Woods Hole Group conducted an ecological assessment of an intertidal shoreline area on Deer Island in Boston Harbor, Massachusetts.  Mussel tissue and sediment were analyzed for alkylated and priority pollutant PAHs to identify the source of hydrocarbons at the impacted site and to support a site ecological risk characterization.  In addition to sample collection, the assessment included a semi-quantitative bioassessment survey of the intertidal biota at the impacted and reference sites.  The tissue analysis required low parts-per-billion detection limits for the PAHs to satisfy risk-based data quality objectives.  Advanced fingerprinting diagnostic techniques were used to identify the source of PAHs in the sediment and tissue residues. Results of the study indicated that PAHs in impacted site bivalves contained a large petrogenic component superimposed on a pyrogenic background observed at the reference sites.  The PAH concentrations found in the sediment were determined not to be a risk to the intertidal bentic resources.