45 CFR §2105.52

1. (a)The Agency may aggregate requests and charge accordingly when it reasonably believes that you, or a group of requesters acting in concert with you, are attempting to avoid fees by dividing a single request into a series of requests on a single subject or related subjects.
   1. (1)The Agency may presume that multiple requests of this type made within a 30-day period have been made to avoid fees.
   2. (2)The Agency may aggregate requests separated by a longer period only where there is a reasonable basis for determining that aggregation is warranted in view of all the circumstances involved.
2. (b)The Agency will not aggregate multiple requests involving unrelated matters.