Abstract
<p>Hydrocarbon-contamination can change hydraulic conductivity (HC) in soils, and hence increase the spreading rate of aqueous toxicants in the ground. A constant head permeameter used in the laboratory to measure HC of soils taken from near the Pitch Lake in Trinidad determined that the HC exceeded that of a reference soil having “normal HC” for a loam. Although water moved rapidly through it, the Pitch Lake soil (PLS) remained dry due to water repellence. Treatment consisted of either of two red mud bauxite wastes mixed at 25 and 50% w/w with PLS at air dry. One of the bauxite wastes had undergone treatment with gypsum several years before and hence contained a greater proportion of calcium ions compared to the other red mud which contained more sodium ions. At 25% w/w the non-gypsum-treated red mud waste decreased HC of the PLS by 50%, and at 50% w/w caused a 10-fold decrease of HC on the PLS. The gypsum-treated red mud waste had no effect on the HC of the PLS. The drastic decrease in HC of the hydrocarbon-contaminated soil implies blocking of hydraulic channels by inorganic particles. The high levels of Na<sup>+</sup> released in the Bayer beneficiation process dispersed and released fine &lt; 5 mµ clay particles from the non-gypsum-treated red muds. This suggests that the rapid movement of aqueous pollutants in such hydrocarbon-polluted soils could be similarly curtailed under field conditions.</p>
Highlights
Water repellent soils normally exhibit low infiltration rates (Blackwell, 2000)
Water repellence of the Pitch Lake soil (PLS) was found to be at the highest value, i.e., extremely water repellent (4), compared with the reference soil, which had a value of highly wetting (0), i.e., showing very rapid water absorbance
The fact that soil aggregates after several days in water, and even aggregates as small as < 2 mm remained dry after several hours of water infiltration showed the extremely hydrophobic nature of the Pitch Lake soils (Figure 4)
Summary
Water repellent soils normally exhibit low infiltration rates (Blackwell, 2000). Hydrophobicity can reduce the affinity for soils to water such that infiltration or wetting may be delayed for periods ranging from as little as a few seconds to in excess of weeks (Hall, 2009). Soil hydrophobicity is thought to be caused primarily by a coating of long-chained hydrophobic organic molecules on individual soil particles, thereby influencing soil hydrological and ecological functions (Takawira et al, 2014). A study by Lourenco et al (2015) confirmed the hypothesis that hydrocarbon contamination induces water repellence and reduces soil moisture retention at low suction (< 100 kPa) for laboratory contaminated soils. Water is not absorbed by such non-wetting soils. In a pilot study of the Trinidad Pitch Lake soils at La Brea:
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
