To evaluate the impact of the Health Impact Assessment (HIA) of the Proposed Cleanup Plan for the Lower Duwamish Waterway Superund Site, this study used a cross-sectional design and qualitative analysis to investigate opinions and attitudes of Cleanup decision makers and stakeholders. Study participants included members of the HIA’s Liaison Committee, Resident Community Advisory Committee, and Tribal Community Advisory Committee, as well as other pertinent respondents identified via the knowledge of the committee participants. Anonymized opinions regarding impacts of the HIA were gathered through semi-structured key informant interviews and focus group discussions with 18 total participants. Collected qualitative data were analyzed following the general framework of Interpretative Phenomenological Analysis. Through identification of emergent and superordinate themes in their responses, participants were found to have perceived a common set of HIA impacts involving characterization of the proposed cleanup decision and its implications; empowerment of vulnerable stakeholders; influence on stakeholders’ and decision makers’ disposition toward issues around the focal decision; and production of material results. Interpretation of respondents’ experiential insights proved useful for characterizing the role of the Duwamish HIA in environmental democracy, and for illuminating related prospects for achieving greater environmental justice in this location and other contexts.