Retardation of organic contaminants in natural fractures in chalk |
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| Authors: | Wefer-Roehl A Graber E R Adar E Yakirevich A Ronen Z |
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| Institution: | Ben Gurion University of the Negev, The Blaustein Institute for Desert Research, Sde Boker, 84990 Israel;Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, The Volcani Center, P.O.B. 6, Bet Dagan, 50250 Israel;972-3-968-3307;fax 972-3-960-4017; |
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| Abstract: | Transport of a conservative compound and two sorbing compounds through fractured chalk was studied using flow-through columns consisting of chalk cores with a single subvertical fracture. Two types of chalk matrix were compared, an oxidized white chalk with low organic carbon content (0.2%), and a gray chalk with a higher organic carbon content (1.3%). Initial rapid breakthrough followed by a delayed approach to a relative concentration of unity for the conservative compound (2,6–difluorobenzoic acid DFBA]) was clear evidence for diffusion into the porous chalk matrix. Matrix diffusion of DFBA was apparently much greater in the gray chalk columns than in the white chalk columns. Breakthrough curves (BTCs) of the sorbing compounds (2,4,6–tri-bromophenol TBP] and ametryn AME]) were retarded in all cases as compared to the conservative compound. Sorption retardation was far greater in the gray chalk as compared with the white chalk, in good agreement with results from batch sorption experiments. BTCs for the conservative compound were relatively nonhysteretic for both white and gray chalk columns. In contrast, BTCs for the sorbing compounds were hysteretic in all cases, demonstrating that sorption was not at equilibrium before desorp-tion began. These experiments suggest that on a field scale, transport of contaminants through fractures in chalk and other fractured porous media will be attenuated by diffusion and sorption into the matrix. |
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