Transport of creosote compounds in a large, intact, macroporous clayey till column

The transport in macroporous clayey till of bromide and 25 organic compound s typical of creosote was studied using a large intact soil column. The org anic compounds represented the following groups: polycyclic aromatic hydroc arbons (PAHs), phenolic compounds, monoaromatic hydrocarbons (BTEXs), and h eterocyclic compounds containing oxygen, nitrogen or sulphur in the aromati c ring structure (NSO-compounds), The clayey till column (0.5 m in height a nd 0.5 m in diameter) was obtained from a depth of 1-1.5 m at an experiment al site located on the island of Funen, Denmark. Sodium azide was added to the influent water of the column to prevent biodegradation of the studied o rganic compounds. For the first 24 days of the experiment, the flow rate wa s 219 ml day(-1) corresponding to an infiltration rate of 0.0011 m day(-1). At this flow rate, the effluent concentrations of bromide and the organic compounds increased very slowly. The transport of bromide and the organic c ompounds were successfully increased by increasing the flow rate to 1353 mi day(-1) corresponding to 0.0069 m day(-1). The experiment showed that the transport of low-molecular-weight organic compounds was not retarded relati ve to bromide. The high-molecular-weight organic compounds were retarded si gnificantly, The influence of sorption on the transport of the organic comp ounds through the column was evaluated based on the observed breakthrough c urves. The observed order in the column experiment was, with increasing ret ardation, the following: benzene = pyrrole = toluene = o-xylene = p-xylene = ethylbenzene = phenol = benzothiophene = benzofuran < naphthalene < 1-met hylpyrrole < 1-methylnaphthalene = indole = o-cresol = quinoline < 3,5-dime thylphenol = 2,4-dimethylphenol < acridine < carbazole < 2-methylquinoline < fluorene < dibenzofuran < phenanthrene = dibenzothiophene. This order cou ld not be predicted from regularly characteristics as octanol/water-distrib ution coefficients of the organic compounds but only from experimentally de termined data. The results indicate that a thin clayey till cover of the ty pe described in this paper does not protect groundwater against contaminati on by low-molecular-weight organic compounds. (C) 1999 Elsevier Science B.V . All rights reserved.