The contamination effects of 2,6-dinitro-N,N-dipropyl-4-trifluoromethylanil (trifluralin) herbicide, widely used in sunflower farming were studied on the fields of Turgutbey irrigation project in Thrace region. Shallow irrigation water wells, drilled by farmers across the irrigation project covering approximately 320 ha fields, were evaluated in the study. Water samples collected from the irrigation wells at monthly intervals along the irrigation season, were analysed for trifluralin residuals. General evaluation of the results obtained during the years of the study showed, that residual concentrations determined in the well waters varied depending on location and time of sampling. It was found out also that the lowest and highest residual concentrations of trifluralin in water samples collected from the investigated wells, were 3.2 and 86.9 ppb, respectively. Higher residual concentrations in larger number of wells were available in the beginning of the season, and incidence as well as concentrations of herbicide residual decrease towards the autumn.