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Electrical Resistance Tomography to Quantify Subsurface Heterogeneity of Hydrogeologic ParametersEPA Grant Number: U915756
Title: Electrical Resistance Tomography to Quantify Subsurface Heterogeneity of Hydrogeologic Parameters
Investigators: Singha, Kamini
Institution: Stanford University
EPA Project Officer: Boddie, Georgette
Project Period: September 1, 2000 through September 1, 2003
Project Amount: $102,000
RFA: STAR Graduate Fellowships (2000) RFA Text | Recipients Lists
Research Category: Fellowship - Geology , Academic Fellowships , Ecological Indicators/Assessment/Restoration
The objective of this research project is to determine how accurately spatially variable hydrogeologic parameters can be quantified through the simultaneous analysis of electrical resistance, borehole-geophysical, hydraulic-test, and tracer-test data at the Massachusetts Military Reservation, Cape Cod, Massachusetts.
Solute transport will be monitored using a doublet saline tracer test in conjunction with time-lapse electrical resistance tomography at the Massachusetts Military Reservation, Cape Cod, Massachusetts. These data will be analyzed simultaneously with other data, including fluid conductivity measurements, solute concentration, hydraulic-test data, and previously collected flowmeter logs in an optimization framework to create a picture of the spatially variable subsurface flow properties consistent with each type of data. Although the above secondary data are directly related to hydraulic conductivity, electrical conductivity and hydraulic conductivity are not entirely analogous. They are related through their common dependence on tortuosity, surface area, and porosity, but electrical conductivity also is a function of other factors such as ion mobility and temperature. As fluid moves with the doublet test, the electrical response will change as the solute fills the pore space. Areas that show increasing electrical conductivity must be filling with saline, and thus have high hydraulic conductivity and connectivity. A plot of electrical conductivity with time for each pixel of data should show which pixels have controlling hydrogeological parameters. These pixel "breakthrough" curves will allow interpretation of solute travel time and average concentration in each pixel, assuming complete displacement of fresh water. These data will be used in conjunction with the flow and solute transport data to update the prior distribution of hydraulic conductivity based on point data and large-scale hydraulic tests.
The challenge is to form a fundamental link of what is seen in the geophysical image to the actual properties and architecture of the subsurface.