Guidebook for the PITTSBURGH GEOLOGICAL SOCIETY Field Trip Saturday May 5, 2001 The Geology, Environmental Geology, and Engineering Geology Of Western Allegheny County, Pennsylvania Trip Leaders: Wendell L. Barner, IT Corporation Brian H. Green, U.S. Army Corp of Engineers, Pittsburgh District Chuck H. Shultz, Slippery Rock University For additional copies of this field trip guidebook, contact: Pittsburgh Geological Society PO Box 58172 Pittsburgh, P A 15209 --------------------- TABLE OF CONTENTS INTRODUCTION .............................................................................................................. 1 PHYSIOGRAPHY .............................................................................................................. ! STREAMS AND TERRACES ........................................................................................... 2 STRATIGRAPHY .............................................................................................................. 2 STRUCTURE ..................................................................................................................... 4 MINERAL RESOURCES .................................................................................................. 5 Fossil Fuels ............................................................................................................. 5 Iron Ore ................................................................................................................... 5 Non-Metallic, Non-Fuel Resources .................................................................................... 6 WATER RESOURCES ...................................................................................................... 7 Road Log ................................................................................................................. 8 Stop 1. Overview ofChartiers Valley ................................................................................. 8 HISTORY ................................................................................................................ 8 Native Americans in the Chartiers Valley ............................................................ 9 The Stoops and Other Early Settlers .................................................................. 11 Stop 2. Monongahela Formation/Pittsburgh, Redstone and Sewickley Members ........... 13 Stop 3 ............................................................................................................................... 13 Stop 4 ............................................................................................................................... 14 Stop 5 ............................................................................................................................... 15 Stop 6 ............................................................................................................................... 15 Stop 7 .......•....................................................................................................................... 16 Scrubgrass Water Project Overview .................................................................. 16 Alternate Route and Field Trip Stops ............................................................................... 17 Stop A-1 ............................................................................................................................ 17 Stop A-2 ............................................................................................................................ 17 Stop A-3 ............................................................................................................................ 18 Main Road Log ................................................................................................................. 18 Alternative Road Log ........................................................................................................ 18 Stop A-4 ............................................................................................................................ 18 Stop 8 ............................................................................................................................... 19 Engineering Geology and Foundation Design for the Braddock Dam In-The-Wet Construction Project. ............................................................................................. 19 IN-THE-WET CONSTRUCTION OF A NEW GATED DAM BRADDOCK LOCKS AND DAM, MONONGAHELA RIVER, PA ........................................ 20 INTRODUCTION .............................................................................................. 20 IN-THE-WET OVERVIEW .............................................................................. 21 FABRICATION OF FLOAT-IN DAM SEGMENTS ....................................... 22 DAM FOUNDATIONS ..................................................................................... 23 TRANSPORT OF FLOAT-IN DAM SEGMENTS ........................................... 24 OUTFITTING OF FLOAT-IN DAM SEGMENTS .......................................... 24 POSITIONING AND SET-DOWN OF DAM SEGMENTS ............................ 25 UNDERBASE GROUTING AND INFILL OPERATIONS ............................. 25 TAILRACE CONSTRUCTION ........................................................................ 26 ~---------- TABLE OF CONTENTS (Continued) COMPLETION OF DAM PIERS ...................................................................... 26 INSTALLATION OF TAINTER GATES ......................................................... 27 CONSTRUCTION OF LEFT CLOSURE WEIR .............................................. 27 CLOSING ........................................................................................................... 27 Stop 9 ............................................................................................................................... 28 Alternate Field Stop A-5 ................................................................................................... 28 Stop 10 .............................................................................................................................. 29 REFERENCES CITED ..................................................................................................... 31 11 Pittsburgh Geological Society May 5,2001 Annual Field Trip GEOLOGY OF THE PITTSBURGH AREA By John A. Harper Pennsylvania Geological Survey INTRODUCTION The first references to geologic topics in the Pittsburgh area date from the early 1800s (Aigster, 1813; Meade, 1828; Daubeny, 1839). However, much of what we now considered to be the basic geologic knowledge of western Pennsylvania languished until Henry Darwin Rogers' First Geological Survey of Pennsylvania examined the entire state in the late 1830s and finally reached publication in the late 1850s (Rogers, 1858). The Second Geological Survey of Pennsylvania under J.P. Lesley provided even more information. Field investigations by Stevenson (1876, 1877 and 1878) and White (1878) produced seminal volumes of geological work during this period, including descriptions of coals, limestones, and other mineral commodities, and geologic maps of the areas studied. Both of these geologists later published syntheses of their work and the works of others (White, 1891; Stevenson, 1906) that helped establish much of the stratigraphic and structural nomenclature of western Pennsylvania. Follow-up studies during the third and fourth surveys provided a wealth of data and interpretations in geologic atlases and folios by Hughes (1933), Johnson (1928, 1929), Munn (1910, 1911a, 1911b), Shaw and Munn (1911), and Woolsey (1905, 1906) that stand, for the most part, as (if you'll pardon the pun) a rock solid foundation for later economic, geologic, geotechnical, and environmental investigations. It was these reports that provided the basis for the six­ county Pittsburgh Regional Environmental Geologic Study (PREGS) during the 1970s (see the synopsis by Briggs, 1977) and many other more recent works. PHYSIOGRAPHY Most of southwestern Pennsylvania lies within the Appalachian Plateaus physiographic province, an area having a generally level surface at an altitude great enough to permit erosion of deep valleys by streams. This level surface results from the essentially flat-lying nature of the bedrock near the earth's surface. The area around Pittsburgh, including Allegheny, Beaver, and Washington counties, is further subdivided into the Pittsburgh Low Plateau Section. The topography in this section is characterized by a relatively small amount of relief (Sevon, 1996). The hilltops in this area stand at about equal elevations, approximately 1,100-1,300 ft (335-400 m) above sea level, or about 350-550 ft (105-165 m) above the level ofthe rivers. By comparison, relief in the neighboring Allegheny Mountain Section to the east (from Chestnut Ridge to the Allegheny Front) commonly exceeds 1,500 ft (460 m) in the vicinity of the prominent high ridges that characterize that section. Most of the hilltops of western Pennsylvania are the remnant of an ancient, relatively broad, relatively flat surface formed during the Cenozoic. This surface has been highly dissected by numerous antecedent streams, at least some of which probably became established during the Mesozoic (Sevon, 1993). This surface sloped very gently toward the northwest, toward the area of the present-day Great Lakes. At least the larger streams probably meandered in broad, shallow valleys cut only a little