Geophysical CSAMT Survey Results and Groundwater Modeling in a Groundwater Appropriation Trial

The role of geophysics in groundwater model development becomes particularly important when much of the model domain has alluvial cover, and the presence or absence of important faults that may influence groundwater flow is unknown. We discuss a good recent example at the Campbell Ranch project in New Mexico, in which much of the study area is covered by unconsolidated Quaternary units, but in surrounding areas where bedrock is exposed, the area is complicated with numerous faults and folds, with complex geologic structure. As a result, subsurface structure that may be significant in the groundwater modeling was suspected, but unknown. Since multiple aquifers were present and the depth of interest was moderately deep (> 3,000 ft), a CSAMT (controlled source audio-frequency magnetotellurics) electromagnetic survey was performed along six survey lines in an effort to better understand the subsurface. The CSAMT survey identified multiple buried faults, several of which proved important in calibration of the groundwater modeling that was used to calculate future impacts on existing wells from proposed new wells.The CSAMT results were presented during a groundwater appropriation trial in New Mexico.