ENHANCED LNAPL RECOVERY IN AN UNSATURATED AQUIFER BY USING A HUMIC ACID

Humic acid (HA) has many attributes that make it a promising surfactant to enhance the mobilization of trapped low-density non-aqueous phase liquids (LNAPL) in an unsaturated sand aquifer. First, the critical micelle concentration (CMC) occurs at a low concentration of 3.4 mg/ml. Second, the HA quickly mobilizes the LNAPL by reducing the interfacial tension of the LNAPL-water interface. Third, simple continuous flushing tests measured up to 81% of the LNAPL was recovered. Fourth, HA is easy and inexpensive to produce. Finally, HA places a low oxygen demand on the natural aquatic system. Disadvantages of using HA are: it readily disperses clays that may promote pore clogging, the HA's surfactant capabilities degrade with time, and the CMC concentration of HA is near 4.25 ± 0.35 mg/ml the 96 hr LC50 for Xenopus embryos as determined by FETAX tests.