9c1b3464_WQP_User_Guide__Definition
[Site Type] Aggregate groundwater use (NWIS only) [Definition] 
An aggregate groundwater site type is used when it is not possible or practical to describe the specific sites as springs or as any type of well including 'multiple wells', or when water-use information is only available for the aggregate. Aggregate sites that span multiple counties should be coded with 000 as the county code, or an aggregate site can be created for each county.
WQP User Guide
Definition