Field Studies of the Electrical Properties of Permeable Reactive Barriers for Monitoring Barrier Aging
Abstract
Permeable reactive barriers (PRB) are a promising technology for the remediation of groundwater containing a range of organic and inorganic contaminants. Although there are number of different types of reactive barriers, some of the most important are constructed from granular zero valent iron (ZVI). One challenge in the large- scale, long-term implementation of PRBs is to monitor the change in barrier properties over time. For example, mineral precipitates can reduce the effectiveness of the barrier by either insulating the reaction surfaces of the ZVI particles and/or by filling the pore space in the barrier and thus reducing its hydraulic permeability. Previous research has shown that resistivity and induced polarization (IP) measurements are sensitive to corrosion and precipitation due to redox reactions between ions in solution and the ZVI mineral surface. New field studies, supported by additional laboratory studies appear to confirm this work. Resisitivity and IP surveys were conducted at a total of seven barriers at four different sites: the Denver Federal Center; Monticello, Utah; the Kansas City, Missouri Department of Energy site, and the Asarco Smelter Site in East Helena, Montana. These surveys used combinations of surface and borehole surveys to characterized barriers. The surveys are repeated at approximately six-month intervals to provide information on temporal changes. In addition, surveys at the Kansas City barrier followed up on earlier research by providing several years of historical data and a new barrier at East Helena Montana has been instrumented with an autonomous monitoring system allowing continuous monitoring of the barrier electrical properties. Results show an increase in both real and imaginary conductivity as barriers age. For new barriers, the conductivity of ZVI is typically a few tens of mS/m, only modestly higher than that of the background sediments surrounding the barrier. For heavily altered barriers such as the Monticello, Utah barrier, the conductivity is typically tens of S/m, a thousand times higher the unaltered barriers. Field values of chargeability (measured using a 1 Hz primary waveform and an integration window centered at 40 ms) also tend to increase from roughly a 100 mV/V at the East Helena Barrier to about 300 mV/V at Monticello. Other sites tend to be intermediate between these extremes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMNS31A1571S
- Keywords:
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- 0694 Instruments and techniques;
- 0925 Magnetic and electrical methods (5109)