Abstracts

241 - Predicting the impact of surface sources on an aquifer: The
role of dispersion
Michael Frind 1 , Marcelo Sousa 1 , John Molson 2 , Emil Frind 1 & David Rudolph 1
1
University of Waterloo, Waterloo, Ontario, Canada
2
Université Laval, Québec City, Québec, Canada
Predicting the impact of contamination sources or BMPs (Beneficial Management
Practices) on aquifer systems in agricultural areas frequently involves three-dimensional
groundwater flow/transport modelling. Most transport models are based on the standard
advection-dispersion equation, with controlling parameters being one longitudinal
and two transverse dispersivities, horizontal and vertical. The longitudinal dispersivity is
generally chosen in relation to the aquifer length scale on the assumptions that dispersion
is related to travel distance and that flow is predominantly horizontal. This poses a
problem if the system includes a vadose zone where flow is predominantly vertical and
highly transient, and where aquifer-scale dispersivities would not be appropriate. Thus,
a dilemma can arise in the choice of the appropriate longitudinal dispersivity under the
standard dispersion formulation. A better way is to apply a new dispersion formulation
that is based on two longitudinal dispersivities, horizontal and vertical, in addition to two
transverse dispersivities, also horizontal and vertical. This approach was first proposed by
Lichtner et al. (2002) but has not seen much use since first publication. We show that for
multilayer systems, the alternative approach will give more realistic results compared to
the conventional approach with a single aquifer-scale longitudinal dispersivity, which can
under certain conditions lead to a significant underestimation of travel time. The practical
significance of this phenomenon in an agricultural context lies in the predictive accuracy
of BMP impact assessments for agricultural areas. It is therefore imperative in predictive
modelling to use an appropriate dispersion model with reasonable dispersivity values.
206 - Trends of nitrate concentrations in groundwater for variable
geological settings in agricultural watersheds
Nishant Mistry, Jana Levison & Beth Parker
School of Engineering – University of Guelph, Guelph, Ontario, Canada
Ralph C. Martin
Plant Agriculture – University of Guelph, Guelph, Ontario, Canada
Ramon Aravena
Earth and Environmental Sciences – University of Waterloo, Ontario, Canada
Shoaib Saleem, Elisha Persaud & Scott Gardener
School of Engineering – University of Guelph, Guelph, Ontario, Canada
Groundwater is the main source of drinking water for rural communities and many urban
cities surrounded by agricultural fields in Ontario. Intensification of agriculture in recent
years combined with climatic changes (including extreme weather events) pose threats to
groundwater quality. Over application of fertilizers can result in leaching of excess nutrients
below the root zone to aquifers. Therefore, a comprehensive understanding of evolving
cropping systems and their potential impacts on groundwater quality in various geological
IAH-CNC 2015 WATERLOO CONFERENCE
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