Modeling focused fracture flow at the Apache Leap Research Site, Arizona, using hydroflow and a coupled model, hydrogeochem

Abstract

A flow code, HYDROFLOW, was calibrated against a controlled laboratory block study. The laboratory block study measured the wetting front advancement through an unsaturated partially welded fractured tuff as the suction pressure at the upper boundary was varied. A multi-component reactive transport code, HYDROGEOCHEM, was then used to simulate a field scale preliminary tracer test. The preliminary tracer test was conducted at the Queen Creek Research Site (QCRS), a jointly funded University of Arizona and U.S. Nuclear Regulatory Commission (USNRC) field laboratory used for testing conceptual models of flow and transport in a fractured tuff environment. The QCRS provides a natural analog to the environment at Yucca Mountain, Nevada, which is being considered for storage of radioactive waste. Queen creek is an intermittent stream hydraulically linked through a fracture network to a monitoring tunnel located 120 meters below the base of the stream channel. Both models assume equivalent porous media, saturated or unsaturated conditions, finite element structure, and variable chemical and hydrologic conditions at all boundaries. Hydrologic parameters for the matrix were determined from laboratory tests conducted on core samples from the site. Fracture parameters were estimated based on observations of fracture behavior as well as information gained from a literature review. Both models exhibit the ability to reproduce the conditions observed~ however, a post-audit of these models on a second data set has not yet been performed to confirm the accuracy of the calibrations.