GROUNDWATER CONTAMINATION BY NITRATES ASSOCIATED WITH INTENSIVE POTATO CULTURE IN QUEBEC

In rural areas, groundwater contamination by nitrates is a problem rel ated to the spreading of organic and chemical fertilizers by farmers a nd, to some extent, to effluents from domestic sewage systems. Health effects of groundwater contamination by nitrates have been assessed se veral times and may lead to important consequences for infants. Follow ing pressures from citizens in 1990, a survey of well water quality ar ound potato fields of the Portneuf county (Quebec) found that nitrate contamination was frequently above the 10 mg-N/l standard. Because thi s first survey was limited to areas of intensive potato culture, it wa s not possible to evaluate the real impact on the groundwater quality for the whole county and the subsequent public health intervention was spread over the entire region. A second survey was carried out in 199 5 to reevaluate the situation using random sampling methods. This latt er study took into account drinking water habits of the population, th e relative importance of potato culture as a source of nitrogen loadin g, the effects of soil types, and waste-water disposal systems as well as land use on nitrate concentration in private well water. The data analysis was carried out by combining GIS and statistical methods to t est hypotheses about the spatial relationship linking measured nitrate concentrations with their immediate environment. This paper presents the major findings from this second study which confirm the impact of intensive potato culture on groundwater nitrate concentrations, mainly localized in sandy soil areas within 2 km of fields. Finally, it illu strates the usefulness of GIS to focus public health interventions. (C ) 1998 Elsevier Science B.V. All rights reserved.