Effect of crude petroleum on water repellency in a clayey alluvial soil

Water repellency was studied in a clayey soil contaminated with light (36.6A degrees API), medium (27.4A degrees API), and heavy (15.0A degrees API) crude oils at concentrations of 1, 2, 4, and 8 %. Higher water drop penetration times (WDPTs) were observed in dry soil as the density and concentration of petroleum increased, resulting in logarithmic functions which could be modeled from API gravity and oil concentration (R (2) = 0.986). WDPTs varied from 2.1 to 8.7 s with light crude, 11.1 to 44.9 s for medium crude, and 39.4 to 134.5 s for heavy crude. Only heavy crude-contaminated soil, at > 2 % resulted in significant hydrophobicity. Critical moisture content in these hydrophobic soils was insignificant at moisture contents > 12.8 % at 2 % heavy crude and > 14.6 % at 4 % heavy crude. Only at a concentration of 8 % heavy crude was the critical moisture content (> 17.2 %) higher than that observed in the field during the dry season (14.8 %). Thus, only (clayey) soil contaminated with very high concentrations of heavy oil is likely to present hydrophobicity in this monsoon climate. This study shows that the development of models to describe soil water repellency may be useful to propose remediation criteria which reduce or avoid the risk of water repellency.