Abstract Today, engineering geologists in private industry occupy key positions in the planning, design, and construction of many different kinds of engineering works. Since the beginning of this century, it typically has been the practice of engineering-construction companies to rely on outside consultants for projects requiring geological expertise. However, with the end of World War II and the rapid development of the early 1950s, engineering-construction companies in North America began to hire geologists as staff members. A recent survey of the older major engineering-construction companies by Bechtel (1986) established that about half of the firms support engineering geology staffs in-house, while half rely solely on consultants, either individuals or specialty groups. Furthermore, many of the companies that retain engineering geologists in-house occasionally supplement their staff input with the services of outside consultants for a variety of reasons, including fulfilling contractual obligations, enhancing the work capabilities in a specific geographic area, or reinforcing expert opinions in controversial situations. Today, some of the major engineering-construction companies that support their own in-house geoscience experts include Bechtel Civil, Inc.; EBASCO Services, Inc.; Fluor Engineers, Inc.; Harza Engineering Company; Morrison-Knudsen Engineering Company; United Engineers and Constructors; and Stone and Webster Engineering Corporation. Bechtel was one of the first engineering companies to hire staff geologists. In the early 1950s, they hired Ben Warner, Victor L. Wright, Robert J. Farina, and Charles P. Benziger to work on a project-by-product basis. However, lack of permanent job status and associated benefits, as well as the inability in those days to advance professionally within the company ranks, was not encouraging to the geologists or beneficial to the company, and consequently, many of these geologists moved on to other professional situations.

Abstract Studies on nuclear power plant siting and licensing are expensive and complex undertakings requiring critical geologic input for the planning, design, and construction phases. Commercial production of nuclear power in the United States began in 1959, in an era when geologic hazards were seemingly not as critical as they are today to designers, constructors, and regulatory agencies. By the early 1970s, however, siting work required a more sophisticated appreciation of geologic hazards such as earthquake effects, subsidence, slope stability, and foundation integrity. These concerns were formalized by the U.S. Atomic Energy Commission (AEC) in 1971 in its "Seismic and Geologic Siting Criteria for Nuclear Power Plants" and in 1972 in the Standard Format. The required Federal license to construct and operate nuclear power plants is awarded through a careful and demanding process. Construction permits are not granted until high levels of assurance are attained as to suitability of the site; the construction process must be observed and monitored. Electric utility applicants for construction permits and operating licenses organize large teams of scientific and technical personnel to compile the Preliminary Safety Analysis Report (PSAR) required for each nuclear power plant. Geologists constitute a key part of these teams, producing site-specific and regional assessments that are accurate enough to withstand scrutiny and timely enough to avoid costly delays in the programmed design-and-construct sequence. Management techniques must be applied to coordinate data-collection efforts and timely release of findings. As soon as a complete set of findings is compiled to the specifications of the Standard Format, the PSAR is accepted for review by the Nuclear Regulatory Commission (NRC). These reports become complex documents and include the responses to subsequent review questions which are included as amendments. The Final Safety Analysis Report (FSAR) includes supplementary reports dealing with geologic findings revealed during construction. Many of the key geologic issues identified in siting and licensing are often analogous to those problems that confront researchers in the geological sciences today, such as evaluation of remote imagery, proof of subsurface stratigraphic continuity, evaluation of potential fault activity, a thorough assessment of ground-water conditions at each site, and subsidence potential including evaluation of dissolution of foundation material. The overriding goal of each applicant utility is the construction of a safe power plant; however, the future of the industry in the United States is dependent on its ability to maintain construction schedules while staying within allotted budgets. Lessons learned from previous sitings have pointed out that effective management and judgment, efficient communication, and coordination contribute to timely and cost-efficient license studies.

Abstract The selection of a site and the development of geologic and seismic design parameters may be facilitated through the use of a three-phase program of investigation. This program is cost effective and expedites management decisions that benefit from current relevant geologic information. A resource review and regional reconnaissance during Phase I serve to eliminate areas of low potential, to focus on favorable areas, and to identify possible problems that may require further study. Preliminary estimates of certain design parameters during Phase I may be used to initiate contract negotiations with a plant supplier. Candidate sites and associated problems can then be examined through analysis of large-scale maps and imagery, preliminary geologic mapping, and subsurface investigation during Phase II. Phase II may lead to preparation of an Early Site Review Report (ESRR) for submission to the Nuclear Regulatory Commission (NRC). A Phase III investigation leading to the preparation of a Preliminary Safety Analysis r Report (PSAR) can be performed concurrently or sequentially on any or all candidate sites recommended at the conclusion of Phase III. This approach is illustrated with examples from Spain and Iran showing how such a program assists in selection and study of possible sites.

Abstract The scope and detail of geologic studies made for a nuclear power plant site far exceed those made for any other type of engineering structure. The regional and local physiography, geomorphology, geologic history, lithology, stratigraphy, and structural geology must be studied through (1) reviewing the literature, (2) discussions with local, academic, State and Federal geologists, geophysicists, and seismologists, and (3) original geologic mapping, geophysical studies, and subsurface investigations. Reviews of previous studies in the region are an important part of the evaluation of any site; they help to identify, and form the basis for, additional detailed studies of particular geologic conditions and features which may be significant to that site. All historical earthquakes that could have been felt at a proposed site should be identified. All historical earthquakes of modified Mercalli (MM) intensity greater than IV or magnitude greater than 3 which have been reported within 200 mi (320 km) of a site are listed and shown on epicenter maps that also show significant tectonic structures within 200 mi of the site. The maximum potential earthquake for the site is evaluated from a consideration of the regional and local geologic setting and the historical seismicity. The maximum vibratory ground motion that safety-related plant structures and equipment are designed to withstand is defined on the basis of an evaluation of the maximum potential earthquake and the assumed location of the earthquake that will produce the maximum vibratory ground motion. Geologic, seismic, and man-made hazards significant to the site are identified and evaluated. The soils and rock underlying a site are investigated to determine their characteristics and behavior under static and dynamic loads. Safety Analysis Reports (SARs) for the site are prepared. They document the studies which were made by the applicant; they also document that pertinent reports and studies by others were considered. The SARs provide the basis for the conclusions as to the geologic suitability of the site and the basis for the parameters selected for engineering design.

Abstract More than a decade has passed since the earliest geologic reports relating to proposed nuclear reactor sites were completed. Then, guidelines were few, and the safety analysis was brief and general. Today, the geologic portions of Preliminary Safety Analysis Reports (PSARs) and Final Safety Analysis Reports (FSARs) are by requirement more complex. Through the cooperative efforts of the Nuclear Regulatory Commission (NRC; formerly the Atomic Energy Commission) and the American Nuclear Society, specific seismic and geologic criteria for nuclear plant sites and a standard format for the presentation of data have been developed. These standards and requirements have shifted the emphasis of power plant siting from one that considered mainly the economics of the site and its proximity to the service area, as in the case of fossil fuel plants, to one that gives important consideration to the geologic suitability of the site. Geologic studies of nuclear plant sites require a comprehensive exposition of the areal and structural geology, hydrology, and seismicity in addition to site exploration of engineering-geology and foundation characteristics, which are the major concerns in geologic studies for fossil fuel plants. For each site a design acceleration (g) value must be derived from studies of local and regional geology and seismicity. In recent years these studies have resulted in more comprehensive as well as more voluminous reports. Such an evolution has its problems. Reports commonly lack coherence and integration of subsurface and surface geology, particularly in the case of geophysical data. Cross reference is hampered when illustrations differ in scale. The geologic safety analysis should include more basic, original field investigations of the areal geology of the site and the surrounding area.

Abstract Geology and seismology studies are becoming increasingly important in nuclear power plant siting decisions. Earthquake hazard assessment is perhaps the most challenging application of these disciplines to siting. Techniques for determination of the probabilities of damaging earthquakes and forecasting of seismic events need further development before they can be routinely applied as prescribed standards to power plant siting. Although the plate-tectonics model provides a functional explanation for the loci of earthquake activity along plate boundaries, the genesis of seismicity within lithospheric plates is less well understood. The seismic potential of numerous mapped, geologic structures in many portions of the North American continent are still matters of conjecture and disagreement. The current siting criteria provide a normative procedure for establishing seismic design bases using the regional earthquake history and structural geology, together with detailed observations at the site. This process of prescribed analysis can, and has, led different investigators to contrasting conclusions. States review the seismic design conclusions of the applicant utility and the safety evaluations of the Nuclear Regulatory Commission (NRC). Outside of the utilities and the NRC, the States are virtually the only other entities with scientific expertise that regularly participate in the siting process. The State role is usually advisory and nonregulatory. States contribute extensive knowledge of regional geology and seismicity to the decision-making process. Increasingly, the State geological surveys provide comments and suggestions to the Federal government and to utilities at an early enough stage so that an extensive and helpful dialogue precedes the State’s ultimate, formal review of siting reports. In this discussion, we examine the State roles in determining the site-specific seismic-design bases for nuclear power plants. We consider the roles and perspectives of other parties as well. The scientific and procedural limitations that affect the siting process are analyzed. Finally, recommendations are made to improve the manner in which conclusions about seismic hazards at nuclear power plant sites are presented.

Abstract The combination of moderate seismic activity, sparsity of seismograph stations and relatively low density of population makes it difficult to assign quantitative seismicity values to most of the central United States. In the New Madrid seismic zone, where the level of seismic activity is higher and the number of seismograph stations is more adequate, one can delineate the active fault zone and determine a magnitude-recurrence relation. These capabilities will be extended to other seismic zones as arrays of seismographs are installed for recording microearthquakes, which will give information on fault delineation, focal mechanism, and magnitude frequency. Only after such information is available will we be able to make positive statements relating seismic activity to specific geologic features. The seismicity data suggest that earthquakes that occur outside the recognized seismic zones or major structural features will have a maximum body-wave magnitude m b of 5.5 and that this maximum value will occur only infrequently. Experience shows that if these relatively minor earthquakes are only a few kilometres deep they may have an epicentral intensity at least as large as VII (observed for an earthquake of m b = 3.8), but their magnitude and area of perceptibility will be small. With the exception of the New Madrid seismic zone and possibly the Wabash Valley seismic zone, a conservatively reasonable value for the maximum body-wave magnitude to be expected in the major seismic and structural zones of the central United States is 6.5. For the New Madrid seismic zone an earthquake of body-wave magnitude equivalent to that of a great earthquake (m b = 7.5) can be expected, on the basis of what has already been experienced in 1811-1812. Because of low anelastic attenuation, the earthquakes in the central United States are felt and cause damage over much wider areas than earthquakes of comparable magnitude in the western United States. Further consequences are that the ground shaking has a longer duration and that the ground-motion spectrum shifts at the larger distances to lower frequencies, which results in relatively low ground acceleration for relatively large ground displacements and a greater effect on high-rise than low-rise structures.

Abstract A critical review is given of the present status of the record of earthquakes in the western United States. Special field studies for siting of nuclear reactors and other major structures have brought to light major modifications and revisions of some earlier inferences on the intensity and fault location of historical earthquakes. For example, the hypocenters of the Washington State earthquake of December 14, 1872, and the Lompoc, California, earthquake of November 4, 1927, have recently been redetermined. Presentation and retrieval of both modern and historical seismicity records are still not optimum, with various errors and inconsistencies—some introduced by computer processing. Increased density of seismographic networks is providing sharper resolution in seismicity mapping. In northern California the pattern of widespread minor seismicity has been defined for the first time; earthquake foci in the Humboldt County region are concentrated in two crustal levels, 0 to 10 km and 18 to 20 km. Use of ocean-bottom seismographs is improving knowledge of the offshore seismicity pattern. Seismotectonic properties of northwestern California, Puget Sound (Washington), and the intermountain seismic belt are now emerging.

Abstract In nuclear power plant siting, redetermination of hypocenters of instrumentally recorded earthquakes in the site region may be better than relying on routinely determined hypocenter locations listed in standard earthquake catalogues. Routinely determined hypocenters, particularly those of small earthquakes or of earthquakes occurring before the mid-1950s, may be so mislocated that they present a misleading picture of the seismo-tectonics of the site region. The preferred method for redetermining a hypocenter depends on the earthquake being considered. The hypocenters of many pre-1954 earthquakes may be more accurately redetermined by now-standard computerized location techniques that were not available when the earthquakes were initially catalogued. Some important earthquakes are so poorly recorded that they cannot be assigned a hypocenter that is mathematically unique; however, it may be possible to pose a hypothesis such that the significance of the earthquake to a proposed power plant can be tested without explicitly locating the earthquake. A well-recorded earthquake whose hypocenter is suspected of being biased by lateral variations of seismic wave velocities can be more accurately located by ray-tracing methods, provided that the lateral variations of velocity are known. In an attempt to infer a fault or seismic zone from a group of hypocenters, a relative-location method—such as the master-event method or joint hypocenter determination—should be used. All methods for determining hypocenters involve assumptions over which seismologists may disagree; in the safety analysis of a nuclear power plant, these assumptions must be explicitly discussed and shown to be conservative as to their implication for the design of the plant. In addition, confidence ellipses should be given for the hypo-central coordinates, in order to assess the errors that might occur even if the assumptions of the location method are correct.

Abstract Remote-sensing data for studies of nuclear power plant sites are acquired by aerial surveys and satellite programs and include satellite photography (Landsat and Skylab); conventional black-and-white, color, and color infrared photography; thermal infrared imagery; radar imagery (side-looking airborne radar); and airborne geophysical surveys, such as aeromagnetic and aeroradiometric surveys. In general, existing data from such surveys are relatively inexpensive to obtain and offer a synoptic overview of the area, provide a large amount of information for the scale involved, and afford a technique of sampling that does not disturb the sample. In current methods of analysis, the photography, images, and maps are brought to a common scale, and existing structural geologic data are compared with a new data set, usually in the form of lineaments. The field investigations that follow include reconnaissance and detailed geologic investigations of the lineaments to detect evidence of faulting; then ground geophysical surveys, boreholes and trench studies are made. These field investigations add "ground data" to the remote-sensing base and aid in evaluating the significance of any geologic structure so defined. Two examples of recent fault studies for nuclear power plant sites, one conducted in the Virginia Piedmont tectonic province and the other in the Maryland Coastal Plain province, illustrate the potential value of remote sensing in the site selection process. When correlation of geologic maps with the several remote-sensing techniques is undertaken early in the planning stages of the siting study, it is possible to locate the nuclear power plant away from potentially hazardous geologic structures or to avoid such ambiguous geologic features as are impossible to adequately define in terms of site safety.

Abstract Microfacies analysis is a mature and sophisticated set of procedures for solving a variety of stratigraphic problems. One of the most important of these problems is the identification and definition of surfaces for stratigraphic correlation. There is virtually no end to the list of potential correlative surfaces that can be defined by microfacies analysis, particularly when used in conjunction with available mathematical techniques for the quantification of geologic data. Such procedures are particularly useful in stratigraphic units characterized by complex fades relationships, such as reef-associated paleoenviron-ments. The utility of microfacies analysis in evaluating potential sites for nuclear power plants and other engineered structures is exemplified by studies performed in conjunction with the NORCO-NP-1 nuclear power plant site in northern Puerto Rico. The definition of three microfacies (Globigerinidea, Nummulites cojimarensis, and A mphistegina spp., in ascending order) within the Quebradillas Limestone (Tertiary) at the NORCO-NP-1 nuclear power plant site demonstrated that two surfaces along which important natural gamma ray peaks occur are strati-graphically controlled rather than being controlled by dislocation surfaces, unconformities, jointing, or karstification. This was accomplished by showing that the surfaces defined by the gamma ray peaks are parallel or subparallel to two deposi-tional surfaces, the base and top of the N. cojimarensis microfacies, within the apparently massive carbonates of the Quebradillas Limestone.

Abstract Determining the time of most recent fault movement is an important part of assessing a possible site for a nuclear power plant. The purpose of this paper is not to present research information but to provide a practical guide to some of the dating techniques available to the engineering geologist working on nuclear power plant siting. Emphasis is placed on the practical aspects, such as usable minerals, conditions necessary for them to yield correct dates, degree of accuracy, sample collection, sample size, and sample packaging. In this paper, we have taken for granted the usual geologic field techniques—such as those used in stratigraphy, paleontology, and structural analysis—for assessing fault history. We discuss laboratory techniques used in conjunction with or supplemental to field methods. The specific radiometric methods discussed are 14 C (carbon-14), fission track, K-Ar (potassium-argon), thermoluminescense, Rb-Sr (rubidium-strontium), and U-Th (uranium-thorium). Racemization of amino acids, paleomagnetism, and fluid-inclusion techniques are the nonra-diometric methods that are discussed. Our experiences with some of these techniques are described as well.

Abstract The critical nature of siting nuclear power plants has led to increased emphasis on exploratory trenching. Trenching is the most definitive of all subsurface exploratory methods; it permits inspection of a continuous geologic section by both geologists and regulatory authorities and makes possible the preparation of a graphic log that delineates both obvious and subtle geologic features. About one of every two nuclear plant licensing efforts utilizes exploratory trenching. Many geologic hazards, such as "capable" faults, can be detected from trench exposures; they may otherwise remain undetected. Trenches must be judiciously located, survey-controlled, excavated safely and adequately shored, logged in detail, and properly diagnosed. Useful techniques of trench logging include thorough cleaning of the trench walls, teamwork between geologist and recorder, logging against a carefully surveyed baseline and vertical reference grid, and panoramic photography. Soils, including paleosols, and glacial and glaciofluvial deposits present some of the most difficult media to log. Trench logs must be thoroughly interpreted and correlated so that they document the geologic conditions governing suitability of the site. Age-determination techniques utilized in exploratory trenching include petrographic analyses, quartz inclusion studies, clay mineralogic analyses, and radiometric methods.

Abstract The safe siting of nuclear power plants requires knowledge of foundation conditions and faulting. Geophysical surveys and measurements are necessary to provide needed data in the early stages of a siting program, in order to supplement geologic studies. Later, detailed licensing studies may require additional geophysical measurements to supplement geotechni-cal engineering studies. Seismic methods are most commonly used for exploring localized geologic and foundation conditions at and near a plant site; gravity and magnetic measurements are often helpful in regional geologic studies. Other geophysical exploration techniques are usually reserved for specialized applications such as the search for subsurface cavities, determination of stratigraphy, slope stability studies, hydrogeology, and locating construction materials. Special seismic techniques are employed to determine dynamic elastic properties.

Abstract Evaluation of nuclear power plant sites from a material stability standpoint requires measurement of in situ dynamic properties. These are derived from measurement of shear-wave propagation velocity in subsurface materials by utilizing either the seismic downhole or seismic cross-hole techniques, or both. The downhole technique is rapid and less expensive than the cross-hole survey but is limited in maximum survey depth and resolution of thin, higher velocity beds. The cross-hole test, although less subject to depth and resolution limitations, requires more boreholes and is therefore more expensive. This test is also more exacting because of borehole drift considerations and timing corrections that may or may not be required for the particular energy source used. Actual field cross-hole examples for several sites of varied subsurface geology illustrate the variation of shear velocity versus material make-up and condition. High shear-wave velocities are characteristic of massive crystalline rock, whereas fractured rock and unconsolidated sediments show progressively reduced values. The combination of the dynamic model with a proposed design earthquake event produces the basic data upon which site evaluation from an engineering standpoint may be made. An example from a deep sand sediment site shows the increased potential for liquefaction as the strength of the design earthquake is increased.

Abstract Miniaturized borehole geophysical equipment designed for use in ground-water investigations can be adapted to investigations of nuclear power plant sites. This equipment has proved to be of value in preliminary and comprehensive studies of interior basins where thick sequences of Quaternary clastic sediment, occasionally with associated volcanic rocks, pose problems of stratigraphic correlation. The unconsolidated nature of the deposits generally requires that exploratory holes be cased, which ordinarily restricts the borehole geophysical studies to the radiation functions—natural gamma, gamma-gamma, neutron-gamma, and neutron-epithermal neutron logs. Although a single log response may be dominant in a given area, correlations derive from consideration of all log responses as a composite group. Because major correlations usually are based upon subtle differences in the physical properties of the penetrated sediment, high-resolution logging procedures are employed with some sacrifice of the quantitative parameters important to petroleum technology. All geophysical field data are recorded as hard copy and as digital information on punched paper tape. Digital data are subsequently computer processed and plotted to scales that enhance the stratigraphic data being correlated. Retention of the data in analog format permits rapid review, whereas computer plotting allows playback and detailed examination of log sections and sequences that may be attenuated on hard copy because of the logarithmic nature of the response to the physical property being examined.

Abstract Ground-water studies for nuclear power plant sites call for extraordinary and extensive effort in comparison to site investigations for more conventional, large engineering structures, primarily to assure the stability and safe operation of the plant. Providing that assurance may require unusually complex design solutions to foundation problems. Basic data collection must be extensive and thorough in response to the requirements of the Safety Analysis Report (SAR) for a detailed and well-documented description on the occurrence and movement of ground water in the site vicinity. The ground-water studies presented in the SAR must demonstrate that normal operation of the plant will not have a serious impact on the ground water and that water levels will not rise to a height that might affect the stability of plant foundations. Further, the studies must be thorough enough to assure that any accidental spill of radioactive fluid will either be dispersed harmlessly or will be intercepted by a monitoring system before the spill could percolate to a usable off-site aquifer.