  We present results from exploratory studies, supported by the Physics Beyond
Colliders (PBC) Study Group, of the suitability of a CERN site and its
infrastructure for hosting a vertical atom interferometer (AI) with a baseline
of about 100 m. We first review the scientific motivations for such an
experiment to search for ultralight dark matter and measure gravitational
waves, and then outline the general technical requirements for such an atom
interferometer, using the AION-100 project as an example. We present a possible
CERN site in the PX46 access shaft to the Large Hadron Collider (LHC),
including the motivations for this choice and a description of its
infrastructure. We then assess its compliance with the technical requirements
of such an experiment and what upgrades may be needed. We analyse issues
related to the proximity of the LHC machine and its ancillary hardware and
present a preliminary safety analysis and the required mitigation measures and
infrastructure modifications. In conclusion, we identify primary cost drivers
and describe constraints on the experimental installation and operation
schedules arising from LHC operation. We find no technical obstacles: the CERN
site is a very promising location for an AI experiment with a vertical baseline
of about 100 m.
