Madison, Wisconsin: University of Wisconsin Water Resources Institute
A sediment mixing approach was taken to systematically vary the organic carbon (oc) and clay content (cm) as a suite of organic-poor, clay-rich sediments. Organic carbon content ranged from 3.2 to 0.4% and clay content ranged from 24 to 51%. Atrazine and alachlor were shown to sorb to both naturalorganic carbon and clay minerals. Partition coefficients to natural organic carbon (Koc) were found to be 196 and 436 liters/kg organic carbon for atrazine and alachlor, respectively. Partition coefficients to the clay fraction were found to be 1.8 and 3.0 liters/kg clay for atrazine and alachlor, respectively. Retardation factors calculated using partition coefficients that ignore numerical phase sorption are low by factors of 2.6 to 2.8 in the subsoils used in this study.