NMP Unit 2 USAR 2.5 GEOLOGY, SEISMOLOGY, AND GEOTECHNICAL ENGINEERING This section provides information regarding the seismic and geologic characteristics of the site and region surrounding the site. Extensive geologic and related explorations were conducted at Unit 2, and can be categorized as: 1) general exploration; 2) bedrock investigation and mapping; 3) supplementary geologic exploration; and 4) rock mechanics investigation. Extensive geophysical surveys were performed, including seismic refraction profiling and downhole logging. The principal consultant for performing these studies was Dames & Moore, as identified in Section 1.4.5. Unit 2 is located on the southeast shore of Lake Ontario near Scriba, within a portion of the Central Lowlands Physiographic Province and the northern part of the Appalachian Basin Geologic Province. Unit 2 is situated within the Eastern Stable Platform Tectonic Province. The results of the investigations indicate that the site is relatively tectonically stable and is free of major active tectonic structures. There are no known capable faults within 8 km of the site, and there is no potential for surface faulting within the site area. The subsurface materials at the Unit 2 site are not adversely affected by collapse, subsidence, or uplift. The ground motion level for the SSE was calculated using conservative correlations sufficiently representative of seismic wave transmission characteristics of the site. 2.5.1 Basic Geologic and Seismic Information Section 2.5.1 provides the basic geologic and seismic information required for evaluation of the content in other sections of Section 2.5. Section 2.5.1 is subdivided on the basis of information pertaining to the region (Section 2.5.1.1) and information pertaining specifically to the site (Section 2.5.1.2). The topics discussed for both the region and site are similar, consisting of physiography, stratigraphy, geologic structure, geologic history, regional geologic hazards, and site engineering geology. 2.5.1.1 Regional Geology This section provides basic regional geologic information required for evaluation of the content in other sections of Section 2.5. Section 2.5.1.1 is subdivided on the basis of general topics pertaining to the regional geology. Regional physiography and geologic setting are described in Section 2.5.1.1.1. The stratigraphy and structural geology of the site region are discussed in Sections 2.5.1.1.2 and 2.5.1.1.3, respectively. A synopsis of the geologic history of the region is provided in Section 2.5.1.1.4. Natural geologic hazards and hazards that might be induced by man's activities are discussed in Section 2.5.1.1.5. Chapter 02 2.5-1 Rev. 22, October 2016 NMP Unit 2 USAR 2.5.1.1.1 Physiography and Geologic Setting Unit 2 is located on the southeast shore of Lake Ontario, in the town of Scriba, Oswego County, NY. It is situated about 10 km (6.2 mi) northeast of the city of Oswego and about 53 km (32.8 mi) northwest of Syracuse, NY (Figure 2.5-1). Physiography The Nine Mile Point site is situated within the Erie-Ontario Lowlands, a subdivision(1) of the Central Lowlands Physiographic Province (Figure 2.5-2) . The Erie-Ontario Lowlands subprovince is bounded on the south by the Appalachian Uplands Province, on the north by the Canadian Shield, and on the east by the Tug Hill Upland and the Adirondack Highlands. To the northeast, the Erie-Ontario Lowlands is separated from the St. Lawrence Lowlands by the Frontenac Axis. The Erie-Ontario Lowlands extend southward from the site about 56 km (35 mi) to the Portage Escarpment which forms the boundary between the lowlands and the Appalachian Uplands Province, and westward into Canada near Niagara Falls. Differential erosion of southerly dipping, relatively more resistant carbonate rock of the Lockport and Onondaga Formations has resulted in east-west trending cuestas within the lowlands. The generally flat to gently undulating topography of the Erie-Ontario Lowlands is superimposed upon an erosional bedrock surface of irregular, low relief. The land surface rises gradually to the south and southeast from an elevation of 75 m (246 ft) above msl at the southern shore of Lake Ontario to an elevation of approximately 152 m (500 ft) above msl at the Allegheny Escarpment. A veneer of glacial deposits such as tills, glaciofluvial sediment, and proglacial lake sediments covers most of the area. The deposits occur as drumlin fields and recessional moraines. Postglacial weathering and stream erosion have modified the terrain only slightly. Geologic Setting The region around the Unit 2 site has been subdivided by geologists into various geologic provinces, that is, large areas that are unified with respect to lithofacies development and gross structural style. The boundaries of geologic provinces typically (although not always) coincide with those of the physiographic provinces identified above. Thus, in the literature, the names are often used interchangeably in descriptions of geologic setting. A regional geologic map (Figure 2.5-3) identifies the geological provinces used in this subsection to characterize the geologic setting. The Unit 2 site is situated within the northern part of the Appalachian Basin geologic province in New York State (Figure Chapter 02 2.5-2 Rev. 22, October 2016 NMP Unit 2 USAR (2,3) 2.5-3) . The bedrock at the site consists of early Paleozoic marine sediment underlain by Precambrian crystalline rock at a depth of approximately 457 m (1,500 ft). The Appalachian Basin is elongate, trending northeast-southwest, and is bounded by the Precambrian rocks of the Canadian Shield to the north, and the Adirondack Massif to the northeast. The latter two are linked by the Frontenac Axis across the St. Lawrence River Valley. To the west, the Appalachian Basin is bounded by the(2) Findlay Arch and its northward extension, the Algonquin Axis . The Findlay Arch represents a structural rise in the crystalline basement rock, over which the Paleozoic sediment thins substantially. Westward, beyond the Findlay Arch, lies the Michigan Basin, another geologic province. The eastern boundary of the Appalachian(4) Basin geologic province is termed the South Mountain Front because rocks to the southeast of the front are(5) metamorphosed, whereas those of the Appalachian Basin are not . In Canada this boundary is approximately equivalent to Logan's Line (Figure 2.5-3). The Appalachian Basin extends as far south as Alabama (Figure 2.5-2). The Unit 2 site is located in a portion of the Appalachian Basin geologic province that is characterized by few deformation features despite the long history of the site bedrock (Sections 2.5.1.1.4 and 2.5.1.2.6). The regional structural geology is presented in Section 2.5.1.1.3, and the site structural geology is discussed in Sections 2.5.1.2.3 through 2.5.1.2.5. Knowledge of the geologic setting is important to the discussion of regional tectonic provinces, which are presented and discussed in Sections 2.5.2.2 and 2.5.2.3 (Figure 2.5-4). 2.5.1.1.2 Stratigraphy The regional stratigraphic succession in New York and adjacent Canada is illustrated by the map (Figure 2.5-3) and cross sections provided (Figures 2.5-5 and 2.5-6). Figure 2.5-7 further depicts the relationship between stratigraphic units investigated at the site and the regional stratigraphy. Precambrian Basement Crystalline basement rocks of Precambrian age are exposed north and northeast of the Unit 2 site in three areas: 1. The Adirondack Massif 80 km (50 mi) northeast. 2. The Frontenac Axis of the Thousand Islands region 121 km (75 mi) north. 3. The Canadian Shield of Ontario and Quebec Provinces, Canada 145 km (90 mi) north. In general, the Precambrian basement rocks of these three areas are divided into two broad(6-8) geologic provinces and several subprovinces and belts which are illustrated on the regional Chapter 02 2.5-3 Rev. 22, October 2016 NMP Unit 2 USAR geologic map (Figure 2.5-3). In western Ontario, the Superior subprovince of the Canadian Shield is separated from the neighboring Grenville subprovince of central and eastern Ontario and Quebec by the Grenville Front (Figure 2.5-3). The crystalline rocks of the Superior subprovince (metamorphosed igneous and sedimentary rock) are of Archean(9) age, that is, more than approximately 2.6 billion years old . Southeast of the Grenville Front, the Grenville subprovince consists of largely high-grade metamorphic rocks, whose ages range from Archean in the northwest to Early and Medial Proterozoic(7,9) (2.6 to 1.1 billion yr ago) near the St. Lawrence valley . The Grenville subprovince consists of both orthogneiss and paragneiss surrounding a central belt of paragneiss. This belt(6) (Figure 2.5-3) is termed the Central Metasedimentary Belt . The terrain of mixed gneisses of Canada and the Adirondacks is understood to represent the pre-Grenville Precambrian "basement" shallow platform upon which the protolithic sediments and volcanics(9) were deposited in Proterozoic time (1.1 to 1.4 billion yr ago) . These particular paragneisses(6,7) are termed the Grenville Series or the Grenville Supergroup . The Late Precambrian sediments underwent progressive, high-grade metamorphism culminating approximately 1.1 billion yr ago, during an event known as the Grenville Orogeny. The sediments were altered to marble, quartzite, quartzofeldspathic gneiss, granulite, leucogranitic gneiss, and amphibolite. The gneisses bordering the Central Metasedimentary Belt in western Ontario consist largely of quartzofeldspathic paragneisses, whereas those in the Adirondack Massif consist(10) of intermediate igneous rocks with granitic rocks and marbles . Local igneous intrusives ranging from felsic to mafic occur throughout the Grenville subprovince.