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Management of Commercially Generated Radioactive Waste - U.S. ...

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F.3 GEOLOGY<br />

F.4<br />

The area in which the reference sites are situated is assumed to occupy a terrace at<br />

an elevation <strong>of</strong> 300 m above sea level (MSL). Several flat alluvial terraces comprise the<br />

main topographic features in the vicinity. Many <strong>of</strong> these terraces are lower than that at<br />

the site and lie at an average elevation <strong>of</strong> 280 m above sea level and, in general, slope<br />

away from the river at grades <strong>of</strong> 2 or 3%. The topography in the area <strong>of</strong> the site is essent-<br />

ially typical <strong>of</strong> that in the region.<br />

The rocks that underlie this region are classified as pre-Cambrian and are very old.<br />

Glaciation probably less than 1,000,000 years in age, as well as recent alluvial deposition,<br />

has mantled the older basement rocks with a variety'<strong>of</strong> unconsolidated materials in the form<br />

<strong>of</strong> glacial moraines, glacial outwash plains, glacial till and river bed sediments. This<br />

cover <strong>of</strong> young soils rests upon a surface <strong>of</strong> glacially carved deeper rock consisting sequen-<br />

tially in depth <strong>of</strong> sandstone, shale and granitic rocks. The upper surface <strong>of</strong> underlying<br />

rock can support unit foundation loads up to 73,000 kg/m 2 . The bedrock surface is<br />

irregular and slopes generally to the east or southeast.<br />

The nearest known or inferred fault is 37 km southeast <strong>of</strong> the site. There is no indi-<br />

cation that faulting has affected the area <strong>of</strong> the site in the last few million years.<br />

Within the last 100 years, only two earthquakes were recorded as having occurred within<br />

160 km <strong>of</strong> the site. The first occurred in 1917 and had an intensity <strong>of</strong> VI on the modified<br />

Mercalli scale. The epicenter was located about 100 km northwest <strong>of</strong> the site. The second<br />

occurred in 1950; it had an estimated intensity <strong>of</strong> V to VI and the epicenter was located<br />

about 130 km north-northwest <strong>of</strong> the site. For construction <strong>of</strong> facilities in this area the<br />

design basis earthquake relates to a horizontal acceleration <strong>of</strong> 0.1 g.

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