Environmental Management Accounting is rapidly evolving from an ethical side-issue into a core business concern. However, traditional management accounting methods and currently available tools provide only limited support. Resource-Event-Agent (REA) is a well-known business ontology that offers a rigorous axiomatic basis for accounting and auditing. The paper demonstrates that on the basis of an extension of REA, it is possible to develop integrated modeling solutions and tools for environmental management accounting and assurance. The focus is on physical resource flow modeling (internal and external).