Fishman Environmental / SWCA was contracted by Maul Foster and Alongi, Inc.(MFA) to investigate the possible effects of petroleum hydrocarbon seeps on local aquatic fauna near the Unocal site in Astoria, Oregon on the lower Columbia River. FES aquatic biologists collected benthic macroinvertebrate invertebrate samples to examine the state of the benthic community in the survey area. Over 89,900 individuals of 29 taxa were collected, identified, enumerated, and analyzed to determine if relative density patterns and community metrics indicated an ecological response to the observed petroleum impacts. Spatial patterns in relative abundance of taxa and functional groups were also examined for correlations with variables including elevation, substrate type, and overhead cover.