This paper explores the influence of local community groups on agency decisionmaking at hazardous waste sites nationwide. The central purpose of this research is to examine the relative influence of two forms of public participation at Superfund sites: Community Advisory Groups (CAGs) and Technical Assistance Grants (TAGs). When citizens mobilize and become involved in the decisionmaking process via CAGs and TAGs, are outcomes systematically different when compared to hazardous waste sites where citizen groups are not active? I utilize a treatment effects regression analysis to isolate the impact of these groups on remedy selection at Superfund sites while adjusting for the non-random formation of local interest groups. The results suggest that even when controlling for other factors that may guide agency decisionmaking, such as site characteristics, the Environmental Protection Agency is more likely to choose health protective clean-up approaches when CAGs and TAGs have formed at Superfund sites. © 2007 by the Association for Public Policy Analysis and Management