PNNL

Abstract

We argue for a cost-effective, long-term North American underground science strategy based on partnership with Canada and initial construction of a modest U.S. Stage I laboratory designed to complement SNOLab. We show, by reviewing the requirements of detectors now in the R&D phase, that SNOLab and a properly designed U.S. Stage I facility would be capable of meeting the needs of North America’s next wave of underground experiments. One opportunity for creating such a laboratory is the Pioneer tunnel in Washington State, a site that could be developed to provide dedicated, clean, horizontal access. This unused tunnel, part of the deepest (1040 m) tunnel system in the U.S., would allow the U.S. to establish, at low risk and modest cost, a laboratory at a depth (2.12 km.w.e., or kilometers of water equivalent) quite similar to that of the Japanese laboratory Kamioka (2.04 km.w.e.). The site’s infrastructure includes highway and rail access to the portal, a gravity drainage system, redundant power, proximity to a major metropolitan area, and a system of cross cuts connecting to the parallel Great Cascade tunnel and its ventilation system. We describe studies of cosmic ray attenuation important to properly locating such a laboratory, and describe the tunnel improvements that would be required to produce an optimal Stage I facility. This strategy would allow the U.S. to add new capabilities in response to the needs of future experiments, building on the experience gained in Stage I. We discuss possibilities for Stage II (3.62 km.w.e.) and Stage III (5.00 km.w.e.) developments at the Pioneer tunnel, should future North American needs for deep space exceed those available at SNOLab. This staging could be planned to avoid duplication of SNOLab’s capabilities while minimizing construction and operations costs. We describe the existing geotechnical record important to future stages, including past tunneling histories, borehole studies and analyses, and recent examinations of the Pioneer tunnel. We also describe the significant broader impacts of this project in improving the efficiency, safety, and security of one of the nation’s key transportation corridors.