Date of Award

Winter 2003

Project Type

Dissertation

Program or Major

Engineering: Civil

Degree Name

Doctor of Philosophy

First Advisor

Thomas P Ballestero

Abstract

During 3 years of investigation at the BBC field site, research has led to developments in bedrock monitoring, groundwater sampling, formation hydraulic testing, and the conceptual model of formation hydraulics. This dissertation presents a field device, two hydraulic test methods, and one method of hydraulic test analysis developed to assist in the hydraulic characterization of fractured bedrock formations. It also presents the use of these tools in the development of the Conceptual Hydrogeologic Model for a fractured bedrock formation contaminated with chlorinated solvents. The field device was named the Multipurpose Packer System (MPS), a discrete-interval isolation system for the sampling and hydraulic assessment of open wellbores completed in heterogeneous formations. A MPS prototype was successfully designed, fabricated, installed, and tested in a well. The MPS advantages included: the minimization of water quality biases and the ability to perform hydraulic tests at isolated borehole intervals. The two field hydraulic tests were named the large drawdown slug test, and the gas injection test. Large drawdown slug tests are defined as those slug tests with initial drawdown larger than 5 m; these were demonstrated to be a valuable hydraulic test to: (a) study well interconnectivity in heterogeneous formations, (b) remove the need to pump large quantities of groundwater, (c) quantify the storage coefficient for monitoring well field data, and (d) assess tight formations. The gas injection test is a field technique for the characterization of hydraulic connections in fractured bedrock; the test is conducted below the water table by gas pressurizing an isolated interval of a borehole. The gas pressurization exceeds the pressure for water removal from the interval, thereby forcing gas to invade fractures that intersect the interval. The induced gas overpressure can be recorded in monitoring wells, allowing well interconnectivity to be described on a site-wide scale. A 1D Finite-Difference radial-flow model for interpretation of hydraulic tests was coded in a JAVA application named HyTests. It was successfully validated and extensively used in this research for identifying the hydraulic parameters of the fractured bedrock. Finally, the conceptual hydrogeologic model that was developed for the site identified: (1) the fractured bedrock connectivity with the other hydrogeologic units in the site, (2) The fractured bedrock hydraulic parameters, and (3) The fractured bedrock recharge mechanisms, flow patterns, and boundary conditions.

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