Arsenic (As) concentrations in the waters of Raccoon Creek in southern New Jersey commonly exceed the State's Surface Water Quality Standard (SWQS) for freshwater of 0.017 microgram per liter (μg/L). In order to assess contribu-tions of As from residential runoff to the creek, samples of runoff water were collected from a detention basin in each of two residential developments underlain by different geologic formations and at the outlets of those basins. Samples of streamwater also were collected from Raccoon Creek adjacent to the developments. The samples were analyzed to determine concentrations of As, selected metals, organic carbon, and nutrients. Soil samples in and downgradient from the basins also were collected and analyzed.