Ground Penetrating Radar Survey of Revolutionary War Cemetery Sudbury, MA - Zip code: 1716

A Report on the Ground Penetrating Radar Survey Of the Revolutionary Cemetery, Sudbury, MA

July 29, 2012

Conducted by Robert W. Perry

TOPOGRAPHIX, LLC Hudson, NH

Requested by Town of Sudbury Historical Commission

Sudbury, MA

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GPR Survey of Revolutionary Cemetery, Sudbury, MA Page 1

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Town of Sudbury Historical Commission July 29, 2012 278 Old Sudbury Road Sudbury, MA 01776 At the request of the Historical Commission for the Town of Sudbury, MA, a Ground Penetrating Radar (GPR) survey of the Revolutionary Cemetery was performed to locate possible unmarked human graves. The results of the survey are documented in this report, as well as the detailed maps that accompany this report. This report provides information on the GPR equipment used in the survey, the survey procedures followed and a summary of the findings.

The maps show the direction of the GPR scans and the location of each anomaly, which is identified with a circle symbol and assigned number. There were a total of 976 anomalies discovered and identified with a high probability of being human graves. In addition, the ground area around each flagged anomaly was probed with a metal rod for possible buried headstones. A total of 244 rock-like substances were struck and are indicated on the accompanying map with the symbol (H) next to the numbered anomaly. GPR field activities started on June 13, 2012 and were completed on July 8, 2012. Regards,

Robert W. Perry


Report on the Ground Penetrating Radar Survey of the Revolutionary Cemetery, Sudbury, MA

Report Summary At the request of the Historical Commission for the Town of Sudbury, MA, a Ground Penetrating

Radar (GPR) survey of the Revolutionary Cemetery was performed to locate possible unmarked human

graves. The survey was conducted on land within the stonewall boundary area of the Revolutionary

Cemetery located in the Town Center. The area was divided into fourteen (14) separate GPR zones for

scanning purposes (see Figure 1).

Figure 1– Target Assessment Areas

A total of 976 anomalies were discovered within the fourteen surveyed areas and assigned a confidence rating for human graves as High Probability. An explanation of the probability designation is explained in a later section of this report. The ground area around each anomaly was probed with a metal rod for possible buried headstones. A total of 244 rock-like substances were struck and are indicated on the accompanying map with the symbol (H) next to the numbered anomaly. Some of the material struck sounded like hard slate-like material used for headstones and other probing struck smaller slate-like materials that could be footstones or broken parts of headstones scatted around the flagged anomaly. In addition, rocks were also used as grave markers which can be observed in the north east corner of the cemetery. I believe this area is referred to as pauper grave burials. GPR field activities started on June 13, 2012 and were completed on July 8, 2012.


GPR Equipment The radar unit used for the project was the SIR-3000, manufactured by Geophysical Survey Systems, Inc. (GSSI). A 400 MHz antenna was used with a scanning rate of 18 scans per-foot at a penetration depth of 10 feet. The scanned data for each zone was collected, processed and analyzed with the results shown as 3D JPEG images on page 8 thru page 14 of this report.

Examples of Commonly Detected Objects The examples shown in Figure 2 are presented for informational use only. The examples illustrate how a single ground-penetrating radar scan along a survey line can reveal a unique hyperbolic (curve) characteristic of each of the targeted objects. Vertical scales include Time (ns) or Dept (ft/m) as well as horizontal scale for ground distance viewed at the top of the images.

Graves (Coffin) Rebar Conduits

Burial Vaults Graves Late 1800s

Figure 2 – Scans of Common Subsurface Objects


GPR Test Scanning To survey and establish the hyperbolic characteristics and soil conditions from known graves within the Revolutionary Cemetery, one area was selected to perform GPR testing. The test scan area contained six marked graves with dated headstones, dating from 1740 to 1842 (see Figure 3). Figure 4 shows the scanned results of the same six graves as they appear as a GPR scan profile. The vertical scale in Figure 4 shows the range of the radar which was preset to a ground depth of 10 feet. It was unique to have a group of graves together with a time span of 102 years pre-dating the Revolutionary and the pre-Civil War period.

Figure 3 – Site Picture of Six Dated Headstones (Revolutionary Cemetery)

Figure 4 - Scan Image of the Six Dated Graves with One Unmarked Anomaly (Revolutionary Cemetery)


Survey Procedures The Ground Penetrating Radar survey was conducted on the land within the stonewall boundary area of

the Revolutionary Cemetery. To prepare the cemetery area for GPR surveying, the area was divided into fourteen (14) scan zones. The boundary lines for each zone were identified by wooden stakes. With the boundary lines established, survey stakes were hammered into the ground four (4) feet apart at both the north and south side of each scan zone. Parallel survey lines were then laid within the length and width of each zone (see Figure 5). These parallel lines defined the rectangular grid area to be scanned.

Figure 5 – Parallel Survey Lines Showing Rectangular Grid Areas

The scanning of each zone was completed in a direction based on the likelihood that burial holes would be perpendicular to the existing headstones with graves oriented in an east-west direction. Each zone was scanned using an X/Y axis grid with a base line of 00 as the starting point. The X axis determines the width and the Y axis determines the length of the rectangular grid area as defined on the accompanying GPR survey map. Using the GSSI survey cart with a 24” wheel width, the cart was positioned at the base line (00) and pushed along the length (Y) of the survey line in a north-south direction. With each pass of the scanner, a plastic red flag was placed at the site of each subsurface anomaly (see Figure 6). Once the scan line was completed, the survey cart was returned to the base line (00) and positioned laterally two feet over along the width (X) grid line to begin the second scan along the survey line. Scanning continued with each subsequent pass until the entire width and length of the GPR grid zone were covered.


Figure 6 – Survey Cart with a 24” Wheel Width and Mounted with a 400 MHz Antenna

Summary of GPR Results The radar records collected for the fourteen zones were of good interpretative quality at a satisfactory penetration depth of 10 feet. Operating by the fact that burial holes are typically longer than two feet, the confidence level rating on whether or not each anomaly could be considered a human grave was determined by the observation of the same anomalous pattern repeating itself in the neighboring two foot lateral scan. - An anomaly detected on one pass along the survey line was rated as Low Probability of human

grave.

- The anomaly detected on the second and third pass along the adjoining lateral survey lines was rated as High Probability of human grave.

In addition to the position of the anomaly along the survey line, the hyperbolic signature of each anomaly was compared to the unique hyperbola characteristic typically observed from the presence of tree roots, layering or bedding of various rocks, ground voids, disturbed soil layers and burial holes. A total of 976 anomalies with High Probability were discovered within the fourteen (14) GPR surveyed areas along with 249 buried headstones, footstones or rock-like substance struck with ground probing. Stonewall Observation Given the close proximity of many of the anomalies discovered along the inside edges of the stonewall, there is a likelihood of additional burials that may lie beneath the stonewall and along the outside perimeter, including the grassy area and walkway on the south side of the cemetery.


Three-Dimensional Imaging

Three-dimensional imaging reveals numerous burials within each of the scan zones. Data from each zone

was collected except for zone 14, which experienced an excessive number of ground obstructions.

For a detailed analysis of the GPR data collected from each zone, the GSSI RAYDAN Interactive 3D

Module was used to assemble the scan data files. Once assembled, 3D Contour Imaging reveals

numerous burials at various depths with the most populated depth of five feet (+/- a foot) within all scan

zones (see Figure 7).

Figure 7 – Contour Imaging Highlights Burials at a Five Foot Level

The following images are screen shots of each zone using the 3D Module software without contour

imaging. Zone 14 and the western portion of zone 13 are excluded because of the excessive number of

surface obstructions. In zone areas where data could not be collected, a technique called Utility Scanning

was used which does not collect data for 3D analyzing. Utility scanning is used to locate and track

underground utilities as well v burials, coffins and vaults.

The raised dark areas on the plane area indicate burials. Please note that due to the maneuvering around

headstones and over surface rocks during the scan data collection, some gaps in scan data occurred.

The 3D images shown on pages 8 through 14 are screen shots to illustrate anomalies (burials) at the most

populated depth of around five feet +/- a foot.


Ground-penetrating radar (GPR) uses a high EM pulse transmitted from a radar antenna to probe the

earth. The transmitted radar pulses are reflected from various materials within the ground, and this

return is detected by the radar receiver. There are a number of factors that come into play when

collecting GPR data:

Collecting GPR data is subject to earth material properties and surface environmental conditions on the equipment. Heat, humidity, ground water saturation, salt, iron deposits as well as interfering effects such as radio frequency, cell phones, sirens including extensive metal structures as cars passing by and traffic lights all have effect on the radar data being collected.

Obstructions along the scan line - having to scan around and between headstones and over rocks.

The batteries used to power the computer have a life span of about 3 to 4 hours under normal operating conditions. If the battery is drained, all GPR data collected will be lost.

Figure 8 – Possible Burials in Zone 1


















Figure 20 – Possible Burials in Zone 13 (Eastern Portion)

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Ground Penetrating Radar Survey of Revolutionary War Cemetery Sudbury, MA - Zip code: 1716