Surfactant/Cosolvent Flushing of LNAPL Contamination

In recent years, in-situ surfactant flushing has been used at several NAPL-contaminated sites to demonstrate the capability of Surfactant Enhanced Subsurface Remediation (SESR) for cleaning-up the contaminated “hot” source zone. Recently, Surbec-ART has developed a low surfactant concentration (< 1 wt%) SESR approach capable of removing significant NAPL mass from the source area. The low surfactant concentration approach has several advantages for chemical flood, including (1) significant savings on chemical use and project cost, (2) minimizing and/or completely eliminating the need for recycling and reuse of surfactant, and (3) improving the above-ground treatment efficiency (e.g., less retention time for breaking the macro- or microemulsion during the oil/water separation stage, foaming). By itself, surfactant flushing can remove a significant portion of the subsurface NAPL. However, surfactant flushing alone may not reduce the subsurface contaminant concentration to a level necessary for site closure. Therefore, a treatment train approach may be used to speed up site closure . Surbec-ART has developed an abiotic and biotic process to couple with surfactant enhanced NAPL removal to remediate sites to established clean-up levels.

Significant results of a full-scale UST remediation project with the low concentration SESR approach will be presented. The Golden UST site is located in the town of Golden, in southeastern Oklahoma. The main contaminant is gasoline fuel as a result of leaking USTs from three former gasoline stations. The depth to the contaminated zone was 5 to 25-foot. Most of the free phase NAPLs were trapped in the shallow zone (5 to 15 ft), which is silty clay and predominantly silt. The treated area covered approximately 45,000 ft². The primary goal of the project was to remove all free phase gasoline. The secondary goal was to demonstrate a significant decrease in soil and groundwater concentrations (one to two orders of magnitude). The tertiary goal was to see how low the final contaminant concentration in groundwater could be achieved, i.e. to achieve the MCLs.

In October of 2001, one pore volume of 0.94 wt% surfactant solution was injected to mobilize and remove the free phase and residual gasoline. After surfactant flushing, low concentrations (< 0.5 wt%) of a chemical oxidant, Fenton’s Reagent, were injected to degrade the dissolved BTEX and any remaining residual phase. Ongoing Phase II post-polishing work (started September of 2002) is to continue the chemical oxidation treatment to achieve the MCLs at Golden site. This polishing task will be completed in December of 2002 (expected). Based on free phase measurements, more than 6,500 gallons of the free phase have been removed. In addition, secondary goals have been achieved, as most groundwater wells and soil sample locations have shown over an order of magnitude reduction in concentration, and tertiary goals have also been achieved in select groundwater wells (i.e., SW-46 from 17.4 mg/L benzene to 0.004 mg/L) and soil sample locations (i.e., DW-1A from 1.9 mg/Kg benzene to non-detected).