SOIL IRON CONTENT EFFECTS ON THE ABILITY OF MAGNETOMETER SURVEYING TO LOCATE BURIED AGRICULTURAL DRAINAGE PIPES

In this study, we investigate the connection between the distribution of soil iron concentration and nanoTesla-scale changes in the magnitude of the Earth’s local magnetic field 0.5 m above the ground surface. Ground-based remote sensing methods have demonstrated the ability to identify subsurface agricultural drainage system locations to aid in hydrological studies and the placement of new drainage systems to augment failing systems. Magnetometer surveys have been successful in identifying drainage system locations under certain soil conditions that appear related to soil iron concentration distributions. An iron rich layer is clearly disturbed by trenching during tile installation in the western part of the study site where a local magnetic high is spatially associated with the drainage system. The eastern part of the study site shows a decrease in the magnetic high spatially associated with the drainage system, less disturbance of an iron rich layer during tile installation, and evidence of iron migration. We have found that the success of magnetometer surveys in identifying drainage pipes at the Oregon State University Research Dairy is related to increased disturbance of iron rich soils or due to post-tile installation iron migration.