Abstract: “Seydisuyu Basin, which is located in the Eskişehir province of Turkey, contains very important agricultural lands. In this paper, the total organochlorine pesticide levels in groundwater of Seydisuyu Basin were investigated by determining Alfa HCH, HCB, Beta HCH, Gama HCH, Aldrin, Cis Heptaclorepoxide, Trans chlordane, Cis chlordane, Dieldrin, 44DDE, Endrin, 44DDD, 44 DDT, Metoxyclor and pesticides with Endosulfan in water samples. Groundwater samples were collected seasonally (2011 – 2012) from 29 wells from the Seydisuyu Basin. According to data observed, although groundwater of the Basin has I. - II. Class water quality in terms of total pesticide concentrations in general, organochlorine pesticide accumulations of some wells were higher than the drinking water limits specified by Turkish Standards Institute (TS266).”

Keywords: Seydisuyu Basin, Organochlorine Pesticides, Drinking Water