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Characterizing groundwater resources is a critical step when analyzing potential mining areas. A vital component of the mining process, water is used for mineral processing, metal recovery, dust mitigation, and the basic needs for on-site workers. Even more importantly, a thorough understanding of groundwater resources is a major factor in understanding the environmental impact of the mine on those resources.

One such groundwater characterization project was led by Knight Piésold and company hydrogeologist Jared King. The project entailed the characterization of a decommissioned gold and silver mine in preparation for permitting future mining scenarios.

Over the course of six months, reverse circulation drilling was conducted throughout the proposed future mining areas. At each borehole, a well was installed and groundwater measurements were taken via an electronic water level indicator. All drilling samples, primarily volcanic and sedimentary rock, were characterized onsite by Knight Piésold geologists.

Developing a relationship between the surface elevation and the groundwater elevation was an important step for Mr. King and the team. The site was located in the Atacama region of Chile, an area with historic faulting and wide ranging surface topography with approximately 500 meters of elevation change. Additionally, the high altitude desert climate experienced significant precipitation variation which in turn impacted the shallow and deep groundwater flow. As such, a basic surface elevation map of the site was plotted using Golden Software’s contouring, gridding, and surface mapping software, Surfer.

Surfer contour mapping software: surface elevation map
A basic surface elevation map of the mine site. Plotted in Surfer.

Due to the highly variable topography of the mine area, Mr. King could not create a groundwater surface using a normal interpolation method as the gridded surface would not match what was observed in the field. Instead, the groundwater level was estimated using an empirical relationship from the data collected during drilling.

Modeling Groundwater Resources in Surfer, contouring and 3D modeling software
Empirical relationship of groundwater elevation and surface elevation collected during drilling. Plotted in Excel®

The groundwater depth surface created from the drilling data revealed several different groundwater regions that behaved somewhat independently. They regions consisted of an upper zone with a shallow hydraulic gradient, a lower zone representing shallow groundwater in the valley-fill, and a zone of transition characterized by both steep surface and groundwater gradients.

Surfer modeling and contour mapping software: Groundwater depth map
Groundwater depth map highlighting three distinct groundwater regions. Plotted in Surfer.

When the groundwater elevation map was draped over the surface elevation map, a strong correlation was viewed. This allowed the group to conceptually understand how the groundwater behaved throughout the arid, high-elevation mining site.

Surfer modeling and contouring mapping software: Groundwater elevation map draped over land surface map
Groundwater depth map highlighting three distinct groundwater regions. Plotted in Surfer.

Additionally, a gradient and slope map was created to better understand the overall flow regime across the study area. These maps also aided in creating a valid conceptual model for the groundwater surface.

Surfer modeling and contour mapping software: Groundwater gradient and slope map
Groundwater gradient and slope map. Plotted in Surfer.

Another important aspect of the hydraulic system analysis is the presence of springs. The location and elevation of the springs helped to confirm the conceptual model of groundwater flow with separate shallow and deep groundwater systems.

Surfer modeling and contour mapping software: Surface map of mine site displaying spring locations
The location of springs and seeps are represented by the blue symbols and are overlaid on the land surface map. This display allowed the team to differentiate the shallow groundwater from the deep groundwater systems. Plotted in Surfer.

Mr. King and the Knight Piésold team are finalizing their study and preparing the conceptual model report for their client. The next phase will entail the simulation of groundwater flow throughout the site. Three dimensional groundwater models will be created by feeding the surfaces generated in Surfer into MODFLOW, a groundwater modeling program developed by the USGS.

Mr. King joined Knight Piésold in 2015. He has 6 years of experience in all aspects of hydrogeology projects throughout the U.S. and Canada. He specializes in hydrogeologic characterization and remediation for the environmental, oil and gas, and mining industries. Mr. King earned his B.Sc. in Environmental Science from the University of New Mexico and his M.Sc. in Environmental Science and Engineering from the Colorado School of Mines.

Knight Piésold is an employee-owned global consulting firm that provides specialized services to the mining, power, water resources, infrastructure, and oil and gas industries. The company consists of engineers, environmental scientists, geoscientists, and technologists who focus on creating value at every stage of a project through quality driven, sustainable, and cost-effective solutions.

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