Publication Summary

Two surveys of the Lower Duwamish Waterway sediment cleanup site were conducted in 2006 to see if SPI results could predict regulatory indicators of sediment quality. Based on this limited study, SPI parameters did not appear to predict sediment quality as defined by numeric sediment quality standards and cleanup screening levels. However, different benthic infaunal communities were identified, and SPI results helped to distinguish between them.

Recommendations were to (1) arrange for more analysis and review of findings, (2) conduct more studies at other cleanup sites, and (3) use SPI more often in early cleanup site investigations, and (4) incorporate latest scientific knowledge about how to assess the health of benthic communities into such investigations.

During 2006, the Washington State Department of Ecology conducted exploratory studies to determine if preliminary Sediment Profile Imaging (SPI) survey results might predict traditional sediment quality indicators and thereby reduce the need for detailed investigations at cleanup sites. One of the sites chosen for these studies was the Lower Duwamish Waterway Superfund site (Seattle).

Surface sediment samples were collected at 30 of the 87 locations in the Lower Duwamish Waterway where SPI photographs had previously been taken. Sediment conventionals, contaminant chemistry, and toxicity were measured, along with characteristics of the in situ benthic community.

SPI survey results distinguished areas of fine sands and silts from sandier sediments and provided evidence that the study site generally had aerobic benthic habitats with relatively complex infaunal communities. Results for sediment conventionals and chemistry supplemented existing data while showing similar distributional patterns. Significant toxicity, measured using two standard test protocols, was found at only four sampling locations.

SPI results had limited ability to predict levels of contaminant chemistry or biological effects that failed regulatory criteria. However, analysis of benthic infaunal results did reveal distinct communities and, more importantly, SPI and sediment quality indicators were capable of distinguishing between them. If regulators determined that one or more of the communities was unacceptably altered or impaired, then future SPI surveys could cost-effectively screen for their spatial distribution and likely cause.

This study, together with other published findings, provides several good reasons to recommend that SPI be used more frequently in cleanup site investigations. The SPI and sediment quality results help fill data gaps and characterize baseline conditions prior to remedial actions and effectiveness monitoring. SPI results can also augment studies of sediment fate and transport, identify areas of severe impact (anoxia, azoic sediments), predict sediment conventional parameters, and provide additional lines of evidence for evaluating benthic community health.

Link to EIM data for User Study ID SPILDW06