Oil spill effects on soil hydrophobicity and related properties in a hyper-arid region

The effects of soil contamination by crude oil have been extensively studied in many parts of the world, revealing considerable impact on soil-water repellency and related hydraulic properties of soil. Yet, knowledge of such effects in hyper-arid regions is still scant. Two major oil spills occurred in the hyper-arid Arava Valley of Israel – one in 1975, and the second in 2014. The objective of this study was to assess the effects of the oil on the soil hydrophobicity and related physical properties. Additionally, decay in hydrophobicity over time was assessed by comparing these soil properties from the 1975 and 2014 contaminated sites. We hypothesized that the degradation of oil over time would cause a decrease in hydrophobicity during this 40-year time span. The study was implemented by on-site monitoring of the soil penetration resistance, water drop penetration time, critical surface tension, and hydraulic conductivity, as well as by laboratory measurements of drop contact angle and soil texture. All of these tests were conducted at the ground surface, at 5-cm, and 10-cm depths of the 1975 and 2014 contaminated sites, as well as for non-contaminated sites nearby. Despite the approximately 3.5 times smaller mean concentrations of total petroleum hydrocarbon at the 1975 site (7800 mg/kg) compared to the 2014 site (26,400 mg/kg), the study results revealed a general similarity of hydrophobicity and related soil properties between them. Therefore, the obtained results negated the study hypothesis, revealing the persistence of hydrophobicity over time.