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Presentation
A Hydraulic Tomography Experiment in Contaminated Fractured Sedimentary Rocks, Newark Basin, New Jersey, USA
2015 GSA Annual Meeting, [Baltimore, MD] (2015)
  • Claire R. Tiedeman, U.S. Geological Survey
  • Warren Barrash, Boise State University
  • Colby Thrash, Clemson University
  • Carole D. Johnson, U.S. Geological Survey
Abstract
In contaminated fractured rocks, fine-scale characterization of the hydraulic conductivity (K) distribution is a critical step towards fully understanding contaminant transport behavior and designing remediation strategies. It is important to characterize K variability within the less-fractured rock matrix as well as across the network of higher-permeability fractures. To this end, a hydraulic tomography experiment was performed in July 2015 in contaminated fractured mudstones in the Newark Basin near Trenton, NJ, with the goal of estimating the K distribution of the rocks at fine scale. The spatial arrangement of seven existing wells (in a circle of 9 m radius with one central well), the use of packers to divide the wells into multiple monitoring intervals, and the deployment of fiber optic pressure transducers enabled collection of a hydraulic tomography dataset comprising high-resolution drawdown observations at an unprecedented level of spatial detail for fractured rocks. The experiment involved 45-minute cross-hole aquifer tests, conducted by pumping from a given packer-isolated well interval and continuously monitoring drawdowns in all other well intervals. The collective set of drawdown data from all tests and intervals displays a wide range of behavior suggestive of highly heterogeneous K within the tested volume, such as: drawdown curves for different well intervals crossing one another on drawdown-time plots; variable drawdown curve shapes; variable order and magnitude of time-lag and/or drawdown for intervals of a given well in response to pumping from similar fractures or stratigraphic units in different wells; and groups of well intervals that show similar responses for different pumping tests. Preliminary assessment of these data, together with a rich set of geophysical logs, suggests an initial conceptual model that includes densely distributed fractures of moderate K at the shallowest depths of the tested volume, connected high-K bedding-plane-parting fractures at intermediate depths, and sparse low-K fractures in the deeper rocks. Future work will involve tomographic inversion of the data to estimate the K distribution at a scale of ~1 m3 in the upper two-thirds of the investigated volume, where observation density is greatest.
Disciplines
Publication Date
November 2, 2015
Citation Information
Claire R. Tiedeman, Warren Barrash, Colby Thrash and Carole D. Johnson. "A Hydraulic Tomography Experiment in Contaminated Fractured Sedimentary Rocks, Newark Basin, New Jersey, USA" 2015 GSA Annual Meeting, [Baltimore, MD] (2015)
Available at: http://works.bepress.com/warren_barrash/47/