| Project Background |
| Gas leakage had been reported seven
times at this residential street location. The source of
the leak was suspected to be associated with abandoned
and undocumented gas light connections, although previous
repair efforts were unsuccessful. In an attempt to locate
the source of the leak, Geo-Graf was retained to perform
a nonintrusive subsurface investigation. |
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| Geo-Graf Investigation |
| Geo-Graf utilized four different nonintrusive
geophysical delineation techniques, including Ground
Penetrating Radar (GPR). A strong GPR leak indication was
detected almost immediately over a 4" cast-iron
low-pressure main within the street in question. However,
gas was detected at the surface 180' away from the GPR
leak indication. The GPR leak indication was excavated
anyway, and the cracked pipe was found. An abandoned
wooden storm sewer was also unearthed beneath the cracked
gas main, providing a path for transportation of the gas
over 180' away from the actual leak source. |
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| GPR Data Profile |
| Please Wait as
the image below loads. It is actual radar data of a
natural gas pipe leak collected by Geo-Graf engineers
utilizing a 550 MHz GPR antenna |
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| Above: A GPR data profile over the
detected natural gas leak location. Previous research
conducted by Geo-Graf indicates that the gas leak is
"visible" to GPR based on the fact that the
leaking gas tends to dry out the subsoil immediately
surrounding the area. This creates a subsurface interface
recognized by GPR. Thus, by subsequently adjusting the
"sensitivity" of the GPR unit, the source of
the leak can be pinpointed. 550 MHz GPR antenna system. |
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