Publication Summary

Two surveys of the wood waste cleanup site in Port Gamble Bay were conducted in August 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, SPI mapped an area of wood waste very similar to one having high % fine-grained sediment and total organic carbon, as well as one occupied by a distinct benthic community.

Recommendations were to conduct (1) more analysis and review of findings, (2) more studies at other cleanup sites, and (3) SPI more often in early cleanup site 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.

Two sites were chosen for these studies: the Lower Duwamish Waterway Superfund site (Seattle) and an area in Port Gamble Bay (Port Gamble) near an historical timber mill and associated log rafting areas. Grab samples were collected for evaluation of sediment quality at 23 of the 32 locations where SPI and other photographs were taken of surface sediments. Samples were analyzed for conventional sediment parameters and characteristics of the in situ benthic community. These were then compared to SPI results.

SPI survey results distinguished areas containing wood waste, combined with fine sands and silts, from sandier sediments lacking substantial amounts of wood. SPI results also provided evidence that the study site generally had an aerobic benthic habitat, and relatively complex infaunal communities.

Patterns of wood waste and related sediment conventionals were similar to patterns previously reported. Statistical evaluation of benthic results revealed several distinct communities. These did not exactly mirror groups of sampling locations that were identified by SPI or conventional results. However, SPI and conventionals could be used in combination to classify or explain much of the variability in the different communities with reasonable accuracy.

Results of this study, together with other published findings, provide good reasons to recommend that SPI be used more frequently in cleanup site investigations. SPI results can augment sediment fate and transport studies, identify areas of severe impact (anoxia, azoic sediments), map the nature and extent of wood waste, predict some sediment conventionals, and provide additional lines of evidence for the evaluation of benthic community health.

Link to EIM data for User Study ID SPI_PG06