Solutions For A Complex World:
Geophysics For Managed Aquifer Recharge
Article by: HGI Staff | hydroGEOPHYSICS
In the United States, groundwater provides drinking water for roughly half of the country’s population. As populations grow and the climate changes, increasing stress is placed on our groundwater resources, and it becomes increasingly important to monitor and maintain these precious resources for future use. While groundwater is a renewable resource, we extract it much more rapidly than natural processes can replenish it in many areas. However, we can give the natural process of groundwater recharge a helping hand through managed aquifer recharge (MAR). MAR uses infiltration basins, injection wells, surface waters, and treated wastewaters to recharge aquifers and increase supplies artificially. However, MAR can be challenging because only certain areas are conducive as subsurface pathways to the water table.
Geophysical methods help understand subsurface geology structures and how the geology either hinders or accelerates managed aquifer recharge rates.
Geophysical technologies are used in MAR projects to answer important questions concerning how water moves through the subsurface. To ensure aquifer recharge is working, project managers need to know if the water is making it to the aquifer, the recharge rate, and how much is reaching the target. Geophysical methods help understand subsurface geology structures and how the geology either hinders or accelerates recharge rates. The primary concern is locating permeable sediments suitable for infiltration. A site’s permeability determines if a pathway exists between the earth’s surface and subsurface water systems. Sand and gravel-rich deposits offer high-volume pathways where water percolates downward and eventually reaches the water table. Sand and gravel areas are electrically resistive compared to unfavorable clay and silt-rich sediments, layers, or lenses, which tend to be more conductive. Geophysical surveying can rapidly and cost-effectively distinguish between geological features that may help or hinder recharge. Geophysical mapping of MAR project sites to assess the potential for infiltration and subsequent aquifer recharge helps develop strategies to optimize recharge rates.
Geophysics can be tailored to the many phases of managed aquifer recharge projects, including supporting the decision-making process for land acquisition for recharge basin development. Purchasing land to build recharge basins is expensive, and geophysics provides an ideal solution to ensure any purchase offers a return on investment. Frequency and time-domain electromagnetics offer ideal tools to characterize an entire property accurately. These methods can rapidly provide spatial and depth coverage to produce a 3D model of each potential MAR project site. This allows the optimum MAR property to be selected, identifying and avoiding subsurface confining layers or complex hydrogeology that could impact recharge.
Mobile towed platforms using geophysical methods are ideally suited for large-scale characterization of subsurface sediments, with 10’s miles of data collection possible in a single day. Electrical resistivity and time-domain electromagnetic methods are used for smaller-scale surveys, providing 2D cross-sections of the subsurface hydrogeology to identify coarser-grained units optimum for infiltration.
When surface real estate is at a premium, managed aquifer recharge is conducted through injection wells. Geophysical surveys can be applied to provide information on the deeper subsurface to aid well design, monitor injections, and assess formation properties for injections. Subsurface investigations can be conducted through surface-based electrical resistivity and time-domain electromagnetic surveys, running borehole geophysical logging, or instrumenting monitoring wells with geophysical arrays to provide single borehole or cross-borehole electrical measurements for characterization and monitoring.
As world populations swell and climate stresses water resources, managing our water supply to support us now and in the future is critical. Geophysics to help managed aquifer recharge becomes a value proposition we cannot ignore when making sure MAR projects are successful. hydroGEOPHYSICS uses unconventional thinking to expand geophysical technologies in new and vital directions to support critical efforts to improve water resources, our environment, and liveability in communities across the United States.
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About HGI | hydroGEOPHYSICS
hydroGEOPHYSICS, Inc. (HGI) has over 30 years of experience providing geophysical services to the environmental, engineering, groundwater, mining, oil & gas, and natural resource exploration industries. We represent value and reliability in a geophysical service provider – our geophysicists, geologists, hydrologists and engineers are dedicated to finding solutions using industry-best equipment and custom-tailored geophysical services with a focus on safety, quality, and innovation. We specialize in the application of 2D & 3D geophysical methods in complex environments, time lapse subsurface monitoring of fluid flow through geologic materials, leak detection & leak location, subsurface characterization, plume mapping, and buried infrastructure detection and mapping.