This paper presents the development and application of a software tool for modeling knowledge to be used in knowledge-based systems or the Semantic Web. The inferential modeling technique, which is a technique for modeling the static and dynamic knowledge elements of a problem domain, provided the basis for the tool. A survey of existing knowledge modeling tools revealed they typically failed to provide support in four main areas: support for an ontological engineering methodology or technique, support for dynamic knowledge modeling, support for dynamic knowledge testing, and support for ontology management. Dyna, a Protégé plug-in, has been developed, which supports the Inferential Modeling Technique, dynamic knowledge modeling, and dynamic knowledge testing. Protégé and Dyna are applied for constructing an ontological model in the domain of selecting a remediation technology for petroleum contaminated sites. Dynamic knowledge testing in Dyna enabled creation of a more complete knowledge model.