I am unsure about ecological capacity and what assimilative capacity mean
My expertise surrounds health capacity and healths service organisation at such events
Our principal is that the event should not adversely impact health service metrics for the population the event is situated ie
Response time for ambulances
Wait times in Emergency Departments
Transfer times from hospital A-B
In addition health services should be provided on site where possible, this can on occasion mean having more medical providers in a field in the middle of a forest than the local 25,000 Annual census ED has on shift at that point in time. it is not unusual to see 400-800 patients at these events, some for minor illnesses, some cardiac arrests and major trauma from falls from flag poles/human pyramid/sound stages etc
There are some good resources available in 2 disaster Medicine Textbooks
Ciottone Disaster Medicine and Koenig and Schultz Disaster Medicine