Mitigation of water repellency in the treatment of contaminated muds using the chemical–biological stabilization process

Abstract

The soil–water relationship was used to evaluate the efficacy of a novel remediation technology, the chemical–biological stabilization process, which focuses principally on soil fertility restoration in agricultural sites. This process was evaluated for the treatment of 150 m³ of bentonitic drilling muds from a closed sulfur mine which contained 70 % fines (<0.05 mm), and which had been contaminated with very weathered hydrocarbons, containing 31 % asphaltenes. This material was monitored for two and a half years, for in situ moisture content, field capacity, and soil water repellency. Additionally, critical soil moisture content for water drop penetration times of <5 and <60 s was monitored. Field capacity increased 46.6 % with respect to initial values and a vigorous vegetative growth was established. Concurrently, water repellency values for molarity ethanol droplet and water drop penetration times were reduced from 5.1 to 3.9 M and 106 to 0.12 h, respectively. Soil in situ moisture content during the driest part of the year (20.3 % humidity) remained above critical values (15.1 % humidity and 19.5 % humidity) to avoid a water repellency of <5 and <60 s, respectively, and water repellency was not observed in the field. Thus, complete mitigation of water repellency was achieved. These findings indicate that the soil–water relationship should be evaluated to achieve an integral soil remediation and that water repellency as a remediation criterion should be complemented with determinations of critical moisture content and actual site information on soil in situ moisture content during the annual cycle.