HR: 09:00h
AN: H11I-04    [Abstracts]
TI: Characterization of spatial variability of hydraulic parameters in fractured rocks: Interpretation of pumping tests at the Altona Flat Rock Experimental Site
AU: Castagna, M
EM: marta.castagna@ing.unitn.it
AF: Dipartimento di Ingegneria Civile e Ambientale, Universita' di Trento, via Mesiano 77, Trento, TN I-38050, Italy
AU: Becker, M W
EM: mwbecker@geology.buffalo.edu
AF: Department of Geology, State University of New York at Buffalo, 876 Natural Science Complex, Buffalo, NY 14260, United States
AU: * Bellin, A
EM: Alberto.bellin@unitn.it
AF: Dipartimento di Ingegneria Civile e Ambientale, Universita' di Trento, via Mesiano 77, Trento, TN I-38050, Italy
AB: We present the results of the interpretation of multiple hydraulic tests conducted at the Altona Flat Rock experimental site, located near Plattsburgh (NY). The purpose of these tests was to establish the nature of flow connectivity in a single sub-horizontal bedrock fracture. The geology of the area is dominated by the Potsdam sandstone which is characterized by sub-horizontal bedding-plane fractures that extend over the scale of kilometres. Seven open boreholes with a diameter of 15 cm have been drilled to a depth of 12.2 m in the formation at reciprocal distances ranging from 7 to 15.8 m. Packer injection tests show the presence of a saturated horizontal fracture at 7.3 meters of depth, which intersects all the wells. The single fracture is characterized by a highly variable aperture which leads to a wide range of hydraulic transmissivity (T) and storativity (S) estimated from slug tests. In order to characterize the hydraulic properties of the fractured rock, a series of pumping tests were performed. The pumping tests were executed at constant rate of 7\;e^-5\; m3/s for about 30 minutes in each well while the drawdown curves were collected in the remaining wells. Cooper-Jacob analyses of the pump tests indicate a large and variable apparent storativity. In highly heterogeneous media, variability in apparent storativity is often interpreted as a test artifact caused by anisotropic and heterogeneous transmissivity. Our objectives in the inversion of the hydraulic data were to (1) attempt to separate true and apparent storativity in the bedrock fracture and (2) investigate improved methods of pump test design that can decouple the influence of storativity and transmissivity on drawdown. The former was investigated primarily using the field data and the later using hypothetical simulations based upon the field data. The inversion was performed within a Bayesian framework by using the pilot point concept and by assuming unknown the stochastic parameters of the spatial variability models of T and S, i.e. mean, variance and integral scales. From this analysis we conclude that, even under the assumption of highly heterogeneous transmissivity field, the field data cannot be inverted without varying both T and S in space. We also find that non-steady pump test designs (e.g. pulse, multi-pulse) may improve decoupling of T and S inversion of cross-hole hydraulic test data.
DE: 1828 Groundwater hydraulics
DE: 1829 Groundwater hydrology
DE: 1869 Stochastic hydrology
SC: Hydrology [H]
MN: 2007 Fall Meeting