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This is a Snowmass 2021 Topical Report for the Underground Facilities and Infrastructure Frontier on Synergies in Research at Underground Facilities: A broad range of scientific and engineering research is possible in underground laboratories, beyond the physics-focused activities described in the other Underground Facilities and Infrastructure Topical Reports. These areas of research include nuclear astrophysics, geology, geoengineering, gravitational wave detection, biology, and perhaps soon quantum information science. This UF Topical Report will survey those other scientific and engineering research activities that share interest in research-orientated Underground Facilities and Infrastructure. In most cases the breadth and depth of research aims is too large to cover in completeness and references to surveys or key documents for those fields are provided after introductory summaries. Additional attention is then given to shared, similar, and unique needs of each research area with respect to the broader underground research community's Underground Facilities and Infrastructure needs. Where potential conflicts of usage type, site, or duration might arise, these are identified.

This report provides the technical justification for locating a large detector underground in a US based Deep Underground Science and Engineering Laboratory. A large detector with a fiducial mass in the mega-ton scale will most likely be a multipurpose facility. The main physics justification for such a device is detection of accelerator generated neutrinos, nucleon decay, and natural sources of neutrinos such as solar, atmospheric and supernova neutrinos. In addition to the physics justification there are practical issues regarding the existing infrastructure at Homestake, and the stress characteristics of the Homestake rock formations. The depth requirements associated with the various physics processes are reported for water Cherenkov and liquid argon detector technologies. While some of these physics processes can be adequately studied at shallower depths, none of them require a depth greater than 4300 mwe which corresponds to the 4850 ft level at Homestake. It is very important to note that the scale of the planned detector is such that even for accelerator neutrino detection (which allows one to use the accelerator duty factor to eliminate cosmics) a minimum depth is needed to reduce risk of contamination from cosmic rays. After consideration of the science and the practical issues regarding the Homestake site, we strongly recommend that the geotechnical studies be commenced at the 4850ft level in a timely manner.

The Galápagos mounds sea-floor hydrothermal system is at least 300,000 years old and once produced manganese-poor sediments, which nearly blanketed the area of the present mounds field. Present-day mound deposits are limited manganese-rich exposures, suggesting that the system has changed from rock- to water-dominated and has diminished in intensity with time.