This project focused on protecting water quality and preventing sediment recontamination by developing and showing proof-of-concept for engineered media filters for treating stormwater runoff at Department of Defense (DoD) facilities. While traditional stormwater control measures (SCMs) generally remove suspended particles, traditional SCMs are often limited in their ability to remove dissolved chemicals, posing risks for re-contamination of sediment, transporting constituents of concern off-site, and exceeding receiving water quality standards. In this work, black carbon (BC) (i.e., biochar) and regenerated activated carbon, and zeolite amendments were evaluated in engineered stormwater media filters for the removal of dissolved metals and trace organic chemicals such as polychlorinated biphenyls, polycyclic aromatic hydrocarbons, per- and polyfluoroalkyl substances, and hydrophilic pesticides and corrosion inhibitors. Project objectives and tasks were designed to develop and build knowledge on design and performance tradeoffs for BC-amended engineered media filters for preventing sediment recontamination and benefiting water quality and possible beneficial use of stormwater runoff. Specific objectives of the project included:

1. Assessment of BC- and zeolitea-mended engineered media mixtures for removal of dissolved chemicals.
2. Development of performance curves with kinetic and flow rate design parameters.
3. Evaluation of engineered media filters under intermittent wetting/drying periods and saturation levels.
4. Modeling of long-term chemical removal performance of engineered media filters.
5. Development of a technical design manual for improved stormwater SCMs and recommended field demonstration testing for future studies.

Column experiments were conducted across various flow rates and flow conditions to assess tradeoffs in filter performance and design. To increase the relevancy of the laboratory experiments, catch basin material collected from a DoD facility was used to generate a representative synthetic stormwater. Long-term downflow gravity-driven column experiments were conducted to assess both the hydraulic and chemical-removal performance of various BC- and zeolite-amended engineered media mixtures. Predictive chemical transport modeling was used to discern the effects of media chemical removal kinetics, filter design, and site characteristics on chemical removal performance. Finally, long-term predictive chemical transport modeling was undertaken to investigate the expected lifetime of filter engineered media at a case study site.

The experimental results demonstrated that BC- and zeolite-amended engineered media filters successfully remove total suspended solids and a suite of dissolved metal and organic chemicals while maintaining adequate hydraulic conductivity. Filter design performance tables accounting for media- and chemical-specific removal summarized expected filter performance across a range of site and filter design parameters. Long-term modeling demonstrated that BC-amended engineered media filters may last decades, at which point the filter lifetime is expected to be governed by hydraulic performance and clogging.

The project targeted both hydrophilic and hydrophobic chemicals, which are important considerations in runoff at DoD sites, to benefit receiving water quality, prevent the recontamination of surrounding aquatic sediments, and facilitate possible reuse. A Technical Design Manual and the TEMPEST Filter Design Tool were created to assist regulators and practitioners to design, construct, and estimate the life span of BC-amended engineered media filters at DoD facilities and beyond to improve the treatment of stormwater runoff, reduce risks of sediment recontamination, and facilitate potential stormwater runoff beneficial use. (Project Completion - 2022)

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.