Modelling the Transport of Crude Oil in the Unsaturated Sandy and Loamy Soil Using Experimental and Statistical Methods

Abstract

Unregulated extraction and transport of crude oil pose significant environmental and public health risks through contamination of air, soil, and groundwater, particularly within the vulnerable vadose zone, where pollutants migrate toward subsurface water resources. This study modelled crude oil transport in the unsaturated zone using laboratory experiments, with sandy and loamy soils at varying column heights (15cm to 60cm). Many models have been developed and used, but fail to effectively depict the actual complexities, hence the need for this study. Polyvinyl chloride (PVC) soil columns were used, and after a 14-day drying period simulating drought, 0.0005m3 of crude oil was introduced into each column. Leaching time and Total Petroleum Hydrocarbon (TPH) concentrations were measured at different depths. In sandy soil, shorter columns had higher TPH concentrations and faster leaching, with leaching time ranging from 37 to 3600 seconds and TPH concentrations decreasing from 28,913mg/l to 103mg/l at depth (C2). In loamy soil, leaching times ranged from 33 to 1500 seconds, with TPH concentrations decreasing from 11,085mg/l to 309mg/l at depth (C2). Statistical analysis revealed a significant difference in concentration at depth between sandy and loamy soils. Predictive models based on Dimensional Analysis were developed for each soil type. The models ignored chemical and biological interactions, assumed steady-state flow, 1-dimensional vertical transport, homogenous media, constant viscosity, absence of preferential flow and a uniform initial crude oil distribution. In conclusion, the sandy soil model (R2 = 0.97) showed better reliability for use than the loamy soil model (R2 = 0.66). It is recommended that prediction be done cautiously with supplementary data when relying on the loamy soil model due to its moderate strength.