Abstracts

and the groundwater system independent of precipitation events and water level changes
in the creek. These tests show that the water level in the storm sewer can be a dominant
influence on groundwater level rise and recession. When the storm sewers fill, flow into the
groundwater system occurs, which reverses when the storm sewer water level drops generating
baseflow to the creek through the storm sewer trench and storm sewer. It is argued
that under certain conditions, dependent on grading of the storm-sewer system and the
hydraulic conductivity of the soils, the storm sewer system may account for the majority of
groundwater-surface water interaction in urbanized watersheds.
240 - Enhanced Field Methodologies for Quantifying the
Vulnerability of Public Supply Wells to Surface Contamination
C.E. Hillier, D.L. Rudolph & A. Wiebe
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo,
Ontario, Canada
Groundwater vulnerability assessment is crucial to ensuring that a municipal drinking
water supply is safe for consumption. In evaluating the vulnerability of a public supply
well, assessment metrics often rely on generalized or assumed hydrogeologic parameters
combined with various modeling tools to categorize the vulnerability. This approach is
often associated with a significant level of uncertainty, which influences the confidence of
decision makers. This study examines the utility of detailed field site evaluation to enhance
well vulnerability assessment for public supply wells. The value of adopting an integrated
monitoring approach that incorporates hydrogeologic, hydrologic, and climatic data is addressed.
A 60-day pumping test was conducted on a public supply well located within the
Regional Municipality of Waterloo adjacent to a perennial stream. A network of groundwater
monitoring wells was installed and instrumented in the vicinity of the well. Hydraulic
head, temperature, geochemistry, isotopes, electrical conductivity, turbidity, and climatic
data were monitored during the pumping test. Several of the data sets will be presented to
illustrate their relevance to assessing the vulnerability of a supply well. Contrasting water
quality data collected from the deep and shallow environments provided insight into the
groundwater flow system. The dilution of calcium and hardness at the pumping well was
attributed to the shallow groundwater contributions, whereas increasing concentrations of
iron and sulfate indicated deeper groundwater contributions. Shallow groundwater temperature
data indicated the downward movement of warmer, near-surface waters during
the course of the pumping test. The temperature in the pumping well and nearby observation
wells decreased as a result of pumping indicating deep colder groundwater was being
drawn upward into the well over time. The combined geochemistry and temperature data
provide evidence of mixing between the shallow and deep groundwater systems, information
critical to understanding the vulnerability of public supply wells to surface contamination.
The evidence presented here demonstrates that data collected from detailed field
investigations during extended pumping tests provides added insight in the assessment of
well vulnerability. The length of the test required will rely on local conditions.
IAH-CNC 2015 WATERLOO CONFERENCE
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