Bioactive Capping: Naphthalene Degradation in Sorptive Capping Media


Bioactive Capping: Naphthalene Degradation in Sorptive Capping Media

Sean M. Carroll (Haley & Aldrich, Inc.)
Kayleigh Millerick and Danny Reible (Texas Tech University)
Jeffrey A. Clock, (Electric Power Research Institute (EPRI))


Sean M. Carroll

Haley & Aldrich, Inc.

Speaker Bio:

Sean Carroll is an engineer and hydrologist at the engineering and consulting firm Haley & Aldrich. He has a B.S. in Civil Engineering from the University of Notre Dame and an M.S. in Hydrology and Water Resources from the University of Arizona in Tucson. He is registered as a Professional Engineer in Massachusetts and is a Licensed Environmental Professional in Connecticut. Focus areas in his work have included subsurface characterization, sediment assessment and remediation design, and assessment and remediation of former manufactured gas plant sites.


PAH contamination in sediments is a significant environmental remediation challenge that many utilities face; removal of contaminated sediments is very costly, and capping remedies typically have long-term monitoring requirements. Active capping remedies can reduce remediation costs, but typically have a limited sorption capacity and therefore a finite design life. The design-driving contaminants are typically the more soluble constituents (e.g., benzene, naphthalene), which migrate from underlying sediment into the cap with upwelling groundwater flow. Biodegradation of such constituents has been observed, but biodegradation rates and variables controlling those rates in sediments or sediment capping systems are not well understood. Such rate information, and understanding the conditions most favorable for biodegradation could improve the efficacy of sediment capping remedies. The goals of this EPRI-funded research were to investigate to what extent biological activity may be occurring in sediment caps, and in the longer term to integrate microbiological, geochemical, sorptive media, and other capping dynamics to enable design and installation of more sustainable and cost-effective capping remedies. Laboratory batch microcosm experiments investigated the potential for bioactivity in capping material. Microcosms were prepared with media (either granular activated carbon [GAC], organophilic clay, or sand), nutrients, and porewater/microbial communities enriched from MGP-impacted sediments. Concentrations of naphthalene and nahAc (a dioxygenase gene associated with transformation of PAHs) were monitored in microcosms for 100 days using high performance liquid chromatography (HPLC) and quantitative polymerase chain reaction (qPCR). Microcosms were studied under four different electron-accepting conditions and compared against slurry microcosms containing sediments. MGP-contaminated sediments were found to contain microorganisms capable of degrading naphthalene under oxic and nitrate-reducing conditions. Biodegradation rates were more rapid when GAC was utilized as the capping material, and indigenous sediment facilitated biodegradation more effectively than sand and organophilic clay. Experiments with naphthalene degradation in sulfate-reducing microcosms remain on-going.


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