Solutions for a complex world: Geophysics for Groundwater Characterization
Article by: Luis Salgado | hydroGEOPHYSICS
In arid and semiarid locations, such as the southwestern US, groundwater is the only source of water due to the scarcity of surface water, making groundwater a valuable resource throughout much of the world. As such, it is vital to determine and ensure the sustainability and viability of this resource for all end users. Geophysical tools offer cost-effective methods for addressing groundwater problems that relate to quality, vulnerability, and availability.
Geophysical tools offer cost-effective methods for addressing groundwater problems that relate to quality, vulnerability, and availability.
hydroGEOPHYSICS, Inc., uses non-intrusive geophysical methods to aid in the characterization, exploration, and protection of groundwater. We tackle each geophysical survey as a unique opportunity, and we apply a distinctive set of tools for every assessment. The application of electrical and electromagnetic methods are well suited for acquiring data to understand the heterogeneity and variability of the subsurface as it relates to water resource problems. In particular, electrical resistivity data are influenced by a range of material properties that can provide useful information for hydrogeology investigations related to the subsurface.
Electrical resistivity data are influenced by a range of material properties that can provide useful information for hydrogeology investigations.
Electrical resistivity profiling can help solve a wide variety of water-related problems. Electrical properties are strongly influenced by the degree of saturation, lithology or grain size variation, or amount of contamination in the subsurface. From acquired data, an image representing a slice of the earth is created, and electrical property contrasts are used to interpret differing hydrogeological conditions. Through color contouring, we visually identify these conditions to demonstrate various degrees of resistivity in the subsurface, which helps identify geological features or highly-saturated media. Further, applying the electrical resistivity multiple times at the same location can hone in on specific changes related to water movement.
Other geophysical tools, such as seismic, magnetic, and gravity methods, offer different insights into the subsurface tailored for groundwater investigations. This includes understanding depth to bedrock and alluvial thickness studies across basins and mapping faults and other structural controls on groundwater movement.
There are numerous applications of geophysical methods for groundwater characterization and hydrogeological assessments. For groundwater exploration, these methods can be used for basin delineation, karst investigations, and fracture mapping to identify features that may represent infiltration zones and that affect potential groundwater pathways. Additionally, plume mapping, contaminant source identification, and vulnerability assessments can be performed through the use of geophysical tools. In mining and recharge projects, time-lapse monitoring can be conducted using geophysical tools to understand storage changes better, investigate fluid movement, and identify preferential flow paths and channeling.
Other examples of groundwater problems that are aided through geophysics include aquifer storage and recovery monitoring, pump test monitoring, geothermal reservoir mapping, perched water table mapping, and groundwater/surface water interactions.
In 2014, HGI conducted an electrical resistivity survey at a gold mine in the united states. The goal was to broaden the hydrogeological understanding of the area and took place near an existing groundwater interception well system downgradient of the mine’s tailings storage facility. In this case, the results of the high-density electrical resistivity survey suggested that electrically conductive targets would yield higher pumping rates than resistive areas, which correlated with the production of existing wells of the area at the time. The conductive targets of the zone were used to help locate successful groundwater extraction wells.
Click plot to view a larger image.
The survey took place near an existing groundwater interception well system downgradient of the mine’s tailings storage facility. The results of the high-density electrical resistivity survey suggested that electrically conductive targets would yield higher pumping rates than resistive areas, which correlated with the production of existing wells of the area at the time. The conductive targets of the zone were identified (blue and purple contours), and these results were used to help locate successful groundwater extraction wells.
About the Author: Luis Salgado | hydroGEOPHYSICS
Luis Salgado is a Field Technician for HGI. He is involved with a broad range of technical projects, assisting project managers with field data acquisition, analysis, and helping with pre- and post-project office tasks. Since joining HGI, Luis has specialized in applying electrical resistivity surveys and equipment deployment in various settings.
Luis gained experience working as a research assistant, laboratory, and field technician during his undergraduate career at The University of Arizona’s Department of Hydrology and Atmospheric Sciences. Luis received a BS Degree in Environmental Hydrology and Water Resources from The University of Arizona in 2017.
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