The objective of this proof-of-concept project is to gain an understanding of processes influencing the effectiveness of particulate amendments for in situ treatment of contaminants in groundwater. Specifically, this project will assess: (i) the availability of sorbed contaminants to commercially available particulate/colloidal activated carbon (PlumeStop) for biodegradation; and (ii) the influence of bacterial adhesion to colloidal activated carbon (AC) on PlumeStop’s sorptive capacity for contaminants of concern. The combination of methodologies detailed in this project will provide an approach for scrutinizing claims regarding sorption/biodegradation of contaminants on particulate amendments for in situ treatment of groundwater.

This project will address contaminant bioavailability, biodegradability, and sorption concepts using model polycyclic aromatic hydrocarbons (phenanthrene) and per‐ and polyfluoroalkyl substances (PFAS) (perfluorooctanesulfonic acid [PFOS]), contaminant classes that drive the cost to complete at Department of Defense (DoD) sites. Carbon-14 (¹⁴C)‐phenanthrene will be used as a model compound to study biodegradation following sorption to AC while ¹⁴C‐PFOS will be used to determine the influence of AC‐bacterial adhesion on contaminant sorption due to its limited biodegradation potential. A continuous flow method utilizing flow cells (10 cm³) will be adopted to simulate contaminant transport and reactivity in model aquifers (loam‐sand) to which PlumeStop has been amended. ¹⁴C‐compounds will be introduced into PlumeStop amended model aquifers with effluent monitored for the determination of breakthrough and sorption capacity calculations. Bacterial influences (biodegradation of sorbed contaminants or decrease in contaminant sorption capacity resulting from bacteria adhesion) will be determined by introducing microorganisms into sterile PlumeStop amended aquifers pre‐ or post‐¹⁴C‐compound addition.

This approach, combining ¹⁴C‐compounds and flow cells, will provide a methodology for the continual monitoring of model aquifers providing high sample density and permitting a robust and rapid analytical approach for particulate amendment assessment. In addition, matrix‐AC‐bacterial interactions will be visualized using environmental scanning electron microscopy and/or time of flight secondary ion mass spectrometry to provide complementary data regarding the distribution of PlumeStop within the model aquifer and where/how bacteria are interacting with AC, aquifer matrix or contaminant of concern.

Particulate amendments are increasingly being used to mitigate contaminant‐groundwater impacts; however, a complete understanding of processes influencing their remediation efficacy is lacking. This lack of understanding (e.g., long‐term sorption capacity, contaminant re‐release) may result in unfavorable remediation outcomes, and negative economic, environmental and human health impacts. This project will deliver fundamental understanding of the influence of contaminant‐AC sorption on biodegradation and the impact of bacterial AC‐adhesion on contaminant sorption. Understanding factors influencing biodegradation and sorption will provide critical information regarding factors influencing the attenuation efficacy of particulate amendments. The results of this project will provide a robust, scientifically defensible strategy for elucidating these impacts and for future assessment of environmental/biological parameters that may impact particulate amendment remediation efficacy. (Anticipated Project Completion - 2022)