You are probably looking at a combination of technics/methodologies to get to a behavorial model :
1. Ethnographic field study (Based on interviewing and observation in situ) two aspects to consider here:
A-Descriptions of the scene: Describe the physical aspects of the work environment, including the layout of workstations, desk space and clutter, collaboration and conversation areas.
B-key events and incidents: What happened, and who did what? What is your impression of these incidents, and what are team members’ thoughts in regard to and interpretations of these events? How do they feel about them?
2. Contextual enquiry ( based on interviewing and observation in situ but more structured and task focused.
Both options are part of Contextual Design methodology but an ethnographic field study is more comprehensive so you could undertake that first before fine-tuninng using a contextual enquiry.
For more details about different approaches and when to use them :
Hope that helps