Formatted Title
3-D CSM Development as a Precursor to Groundwater Flow Modeling
Background/Objectives
Two-dimensional (2-D) visualizations often are insufficient at accurately representing the problem statement at complex geological and hydrogeological sites. Additionally, 2-D information can be difficult to dissect, inconsistencies/errors hard to identify, and time consuming to evaluate. At complex sites, three-dimensional (3-D) geological models are often crucial for data compilation from multiple sources, development of a robust CSM and effective visual generation. This approach supports efficient groundwater modeling applications through direct translation from 3-D space to a representative model structure, where the subjective guesswork of constructing model layers is minimized, resulting in a more realistic and representative subsurface structure. These components more readily enable project stakeholders to understand site complexity and relationships.
Approach/Activities
Various data types and informational sources via online databases are compiled. Once assembled, source information is managed in Leapfrog Works, a 3-D geological modeling platform to begin developing a 3-D CSM. Incorporating and maintaining data in the 3-D environment is efficient because it allows data management, visually, for otherwise difficult to interpret subsurface results, previously not as efficient or obtainable. The process also identifies data gaps and informs the CSM.
Before building a geologic model, borehole geology is re-categorized into specific stratigraphic/ hydrogeologic units (upscaling). Within 3-D space, this process results in a more consistent interpretation representative of site geology. Upscaled borehole data are then used in combination with other sources to create the geologic model.
The geologic model is then used as a foundation for layer structure and grid discretization within modeling codes such as MODFLOW or FEFLOW. Additionally, properties such as hydraulic conductivity and porosity can be established within the 3-D interface. Moreover, high-resolution hydraulic conductivity values from downhole tools such as nuclear magnetic Rresonance (NMR) can be interpolated and establish hydraulic properties, spatially. Similarly, chemical data can be managed and visualized where 3-D plumes can support fate and transport modeling.
Integrating 3-D CSM development with groundwater modeling provides a high degree of quality control, greater flexibility, and allows for dynamic data overview. Several case studies will be presented to demonstrate the value and effectiveness of this approach.
Results/Lessons Learned
The synthesis of available data into a 3-D CSM prior to numerical modeling efforts results in a streamlined and dynamic approach towards lithological interpretation that is easily synthesized into a coherent geological model. Because the 3-D environment assists in presenting system complexity and numerical modeling results, numerical groundwater modeling assumptions and output are more robust and defensible. Simplifying assumptions are still relevant, but the ability to compile various streams of available information, in 3-D, allows for a higher degree of control and understanding. Building a comprehensive 3-D CSM can be involved; however, it is extremely valuable for understanding, accurate system representation, and should be an essential component of the groundwater modeling process. Moving forward, the generated 3-D CSM will be a visual database/tool for any site, increasing stakeholder value. In summary, this powerful workflow can and should also be used for a multitude of applications in addition to flow modeling such as planning site characterization investigations, supporting remedial infrastructure needs, developing remedial plans, monitoring progress, and allowing for optimized reporting.