When making decisions impacting public utility and encouraging and/or enforcing behavioral rules, public administrators need to rely on data and knowledge supporting their choices, which can be used to better inform those citizens who will be affected by such decisions. Many open data repositories exist and can be accessed and used by both decision makers and citizens. Similarly, semantic tagging is now commonly used as a way to allow users provide their own knowledge to be associated to data. In this paper, we present a novel participatory system which allows traditional databases and semantic tagging modules coexist in the same knowledge base, and provides the users with query enrichment functionalities to enable ontology-based query expansion. We describe CroSSE, our CrowdSourced Semantic Enrichment query system architecture, define the enrichment specification language, and discuss a use case in which the proposed technology is being applied in a participatory e-government setting. The use case is in the context of our SmartGround EU funded project, in which a relational database platform is designed to collect data of interest concerning secondary raw materials from mines as well as municipality waste. CroSSE semantic enrichment architecture interacts with this platform to expand queries and results on the basis of users' domain knowledge.