Sorption of trichloroethene onto stylolites

Batch and double reservoir diffusion cell experiments are used to investigate sorption of trichloroethene onto stylolites. Stylolites are common features in carbonate rock formations, and might contain high amounts of organic matter. Due to the hydrophobic character of TCE, its transport in fractured carbonate aquifers could be significantly affected due to these aforementioned features. No research has been carried out to evaluate the impact of stylolites on organic pollutant transport. The main objectives of this experimental research are to verify TCE sorption onto stylolites, and to derive sorption and diffusion parameters describing the solute/rock interaction. Test results show that stylolites from the Lockport Formation in Southern Ontario, Canada contain significant amounts of organic carbon. Discrepancies are noted between carbon analyzer data and estimates from batch experiments and these might be due to TCE sorption also onto a clay mineral phase in stylolites or due to selective sampling. Adsorption and desorption behavior of TCE is investigated in specially designed double reservoir diffusion cells made out of stainless steel and Teflon. Three semi-analytical solutions for one-dimensional, reactive tracer migration through a porous medium are derived and used to evaluate TCE time-concentration profiles. Experimental data can best be modeled using a kinetic Langmuir sorption formulation with a maximum sorption capacity of 1.3 to 4.6 mu g/g and a kinetic sorption constant of 4 x 10(-7) to 5 x 10(-7) l/mg s(-1). TCE desorption into the exit reservoir is found to be a very slow kinetic process. No retardation is observed during TCE migration through a clay and organic matter free dolostone sample. TCE seems not to interact with calcareous mineral phases and moves conservatively. Bromide diffusion curves yield geometry factors (gamma) for dolostone ranging between 0.05 and 0.13. From this study it can be concluded that TCE sorption is of importance when modeling TCE migration in fractured, stylolitic limestone aquifers where diffusion into the rock matrix takes place. Temporal TCE storage in rock matrix stylolites and fracture wall stylolites has to be taken into consideration when evaluating actions of remediation at organic spill sites. (C) 1999 Elsevier Science B.V. All rights reserved.