Flood containment facility
From Halopedia, the Halo wiki
On Alpha Halo there was a Flood Containment Facility that was used by The Forerunners to contain the Flood while studying them.
Discovery
During the events of Halo 1, UNSC forces, led by Captain Jacob Keyes, attempted to take what they thought at the time was a Covenant weapons cache hidden in a swamp. The facility turned out to be a Flood Containment Facility that the Covenant had released the Flood and then realising their mistake had attempted, unsuccessfully to recontain them. The area soon was completely overrun by the Flood, as the organisms continued to damage the containment areas and allowed even more Flood to escape and multiply. This area is presumed destroyed along with the rest of Installation 04.
