Set-Up of the Soil Columns

The glass columns used in this study were 38.5 cm long and had a diameter of 4,5 cm. The first 30 cm of the columns were filled with contaminated soil material from the saturated zone of the Testfeld Slid site. The remaining 8.5 cm were filled with water only. Five sampling ports P1-P5 were installed along the column with P1-P4 located throughout the soil-filled part of the column and P5 at the water-filled section. The concentrations recorded at P5 were used to represent the outlet concentrations of the column. In addition, the water was sampled before entering the column. 

A mineral medium containing a mixture of aromatic hydrocarbons and sulfate was pumped bottom to top through the columns for a period of 79 days. The flow rate as well as the concentrations of solutes were not constant throughout the experiment. The inflow concentrations for toluene varied between 17 pM and 154 pM, those for o-xylene between 0 and 58 pM and those for sulfate between 230 pM and 1179 pM. o-Xylene was injected throughout the whole period, while toluene injection lasted only up to day 52 of the experiment. The mean flow rate was 450 mL d .  

In this experiment the same type of column was used as in Experiment 1. Experiment 2 was run for 109 days. The mean flow rate was reduced to 290 mL d for the initial 22 days and was further reduced to 150 mL d for the remaining 87 days. Concentrations were only recorded at the column inlet and outlet. As in Experiment 1 the inflow concentrations for o-xylene and toluene varied with time, with maximum concentrations of 374 pM of toluene and 478 pM of o-xylene. o-Xylene was added more or less constantly throughout the experiment, while four periods of elevated toluene concentrations were applied. Period 1 lasted from the beginning of the experiment until day 11 with a mean toluene concentration of approximately 120 pM, and periods 2 and 3 lasted from day 53 until day 74 and from day 82 until day 101, respectively, with mean toluene input concentrations of approximately 50 pM. Period 4 from day 101 until the end of the experiment (day 109) was characterized by distinctly increased input concentrations for toluene of about 300 pM. Between these periods inflow concentration for toluene were less than 10 pM. The intemiittent supply of toluene should promote the observation of the effects of toluene on o-xylene degradation. 

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