Integrated Structural and Hydrologic Charactrization of Fault Zone Permeability at Well Field to Regional Scales

点击翻译按钮获取中文摘要

0610027GECurrent understanding of fault-zone permeability at regional scales is limited. Particularly,permeability measurements across faults are scarce. Yet, there are clear indications that faultshave large hydrogeologic impacts on various geologic processes at this scale, as evidenced byvariable hydraulic head gradients, geochemical and geothermal anomalies across faults. Thereremain questions that are scientifically fundamental and practically significant regarding largescalepermeability of fault zones and their impact on aquifers. For example, how geologic andhydrologic information can be best integrated to effectively constrain regional-scale faultpermeability? While existing knowledge on fault permeability at small scales is indispensablescientifically, ultimately, it is the regional-scale permeability that is needed in conceptual andnumerical models for solving problems related to water resource management and transport offluid, solute, and energy in the Earth's crust.The scientific objective of this research is to characterize fault-zone permeability at the wellfieldto regional scale with constraints from field-based structural observations, hydrogeologictesting, and interpretation from conceptual and numerical modeling. The basis hypotheses arethat distinctive hydrogeologic responses around a fault could be observed from cross-faultaquifer tests and that fault-zone permeability features could be established from a comprehensiveunderstanding of the outcrop structural characteristics, borehole data of host rocks, andhydrogeologic tests conducted at multiple scales. Using the Elkhorn thrust fault in Colorado as afield site, the research plan consists of the following: (1) to characterize the geology and internalstructure of the fault zone to better understand the influence of juxtaposition of differentlithologies on fault-zone hydrogeologic properties, (2) to drill and core new boreholes throughthe fault zone to obtain direct field observations for fault-zone permeability, (3) to conduct crossfaultpumping tests in the new and preexisting holes to provide the much need directmeasurements on fault-zone permeability, and (4) to develop a fault-zone permeability model,through numerical modeling that integrates geologic, hydrogeologic, and geophysical field data.Three aspects of the intellectual merit are recognized. First, the study takes a new directionin characterizing fault-zone permeability by closely linking geologic observations andhydrogeologic testing data. Second, this proposed research offers the opportunity to gainhydrogeologic insight into a particular type of fault that is common but highly understudied - a thrust fault with a crystalline hanging wall and sedimentary footwall at regional basin scales. Finally, the cross-fault permeability tests coupled with geologic characterization planned in this research will be a significant advance in characterizing fault-related permeability by providing much-needed field measurement data.The major aspect of the broader impact of this proposed research is on enhancingundergraduate students experience in hydrogeology, in addition to training graduate students and contributing to better groundwater resource management in the western US. This research will benefit a large group of undergraduate students. Undergraduate students will be involved in all stages of this project. Specific approaches to implement this commitment include: (1) Recruit top undergraduates to conduct honor theses, (2) Field exercise related to an upper-division hydrogeology class. Groundwater level mapping and aquifer tests can be incorporated into class related activities, and (3) Drilling new boreholes will be coordinated so that students can observethe operation. Finally, the PIs plan to co-teach a two-credit two-week summer undergraduate field hydrogeology class. The research will provide an excellent venue for many different projects for this field class and help to realization of this plan.