Here are my naive layperson thoughts about what to say to Caleb offered to you for refinement:
A history of the area - how there came to be a park in the midst of an urban area
How the restoration project came into being
The complementary roles of PCD, City of Fircrest, and working volunteers
An exploration of the restoration area with focus on the human impact on the ecology and what restoration is called for
Conversation with the leader of the volunteer group and willing volunteers
Filming of work in progress
Depending on timeline, revisit the area when restoration is complete, highlighting what's changed and getting some "user" comments
Lessons learned
I'm thinking that the purpose of the documentary would be:
creating content for the library of video you have mentioned we would need to approach community TV
documenting an upbeat story that shows how local communities can make a difference in the environment
drawing some parallels between this very small ecological study with what's going on in the larger world environmentally
providing public awareness of CCL and how we can be a part of creating environmental awareness (think we might want to be under the rubric of Citizen's Climate Education vs. Lobby)
highlighting local climate change effects and how local communities might mitigate and adapt to those effects