Abstracts

the environment and (in the few studies available) concentrations observed in transition
zones were often higher than fresh water quality criteria for the protection of aquatic life.
Approximately 40 science needs and data gaps were identified, which indicates overall
impacts of contaminated groundwater discharges cannot be precisely determined at this
time. Priorities for future work to help support science-based decision making include: 1)
developing rapid inexpensive site characterization tools that can identify contaminated
groundwater discharges and collect data on the scale needed to accurately predict ecological
and human exposures, 2) determining the ecological value and connectivity of the
transition zone to the overall aquatic ecosystem and its sensitivity to contamination for
use in cost benefit analyses, and 3) integrating contaminant hydrogeology, ecological, and
ecotoxicological studies from the beginning of investigations to ensure critical relationships
and problems are identified.
158 - Factors influencing the accumulation and transport of E.
coli near the shoreline at freshwater beaches
Ming Zhi Wu, Denis M. O’Carroll, Laura J. Vogel, & Clare E. Robinson
Department of Civil and Environmental Engineering, Western University, London,
Ontario, Canada
Greater understanding of the fate and transport of microbial pollutants at the sediment-water
interface of lakes is required to inform beach water quality policy and management programs.
Studies have indicated that foreshore sands at beaches can act as a reservoir of fecal
indicator bacteria (FIB) such as Escherichia coli (E. coli) and subsequently be an important
non-point source of FIB to lake water (e.g. Beversdorf et al., 2007; Ge et al., 2010). This
can result in a beach being posted with a water quality advisory. While prior research has
focused on the mechanisms by which FIB is released to surface water (e.g. Halliday et al.,
2014; Phillips et al., 2014), factors controlling the accumulation of E. coli (and also other
bacteria and colloids) in the foreshore sand is not well understood.
This study focuses on developing a mechanistic understanding of the role of groundwater-lake
interactions (i.e., low-energy lapping waves) in the accumulation and transport of
E. coli in the saturated foreshore sand reservoir of freshwater beaches. Numerical modelling
was conducted utilising the finite element solver COMSOL, and incorporated
groundwater transport, attachment of the bacteria to sand grains (using colloid filtration
theory (Yao et al., 1971)), and microbial die-off. The influence of bacterial, beach and wave
parameters (e.g. beach slope, inland groundwater flow, wave height, bacterial attachment
efficiency) on E. coli deposition is assessed. Sensitivity analyses were conducted under both
steady-state and varying wave conditions. The findings from this study are important in
understanding the impact of groundwater and surface water interactions in the transport
of bacteria, using E. coli as an example, at the sediment-water interface of freshwater lakes.
106 IAH-CNC 2015 WATERLOO CONFERENCE