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our cooperators and colleagues and with administrative and congressional officials.

Vince described the need to communicate as "one final problem that is in itself not primarily of a scientific character but is as difficult and important as the others—namely, the problem of communicating the results of our work to the public in a way that they can be understood and used."

The science of our Earth is as dynamic and as challenging as the planet we seek to understand and describe. The issues we deal with in the following pages underscore the importance of a continued dedication to the earth sciences. If we are to meet the challenges of the Earth's dynamic nature, unlock its critical resources, and build toward a safe and sound "second America," we must work hard, and we must work together as scientists, planners, managers, and legislators. Through the intensive cooperative framework that has been developed during the Geological Survey's long history with more than 1,000 other Federal, State, and local agencies and governments and through exchanges with academic and private industry organizations as well as with our many professional and scientific counterparts, we will work to ensure that the Nation has and will continue to have the necessary earth-science information. As public scientists, we remember the example set by former Director McKelvey, and we rededicate ourselves to making continued strides in understanding the Earth and in providing knowledge in a useful fashion to the Nation that we serve.

J. Furt

Dallas L. Peck
Director

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Vallecitos Nuclear Center, Pleasanton, Calif. (Photograph by Darrell Herd, U.S. Geological Survey.)

PERSPECTIVES

LOW-LEVEL RADIONUCLIDE TRANSPORT:

A CASE STUDY By Barbara J. Ryan

Introduction

Shallow land burial is the predominant method of disposing of low-level radioactive wastes in the United States. Wastes from private and commercial sources historically have been buried in six commercial repositories, three of which are currently active, while wastes generated by the Federal Government have been disposed of at seven sites (six are currently active) operated by the U.S. Department of Energy (fig. 1). The Low-Level Radioactive Waste Policy Act of 1980 (Public Law 96-573) and the Low-Level Radioactive Waste Policy Amendments Act of 1985 (Public Law 99-240) may result in the establishment of eight or more new commercial disposal sites by 1990. Under the provisions of the acts, each State is responsible for the disposal of low-level radioactive waste generated within its borders. To comply with the acts, most States are joining in compacts with neighboring States to develop regional disposal sites.

The U.S. Geological Survey has participated directly and indirectly (as a technical consultant to the U.S. Department of Energy, the U.S. Nuclear Regulatory Commission, and the U.S. Environmental Protection Agency) in hydrogeologic investigations at many of the low-level radioactive waste disposal sites around the country. Field studies have been (and in some instances continue to be) conducted at the following disposal sites and other related areas: Argonne National Laboratory, III.; Barnwell, S.C.; Beatty, Nev.; Bellfield, N. Dak.; Idaho National Engineering Laboratory, Idaho; Maxey Flats, Ky.; Oak Ridge, Tenn.; Savannah River Plant, Ga.; Sheffield, IlI.; Weldon Spring, Mo.; West Valley, N.Y.; and Wood River Junction, R.I. Studies of these sites have identified many of the hydrogeologic problems encountered in shallow land burial of low-level radioactive wastes. The objective of the ongoing Geo

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Figure 2. Aerial view, looking west, of the Sheffield, Ill., low-level radioactive waste disposal site, summer 1985. (Photograph courtesy of Jerry Abbey Aerial Photography, Cambridge, Ill.)

logical Survey Low-Level Radioactive Waste Program is to develop hydrogeologic guidelines that can be used by the U.S. Department of Energy to select and operate new sites for the disposal of low-level radioactive wastes and to provide advice and the results of studies of processes, environments, and techniques of hydrogeologic evaluations.

This perspective describes briefly the Sheffield, Ill., study, including the numerous avenues by which radionuclides can be transported through the hydrogeologic environment, and some of the conclusions reached during the 10 years that a team of Geological Survey scientists has been investigating the Sheffield site.

Site Description

The low-level radioactive waste disposal site near the northwestern Illinois town of Sheffield is situated on 20 acres of rolling terrain (fig. 2). Twenty-one trenches were constructed in glacial deposits and filled with radioactive waste from August 1967 through April 1978. Burial operations were suspended in 1978 when licensed burial space was depleted.

Nineteen of the 21 trenches were constructed in undisturbed deposits; the base of each trench was at least 10 feet above the water table. Two trenches were constructed above the existing land surface (like a raised bed) in fill consisting of compacted soil. Trenches ranged in length from 35 to 580 feet, in width from 8 to 70 feet, and in depth from 8 to 26 feet. Typical trench dimensions and the method of waste material deposition are shown in figures 3A, 3B, and 3C. Approximately 3,200,000 cubic feet of waste were buried in the 21 trenches.

Role of the U.S. Geological Survey

In 1976, the Geological Survey began a study of the mechanisms and avenues by which radionuclides might move within and from the Sheffield site. Because it was anticipated that water movement would play a primary role in releasing radionuclides from the trenches, the following aspects of the hydrologic environment were studied: (1) climatology; (2) surface hydrology, including runoff, sediment transport, and surface collapse; (3) geology;

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