Twenty time slices were generated for each geophysical project area GPR data set. Once 

the initial gridding process was completed, a low-pass filter was applied to the dataset 

to smooth noisy data in the time slices. Two-dimensional time-sliced radar data were 

generated in the pixel map menu (Goodman 2012:46,89-101) for the survey grids at 

OCHN (Figure 11) and OCHS (Figure 12). In addition, the original processed grid slices 

and the low-pass filtered grid slices can be exported in the Surfer grid format. The lowpass filtered surfer grid files are transformed into image and contour plots in Surfer. The 

final step in processing the GPR data was to create the 3D binary files from the 2D grid 

files for the generation of a 3D volume display of the GPR data (Goodman 2012:51-58). 

Generally, one time slice is selected for further display and analysis for each 

survey grid since the animated 3D view of the radar data does not translate to the report 

document format. Time slice 3, from 6 to 11 ns (Figure 13), is selected as the representative 

slice for further analysis of the GPR data from the North Transept geophysical project 

area. The amplitude strength of the GPR data from OCHN, before the application of 

the low-pass filter, ranges from 773,176 to 92,043,583 with a mean of 11,468,339 and a 

standard deviation of 10,924,393. Time slice 3, from 6 to 11 ns (Figure 14), is selected as 

the representative slice for further analysis of the GPR data at the OCHS geophysical 

project area. The amplitude strength of the GPR data from OCHS, before the application 

of the low-pass filter, ranges from 3,161,056 to 76,497,891 with a mean of 18,085,129 and a 

standard deviation of 10,806,037. The gain may be readjusted for any time slice or for the 

entire time-slice dataset (Goodman 2008:41-47). In order to create a three-dimensional 

display of the GPR time-sliced data, the existing time slices are interpolated to create 

normalized grids (Goodman 2008:48-49). The interpolations value is set to 5 and the new 

interpolated grids are all normalized. The next step is to create the 3D time-slice dataset. 

The number of grids is now equal to 96 (((20-1)*5)+1). The 3D data may be displayed as 

a series of z slices in the creation of a 3D cube with a jpeg output for animating the 3D 

cube (Goodman 2008:50). 

DESCRIPTION OF GEOPHYSICAL INTERPRETATION OF 

CULTURAL RESOURCES LOCATED

Andrew David (1995:30) defines interpretation as a “holistic process and its 

outcome should represent the combined influence of several factors, being arrived at 

through consultation with others where necessary.” Interpretation may be divided into 

two different types: the geophysical interpretation of the data and the archaeological 

interpretation of the data. At a simplistic level, geophysical interpretation involves the 

identification of the factors causing changes in the geophysical data. Archeological 

interpretation takes the geophysical results and tries to apply cultural attributes or 

causes. In both cases, interpretation requires both experience with the operation of 

geophysical equipment, data processing, and archeological methods; and knowledge of 
11

the geophysical techniques and properties, as well as known and expected archeology. 

Although there is variation between sites, several factors should be considered in the 

interpretation of the geophysical data. These may be divided between natural factors, 

such as geology, soil type, geomorphology, climate, surface conditions, topography, soil 

magnetic susceptibility, seasonality, and cultural factors, including known and inferred 

archeology, landscape history, survey methodology, data treatment, modern interference, 

etc. (David 1995:30). It should also be pointed out that refinements in the geophysical 

interpretations are dependent on the feedback from subsequent archeological 

investigations. The use of multiple instrument surveys provides the archeologist with very 

different sources of data that may provide complementary information for comparison 

of the nature and cause (i.e., natural or cultural) of a geophysical anomaly (Clay 2001; 

Kvamme et al. 2006). Each instrument responds primarily to a single physical property: 

magnetometry to soil magnetism, electromagnetic induction to soil conductivity in the 

quadrature phase component and magnetic susceptibility in the in-phase component, 

resistivity to soil resistance, and ground-penetrating radar to dielectric properties of the 

soil (Weymouth 1986:371). 

Analysis of the ground-penetrating radar data from the two transept geophysical 

project areas indicates the presence of numerous GPR targets. In the North Transept, 

a series of strong or high amplitude planar reflections along the south side of the room 

suggests the presence of the original exterior stairs, which are intact beneath the stone 

slab floor (Figure 15). In addition, a strong hyperbolic reflection in the center of the 

room represents a utility line running between the original part of the Old Courthouse 

and the North Wing. The GPR data from the north side of the transept suggest the area 

under the stone floor is filled with non-reflective material such as soil or sand. In the 

South Transept, a series of strong or high amplitude planar reflections along the north 

side of the room also suggests the presence of the original exterior stairs, which are 

intact beneath the stone floor (Figure 16). In addition, two areas of strong hyperbolic 

reflections appear to represent utility lines running beneath the stone floor between 

the original part of the Old Courthouse and the South Wing. Two additional areas on 

the south side of the transept are identified as strong or high-amplitude hyperbolic 

reflections. It is possible that the strong GPR reflection near the center of the room 

represents a utility corridor, but both may indicate larger rubble used in the fill to level 

the floor. 

NATIONAL REGISTER EVALUATION OF CULTURAL 

RESOURCES LOCATED

The Jefferson National Expansion Memorial was established in 1935 under 

Executive Order 7253 by President Franklin D. Roosevelt, which included the old 

Courthouse although it was not acquired until 1940 (NPS 2009:A-1/A-2). The Old 

Courthouse was listed on the National Register of Historic Places in 1966 as part of 

the nomination package for The Gateway Arch, the Old Courthouse, and the Old 

Cathedral National Register of Historic Places Inventory – Nomination (AECOM 2010: 

D-1/D-10; Bellavia 1996:231-239). The Old Courthouse derived its significance from its 

architecture, art, engineering, and law.
12

The geophysical survey of the two transepts in the Old Courthouse was 

conducted as part of the National Park Service’s archeological investigations associated 

with the proposed locations for ADA compliant elevator(s) to provide disabled access 

to the upper floors in the building. The ground-penetrating radar data strongly suggest 

the presence of the original exterior stairs on the north and south side of the Old 

Courthouse building.

This report has provided a review and analysis of the geophysical data collected 

during the ground-penetrating radar survey of the two transepts located on the first 

floor of the Old Courthouse at Jefferson National Expansion Memorial in St. Louis, 

Missouri. The use of geophysical survey techniques at the Old Courthouse indicates 

the usefulness in collecting basic background geophysical data concerning the nature 

and extent of the architectural features and modifications to historic structures. 

Based on the information provided by the geophysical survey methods, it is apparent 

that the geophysical data set yielded useful information for the determination of the 

integrity and significance of the buried architectural resources associated with the 

Old Courthouse building at JEFF. While the ground-penetrating radar survey results 

provided data on the nature of the buried architectural resources, ground-truthing 

through archeological excavation will provide definitive information on the nature of 

these geophysical anomalies.

National Register Recommendations with Justifications for Eligible, Not Eligible, 

Need More Information from Testing, Etc

The geophysical survey of the North and South transepts on the first floor of 

the Old Courthouse at JEFF yielded baseline data for the evaluation of the architectural 

features buried under the stone floors in the two transepts. The ground-penetrating 

radar survey data indicate that remains of the original exterior stairs to the Old 

Courthouse are present under the existing stone floors in the two transepts along with 

subfloor utility lines. The geophysical data collected in the Old Courthouse indicate 

the architectural features identified in the GPR data add further support to the existing 

National Register of Historic Places listing under Criterion C. 

Site Integrity and Conservation/Stabilization/Avoidance Recommendations

The geophysical project areas contain intact architectural remains of the original 

1839 Old Courthouse. The resulting architectural integrity of buried architectural 

resources is extremely high. Additional archeological investigations are needed to 

determine the nature and cause of the geophysical anomalies noted in the groundpenetrating radar surveys conducted during this project.

EFFECTS OF PROJECT ON RESOURCES

The geophysical project has identified numerous buried architectural resources 

that appear as intact features in the data beneath the transept floors on the first floor of 

the Old Courthouse. The project represents a positive effect for the identification and 
13

location of the original exterior stairs associated with the 19th-century construction of 

the Old Courthouse between 1839 and 1864.

LOCATION OF ARTIFACTUAL MATERIALS AND RECORDS 

FROM THE WORK

No artifacts were collected during the project. The geophysical data and 

associated documentation are part of the JEFF accession number 1294. The materials 

are also temporarily curated under MWAC accession number 1537 until the entire 

collection is returned to JEFF.
14
15

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23

SUMMARY MANAGEMENT RECOMMENDATIONS:

[ ] CLEARANCE NOT RECOMMENDED (explain): 

[ ] CLEARANCE RECOMMENDED (explain):

[ X ] CLEARANCE RECOMMENDED WITH CONDITIONS (explain): 

The present ground-penetrating radar survey of the North and South transepts 

indicate that the original exterior stairs appear to be intact beneath the stone slab floor. 

The survey data also suggests that fill was added to level the present transept floors 

before the stone slab flooring was placed in the two transepts. It is recommended 

that ground-truthing is needed to determine the nature, extent, and significance of 

the GPR reflections in the two transepts before the proposed ADA elevator shafts are 

constructed.
24
25

FIGURES

Figure 1. Location of the geophysical project at the Old Courthouse, Jefferson National 

Expansion Memorial, St. Louis, Missouri.
26

Figure 2. General view of the Old Courthouse in St. Louis, Missouri (view to the northwest).
27

Figure 3. Drawing of the Old Courthouse expansion projects between 1838 and 1852 showing 

location of exterior entry stairs (BVHA 2013: Figure 35)
28

Figure 4. View of the Old Courthouse in 1852 with exterior entry stairs visible on the south 

side (from the Missouri History Museum collection, reference n17030).

Figure 5. Location of the North and South Transept geophysical project areas.
29

Figure 6. General view of the North Transept (view to the east).

Figure 7. General view of the South Transept (view to the east).
30

Figure 8. Sketchmap of the North Transept geophysical project area. 

Figure 9. Sketchmap of the South Transept geophysical project area. 
31

Figure 10. Conducting the ground-penetrating radar survey with the GPR cart and 400 MHz antenna 

in the North Transept geophysical project area (view to the west southwest).

Figure 11. Ground-penetrating radar time slice survey data from the North Transept geophysical 

project area.
32

Figure 12. Ground-penetrating radar time slice survey data from the South Transept geophysical 

project area.

Figure 13. Image and contour plots of the ground-penetrating radar time slice 3 (6-11 ns) survey data 

from the North Transept geophysical project area.
33

Figure 14. Image and contour plots of the ground-penetrating radar time slice 3 (6-11 ns) survey data 

from the South Transept geophysical project area.

Figure 15. Interpretation of ground-penetrating radar data from time slice 3 (6-11 ns) from the North 

Transept geophysical project area.
34

Figure 16. Interpretation of ground-penetrating radar data from time slice 3 (6-11 ns) from the South Transept geophysical project area.