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Open-File Report 2014–1187

A Ground-Based Magnetic Survey of Frenchman Flat, Nevada National Security Site and Nevada Test and Training Range, Nevada—Data Release and Preliminary Interpretation

By Jeffrey D. Phillips, Bethany L. Burton, Erika Curry-Elrod, and Sigmund Drellack

Thumbnail of and link to report PDF (13.6 MB)Introduction

The Nevada National Security Site (NNSS, formerly the Nevada Test Site) is located in southern Nevada approximately 105 kilometers (km) (65 miles) northwest of Las Vegas. Frenchman Flat is a sedimentary basin located on the eastern edge of NNSS and extending eastward into the adjacent Nevada Test and Training Range (NTTR).

In late September 2010, the U.S. Geological Survey (USGS) conducted a ground-based magnetic survey of the northeast portion of Frenchman Flat within the NNSS and within the adjacent NTTR. The survey was designed to address two questions of importance to the siting of new monitoring wells near (down-gradient of) or within groundwater-contaminant plumes resulting from the Milk Shake and Pin Stripe underground nuclear tests:

Question 1—What is the horizontal extent of the basalt flow (the Basalt lava flow aquifer or BLFA) encountered in three wells (UE5k, UE5i, and ER-5-3) within the alluvial section at depths ranging from 268 to 290 meters (m) (880 to 950 feet [ft]), and having a thickness between 9 and 21 m (30 and 70 ft)? Exploratory Hole UE5k is located near Emplacement Hole U5k, site of the Milk Shake underground nuclear test (U.S. Department of Energy, 2000). Characterization well ER-5-3 is located approximately 670 m (2,200 ft) west-northwest of the Milk Shake test.

Question 2—Does basin and range normal faulting observed in the hills north of Frenchman Flat continue southward under alluvium and possibly disrupt the Topopah Spring Tuff of the Paintbrush Group (the Topopah Spring welded tuff aquifer or TSA) east of the Pin Stripe underground nuclear test, which was conducted in Emplacement hole U11b?

First posted November 14, 2014

For additional information, contact:
Director, Crustal Geophysics and Geochemistry Science Center
U.S. Geological Survey
Box 25046, MS 964
Denver, CO 80225
http://crustal.usgs.gov/

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Suggested citation:

Phillips, J.D., Burton, B.L., Curry-Elrod, Erika, and Drellack, Sigmund, 2014, A ground-based magnetic survey of Frenchman Flat, Nevada National Security Site and Nevada Test and Training Range, Nevada—Data release and preliminary interpretation: U.S. Geological Survey Open-File Report 2014–1187, 144 p., 1 pl.,  https://dx.doi.org/10.3133/ofr20141187.

ISSN 2331-1258 (online)



Contents

Introduction

Geologic Setting

A Ground-Based Magnetic Survey

Analysis and Interpretation of the Magnetic-Profile Data

Conclusion

References Cited

Appendix A. Ground Magnetic Data as Collected

Appendix B. Ground Magnetic Data Reordered into Lines

Appendix C. U.S. Geological Survey Procedure for Ground-Based Magnetic Data Collection

Appendix D. Previous Geophysical Work


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