Fig. 3. Tile drainage and herbicide concentration in the drainage from May 1992 to April 1995 with either drainage (D) or controlled drainage–subirrigation (CDS). Arrows denote time of herbicide application. Vertical bars are standard error of treatment means (n = 8). Dashed lines are Canadian interim maximum acceptable concentration (triazine = 5 µg L^-1 and metolachlor = 50 µg L^-1)