Assessing the risk of groundwater nitrate contamination in the region of waterloo, ontario

Abstract

In many areas of Ontario concentrations of nitrate in groundwater at levels above the Ontario drinking water limit of 10 mgL-1 constitute a serious threat to municipal drinking water supplies. In the Region of Waterloo permeable soils and high nitrogen application rates on farmland combine to produce high risk zones in a significant portion of the rural landscape. This study assesses the potential risk of agricultural land use on nitrate contamination in four well fields located west of the cityof Waterloo. Secondary data from government documents and consultants’ reports were used to develop GIS layers for soil drainage and nitrogen application rates by land use system. These layers were combined to produce a measure of risk of nitrate groundwater contamination associated with the combined effect of both factors. Results indicate that approximately 45% of the study areais at high risk. Two well fields, one of which was closed becausenitrate levels exceeded the Ontario drinking water limit, have nearly 60% of their recharge areas in the high risk category. If this situation is to be improved, programs directed towards changing current nutrient management practices must be instituted. © 1999 Taylor & Francis Group, LLC.