translate English to French: Where agricultural sources of nitrate were likely, such as in tile drainage water and in wells located on farms, 5 to 25% of samples contained nitrate–nitrogen above the guideline for drinking water.
Par ailleurs, de vastes secteurs de tills argileux recouvrant des formations aquifères glaciaires et rocheuses ralentissent l’écoulement de l’eau et le processus de lessivage.