"Ante-operam" significa prima del lavoro, prima dell'opera, ecc.

In inglese credo che si riferisca alle formalità, accertamenti, e a tutto quello che deve essere fatto "before the (construction) work" oppure "performed before the works are started", o cose del genere.
Ci sono un po' di risultati in Google se fai la ricerca in inglese con "ante operam"

http://www.asecap.com/presentations-vienna-2005/presentation...
The socio-economic and environmental monitoring plan has the objective of evaluating
the environmental qualities of the territory impacted by the works. The monitoring will be
based on periodic as well as continuous (survey campaigns and continuous monitoring
stations with automatic measuring systems) surveys organised as follows:
- before the construction work (Ante Operam)
- during construction work (work in progress)
- during the first 12 months of operation (Post Operam)