Full-Scale Implementation of Aerobic Biooxidation to Deplete Groundwater Contaminants from Coal Tar
Dr. Randy Sillan, P.E., Principal Environmental Engineer, AECOM
Co-Author: Randy Keyser, P.G., NextEra Energy/FPL
Aerobic biooxidation of dissolved-phase hydrocarbons (including tar-related compounds) occurs naturally or via engineered applications. During aerobic biooxidation, microorganisms utilize hydrocarbons as electron donors in the presence of oxygen as the primary electron acceptor. Biosparging is a proven, effective remediation technology to enhance aerobic biooxidation of dissolved hydrocarbons typically observed in groundwater at coal tar sites. Enhancing biooxidation in the DNAPL tar source area accelerates dissolution of hydrocarbons from the DNAPL and changes the composition of the DNAPL. A NAPL dissolution model that includes a Raoult’s Law solubility model was developed to evaluate the ability to effectively remove hydrocarbons and groundwater contaminants from DNAPL and meet groundwater criteria. The solubility model includes specialty laboratory methods developed for tar and creosote sites. Biosparging was implemented at a former MGP in Daytona Beach. The onsite water-gas tar DNAPL is a source of dissolved-phase VOCs and PAHs to groundwater. After a pilot study, the biosparge system was expanded in 2016 to stop offsite mass flux and achieve groundwater criteria offsite. Biosparge system operation provided data to evaluate DNAPL weathering and use the DNAPL depletion model to estimate the time required to effectively remove groundwater contaminants from the DNAPL. Biosparging decreased the mass fraction of isopropylbenzene and naphthalene in the NAPL by 98% and 92%, respectively, in 2 years. Biosparging also significantly decreased the mass of aliphatic and aromatic hydrocarbons in the NAPL up to C40. The NAPL depletion modeling showed that biosparging is an effective strategy to remove groundwater contaminants from MGP tars in a reasonable time (<10 years). In 2020, horizontal air sparge wells were installed to expand the biosparge system to the tar source area. The presentation will include development and application of the NAPL depletion model and results from biosparge operations at the Daytona MGP site.
Dr. Sillan is a Principal Environmental Engineer with AECOM and has over 20 years of experience as an environmental consultant and professional engineer. Undergraduate and graduate degrees are from the University of Florida where his doctoral research focused on innovative NAPL assessment and remediation. He currently supports a broad range of rail, utility, and industrial clients as the technical lead or subject matter expert. Dr. Sillan also chairs the committee that develops the professional environmental engineering exam for the National Council of Examiners for Engineering and Surveying (NCEES).