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Site name: Fort Riley Post Cemetery

A ground penetrating radar survey was conducted in a 20 x 40 m portion of the oldest section of the Post Cemetery, at Fort Riley, Kansas, in July, 2002. The survey was undertaken to ascertain the utility of GPR technology for prospecting for graves at this site, to locate and map areas unlikely to contain graves, and to investigate the possibility of mass graves that were reportedly placed within the cemetery during the cholera epidemic of the 1855. A GSSI SIR 2000 was employed with a 400 MHz antenna and survey wheel, with 40 transects of data collected, each separated by 50 cm, using a 35 nS time window. Time slicing techniques indicated clear clusters of anomalies, possibly pointing to mass graves, more isolated anomalies revealing possible individual graves, and numerous linear anomalies that are interpreted as historic trails through the cemetery. Clear definition of individual graves was disappointing in the time sliced data, however, owing to an indistinct and speckled appearance resulting from anomalies of greatly varying amplitudes. Manual methods were therefore employed that tagged individual hyperbolas in each profile (likely candidates for graves). The resultant composite map of tagged features more clearly indicates individual anomalies that could indicate graves, zones of many overlapping anomalies (mass graves?), the ubiquitous linear features, and relatively large areas devoid of anomalies that are less likely to contain graves.

An aerial photograph of the 20 x 40 m survey area in the oldest part of the cemetery shows monuments at the time of the survey. Maps from 1907 and 1918 are superimposed showing interpreted grave locations at those times.

Type of survey: Ground penetrating radar; Instrument: Geophysical Survey Systems, Inc., SIR-2000, withh 400 MHz antenna; Prospection depth: about 2.1 m; Sampling interval: 0.5 x 0.04 m (with survey wheel); Range: 35 nS; Area surveyed: 20 x 40 m in 40 transects, each separated by 0.5 m; Date of survey: 7/02.

Comments: Most of the 40 GPR profiles indicated numerous hyperbolas at regularly spaced intervals, suggestive of graves.

A time slice from 5-15 nS shows numerous anomalies (left figure), including several linear features interpreted as compacted trails or walkways through the cemetery. Individual graves are mostly indistinct in this image, largely resulting from anomalies of greatly varying amplitudes. With graves likely indicated by distinct hyperbolas in each of the individual profiles (see above), the 40 profiles were therefore manually interpreted and a map was constructed showing the loci of the principal hyperbolas (right figure). Many of these features can more confidently be interpreted as graves when they do not delineate long, linear arrangements larger than a typical 1 x 2 m grave, and when they do not occur in isolation indicating an anomaly smaller than what might be expected for a grave. Clusters of numerous hyperbolas may possibly indicate mass graves,

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(updated: 10/02)