MODELING FAULT ZONE HYDROGEOLOGY THROUGH THE INTEGRATION OF PUMPING TEST AND GEOPHYSICAL DATA, ELKHORN FAULT, PARK COUNTY, COLORADO

Fault zones are ubiquitous in groundwater aquifers and can play a significant role in fluid transport at local to regional scales. Fault-zone permeability structure controls whether the fault behaves as a barrier, conduit, or combined barrier-conduit for fluid flow. Although much work has been done to measure local- to well-scale permeability, larger-scale measurements are critical to understanding the regional hydrogeologic effects of faults. This study models fault zone permeability at the well-field scale to assist in characterizing the regional hydrogeologic effects of the Elkhorn Fault in Park County, Colorado. The Elkhorn fault is an inactive Laramide-aged thrust fault with a sedimentary footwall and fractured Proterozoic, crystalline hanging wall. Pumping test data from wells near the fault are analytically modeled to attempt to characterize the permeability of the fault zone. Electromagnetic, resistivity, and gravity data are used to constrain the location and geometry of the fault and combined with borehole geophysical logs and core samples to aid in the interpretation of the hydrogeologic complexity of the fault and its associated damage zone. Integration of geophysical and hydrogeologic data leads to the development of a more robust interpretation of fault zone permeability than possible by a single-discipline approach.