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Assessment of the Viability of a Natural Urban Wetland in the Treatment of Stormwater

Stormwater runoff generated from urban areas can be a source of contamination and may
negatively impact receiving waters. Best management practices, including the use of treatment
wetlands, are recommended to minimize impacts and maintain the quality of water bodies
receiving stormwater discharge. This study focuses on the viability of a natural wetland in the
treatment of urban runoff. Kuhn Marsh is a natural urban wetland located in Dartmouth, NS. The
wetland is approximately 2 ha in size and the primary inlet is a stormwater outfall servicing a 28
ha urban drainage area. Kuhn Marsh has been receiving stormwater generated from the urban
drainage area for decades. A wetland drainage area of approximately 9 ha contributes to surface
runoff downstream of the wetland inlet. Project objectives are defined as: (i) characterization of
the hydrology and hydraulics of the wetland system, (ii) characterization of contaminant fluxes
within the wetland system, and (iii) analysis of the treatment performance of Kuhn Marsh.
Research strategies used to achieve project objectives include physical and hydrologic
characterization of the wetland and contributing watersheds as well as surface and ground water
quality analysis. Monitoring was conducted in the wetland during both baseflow and stormflow
conditions from May 2011 through October 2012, with the exception of November 2011 to
January 2012. Surface water samples were analyzed in the laboratory for TSS, TOC, TN, TP,
turbidity, E.coli, and a suite of heavy metals including Fe, Pb, Cu, Cd and Zn. In-situ surface
water monitoring included DO, temperature, conductivity and pH. Groundwater samples were
analyzed for E.coli and microbial source tracking was performed on all well samples in addition
to samples from the inlet and outlet of the wetland. Results from the well samples and the
wetland outlet were inconclusive, however the wetland inlet showed human source bacteria
indicating potential sewer cross connections within the stormwater system. It was determined
that the wetland is an area of groundwater discharge, with groundwater accounting for an
average of 50% of the volume discharging through the outlet control structure. Largely due to
groundwater influence, Kuhn Marsh shows no peak flow dampening or volume reduction
between inlet and outlet. Minimal hydraulic retention times, between 2 and 4 hours, were
calculated during stormflow conditions, indicating potential short circuiting of flows through the
wetland. Wetland treatment performance was analyzed on a concentration and mass reduction
basis and on the number samples that exceeded parameter guidelines at the outlet of the wetland.
Guideline exceedances were reported for the majority of samples taken and increases in
concentration between inlet and outlet resulted in a larger number of samples exceeding
guidelines at the outlet. Despite dilution from groundwater discharge, minimal to no
concentration reduction was reported between the inlet and outlet of the wetland. Mass reduction
did not occur between the inlet and outlet and Kuhn Marsh was found to be a source of all
contaminants sampled. Results of this study show that Kuhn Marsh is no longer acting as a
reservoir for stormwater contaminants and, based on the fact that the wetland has been receiving
stormwater input on the order of decades, study results may be indicative of the long-term
treatment capacity of a stormwater treatment wetland. In the future, comprehensive sampling of
groundwater is recommended to determine if contaminants are entering the wetland via
groundwater discharge, and if possible, surface water sampling should be conducted on a finer
scale to better estimate mass fluxes and contaminant loading rates.
Date19 July 2013
CreatorsMcGuigan, Janeen
Source SetsLibrary and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada
Detected LanguageEnglish

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