Evaluating the Water Quality Benefits of a Bioswale in Brunswick County, North Carolina (NC), USA

Abstract

Standard roadside vegetated swales often do not provide consistent pollutant removal. To increase infiltration and pollutant removal, bioswales are designed with an underlying soil media and an underdrain. However, there are little data on the ability of these stormwater control measures (SCMs) to reduce pollutant concentrations. A bioswale treating road runoff was monitored, with volume-proportional, composite stormwater runoff samples taken for the inlet, overflow, and underdrain outflow. Samples were tested for total suspended solids (TSS), total volatile suspended solids (VSS), enterococcus, E. coli, and turbidity. Underdrain flow was significantly cleaner than untreated road runoff for all monitored pollutants. As expected, the water quality of overflow was not significantly improved, since little to no interaction with soils occurred for this portion of the water balance. However, overflow bacteria concentrations were similar to those from the underdrain perhaps due to a first flush of bacteria which was treated by the soil media. For all sampling locations, enterococci concentrations were always higher than the USEPA geometric mean recommendation of 35 Most Probable Number (MPN)/100 mL, but there were events where the fecal coliform concentrations was below the USEPA's 200 MPN/100 mL limit. A reduction in TSS concentration was seen for both overflow and underdrain flow, and only the underdrain effluent concentrations were below the North Carolina's high quality water limit of 20 mg/L. Comparing results herein to standard swales, the bioswale has the potential to provide greater treatment and become a popular tool.There are many external factors impacting the fate of bacteria in a watershed including: a variety of sources (domestic pets, wild birds and animals, and human waste) [12] and various environmental factors (temperature, light intensity, and predation) [13][14][15][16], and treatment within stormwater control measures (SCMs). Removal mechanisms for bacteria include filtration, adsorption to a soil, desiccation, and predation [14]. Biofilm development may enhance adsorption to a soil [17,18]. However, bacteria can be difficult to permanently sequester, due to the potential to reproduce in a soil [13,19].Little research is available regarding whether bioretention media promotes bacterial sequestration or provides an environment for growth [20]; through growth and resuspension, media could act as a source of bacteria to stormwater runoff. While 'true' pathogens are the biggest concern, fecal indicator bacteria (FIB) are the regulatory metric used to monitor water quality and public health decision making [21][22][23][24]. Fecal indicator bacteria (FIB) include Escherichia coli (E. coli), enterococci, and total and fecal coliforms [16]. While not pathogenic, FIB are associated with fecal matter, thus signaling the potential presence of human pathogens [25]. In addition, FIB are usually found in higher numbers, have a higher survival rate, and are easier and more economical to detect in laboratory testi...

Decision-Support System for LID Footprint Planning and Urban Runoff Mitigation in the Lower Rio Grande Valley of South Texas

“…The structure is highly vegetated with grass throughout its length and sloped sides to improve the surface runoff and infiltration, which was also encountered in our modeled bioswale. Before infiltration, the structure also causes the runoff water to pool on the surface temporarily [61,62]. On the other hand, BR alone might induce a similar outlet peak discharge (0.046 m 3 /s) and runoff volume reduction (90-95%) to a wet pond, with much less land utilization (0.93 ha) than porous concrete pavement and wet pond in a 4-5 ha commercial development in Brownsville, TX.…”

Framework for the preservation of ephemeral natural channels through greenswales: Learnings from the case of Chandigarh

“…Therefore, the pollutants get accumulated on the catchment surface in the dry weather and, in the wet weather, the stormwater runoff carries pollutants to the streams, which harm the aquatic ecosystem, and affect the quality of drinking water supply (EPA, 2010b;Gavrić, Leonhardt, Marsalek, & Viklander, 2019). Green covers lter the surface runoff and reduce water pollution (Purvis et al, 2018). In urban catchments, stormwater gets directed to streets, gutters, and channels that convey the water rapidly downstream (Usda, 1986).…”

Evaluating the Hydrologic Benefits of a Bioswale in Brunswick County, North Carolina (NC), USA

“…The surface of the bioswale was a triangular in shape with 4:1 H:V side slopes ( Figure 3 and Table 2). Previously published research on the water quality performance of this bioswale includes a full description of the bioswale construction and additional profiles [47]. The total bioswale storage was 36.9 m 3 , with 22.7 m 3 of media porosity storage and 14.2 m 3 of surface storage.…”

“…While overflow composed over one-half of outflow for the overflow events and underdrain flow was appreciable for three events, this volume was noticeably lower than the cumulative rainfall and exfiltration. In total, 99% of inflow was filtered by the soil media, providing water quality treatment [47]. A statistically significant (α = 0.05) exfiltrated volume was reported only for the category containing all inflow events ( Table 5).…”