There are some very useful evaluation tools identified on the National Co-ordinating Centrer for Public Engagement website that relate to evaluation models and process that community groups can use to evaluate their social impact.
The Research Excellence Framework (REF) is the framework of evaluation that all universities must use to demonstrate their engagement with the public in order to justify their research status and funding.
The NCCPE facilitates links between universities and community organisations that help to evaluate the role and the social impact of the work that is undertaken in these social sector groups and bodies.
There are many casestudies listed on the NCCPE site that give examples of how universities have worked with community groups to evaluate their work. This might be useful in helping to develop local models of evaluation with local researchs and community media practioners.