The most comprehensive guide to date on access to environmental justice on the EU level was just published by ClientEarth. The publication that is available at the this link was written by ClientEarth in the EARL project.
The EARL project is run jointly by Justice & Environment and CE. Its objective is to raise awareness of legal professionals on access to justice in environmental matters. Within the project, there have already been 5 training sessions held in Budapest, Limoges, Vienna, Warsaw and Zilina.
You can find more information on the project here.