bacterial removal efficiency of a bioswale located in lockwood fo
DESCRIPTION
for swale researchTRANSCRIPT
Acknowledgments: Lucas Lyerly, Michael Cline, Steve Carr, & Megan Miller (Coastal Carolina University, Conway SC) North Carolina Department of TransportaEon (NCDOT)
Jeffrey D. Barley & Dr. Susan Libes (Coastal Carolina University, Conway SC) Ryan Winston, Bill Hunt, & Shawn Kennedy (North Carolina State University, Raleigh NC)
Bacteria Removal Efficiency of a Bioswale located in Lockwood Folly, a Coastal Watershed in North Carolina.
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1SW 2UD 3OF
MPN
/100mL
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Enterococci faecalis
Abstract: Sites & Methods:
Results:
NC Department of TransportaEon (NCDOT) has obtained, through partnerships with private sector, an engineered soil to enhance removal of fecal bacteria when used in conjuncEon with stormwater Best Management PracEces, such as bio-‐retenEon cells. The efficacy of this media is being tested at a site in Lockwood Folly, NC where a TMDL for fecal coliforms was approved by the NC Department of Natural Resources in 2010 to address shellfish harvesEng impairments in the nearby estuary. Mechanisms for bacterial removal are a\ributed to: (1) retenEon of parEcles to which microbes adsorb and (2) mortality due to grazing by protozoans harbored by the soils. Funding is being provided by NC DOT as part of a program to evaluate pollutant removal efficiencies of various BMPs for road runoff treatment. NCDOT’s NPDES permit requires the retrofit of 50 stormwater BMPs in each 5 year cycle; they opEmize their retrofits through results of research. The results of this assessment work are of much interest to South Carolina due to the large number of monitoring sites with fecal bacteria impairments that are located in seangs similar to the Lockwood Folly watershed, the relaEvely low cost of the media, and the opEon of retrofiang exisEng BMP’s to enhance bacteria removal.
The test site at Lockwood Folly was constructed in 2012 by installing a 200-‐c linear strip of media, 3-‐c deep in a pre-‐exisEng stormwater swale that runs parallel to a secondary state road (NC 211) maintained by NCDOT. The removal efficiency of this bioswale is being evaluated by measuring bacteria transport into and out of the media during storm events. For each event, flow-‐weighted samples are being collected at the inlet and outlet of the bioswale using ISCO auto-‐samplers oufi\ed with water level sensors. The samples are being analyzed for two fecal indicator bacteria (Enterococcus and Fecal coliform), for turbidity, total & volaEle suspended solids, and conducEvity. Sample collecEon and processing is being performed by Coastal Carolina University’s Environmental Quality Laboratory.
Discussion: The data collected to date have shown that the bio-‐media has been reducing the concentraEons of each parameter measured with the excepEon of ConducEvity. Enterococcus faecalis has had an average reducEon of about 3,000 Most Probable Number per 100 mL (MPN/100mL). Fecal coliform has had an average reducEon of about 1,000 MPN/100mL. TSS has been reduced by about 30 mg/L, VSS by about 10 mg/L and turbidity by about 10 NTU. ConducEvity, however, has shown a slight increase, averaging about 5 µS/cm. As indicated by a large event sampled on 7/4/14 (Hurricane Arthur: Event 4), high flow rates may reduce or even reverse the effecEveness of the media. During this even, the flow through the media was high and the Enterococcus faecalis values were slightly increased acer passage through the media. A total of 18 events will be sampled over the next year. Discharge is being measured and will be used to infer loadings and removal efficiencies of the bacteria and turbidity.
Overall, to this point, the bio-‐media has been performing the way it was designed. Bacteria levels and suspended solids have been reduced during the past five sampling events. Flow rates will also be reviewed in the future to determine the media’s performance during different types and strength of storm events and strength of runoff. If the bio-‐media conEnues to perform as designed in Lockwood Folly it could become a desirable filtering method to reduce bacteria, nutrients, and suspended solids from storm water runoff out through the country.
Summary:
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Turbidity
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1SW 2UD 3OF
MPN
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Fecal coliform
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1SW 2UD 3OF
µS/cm
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Conduc@vity
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1SW 2UD 3OF
mg/L
site
Total Suspended Solids
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Vola@le Suspended Solids
The Media: The Department of Biological and Agricultural Engineering at NC State University has developed a “bouEque” media that can be made locally from easily accessible and low-‐cost materials. This media, combined with the local vegetated landscape, is designed to naturally reduce and/or remove fecal bacteria and parEculate materials from stormwater runoff.
The upstream sampling site (1SW) collects stormwater runoff before it is treated by the bio-‐media. This site is configured to pool the runoff allowing the auto-‐sampler to collect water before it moves into the media.
The Overflow (3OF) sampling site is designed to collect any water runoff that flows over and/or around the media. CollecEon is based on a volumetric discharge threshold.
The Underdrain (2UD) sampling site is located downstream of the bio-‐media. CollecEon is based on a volumetric discharge threshold. The sampling site is covered to reduce contaminaEon from direct rain or sheet flow running over the media.
0.71
1.34
0.74
2.73
1.58
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Event 1 (4/16/14) Event 2 (6/21/14) Event 3 (6/24/14) Event 4 (7/4/14) Event 5 (7/25/14)
Inches
MPN
/100mL
Sampling event
Fecal coliform Swale Under Drain Over Flow Rain Fall (inches)
0.71
1.34
0.74
2.73
1.58
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1.5
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2.5
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0.0 5.0
10.0 15.0 20.0 25.0 30.0 35.0
Event 1 (4/16/14) Event 2 (6/21/14) Event 3 (6/24/14) Event 4 (7/4/14) Event 5 (7/25/14)
Inches
NTU
Sampling event
Turbidity Swale Under Drain Over Flow Rain Fall (inches)
0.71
1.34
0.74
2.73
1.58
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0.5
1
1.5
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2.5
3
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Event 1 (4/16/14) Event 2 (6/21/14) Event 3 (6/24/14) Event 4 (7/4/14) Event 5 (7/25/14)
Inches
MPN
/100mL
Sampling event
Enterococcus faecalis Swale Under Drain Over Flow Rain Fall (inches)