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Bromide transport before, during, and after colloid mobilization in push-pull tests and the implications for changes in aquifer properties

Nikolaidis Nikolaos, Lucas A. Hellerich, Peter M. Oates, Philip M. Gschwend, Charles F. Harvey, Carol R. Johnson

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URI: http://purl.tuc.gr/dl/dias/98C91BEC-D3CD-48C4-92C2-2A93099385E7
Year 2003
Type of Item Peer-Reviewed Journal Publication
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Bibliographic Citation Hellerich L.A., P.M. Oates, C.R. Johnson, N.P. Nikolaidis, C.F. Harvey, and P.M. Gschwend, "Bromide Transport Before, During, and After Colloid Mobilization in Push-Pull Tests and the Implications for Changes in Aquifer Properties", Water Resources Research, Vol. 39, no. 10, Oct. 2003. DOI: 10.1029/2003WR002112 https://doi.org/10.1029/2003WR002112
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Summary

Bromide breakthrough curves from push-pull tests were obtained at two wells before, during, and after citrate injections to assess how citrate-induced colloid mobilization affected physical aquifer transport properties. Tailing and incomplete bromide recoveries (67–95%) could not be fit with a conservative advection/dispersion model, and the results of batch tests using aquifer solids implied bromide was not significantly sorbing. Thus we modeled the bromide returns considering advection, dispersion, and rate-limited diffusive mass transfer between mobile and immobile regions by fitting αr, the radial dispersivity; α, the rate-limited mass transfer coefficient; and β, the volumetric ratio of immobile-to-mobile domains. Statistical t-tests indicated that the changes in aquifer transport parameters at a well where colloid mobilization was limited were not significant at a 95% percent confidence level. However, the substantial colloid mobilization at a second well corresponded to significantly decreased αr and β, while increasing α between premobilization and both mobilization and postmobilization. The changes in aquifer parameters and their correlation to the recovered colloidal mass are consistent with the idea that pore-clogging colloids were mobilized and/or reorganized during citrate injections. The results suggest that flushing a site under the right conditions with citrate could open up immobile regions and substantially reduce remediation time and costs by liberating contaminants whose transport would otherwise be diffusion limited.

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