15
An
Ultra-Precise System for Electrical Resistivity Tomography Measurements—Multi-Phase
Technologies, LLC, 310 Rebecca Drive, Sparks, NV
89436; 775-425-9606
Dr.
Douglas J. LaBrecque, Principal Investigator, dlabrecque@mpt3d.com
Ms.
Marjorie O. LaBrecque, Business Official, mlabrec913@yahoo.com
DOE
Grant No. DE-FG02-05ER84289
Amount:
$493,755
One
of the most widely used geophysical methods for monitoring flow within the
shallow subsurface is Electrical Resistivity Tomography (ERT).
The latest generation of ERT systems can monitor data to a precision of
around 1%, allowing in situ changes to be interpreted within a few
percent. In turn, subsurface
temperature changes can be monitored to within a few degrees Centigrade, low
levels of tracers – only slightly higher than background variations – can be
tracked, and fracture propagation on a site of several thousand square meters
can be watched. This project will
make improvements to hardware and data collection procedures that will raise ERT
precision by an order of magnitude. In
Phase I, modifications were made to a number of interdependent hardware and
software systems, resulting in reductions in both random and systematic noise
sources. Random noise was reduced by
implementing longer data averaging periods and by improving stacking algorithms.
Systematic noise was reduced by
improving hardware design, including the isolation of transmitter and receiver
paths in the multiplexer and the use of temperature-stabilized higher-precision
components to improve calibration. Electrode
and cable effects also were found to be larger sources of noise than
anticipated. Phase II will
investigate the use of alternative materials for the electrode and cable, in
order to mitigate the noise from these sources.
Alternative data collection strategies will be investigated. Improvements
to hardware and software will focus on calibration. Field
trials will be held in difficult environments, such as the Idaho National
Laboratory, Box Canyon fractured rock study area, and Vadose Zone Research Park.
Commercial Applications and other Benefits as
described by the awardee: An improved ERT technology should increase
measurement precision, increase resolution, and enhance effectiveness in
existing monitoring applications without significantly increasing costs. These
improvements should broaden the range of applications for the method,
particularly in monitoring flow in the shallow subsurface. The
DOE complex alone has been estimated to contain 200 million cubic meters of
contaminated soils, including those at the Hanford Reservation, the Savannah
River Site, the Idaho National Laboratory, and the Nevada Test site.