URBAN PARTICLE AND POLLUTANT CAPTURE VIA STORMWATER FILTER FACILITIES AND THE CONCOMITANT WATER QUALITY AND HYDROLOGICAL BENEFITS
Davis, Allen P
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Bioretention and sand filters are increasingly adopted as stormwater best management practices (BMPs) to remedy hydrology and water quality impairment from urban development. However, connection between BMP hydrological and water quality benefits and limits of BMP media (pollutant breakthrough, clogging, and long-term pollutant accumulation) are still unclear. This study investigated these issues through field hydrological and water quality monitoring, media core collection and analysis, and laboratory column tests. Results indicate that bioretention facilities can achieve substantial hydrological benefits through delaying / reducing peak flows and decreasing runoff volume. Bioretention effluents exhibited good water quality for nearly all monitored pollutants except for copper and phosphorus, the latter of which may be attributed to media organic matter dissolution. Bioretention effectively removed suspended solids, lead, and zinc from runoff. The runoff volume reduction promotes pollutant mass removal and links BMP water quality benefits with hydrological performance. However, effluent nutrients (phosphorus, nitrogen species) and Total Organic Carbon levels were slightly higher than those of the influent. Chloride was significantly exported. Laboratory column tests show that bioretention media is limited by clogging and particle breakthrough is not expected. Clay components in urban runoff play an important role in media clogging. A bioretention filtration model is developed, which describes the column test results and can be used to predict bioretention performance. The investigation concludes that urban particles cannot penetrate into bioretention media for more than 5 to 20 cm. Media analyses indicate that most captured metals affiliated with the trapped urban particles and the media collected within the top BMP layer. A small fraction of captured metals are soluble-exchangeable; the majority of the metal / media and metal / trapped urban particle affiliations are stronger. Substantial metal accumulation at the BMP surface was observed, suggesting maintenance needs. Captured phosphorous showed weaker media affiliations compared to those of the metals. Based on these discoveries, a shallow bioretention design is recommended, which can substantially reduce construction costs and increase the popularity of bioretention, resulting in more hydrological and water quality benefits.