In Situ Surfactant Washing of Polychlorinated Biphenyls and Oils from a Contaminated Site

Abstract

AbstractOver the past four years, we have been developing an in situ surfactant‐washing method to decontaminate soil systems. This study addresses another major step in that development: a field test of the surfactant‐washing method at a site contaminated with polychlorinated biphenyls (PCBs) and oils. A test plot, 10‐ft diameter by 5‐ft deep, was selected in an area of high levels of contaminataion. The study involved applying a surfactant solution on the plot to wash the site material and carry the leachate down to the depressed water table, where it was collected by pumping a recovery well installed through the center of the plot. The leachate pumped to the surface was biotreated to degrade the oils and surfactant, and the PCBs were removed from the leachate by an activated carbon system. Soil cores from the test plot indicated concentrations of up to 6,223 mg/kg PCBs and 67,000 mg/kg oils. The test plot initially contained about 15 kg of PCBs and 157 kg of oils. The hydraulic response of the test plot to washing was monitored by measuring the water levels in wells around the test plot and the fluid pressure and saturation through the plot. These real‐time data were used to adjust the surfactant‐application rate to minimize lateral spread of the surfactant and leachate and the pumping rate to capture all the leachate by the recovery well. The response of contaminant concentrations in the test plot to washing and the performance of the leachate‐treatment system were also monitored during the test by collecting and analyzing samples from the recovery well and from the treatment system. An on‐site laboratory was used for these analyses. During the 70 days of the washing test, 5,375 gallons of a 0.75% aqueous surfactant solution was applied on the test plot at an average rate of 77 gal/day. During the same period, 10,981 gallons of leachate were recovered at an average rate of 157 gal/day. A total of 1.6 kg of PCBs and 16.9 kg of oils (about 10% of the initial mass) was washed from the test plot during the test. Maximum concentrations of 65 mg/1 PCBs and 709 mg/1 oils were measured in leachate samples. The leachate was adequately treated before it was discharged. These test results indicate that in situ surfactant washing is a promising candidate for the remediation of contaminated soil systems.