Geophysical Testing and Grave Detection at the Nashville City Cemetery, Tennessee
Stephen J. Yerka
Archaeological Research Laboratory
Dept. of Anthropology, University of Tennessee, Knoxville
In April of 2009, personnel from the Archaeological Research Laboratory (ARL) at the University of Tennessee’s (UT’s) Department of Anthropology conducted an exploratory geophysical survey at the Nashville City Cemetery. The primary objective of the survey was to identify any possible unmarked graves or other subsurface anomalies within the project area. The research design for this study included the use of several different geophysical instruments including ground penetrating radar (GPR), soil resistivity, and geomagnetic survey. The project area was selected in coordination with the Nashville Metro Historic Commission, and provided the opportunity to obtain geophysical survey data over areas with a high potential for containing unmarked graves, and areas of known, marked burials. The goal of the research design was to develop a survey strategy on a sample of the City Cemetery that would provide information for developing the most efficient and cost effective means for obtaining reliable and positive data results for other portions of the cemetery.
The study covered an area greater than 4000 m2, with different instruments overlapping collection units. The project was mapped with a total station and imported into GIS software in order to correlate results with mapping surveys that have been completed previously at the cemetery. The GPR survey was conducted with a GSSI SIR-3000 unit with a 400 MHz antenna, the soil resistivity was recorded using a Geoscan MPX-15 soil resistance meter, and the geomagnetic survey was completed using a Bartington 601 fluxgate gradiometer. Although some onsite interpretation was possible, the results of the data collection are most easily understood after statistical processing. Processing was accomplished using several proprietary software packages that will be discussed briefly in this paper.
Each geophysical technique produced survey results containing anomalies that are highly likely to indicate unmarked graves. Not all techniques detected anomalies equally well, but the GPR survey and the geomagnetic survey both performed very well in this testing situation. The nature and character of the anomalies detected by the GPR and gradiometer differ in response, and in some cases anomalies detected by one instrument were not detected by the other. This paper will discuss these differences as well as the different target types associated with an historic cemetery and how they may be characterized through geophysical investigation. These target types include not only burials, but also burial shafts, other ground disturbance associated with interment or removal, buried grave markers, buried family enclosures, old walkways/roadways, and modern disturbance or contamination. Future research at the cemetery should use a combination of large-scale gradiometer survey paired with focused GPR survey to obtain the highest probability for identifying unmarked graves at the Nashville City Cemetery.
Stephen Yerka is an IT Specialist with the University of Tennessee, Knoxville. He has been working with the Archaeological Research Laboratory (ARL) for the last six years, and currently manages IT related operations for the firm including DBMS, GIS and Geophysical services. The Archaeological Research Laboratory (ARL) is a consulting, cultural resource assessment, and research unit dedicated to the conduct of high quality and timely work for government agencies and private entities, while providing hands-on learning experiences and opportunities for students, educators, and the interested public. Stephen has conducted geophysical survey projects throughout the Southeast on prehistoric, historic and forensic sites. He currently serves also as an instructor for the National Forensic Academy, Oak Ridge, Tennessee instructing on the use of geophysics for forensic investigation.