In 1990, a two year study was undertaken to determine the effects of water table management on the movement of the herbicide prometryn in an organic soil in southern Qu#xE9;bec. Three water table management systems were used: controlled drainage, subsurface irrigation, and subsurface drainage. Results indicate that most of the prometryn movement through soil and into groundwater occurred during the first few months following application. In the subsurface drainage field, the concentrations of herbicide in groundwater were mostly higher than the drinking water quality standard of 10#x2002;#x3BC;g/L. When subirrigation or controlled drainage was used, the concentration fell significantly below this level, indicating their usefulness in reducing the amount of prometryn reaching the groundwater. The study also demonstrated that, in an organic soil, pesticide movement was affected mainly by the water balance. The negative water balance during dry periods caused the soil water and pesticide to move upwards. This phenomenon was enhanced when the water table was close to the soil surface and the contaminant was positioned higher in the soil profile, which improved the opportunity for degradation of the chemical before it reached the drains. On the other hand, during high rainfall events and periods of positive water balance, the contaminant was readily leached through the soil profile.
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