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Placement of Vegetated Filter Strips (VFS) along roadways may facilitate removal of nutrients from stormwater runoff. The objective of this research is to compare water quality performance of a VFS containing engineered media to that of typical Florida sandy soil. Storms of variable intensity were simulated over two 1:1 scale physical models of typical one- and two-lane roadway shoulders, one with engineered media (treatment), and one without (control). Simulated roadway runoff was introduced as sheet flow from the roadway and precipitation was applied with a rainfall simulator. Samples of runoff and infiltrate were tested for Dissolved Oxygen (DO) concentration and pH at regular intervals along each model and analyzed to detect changes both in time and location. Within four hours of the experiment start, pH decreased on average by 0.74 ± 0.21 in the treatment model, and less so (by 0.39 ± 0.16) in the control model (p<0.0001). pH continued to decrease with time in both models, though more significantly in the treatment model. The DO saturation decreased in the treatment model by a mean 12.18 ± 18.54% and increased in the control model by a mean 6.74 ± 13.21% over 4 hours (p<0.001). However, DO monitoring over 72 hours indicated minimum DO concentrations of 5.83 ± 1.28 mg/L and 7.84 ± 0.92 mg/L in treatment and control models, respectively, suggesting that pore water was not oxygen limited. This analysis provides a deeper understanding of how nutrient removal processes may have varied within each media type. [ABSTRACT FROM AUTHOR]

As a new strategy for treating excess nutrients in roadway runoff, a self-filtering roadway could be accomplished by including engineered infiltration media within a vegetated filter strip (VFS) located in the roadway shoulder. However, nutrient removal performance will depend on the design to effectively infiltrate roadway runoff and the capacity of subsurface media to sequester or remove nutrients from infiltrated runoff. The objective of this study is to test hydraulic and nutrient removal performance of a roadside VFS over varied rainfall-runoff event sizes and filter widths. Two identical 1:1 scale physical models of roadway shoulders and embankments, one containing engineered media (Treatment model) and the other without (Control model), were tested with simulated rainfall and runoff from 1- and 2-lane roadways. Overall, 32 paired hydraulic experiments and 28 paired nutrient removal experiments were completed to assess performance across frequent and extreme rainfall-runoff events. The results indicate that scalability of performance with filter width varied by parameter. Runoff generation scaled predictably with filter width, as runoff generated close to the pavement and total infiltration increased with filter length. A 6 m-wide VFS containing the engineered media infiltrated all rainfall-runoff except during the most extreme storm events (1-h storms of 76.2 mm and 50.8 mm), where respectively 35% and 22% of rainfall-runoff did not infiltrate and left the system as surface runoff. A majority of phosphorus was retained within a 1.5 m filter while nitrate removal was not observed until 6 m. The Treatment model strongly outperformed the Control model with respect to nitrate (arithmetic mean ± standard deviation of 94 ± 6% reduction vs. 23 ± 64% increase, p <.001) and total nitrogen removal (80 ± 5% vs. 38 ± 23% reduction, p <.001) due to higher rates of microbially-mediated denitrification in the Treatment model. The two models performed comparably with regard to phosphorus reduction (84 ± 9% vs. 82 ± 12% reduction). A minimum 6 m filter width is recommended to ensure sufficient infiltration of runoff and nitrogen removal. Results of this study address uncertainty regarding nutrient removal performance of VFS in urban runoff applications and highlight a potential strategy for standardizing VFS performance across varied soil properties by including engineered media within the filter. [Display omitted] • Engineered media can be used within a road shoulder VFS to treat urban runoff. • A VFS with engineered media removed more nitrate and total nitrogen than sandy soil. • Denitrification rates were greater in engineered media than in sandy soil. • Greatest nitrogen removal was observed with a 6 m filter width. • Infiltration rate through engineered media was adequate for roadway drainage. [ABSTRACT FROM AUTHOR]