Control of Highway Stormwater During Event and Interevent Retention in Best Management Practices

Volumetric clarification-type best management practices that provide storage through detention-retention are more frequently incorporating adsorptive filters. This study examines the hydraulic and chemical response of a volumetric clarifying filter (VCF) system to 1,088 m(2) concrete-paved watershed loadings in Baton Rouge, Louisiana, for fully captured events. VCF deployment incorporates aluminum oxide-coated media for phosphorus adsorption after it was demonstrated that common media (perlite and sand) were ineffective for adsorption. While event mean head loss is less than 25 mm, instantaneous values are flow dependent, as are filter surface loading rates. Filter ripening head loss is small but evident for the cumulative volume treated for 19 events. During interevent retention, oxidation-reduction drops to anoxic levels after 48 h, continuing a gradual decrease with interevent time. During storage, nitrate decreased (denitrification) and ammonia nitrogen increased (with an increase in NH3), and phosphorus partitioning remained stable. Results indicate that while interevent runoff retention is a common practice, the coupled hydrochemical behavior and fate of runoff chemicals subject to storage must be integrated into such unit operations. Results indicate that best management practices require more frequent maintenance and sludge removal.