Publication Summary

To evaluate the effectiveness of source control efforts in reducing the input of problem chemicals to Sitcum Waterway, samples of settling particulate matter (SPM) and in-place bottom sediments were collected between July 1990 and June 1991. All SPM samples were collected with the use of moored sediment traps. Chemical analyses focused on arsenic, copper, lead, zinc, polynuclear aromatic hydrocarbons (PAH), and dibenzofuran which were identified as problem chemicals in the waterway during the Commencement Bay Nearshore/Tideflats (CBNT) Remedial Investigation (Tetra Tech, 1985).

To evaluate the effectiveness of source control efforts in reducing the input of problem chemicals to Sitcum Waterway, samples of settling particulate matter (SPM) and in-place bottom sediments were collected between July 1990 and June 1991. All SPM samples were collected with the use of moored sediment traps. Chemical analyses focused on arsenic, copper, lead, zinc, polynuclear aromatic hydrocarbons (PAH), and dibenzofuran which were identified as problem chemicals in the waterway during the Commencement Bay Nearshore/Tideflats (CBNT) Remedial Investigation (Tetra Tech, 1985).

The spatial distribution of contaminants in this study indicates that the major sources of problem chemicals to Sitcum Waterway are Terminal 7, in the vicinity of Berth B, and the North Corner Drain. The highest concentrations of problem metals (arsenic, copper, lead, and zinc) and organics (PAHs, and dibenzofuran) associated with SPM were measured at these two locations. This finding agrees with previous investigations in the waterway. In addition, concentrations (averaged over the study period) of zinc, and high molecular weight PAHs (HPAH) near the North Corner Drain, low molecular weight PAHs (LPAH) and dibenzofuran along Terminal 7, Berth B exceeded cleanup objectives for the CBNT and/or Ecology's Sediment Management Standards. These sediments could therefore be expected to adversely affect marine benthic communities.

In most instances, little difference is evident between present (SPM) and historical (bottom sediment) concentrations of problem metals and organics in Sitcum Waterway. Noteworthy exceptions are lead and zinc levels at Terminal 7, Berth B, which appear to be decreasing over time. Decreases in lead and zinc concentrations near Terminal 7 are probably the result of source control actions taken by Ecology, which resulted in the cessation of black ore (i.e., lead and zinc) handling at Terminal 7, as of July 1991. Arsenic and zinc at the head, and zinc at the mouth of the waterway are the only metals which showed any indications of increasing levels. The observed trends in Sitcum Waterway contaminant levels should be viewed with caution, since they are based on a limited amount of data and a portion of the SPM collected by the sediment traps is probably resuspended bottom sediments.

Sedimentation rates for Sitcum Waterway calculated from sediment trap data ranged from 2.1-5.7 g/cm2/yr with a mean of 3.5 g/cm2/yr. Estimated resuspension rates for bottom sediments ranged from 2.2 to 2.9 g/cm2/yr. Current velocities are generally low in the waterway even during periods of high tidal exchange. Velocities £4 cm/sec occur approximately 90% of the time at head and 50% of the time at the mouth. However, ship traffic and associated tugboat activity could have a substantial short-term impact on currents in a localized area. Vertical profiles of temperature, salinity, and light transmittance indicate that a fairly thick (approximately 5 ft.) layer of turbid freshwater, most likely from the Puyallup River, is present to some extent throughout the year in Sitcum Waterway.