Abstract
Non-point source pollution of stormwater contributes high contaminant loads into surface water bodies and poses a threat to the ecosystem, public health and economy. Although (pre)treatment standards have not been introduced at the federal level, Rhode Island (RI) has set minimal contaminant reduction standards for stormwater using structural best management practices (BMP). As BMP performance depends highly on geographical location and climate, and the Northeastern United States experiences broad ranges of temperatures throughout the year along with long intermittent periods between precipitation events, stormwater treatment can be challenging. In this field study, two tree filters were evaluated: a conventional unit (CTF) with sand/shale mix as filter media, and a modified tree filter (ITF) with an added layer of red cedar wood chips amended with 3-(trihydroxysilyl)propyldimethyloctadecyl ammonium chloride. Both BMPs were monitored for 346 days primarily for Escherichia coli and polycyclic aromatic hydrocarbons (PAH). Both tree filters met or outperformed RI’s standards for bacteria removal (60%) and TSS (85%), making them a good choice for BMP use in this climate. Total suspended solids, E. coli, PAHs, nitrate, and phosphate removal is higher in ITF. A controlled field scale tracer test using E. coli confirmed these results.
Highlights
Areas with shallow water tables are vulnerable to stormwater and agricultural runoff contamination, as high contaminant loads are introduced from untreated surface water runoff during storm events, resulting in water quality issues, beach closings, and impairing the economic activities of communities [1,2,3,4,5,6]
One conventional with a sand/shale and peat mix and one innovative filter matrix, containing an additional layer consisting of antimicrobially amended red cedar wood chips were compared for their contaminant removal capabilities in a field pilot study
Over the course of a one year period starting in November 2013, tree filter (TF) influent and effluent was sampled for organic and inorganic constituents, including E. coli
Summary
Areas with shallow water tables are vulnerable to stormwater and agricultural runoff contamination, as high contaminant loads are introduced from untreated surface water runoff during storm events, resulting in water quality issues, beach closings, and impairing the economic activities of (coastal) communities [1,2,3,4,5,6]. A popular type of BMPs is a stormwater retention system While these BMPs may treat total suspended solids (TSS) effectively [11,12], few systems exist that address bacterial removal. Two of such systems are BactoLoxx (Filtrexx, Goffstown, NH), and Bacterra (Filterra Bioretention Designs, Ashland, VA, USA). Recent studies on bacteria removal in a wide range of structural BMPs concluded that bacteria treatment was ineffective and unreliable, as the removal of pathogens primarily relied on attachment/collection and not inactivation [13,14]. This is because sorbed pathogens can remain viable during attachment [15,16,17]
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