Estimation of the Time Periods and Processes for Penetration of Selected Spilled Oils and Fuels in Different Soils in the Laboratory

The subsequent distribution, fate and effects of inland oil spills from transportation (tanker trucks, rail road cars, etc.) in which fuels (diesel fuel, gasoline, home heating oils, etc.) are released to the environment have come under study as it was realized that the number of such accidents and accumulative volume of spilled fuels were quite large. The fate and behaviour of spilled fuel on soils mainly depend on soil type, amount and type of fuels both prevailing weather conditions. Experiments were simulated in the laboratory to determine the factors and processes and rates that influence and determine the distribution and abundance of fuels in soils following experimental spills to identify risks to ground waters from accidental spills.

In the laboratory, special column experiments, with soils found in Finland, found that the most vulnerable soil types (as expected) were the sandy soils, where hydrocarbon vertical seepage velocities in gravely sandy soils varied between 2.8 m/h (diesel oil) and 13.2 m/h (gasoline). However, one would expect in the environment for these velocities to be lower because of horizontal seepage and backpressure caused by saturated zone. Nevertheless, results suggest that in Finnish shallow soils gasoline-like fuels can easily reach the groundwater 2–4 m below the ground level.

Results suggest that emergency response actions must be taken by emergency services within a few hours to prevent pollution of the groundwater (short-term retention of gravely sand 3.1 wt.% for gasoline and 4.5 wt.% for diesel oil, respectively). The majority of Finnish soils are till, which had even better short-term retention capacities (5.8 wt.% for gasoline and 6.6 wt.% for diesel oil in sandy till), and where seepage velocities (0.1–0.2 m/h) were only a part of those determined for gravely sandy soils. In most cases emergency services has at least 2 h time to stop spreading of fuel to prevent pollution of the groundwater. The distribution processes for spilled fuel on ground can be described as: advection, molecular diffusion or mechanical dispersion, with the spreading type to be dependent on a soil type and its geology. In addition, weather conditions (especially temperature and wind speed), diameter of a pool and soil type, for gasoline-like volatile compounds vaporization can be very effective, so that only a portion of spilled oil penetrates into the soil. The data suggest that a spill of gasoline on soil with a hydraulic conductivity less than 1 Darcy (1×10⁻⁵ m/s) during the summer time will mostly vaporize before seeping into the soil.