The Washington State Department of Ecology identified surface runoff as the most significant contributor of toxic chemicals to Puget Sound during earlier phases of the Puget Sound Toxics Loading Analysis. The objectives of the current study were to refine previous estimates of contaminant load contributions to Puget Sound via surface runoff by monitoring contaminant concentrations and discharge from four land uses: commercial/industrial, residential, agricultural, and forest/field/other. From 2009 to 2010, samples were collected from 16 streams in the Puyallup and Snohomish watersheds during two baseflow events and six storm events. Each stream received surface runoff primarily originating from one of the four land uses. Samples were analyzed for an extensive list of organic compounds, heavy metals, and conventional water quality parameters. The majority of the chemicals analyzed were detected more frequently and at higher concentrations during storm events than baseflow conditions among all land uses. Contaminant concentrations and area-normalized loading rates were generally higher in the commercial/industrial basins and lower in the forested basins than the other land-use categories for both flow conditions. The fall storm had the highest incidence of oil and grease, TPH lube oil, triclopyr, and other parameters.