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<br />0D22~ 1 <br /> <br />Durango Pumoing Planl- Slage 1 <br /> <br />combination ofthe Quaternary deposits, including slope wash, alluvium, <br />and glacial outwash terrace deposits that will be encountered at the site. <br /> <br />2. Bedrock. - Bedrock at the proposed pumping plant site includes the younger <br />Menefee Formation and the older Point Lookout Sandstone both of the Upper <br />Cretaceous Age Mesa Verde Group. On a regional scale, the Menefee Formation <br />conformably overlies the Point Lookout Sandstone, however, within the site, the <br />Menefee is down-dropped on the southeast side of a northeast trending normal <br />fault (Fault F-I) and is juxtaposed against the Point Lookout Sandstone (see <br />Drawing 69-529-5). Bedrock lithologic descriptions were developed primarily <br />from drill core obtained at the pumping plant site and represent only that portion <br />of the respective geologic units encountered during drilling. The lack of marker <br />beds in the Point Lookout Sandstone prevented correlation of individual beds on <br />the geologic sections. Numerical rock descriptors used in the geologic logs are <br />described in the Bureau of Reclamation Engineering Geology Field Manual. <br />Excavation at the pumping plant will encounter the Point Lookout Sandstone. <br />The Menefee Formation, lying south and east of the pumping plant excavation, <br />will be encountered in several trench excavations southeast ofthe fault. <br /> <br />a. Menefee Formation. - <br /> <br />( <br />~ <br /> <br />The Menefee Formation consists of interbedded sandstone and <br />siltstone with occasional beds of coal and shale. The sandstone is <br />typically fine to medium grained, quartzose, predominantly thinly <br />to medium bedded, locally crossbedded, and light gray. Intense <br />weathering, with iron staining throughout, generally extends less <br />than five feet below the top of rock and grades with increasing <br />depth to slightly weathered to fresh rock. The slightly weathered <br />rock is typified by occasional iron stains which are restricted to <br />joint, fracture, and bedding surfaces. The sandstone is generally <br />moderately to well cemented, moderately hard to hard, and <br />requires a moderate to heavy hanuner blow to break core along <br />bedding. Occasional coal and carbonaceous siltstone is present as <br />laminae along bedding. <br /> <br />2) The siltstone is often sandy, occasionally carbonaceous, <br />predominantly latninated to very thinly bedded, well indurated, and <br />dark gray. It is slightly more susceptible to weathering and erosion <br />than the sandstone and is, therefore, most often observed near the <br />top of rock as softer interbeds within a more resistant sandstone <br />unit. The siltstone ranges from soft where intensely weathered to <br />moderately hard where fresh. <br /> <br />3) Shale generally occurs as interlaminae within siltstone beds. It is <br />laminated with planar to convoluted bedding, is dark gray, and <br />moderately soft. It slakes upon being exposed to air. The core can <br />usually be broken across bedding with moderate manual pressure. <br />The coal is black, brittle, laminated to thinly bedded, slightly <br />weathered to fresh with occasional iron staining along bedding and <br />fracture surfaces, moderately soft, and intensely fractured. <br /> <br />1) <br /> <br />Geology <br />00320 - 9 <br />