Environmental planning systems have traditionally treated technically contentious publics as obstacles to consensus-building and efficient decision-making. Yet communities living alongside environmentally controversial developments increasingly challenge not only the social legitimacy of planning decisions, but also the scientific assumptions underpinning Environmental Impact Assessment (EIA) processes themselves. Drawing upon literature from planning theory, environmental justice, science and technology studies, and citizen science, this paper argues that planners should engage more rather than less with such “awkward” publics. In particular, the paper advances the concept of the “community scientist”: locally embedded citizens, campaign groups and non-governmental organisations who gather, interpret and mobilise environmental data from the bottom up, often in collaboration with universities or independent experts. This paper argues that these actors represent an important form of situated and experiential expertise that conventional technocratic planning systems frequently marginalise. Rather than viewing contentious participation as irrational, disruptive or anti-scientific, planners should recognise community science as a potentially valuable form of co-produced environmental knowledge, particularly in relation to air pollution, cumulative impacts and lived environmental risk. The paper further suggests that greater engagement with community scientists reconnects contemporary planning practice with earlier civic planning traditions associated with Patrick Geddes and the principle of “survey before plan”. Ultimately, the paper contends that the future legitimacy of environmental planning may depend upon planners becoming more willing to work with technically informed dissent rather than attempting to neutralise it.