Geophysical characterization and monitoring of subsurface drip irrigation, Powder River Basin, Wyoming, USA

Abstract

Water that has been co-produced with coal bed methane in the Powder River Basin, Wyoming, is being applied to agricultural fields using subsurface drip irrigation (SDI). Ground-based frequency-domain electromagnetic (EM) data are acquired over several fields in order to monitor changes in subsurface electrical properties related to the SDI operations. These data indicate spatial variability in soil properties across the site, as well as a systematic increase in conductivity in one field observed on three repeat surveys carried out over one year. A quantitative assessment of changes in subsurface properties requires inversion of the EM data to recover the true distribution of electrical resistivity with depth. Data calibration and filtering procedures are presented that correct for systematic and random errors in the data, which results in improved inversion estimates.