ANALYTICAL MODELLING OF ATTENUATION OF VOLATILE PETROLEUM HYDROCARBONS IN THE VADOSE ZONE

We applied the measured kapp and Kd parameter values in an analytical model to estimate 
the extent of the volatile petroleum hydrocarbons from a known source zone, and to compare the 
model analyses results based on batches experimental data with results based on parameters determined 
in a field lysimeter experiment. The analytical results of how far a constituent can migrate from 
a 50cm source zone before its attenuation, based on the field lysimeter date, the distance (r 95%) 
ranged from 75cm to 350 cm away from the source zone. 75 to 100cm distance from the source zone 
illustrates the 95% attenuation of toluene and n-octane respectively. While the attenuation distance of 
cyclohexane and methylcyclopentane was 200 and 250cm respectively, n-pentane, n-hexane and isooctane have 95% attenuation distance of 350, 200 and 225cm respectively. These data suggest that the 
significant differences in the attenuation distance from the source zone between the laboratory data 
and the field data was related to the difference in the apparent biodegradation rates, which were faster 
for the soil investigated in the laboratory in this study. The data presented illustrate the phenomenon 
of biodegradation and sorption of VPHs in the unsaturated zone and the analytical model analyses 
data results demonstrate the VPHs extent of migration form source zone under different scenarios 
(source zone radius, biodegradation rate and sorption distribution coefficients). All data show that 
biodegradation by indigenous microorganisms is the key parameter controlling the fate and transport of 
contaminants in the subsurface.