This project will focus on preventing sediment recontamination by design of improved best management practices (BMPs) for treating stormwater runoff. The project will evaluate the use of black carbon (BC), i.e., biochar and granular activated carbon (GAC), in biofilters for the removal of contaminants, such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), per- and polyfluoroalkyl substances (PFAS), and metals along additional media amendments, or design system amendments.

Examples of design system amendments to be examined in this project include vegetation, compost, and inlet and outlet controls to enhance effectiveness of the media. Project objectives and tasks are designed to build knowledge on potential performance and balance media sorption and hydraulic properties for BC-amended columns to prevent sediment recontamination. Specific objectives include:

1. Assessment of BC types for removal of contaminants from runoff;
2. Development of performance curves with kinetic and flow rate design parameters;
3. Evaluation of the transformation of organic contaminants in BC-amended biofilters;
4. Long-term performance modeling of BC-amended biofilters for breakthrough based on different design criteria; and
5. Development of a technical design manual for improved stormwater BMPs and recommended field demonstration testing for future studies.

Information from bench studies and modeling will improve our understanding of the fate and transport processes of these contaminants in a BC-amended biofilters and will be used to demonstrate their long-term effectiveness as a cost-effective treatment strategy to prevent sediment recontamination by runoff.

The hypothesis for this study is that BC-amended biofilters will be more effective than conventional biofilters in removal of stormwater contaminants at Department of Defense (DoD) facilities. In addition, it is hypothesized that biochar will be a cost-effective alternative to GAC. These hypotheses will be tested by determining the relationship between flow rate and contaminant removal, and optimizing system parameters via performance curves for optimal system kinetics. It is also hypothesized that vegetation and mulch or compost, will extend the life of BC-amended biofilters by inducing degradation. Contaminated soils/sediments collected from catch basins from various DoD facilities will be used in a constructed flume with a rain simulator to generate runoff for use in laboratory tests. Sediments will be selected and mixed to produce a representative sample contaminated with PCBs, PAHs, PFAS, and metals. The tests will determine how percolation rate, biofilter design, kinetics, vegetation, and microbial activity affect the extent of contaminant removal in BC-amended biofilters. This will be accompanied by modeling efforts to assess the feasibility and performance of BC-amended biofilters at DoD facilities. This will aid in understanding the planning, specifications, and design supporting a future field study that would demonstrate the effectiveness of the improved BMP under real-world conditions.

This work specifically targets PAHs, PCBs, PFAS, and metals, which are important contaminants in runoff at DoD sites, to prevent the recontamination of surrounding aquatic sediments and surface waters. Specifically, the goal of this project is to design a stormwater management strategy to remove contaminants from runoff. This project seeks to determine the types of BC amendments, inlet and outlet controls, and organic amendments (i.e., compost, mulch, and/or vegetation) most suitable for the contaminant removal in stormwater biofilters. The research team will develop performance curves that can optimize flow rates and removal so that DoD facilities can optimize removal based on their target contaminants of interest and climate regimes. The work on long-term performance modeling will aid users in determining when breakthrough occurs, which will be useful for operation and maintenance of the biofilters. Finally, a technical design manual for improved stormwater BMPs will be developed and be made available to all DoD facilities, which will be directly targeted to prevent sediment recontamination of these sites. (Anticipated Project Completion - 2023)

Pritchard, J.C., K.M. Hawkins, Y.M. Cho, S. Spahr, S.D. Struck, C.P. Higgins, and R.G. Luthy. 2022. Black Carbon Amended Engineered Media Filters for Improved Treatment of Stormwater Runoff. Environmental Science & Technology, 3(1):34-46. doi.org/10.1021/acsenvironau.2c00037.  

Spahr, S., M. Teixido, D.L. Sedlak, and R.G. Luthy. 2020. Hydrophilic Trace Organic Contaminants in Urban Stormwater: Occurrence, Toxicological Relevance, and the Need to Enhance Green Stormwater Infrastructure. Environmental Science: Water Research and Technology, 6(1):15-44. doi.org/10.1039/c9ew00674e.