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In November 2013, U.S. Geological Survey streamgaging equipment was installed at a historical water-quality station on the Duwamish River, Washington, within the tidal influence at river kilometer 16.7 (U.S. Geological Survey site 12113390; Duwamish River at Golf Course at Tukwila, WA). Publicly available, real-time continuous data includes river streamflow, stream velocity, and turbidity. Between November 2013 and March 2015, the U.S. Geological Survey collected representative samples of water, suspended sediment, or bed sediment from the streamgaging station during 28 periods of differing flow conditions. Samples were analyzed by Washington-State-accredited laboratories for a large suite of compounds, including metals, dioxins/furans, semivolatile compounds including polycyclic aromatic hydrocarbons, pesticides, butytins, polychlorinated biphenyl (PCB) Aroclors and the 209 PCB congeners, volatile organic compounds, hexavalent chromium, and total and dissolved organic carbon. Metals, PCB congeners, and dioxins/furans were frequently detected in unfiltered-water samples, and concentrations typically increased with increasing suspended-sediment concentrations. Chemical concentrations in suspendedsediment samples were variable between sampling periods. The highest concentrations of many chemicals in suspended sediment were measured during summer and early autumn storm periods. Median chemical concentrations in suspended-sediment samples were greater than median chemical concentrations in fine bed sediment (less than 62.5 μm) samples, which were greater than median chemical concentrations in paired bulk bed sediment (less than 2 mm) samples. Suspended-sediment concentration, sediment particle-size distribution, and general water-quality parameters were measured concurrent with the chemistry sampling. From this discrete data, combined with the continuous streamflow record, estimates of instantaneous sediment and chemical loads from the Green River to the Lower Duwamish Waterway were calculated. For most compounds, loads were higher during storms than during baseline conditions because of high streamflow and high chemical concentrations. The highest loads occurred during dam releases (periods when stored runoff from a prior storm is released from the Howard Hanson Dam into the upper Green River) because of the high river streamflow and high suspended-sediment concentration, even when chemical concentrations were lower than concentrations measured during storm events. Introduction The Lower Duwamish Waterway (LDW) is the final 8-km-long reach of the Green/Duwamish River. The LDW enters Puget Sound’s Elliott Bay in Seattle, Washington (fig. 1) and is the site of intense current and historical anthropogenic influence that has resulted in contaminated sediments. Land uses include numerous residential, industrial, and commercial activities such as manufacturing of airplane parts, boats, concrete, food processing, marinas, and roads. In 2001–02, the U.S. Environmental Protection Agency (EPA) and the Washington State Department of Ecology (Ecology) required remedial investigations and feasibility studies on the 1.8 km2 LDW under the Federal Superfund law and the Washington Model Toxics Control Act because of concerns about human health risks from exposure to contaminated sediments. The main contaminants of concern for human health include polychlorinated biphenyls (PCBs), dioxins/furans, carcinogenic polycyclic aromatic hydrocarbons (cPAHs), and arsenic. Additionally, about 47 compounds (including individual metals, polycyclic aromatic hydrocarbons [PAHs], phthalates, and other volatile and semivolatile organic compounds) have numeric criteria in the Ecology Sediment Management Standards for protection of the benthic community. Five locations with highly contaminated sediment were identified for early cleanup, and those cleanup activities are complete or near completion (with a target date of 2015). The EPA’s final cleanup plan for the remaining areas was released in November 2014 and includes using combinations of dredging, capping, natural sedimentation, and enhanced natural recovery. Chemical Concentrations and Instantaneous Loads, Green River to the Lower Duwamish Waterway near Seattle, Washington, 2013–15 By Kathleen E. Conn, Robert W. Black, Ann M. Vanderpool-Kimura, James R. Foreman, Norman T. Peterson, Craig A. Senter, and Stephen K. Sissel 2 Chemical Concentrations and Instantaneous Loads, Green River to Lower Duwamish Waterway, Washington, 2013–15 Figure 1. U.S. Geological Survey (USGS) sampling station relative to the Lower Duwamish Waterway, Seattle, Washington. Modified from Conn and Black (2014). watac13-0877_fig 01 Tukwila Lake Washington Elliott Bay Green River Black R iver Damish iver Seattle Damish iver 2013 NAIP (National Agricultural Imagery Program) 1 meter imagery, U.S. Department of Agriculture’s Farm Service Agency, Washington State Plane South, NAD83 12113390 8 0 16.7 18 Washington Figure location EXPLANATION USGS sample site Lower Duwamish Waterway 0 2 0.5 1 1.5 MILES 0 2 0.5 1 1.5 KILOMETERS Approximate river kilometer 18 122°15' 122°18' 122°21' |
