TY - JOUR
T1 - What does hydraulic tomography tell us about fractured geological media? A field study and synthetic experiments
AU - Zha, Yuanyuan
AU - Yeh, Tian Chyi J.
AU - Illman, Walter A.
AU - Tanaka, Tatsuya
AU - Bruines, Patrick
AU - Onoe, Hironori
AU - Saegusa, Hiromitsu
N1 - Funding Information:
The work was supported by the U.S. Environmental Security Technology Certification Program (ESTCP) Grant ER-201212. This research was supported in part by the NSF EAR Grant 1014594. The first author acknowledges the support of “ China Scholarship Council ”. Tian-Chyi Jim Yeh also acknowledges the Outstanding Oversea Professorship award through Jilin University from Department of Education, China. Walter A. Illman was supported in part by the Discovery Grant from Natural Sciences & Engineering Research Council of Canada (NSERC). The constructive suggestions and comments from the Associate Editor and two anonymous reviewers are appreciated.
Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2015/12/1
Y1 - 2015/12/1
N2 - Between 2005 and 2010, Japan Atomic Energy Agency conducted four long-term, independent pumping tests in a fractured granite formation at the Mizunami Underground Research Laboratory (MIU) site in Mizunami city, central Japan. During these tests, drawdowns were monitored at different depths along several deep boreholes. These tests become one of the few, if not the only, hydraulic tomographic survey conducted in the world over thousands of meters in a fractured geologic medium with several fault zones. We analyzed the drawdown-time data set associated with each pumping test independently, and then the data sets from all pumping tests jointly to derive the spatial distributions of hydraulic conductivity (. K) and specific storage (. Ss) of the medium. These estimated distributions revealed some large-scale high K and low K zones. While the low K zones corroborated well with known low permeable layers and fault based on geological investigations, there were no clear geological features that can be related to the large-scale high K zones. In order to understand and substantiate these high and low K zones, we simulated a hydraulic tomographic survey in a synthetic fractured aquifer, which bears similar geologic features (i.e., formations, fractures, and faults) at the MIU site, with exception that the hydraulic properties, fracture and fault distributions were known exactly. Results of the simulation show that not only are the identified high K zones related to fracture networks connected with pumping and observation locations of each pumping test but also their values reflect the degree of connectivity of the network. Afterward, we investigated the extent of the improvement of characterization of the fault and fractures through the use of deploying dense monitoring intervals and late-time flux measurements.
AB - Between 2005 and 2010, Japan Atomic Energy Agency conducted four long-term, independent pumping tests in a fractured granite formation at the Mizunami Underground Research Laboratory (MIU) site in Mizunami city, central Japan. During these tests, drawdowns were monitored at different depths along several deep boreholes. These tests become one of the few, if not the only, hydraulic tomographic survey conducted in the world over thousands of meters in a fractured geologic medium with several fault zones. We analyzed the drawdown-time data set associated with each pumping test independently, and then the data sets from all pumping tests jointly to derive the spatial distributions of hydraulic conductivity (. K) and specific storage (. Ss) of the medium. These estimated distributions revealed some large-scale high K and low K zones. While the low K zones corroborated well with known low permeable layers and fault based on geological investigations, there were no clear geological features that can be related to the large-scale high K zones. In order to understand and substantiate these high and low K zones, we simulated a hydraulic tomographic survey in a synthetic fractured aquifer, which bears similar geologic features (i.e., formations, fractures, and faults) at the MIU site, with exception that the hydraulic properties, fracture and fault distributions were known exactly. Results of the simulation show that not only are the identified high K zones related to fracture networks connected with pumping and observation locations of each pumping test but also their values reflect the degree of connectivity of the network. Afterward, we investigated the extent of the improvement of characterization of the fault and fractures through the use of deploying dense monitoring intervals and late-time flux measurements.
KW - Fracture and fault hydrogeology
KW - Fracture connectivity
KW - Hydraulic tomography
KW - Inverse modeling
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U2 - 10.1016/j.jhydrol.2015.06.013
DO - 10.1016/j.jhydrol.2015.06.013
M3 - Article
AN - SCOPUS:84947036036
SN - 0022-1694
VL - 531
SP - 17
EP - 30
JO - Journal of Hydrology
JF - Journal of Hydrology
ER -