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Title: Thermal treatment of low permeability soils using electrical resistance heating

Abstract

The acceleration of recovery rates of second phase liquid contaminants from the subsurface during gas or water pumping operations is realized by increasing the soil and ground water temperature. Electrical heating with AC current is one method of increasing the soil and groundwater temperature and has particular applicability to low permeability soils. Several mechanisms have been identified that account for the enhanced removal of the contaminants during electrical heating. These are vaporization of liquid contaminants with low boiling points, temperature-enhanced evaporation rates of semi-volatile components, and removal of residual contaminants by the boiling of residual water. Field scale studies of electrical heating and fluid extraction show the effectiveness of this technique and its applicability to contaminants found both above and below the water table and within low permeability soils. 10 refs., 8 figs.

Authors:
 [1]
  1. Univ. of California, Berkeley, CA (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab., TN (United States)
OSTI Identifier:
447174
Report Number(s):
ORNL/TM-13305
ON: DE97050722; TRN: 97:001173-0015
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Aug 1996; Related Information: Is Part Of In situ remediation of DNAPL compounds in low permeability media fate/transport, in situ control technologies, and risk reduction; PB: 318 p.
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 02 PETROLEUM; NONAQUEOUS SOLVENTS; EVAPORATION; SOILS; ELECTRIC HEATING; ORGANIC WASTES; COST; EFFICIENCY; CLAYS

Citation Formats

Udell, K.S. Thermal treatment of low permeability soils using electrical resistance heating. United States: N. p., 1996. Web. doi:10.2172/447174.
Udell, K.S. Thermal treatment of low permeability soils using electrical resistance heating. United States. doi:10.2172/447174.
Udell, K.S. 1996. "Thermal treatment of low permeability soils using electrical resistance heating". United States. doi:10.2172/447174. https://www.osti.gov/servlets/purl/447174.
@article{osti_447174,
title = {Thermal treatment of low permeability soils using electrical resistance heating},
author = {Udell, K.S.},
abstractNote = {The acceleration of recovery rates of second phase liquid contaminants from the subsurface during gas or water pumping operations is realized by increasing the soil and ground water temperature. Electrical heating with AC current is one method of increasing the soil and groundwater temperature and has particular applicability to low permeability soils. Several mechanisms have been identified that account for the enhanced removal of the contaminants during electrical heating. These are vaporization of liquid contaminants with low boiling points, temperature-enhanced evaporation rates of semi-volatile components, and removal of residual contaminants by the boiling of residual water. Field scale studies of electrical heating and fluid extraction show the effectiveness of this technique and its applicability to contaminants found both above and below the water table and within low permeability soils. 10 refs., 8 figs.},
doi = {10.2172/447174},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1996,
month = 8
}

Technical Report:

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  • Electrical resistance tomography (ERT) was used to monitor six-phase ohmic heating used for the insitu remediation of volatile organic compounds from subsurface water and soil at the Savannah River Site, near Aiken, South Carolina. The changes in electrical conductivity caused by six-phase ohmic-heating in a clay layer located in the vadose zone were monitored during a period of approximately 2 months, before, during and after heating. From an array of electrodes located in 4 boreholes, we collected electrical resistivity data between five pairs of adjacent holes pairs. This data was used to calculate tomographs which showed the electrical conductivity changesmore » along five vertical planes. The difference tomographs show the combined effects of moisture redistribution and heating caused by six-phase heating and vapor extraction. The tomographs show that most of the clay layer increased in electrical conductivity during the first 3 weeks of the 4 week long heating phase. At this time, the electrical conductivities near the center of the heating array were twice as large as the pre-heat conductivities. Then the electrical conductivity started to decrease for portions of the clay layer closest to the vapor extraction well. We propose that the conductivity decreases are due to the removal of moisture by the heating and vacuum extraction. Parts of the clay layer near the extraction well reached electrical conductivities as low as 40% of the pre-heating values. We propose that these regions of lower than ambient electrical conductivities are indicators of regions where the vapor removal by vacuum extraction was most effective. At the end of the heating phase, our estimates suggest that the clay saturation may have dropped to as low as 10% based on the observed conductivity changes.« less
  • Electrical resistance tomography (ERT) was used to monitor a radio-frequency heating process for the insitu remediation of volatile organic compounds from subsurface water and soil at the Savannah River Site, near Aiken, South Carolina. A dipole antenna located in a horizontal well in the unsaturated zone was used to heat a contaminated clay layer. The heat-induced changes were tomographically imaged by their effects on the formation electrical resistivity. The resistivity changes observed appear to be related to heating and vaporization of the pore water, formation of steam condensate, and infiltration of rainwater through the heated zones and adjacent areas. Theremore » is a clear asymmetry downward in the resistivity decreases associated with the heating process. The resistivity decreases observed in the vicinity of the heating well are believed to be caused by the heating and downward migration of warm water originally located within a radius of a few feet around the heating well; the magnitude of the change is between 10--20%. The decreasing resistivity implies an increasing rate of radio wave attenuation as heating progressed; therefore, the rate of energy deposition around the heating well increased while the penetration distance of the radio waves decreased. Saturation changes in the clay near the antenna during heating were estimated to be 50--55% based on the observed resistivity decreases. Resistivity changes observed at distances greater than 3 meters to one side of the antenna appear to be related to rainwater infiltration. We propose that gaps in near surface clay layers allow rainwater to migrate downward and reach the top of clay rich zone penetrated by the antenna borehole. The water may then accumulate along the top of the clay.« less
  • This paper summarizes the effect of heating on the distribution of organics in the subsurface, briefly reviews technologies used to inject heat in-situ, and finally illustrates the dramatic effect of heating on contaminant removal rates using a controlled laboratory simulation.
  • To test the feasibility of using bioremediation to treat soils from manufactured gas plant (MGP) sites, the Gas Research Institute (GRI) sponsored a laboratory soil bioremediation program that examined two systems for conventional biological treatment: engineered, prepared bed reactors (land treatment) and slurry reactors. Using laboratory-scale soil pan and slurry reactors to simulate land treatment and full-scale slurry systems, studies on six soils demonstrated that reductions of polynuclear aromatic hydrocarbons or PAHs (the chemicals of principal concern in these soils) occurred initially, but concentrations in soils eventually leveled off to a plateau concentration which represents the treatment endpoint. Statistically significantmore » reductions were observed in slurry reactors for all soils, but the endpoint varied from 5 to 15,000 mg/kg. Slurry reactors always treated to lower concentrations of total PAHs than did soil pan reactors, but the treatment endpoints in slurry reactors were similar to the treatment endpoints in pan reactors for the three soils with less than 10% silts and clays.« less
  • Electrical resistance sintering was applied to the production of composite compacts consisting of particles of a heavy metal (Fe, Th, U) in an Al matrix and to the production of Zr powder compacts. Two procedures were used for producing the composite heavy metal --Al compacts. One consists of cold compacting a mixture of the powders, sintering the compact by electrical- resistance heating, and hot working the sintered compact. For the other procedure, the green composite compact was hot worked by extrusionwithout an intermediate-resistance sintering step. The highest percentage of the heavy metal possible in the composite compact which allowed extrusionmore » of the compacts without defects was obtained by using a pure Al case around a core of the heavy metal -- Al powder mixture. Resistance -sintered compacts of pure Zr powder having good ductility could be produced if the Zr powder was prepared, stored, and compacted without access to atmospheric gases. If these precautions were taken, the compacts were ductile regardless of whether the final resistance sintering was done in air or in an atmosphere of A. Discussions of the tensile properties of Zr compacts, the extrusion of Zr, the extrusion of green Mg powder, compacts, and the resistance sirtering of graphite are included in an appendix. (B.J.H.)« less