Re-occuring Service - Need for BPA/BOA?

I am in a DoD organization looking for some guidance/policy/regulation, etc. on when it is appropriate to have a BPA or BOA for re-ocurring services.

A service is required several times a year on an as-needed basis, and the total amount expended upon these services will exceed $2,500 in a one-year period. Individual purchases do not exceed $2,500. FAR Parts 13 and 16 give general guidance on how and why to establish a BPA or BOA. I would like the regulation (if such regulation exists) on why a BPA or BOA would have to be established if the collective dollar amount expended for these services exceeds the micro-purchase threshold for services in a one-year period.