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Bromide transport before, during, and after colloid mobilization in push‐pull tests and the implications for changes in aquifer properties
Author(s) -
Hellerich Lucas A.,
Oates Peter M.,
Johnson Carol R.,
Nikolaidis Nikolaos P.,
Harvey Charles F.,
Gschwend Philip M.
Publication year - 2003
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2003wr002112
Subject(s) - aquifer , colloid , advection , mass transfer , clogging , bromide , mobilization , dispersion (optics) , diffusion , geology , soil science , environmental engineering , chemistry , environmental science , geotechnical engineering , chromatography , groundwater , thermodynamics , physics , inorganic chemistry , history , archaeology , optics
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 α r , 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 α r 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.