The United States Geological Survey (USGS) continues to develop improvements in remediation monitoring using electrical resistivity tomography in order to identify and correct contamination at various sites. The methods developed provide information about water-quality and other information that are more cost-effective and reliable than methods used in the past.
Massachusetts Military Reservation
In conjunction with Stanford University, scientists with USGS used electrical resistivity tomography, which is similar to a CAT scan used on humans, to monitor a salne tracer in a sedimentary aquifer. The tests indicated contrasts in three dimensions, allowing researchers to calibrate ground-water flow, and provided information regarding aquifer heterogeneity using new methodology. The tests were conducted at the Massachusetts Military Reservation in Cape Cod in 2005.
Naval Industrial Reserve Ordnance Plant
Using time-lapse borehole radar tomography, scientists from USGS and the US Navy injected a vegetable oil emulsion in areas contaminated by chlorinated hydrocarbons in an effort to stimulate microbial degradation. The radar tomography was able to indicate the extent of altered chemistry in the ground water at the Naval Industrial Reserve Ordnance Plant in Fridley, Minnesota.
Loring Air Force Base
On the site of what was the former Loring Air Force Base in Limestone, Maine, researchers used borehole radar tomography and reflection techniques in a fractured limestone aquifer that had been contaminated with chlorinated hydrocarbons. The radar results allowed scientists to estimate the degree of steam invasion, as well as the extent of the invasion, within the aquifer.
Estimating Hydrologic Properties
Increasingly, USGS scientists are using geophysical tomography methods to estimate hydrologic properties in both sedimentary and fractured-rock aquifers. The tests are being used to determine porosity, solute concentration and water content using new modeling approaches. These new approaches are making it possible for researchers to predict loss of information caused by blurring and streaking sometimes caused during electrical resistivity imaging. By combining the two processes, researchers say they are better able to compile hydrologic properties between boreholes.
These experiments provide evidence of the importance of electrical resistivity tomography, as well as other new methods in geophysical survey methods that are providing better information regarding contamination of various land areas. They are also providing information on how scientists can begin the process of correcting those contaminated sites and making them viable for humans or animals again.