Formatted Title
In Situ Chemical Oxidation and Aerobic Bioremediation Used to Treat Tetrahydrofuran
Background/Objectives
An industrial facility in the Midwest, which had previously employed tetrahydrofuran (THF) in its operations, resulted in contamination of shallow soil and groundwater, reaching concentrations as high as 1,500 mg/kg and 400 mg/L, respectively. THF, a suspected carcinogen, is an emerging contaminant at many industrial sites due to its risk to human health. Due to the potential risk pathways at the site, the governing environmental regulatory agency mandated the remediation of THF. An in situ remediation approach was favored due to its non-intrusive nature and cost savings when compared to soil/groundwater removal. Because of the novelty of this contaminant, little information was available regarding suitable techniques for THF remediation in the subsurface. This posed a significant obstacle to achieving progress toward site closure. A literature review demonstrated that THF has been degraded using advanced oxidation methods in wastewater treatment processes. Thus, a remediation program consisting of in situ chemical oxidation (ISCO) and aerobic bioremediation offered the highest probability of success and was selected for the project.
Approach/Activities
Treatability studies tested a mixture of catalyzed sodium persulfate to promote direct ISCO and a calcium peroxide-based oxygen releasing compound (ORC) to promote anaerobic bioremediation. The microcosm studies were performed by an independent laboratory at varying dosages to demonstrate the efficacy of this concept and to optimize the final dosage for a full-scale application. The test involved mixing a reagent with site soils/groundwater at both low and high dosages and allowing it to react for 28 days. The low dosage consisted of 10 g/L of catalyzed sodium persulfate and 1.3 g/L of ORC. The high dosage consisted of 50 g/L of the catalyzed sodium persulfate and 6.5 g/L of the ORC. Following the successful treatability test, a full-scale treatment was implemented using the ISCO and aerobic bioremediation approach. Approximately 20,000 pounds of catalyzed sodium persulfate was mixed with water to create a 15-20% solution and applied using direct push technology (DPT). After completing the sodium persulfate injection, 2,000 pounds of ORC was applied into the same injection points.
Results/Lessons Learned
The laboratory treatability showed that after 28 days, THF concentrations were reduced by nearly 65% when using the low dose and >99% when using the higher dose. The results demonstrated the efficacy of this ISCO-to-bio approach. Following the full-scale treatment, the results of the post-application sampling indicated a reduction of THF in both soil and groundwater of up to 99% which significantly reduced the plume footprint. To achieve the required, plume wide treatment, supplemental applications were conducted to reduce THF in recalcitrant hot spots. This presentation provides practitioners with a remedial framework for the successful treatment of novel and emerging contaminants such as THF to navigate toward site closure. The importance of the distribution of the reagents and application specifications will be highlighted during this talk as it pertains to optimizing treatment. The results from these efforts indicate that a combined treatment of ISCO and aerobic bioremediation is effective for addressing this emerging contaminant.