Nondestructive Geophysical Surveys For Delineating Buried Tombs And Identifying Their Environmental Status

A number of ring roads and highways surrounding the highly populated city of<br>Cairo, Egypt are currently under construction. To the south of Cairo, part of these roads is<br>planned to cross a graveyard of unknown layout. Site observation indicates that a<br>significant part of this site is a constant drain for sewage and household water. Due to the<br>sacred nature of the site, non-destructive, geophysical tools (Electromagnetic, electric<br>resistivity, and Ground Penetrating Radar”GPR”) were decided upon for delineating buried<br>tombs and identifying their environmental status.<br>An exhaustive sequence of 2-D data processing techniques was applied to the EMdata<br>to minimize the disturbed electrical conductivity pattern imposed by the infiltrated<br>wastewater. Observed and buried graveyard boundaries were delineated on the high-pass<br>(0.15 cycle/m) filtered conductivity map. Buried tombs (2.5m x 2m) were detected as high<br>conductivity anomalies indicating that tombs may be filled with soil and/or infiltrated<br>wastewater. EM-method succeeded in delineating the area1 extent of the buried graves; the<br>GPR-technique complemented this information by determining their depth of burial. .<br>A dc-resistivity profile was performed at an abnormally high EM-anomaly, using<br>dipole-dipole array, to delineate the extent of infiltrated sewage water and its spreading<br>direction. An 2-D inverse resistivity model revealed a very low resistivity (0.24-0.91<br>Ohmm) anomaly, indicating its saline sewage water, spreading at the shallow part of the<br>resistivity section and possessing the highest thickness, about 2.0m, at the northeastern part<br>of the section close to the nearby housing utilities.<br>GPR survey lines, at 500 MHz central frequency, was conducted at two selected<br>EM-anomalies to essentially map the depth of the buried graves. The graves are located<br>within the depth range of l-1.8m. The observed radar wave attenuation suggested soil<br>contamination with saline wastewater.