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46 UPTAKE AND RELEASE OF HAZARDOUS CHEMICALS BY SOIL MATERIALS Ju-Chang Huang, Professor Brian A. Dempsey, Assistant Professor Shoou-Yuh Chang, Assistant Professor Hossein Ganjidoost, Graduate Research Assistant Department of Civil Engineering University of Missouri-Rolla Rolla, Missouri 65401 INTRODUCTION In many places of the nation, ground water has been contaminated with various concentrations of chloroorganic solvents, such as 1,1,1-trichloroethane (TCA), trichloroethylene (TCE), and tetrachlo- roethylene or perchloroethylene (PCE). Most of the contaminations have originated from the previous dump of these chemicals into unsealed ponds or landfill sites [1]. Since these organic solvents are highly volatile, a good portion of these chemicals has escaped into the air upon their disposal. However, once covered by soil and refuse, or having seeped into the subsurface environment, little volatilization can occur. As the chloroorganic solvents are seeping into and through the ground, they can be adsorbed by minerals and particulate organic materials. This adsorption process tends to increase the retention time of volatile organic compounds (VOCs) in the soil. They travel more slowly than inert and unreactive salts. Nevertheless, plumes of these solvents have been detected quite far away from the initial site of contamination, indicating only a moderate ability to be adsorbed by soils and minerals [2,3]. In many areas heavily polluted with VOCs, plans have been made or are being considered to pump ground water to the surface and then subject it to air stripping to remove the highly volatile chloroorganic solvents [4], Although this kind of remedial action appears to be appropriate in removing volatile chloroorganics, it is difficult to estimate the length of pumpage required to achieve adequate cleanup of the subsurface water. This is because one of the major factors governing the future transport and cleanup of these chloroorganic solvents in the subsurface environment is the sorption and desorption reactions of these organics in the saturated and unsaturated soils. For a typical polluted area, a fairly accurate account of the total amount of organic solvents disposed on a given site may be known. However, since a large portion of the disposed VOCs may have been lost into the atmosphere through volatilization, the exact amount of these chemicals entering the ground, their distribution along the soil depth (in the unsaturated zone) as well as in the polluted plume (beneath the ground water table) are normally difficult to define, particularly when the acquired field data show a lack of consistency. This has commonly happened because the volatility of these organic solvents has often introduced a significant degree of experimental errors in the chemical analysis unless proper extraction and analytical protocols are followed. In general, the chlorinated solvents may be present in the pure form (perhaps in droplets held in the soil matrix by capillary forces), adsorbed on the sediment phase, or in the aqueous phase. The chemical distributions between the latter two phases are described by adsorption isotherms. By establishing accurate adsorption and desorption isotherms for a specific adsorbate-adsorbeni combination, the following advantages may be derived: 1. The adsorption isotherm will allow an engineer to make an estimate of the total quantity of each organic solvent that has been retained on the saturated sediment phase based on its aqueous concentration found in ground water. 2. The adsorption isotherm will also allow him to check the validity of the field data which have been collected from the polluted plume in any contaminated site. This may be done by comparing the chloroorganic concentrations in both the sediment and the aqueous phases and then determining whether these data coincide with the established isotherm relationships. 390
Object Description
Purdue Identification Number | ETRIWC198646 |
Title | Uptake and release of hazardous chemicals by soil materials |
Author |
Huang, Ju-Chang Dempsey, Brian A. Chang, Shoou-Yuh Ganjidoost, Hossein |
Date of Original | 1986 |
Conference Title | Proceedings of the 41st Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,37786 |
Extent of Original | p. 390-400 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
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Description
Title | page 390 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 46 UPTAKE AND RELEASE OF HAZARDOUS CHEMICALS BY SOIL MATERIALS Ju-Chang Huang, Professor Brian A. Dempsey, Assistant Professor Shoou-Yuh Chang, Assistant Professor Hossein Ganjidoost, Graduate Research Assistant Department of Civil Engineering University of Missouri-Rolla Rolla, Missouri 65401 INTRODUCTION In many places of the nation, ground water has been contaminated with various concentrations of chloroorganic solvents, such as 1,1,1-trichloroethane (TCA), trichloroethylene (TCE), and tetrachlo- roethylene or perchloroethylene (PCE). Most of the contaminations have originated from the previous dump of these chemicals into unsealed ponds or landfill sites [1]. Since these organic solvents are highly volatile, a good portion of these chemicals has escaped into the air upon their disposal. However, once covered by soil and refuse, or having seeped into the subsurface environment, little volatilization can occur. As the chloroorganic solvents are seeping into and through the ground, they can be adsorbed by minerals and particulate organic materials. This adsorption process tends to increase the retention time of volatile organic compounds (VOCs) in the soil. They travel more slowly than inert and unreactive salts. Nevertheless, plumes of these solvents have been detected quite far away from the initial site of contamination, indicating only a moderate ability to be adsorbed by soils and minerals [2,3]. In many areas heavily polluted with VOCs, plans have been made or are being considered to pump ground water to the surface and then subject it to air stripping to remove the highly volatile chloroorganic solvents [4], Although this kind of remedial action appears to be appropriate in removing volatile chloroorganics, it is difficult to estimate the length of pumpage required to achieve adequate cleanup of the subsurface water. This is because one of the major factors governing the future transport and cleanup of these chloroorganic solvents in the subsurface environment is the sorption and desorption reactions of these organics in the saturated and unsaturated soils. For a typical polluted area, a fairly accurate account of the total amount of organic solvents disposed on a given site may be known. However, since a large portion of the disposed VOCs may have been lost into the atmosphere through volatilization, the exact amount of these chemicals entering the ground, their distribution along the soil depth (in the unsaturated zone) as well as in the polluted plume (beneath the ground water table) are normally difficult to define, particularly when the acquired field data show a lack of consistency. This has commonly happened because the volatility of these organic solvents has often introduced a significant degree of experimental errors in the chemical analysis unless proper extraction and analytical protocols are followed. In general, the chlorinated solvents may be present in the pure form (perhaps in droplets held in the soil matrix by capillary forces), adsorbed on the sediment phase, or in the aqueous phase. The chemical distributions between the latter two phases are described by adsorption isotherms. By establishing accurate adsorption and desorption isotherms for a specific adsorbate-adsorbeni combination, the following advantages may be derived: 1. The adsorption isotherm will allow an engineer to make an estimate of the total quantity of each organic solvent that has been retained on the saturated sediment phase based on its aqueous concentration found in ground water. 2. The adsorption isotherm will also allow him to check the validity of the field data which have been collected from the polluted plume in any contaminated site. This may be done by comparing the chloroorganic concentrations in both the sediment and the aqueous phases and then determining whether these data coincide with the established isotherm relationships. 390 |
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