Findings and Recommendations

SCIENTIFIC FINDINGS

The analysis of the current opportunities and challenges for deep underground science leads to three scientific findings.

1. Deep underground science is an essential component of research at the frontier. Underground experiments are critical to addressing some of the most compelling problems of modern science and engineering; and long-term access to dedicated deep underground facilities is essential.

• The nature of the dark universe, the stability of matter and the properties of neutrinos are urgent questions of physics and astrophysics, to which deep underground experiments will make contributions that cannot be obtained by other means.
   
• Research on subsurface microbial ecosystems offers unique opportunities for the study of novel microbes, their genomics and evolutionary biology in isolated, slowly changing environments. Such studies may offer insight into the origins of life on earth and the search for life on other planets.
   
• Deep underground studies will address central questions in earth science, including the origin of the earth's magnetic field, the role of material properties in planetary processes, and the understanding and prediction of catastrophic natural events such as earthquakes.
   
• A fundamental understanding of the complex mechanisms operative in a large rock mass is important for modern engineering and requires large-scale underground facilities.

Underground research has already led to unexpected discoveries and has generated fundamental shifts in our understanding of nature. Cross-disciplinary synergies among these disciplines add new research avenues.

2. Disciplines in transformation. Deep underground experiments have for some time constituted an important component of physics and astrophysics. Biologists, earth scientists and engineers have long made observations underground and have in recent years also recognized the extraordinary potential of deep underground experiments.

3. Benefits to society. Investment in deep underground experiments can yield important societal benefits. Underground construction, resource extraction, management of water resources, environmental stewardship, mine safety and national security are prominent examples. By creating a unique multidisciplinary environment for scientific discovery and technological development, a deep underground laboratory will inspire and educate the nation's next generation of scientists and engineers.

PROGRAMMATIC FINDINGS

Our previous analysis of facilities for deep underground science can be summarized in two programmatic findings.

1. Worldwide need for underground space. The rising interest in deep underground science; the diversification of underground disciplines; the increase in the number of underground researchers; and the increased size, complexity and duration of experiments all point to a rapidly rising demand for underground laboratory space worldwide. The opening of numerous facilities outside the U.S. attests to the gap between supply and demand, especially at very great depth.

2. Need for a U.S. world-class deep multidisciplinary facility. The U.S. is among the very few developed countries without a deep underground facility (≥ 3000 m.w.e). In an international environment where deep underground space is at a premium, a U.S. Deep Underground Science and Engineering Laboratory would provide critical discovery opportunities to U.S. and foreign scientists, place the U.S. in a stronger strategic position in deep underground science, and maximize the benefits of underground research to the nation.

RECOMMENDATIONS

1. Strong support for deep underground science. The past decade has witnessed dramatic scientific returns from investments in physics and microbiology at great depths. Underground research is emerging as a unique and irreplaceable component of science, not only in physics and astrophysics, but also in biology, earth sciences and many disciplines of engineering. We recommend that the U.S. strengthen its research programs in subsurface sciences to become a world leader in the multidisciplinary exploration of this important new frontier.

The discovery of neutrino mass and oscillations, the first observation of the neutrino burst from a core-collapse supernova, the recognition of the existence of life under conditions little different from those that may be present on other worlds–all have underscored the advances made possible by access to deep sites. As explained in the findings, there is a broad and compelling suite of underground experiments that address some of the most fundamental questions in physics, astrophysics, cosmology, microbiology, geosciences, and engineering There can be little doubt that increased effort in this area will yield tremendous scientific dividends, including totally unexpected results. Many fields and programs seek funding, but in only a few cases is the evidence for successful return on that investment as clear as it is in underground science.

2. A cross-agency Deep Science Initiative. In order to broaden underground research and maximize its scientific impact, we recommend that the U.S. science agencies collaborate to launch a multidisciplinary Deep Science Initiative. This initiative would allow the nation to focus the whole range of underground expertise on the most important scientific problems. It would aim at optimizing the use of existing or new underground facilities and at exploiting the complementary aspects of a variety of rock formations. The Deep Science Initiative should be coordinated with other national initiatives and take full advantage of international collaboration opportunities.

The premise of this recommendation is that the U.S. has access either on its territory or through international collaboration to a large reservoir of expertise and a number of assets (underground facilities, accelerators, seismic networks, sequencing and protein synthesis facilities). A cross-agency initiative would allow optimal use of these capabilities, and of additional resources recommended above. It is the best way to maximize the profoundly transformative effect of a unified program on all of the fields involved, both because of the phenomena it will undoubtedly discover and by virtue of the changes in the way of doing research that it will engender within and across disciplines. Historically, synergies like the ones that are emerging have provided a strong foundation for discovery.

Some of the facilities needed for this exciting program already exist in the U.S. and in other nations. Specific experiments should use the facilities (or combinations of facilities) most adapted to their purposes. The special features of, for example, WIPP, in a salt formation with very low natural radioactivity, are unique in the U.S. For biology, earth sciences and engineering, much can be learned from the diversity of rock types available world-wide. The program should support experiments in sedimentary rock, for instance, even if no dedicated facilities exist. In each case the science must drive the choice of facility or experiment, and not the other way around.

On the organizational side, such an initiative should ally all agencies and disciplines with a stake in underground science. In addition to the National Science Foundation (particularly the four directorates Mathematical and Physical Sciences, Geosciences, Biological Sciences, and Engineering), natural partners include DOE (High Energy Physics, Nuclear Physics, Basic Energy Sciences, and Biological and Environmental Research), USGS, NASA (for astrobiology) and potentially NIH (for some genome studies and potential medical applications). Although NSF has been designated by the Office of Science and Technology Policy as the lead agency for such a program, the other agencies should be involved from the start in the development of common goals, funding structures and advising and review mechanisms.

In order to go beyond a mere relabeling of activities, such a Deep Science Initiative will require strong scientific coordination mechanisms that assure:

• Development of a coherent long-term scientific strategy and the support of an R&D program.
   
• Optimal use of all U.S. and international assets, and coordination with other national initiatives (e.g. neutrino beams at accelerators, Earth Scope, Secure Earth).
   
• Cross-disciplinary prioritization of projects within underground science, taking into account discipline-specific prioritization.
   
• Maximization of benefits to society, through the involvement of industry and other sectors, and a coordinated education and outreach program.

Such coordination tasks represent formidable challenges that would require both novel solutions and application of the best current practices of cross-agency and cross-disciplinary collaboration.

3. A Deep Underground Science and Engineering Laboratory. The U.S. should complement the nation's existing assets with a flagship world-class underground laboratory providing access to very great depth (approximately 2200 meters or 6000 meters water equivalent) and ample facilities at intermediate depths (approximately 1100 meters or 3000 meters water equivalent) currently not available in the U.S. Such a Deep Underground Science and Engineering Laboratory (DUSEL) should be designed to allow evolution and expansion over the next 30 to 50 years. Because of this long lifetime, the initial investment must be balanced with the operating costs. For maximum impact, the construction of DUSEL should begin as soon as possible.

WORLD-CLASS CHARACTERISTICS

Although the Deep Science Initiative is larger than DUSEL, DUSEL will be the focus of the initiative and therefore should offer world-class characteristics in terms of depth, access, environmental control, safety, evolutionary capabilities and operation costs.

• Depth. The scientific frontier is at large depth. Although Canada's SNOLAB can accommodate the immediate needs of U.S. physicists in the coming few years (i.e. for experiments currently approved for construction), no long-term dedicated facilities at large depth are available to other sciences. The need for deep space for the physical sciences increases as experiments become larger and more sensitive. Consideration of the expected range for experimental searches and the cosmic-ray backgrounds indicate that a "deep campus" at approximately 6000 m.w.e. with a future capability for still deeper sites will meet the needs of the participating sciences for the foreseeable future. Not all experiments require such depths. Their needs can be met at an intermediate campus at approximately 3000 m.w.e. These new facilities would complement existing shallower U.S. facilities.
   
• Access. Quality of access is a key characteristic. The research community has engaged in lively debate about the relative merits of vertical access, ramps and horizontal access. Whatever the final technical solution, size matters. Ideally, the access should allow researchers to bring to significant depth small trailers (roughly 6 m long, 2.5 m wide and 2.5 m tall, approximately the standard ISO size for a "20 foot") of 5 tons. This capability is important for small experiments, because the trailers can be assembled at investigators' institutions and brought underground with minimum disassembly. In addition, scientists should have as close as possible to round-the-clock access to their experiments, 365 days per year. It is also essential to have assured long-term access for at least 30 years.
   
• Environmental control. Environmental control is another essential characteristic. The control of dust (class = 10000, and as low as class 100 for specific experiments) and humidity are important for many experiments. Access to pristine rock volume is essential for biology experiments that focus on indigenous life as we do not know it. Great precautions must be taken to prevent contamination by site exploration and construction or by prior mining activities.
   
• Safety. Safety considerations are essential, and DUSEL will need to develop policies and practices that meet or exceed the relevant codes. Such stringent safety policies may lead to restrictions on certain materials (e.g. low-flash-point flammable liquids or high-toxicity materials), to specific safety measures for large volumes of cryogens or to restrictions on the induction of fracture motion. If scientific arguments point to the need for a potentially dangerous activity, the laboratory must work actively with the experimenters and experts in underground safety to determine whether methods can be devised to carry out the experiment while guaranteeing the complete protection of personnel, the laboratory and the environment. Such measures will yield advances in underground safety that may find application in the commercial and mining sector.
   
• Expansion capability. An important attribute of the laboratory is expansion capability. Although an initial set of cavities would be built to house the first suite of experiments, a successful laboratory must accommodate the experiments needed in 20 years. This requires separation between "clean" and "dirty" accesses in the layout of the facility, and minimization of construction disturbance to running experiments.
   
• Cost. The operation and upgrade costs over the long lifetime of the laboratory (30-50 years) must be balanced with the initial investment for optimization of the program. A laboratory that is inexpensive to build but expensive to operate may not be viable.
   

THE INITIAL SCIENTIFIC PROGRAM

For a deep underground laboratory, science begins on the day of the decision to explore a particular site. Four phases can be identified:

• Before excavation. As physicists conduct R&D and use low-radioactive-background counting facilities to select the purest materials for their equipment, earth scientists, hydrologists and rock engineers fully characterize the site with instrumented boreholes and imaging. Biologists and geochemists use the boreholes for sampling the water in the rock and constructing a fluid-flow model for the site.
   
• During excavation. Earth scientists and engineers test imaging methods and carefully monitor rock motion and modification of stress during construction. Biologists sample rocks and fluid-filled fractures ahead of the excavation front.
   
• The first suite of experiments. A deep campus could include an ultradeep underground observatory for biological and bioengineering research; two medium-block experiments where geologists and rock engineers conduct tests on the rock; four cavities for the next generation of dark matter, neutrinoless double beta decay and solar neutrino experiments and a new experiment to be determined. Although experimentalists would prefer separate cavities, larger cavities able to accept several experiments may be cheaper to build and more flexible in the long run. Space for test facilities and small experiments, together with offices and a conference room. Such a program would need at least 25,000 m3 of usable space. An additional volume of at least 20,000 m3 at intermediate depth would house facilities and experiments that do not need the greatest depth. Examples include an underground accelerator, a supernova burst experiment, solar neutrino experiments with high background-rejection capability, intermediate-depth block studies and biology observatories. Low-radioactive-background counting areas, assembly areas, and underground fabrication facilities including germanium and copper refining would be located on this intermediate campus. Far from the rest of the laboratory, geoscientists could perform fracture-propagation and earthquake-nucleation experiments. The educational outreach module should be underground but with easy access, preferably with observation space for ongoing scientific activities.
   
• Extensions in the first 10 years. The initial design should permit extensions in the first 10 years of the laboratory: an obvious case is a large cavity or cavities for proton-decay and neutrino-oscillation experiments, with a total volume of approximately 500,000 m3. A neutrino beam would be pointed to DUSEL. In the most-studied scenarios (neutrino beam of approximately 3 GeV energy, produced at Fermilab), a broad optimum occurs around 2500 km and distances between 1000 km and 5000 km are adequate. The depth of this detector would be chosen after a careful analysis of its multiple physics objectives, costs, and the competence of the rock. A depth in the vicinity of 3000 m.w.e. is envisaged. Other possibilities for extension include a large low-pressure gaseous tracking chamber for dark matter and/or double beta decay experiments. Low-vibration facilities for atomic, molecular and optics experiments could also be constructed at a relatively shallow level and isolated from the rest of the laboratory, to minimize disturbance from ongoing construction or rock mechanics experimentation.