This is the ninth in the 2021 Monthly Online Presentation Series!
New York City has a complex geologic history spanning more than 1.1 billion years The bedrock that makes up New York City are composed of igneous, sedimentary and metamorphic rocks. The oldest rock in New York City is the Fordham Gneiss, a metamorphic rock. All the bedrock outcrops are exposed in the boroughs of the Bronx, Manhattan, Northwest Queens and Staten Island. Most of the bedrock that was exposed have been removed by excavations for foundations of buildings and other structures, installation of subsurface utilities, construction of subway and railroad routes and construction of streets and highways which are covered by concrete sidewalks and asphalt street pavements. A soil cover of unconsolidated deposits composed of sand, silt and clay with variable amounts of gravel, pebbles, cobbles and boulders covers the bedrock. These deposits span more than 65 million years and are resting on the bedrock of New York City. Today most of the shallow soil cover throughout the five boroughs is urban fill. They are transported soils from urban activity that includes digging, drilling, tunneling and excavating the surface and subsurface soils and then these spoils are dumped throughout New York City. Mixed with the urban fill are contaminated materials that have an environmental impact to humans. The source of these contaminated soils come from leaking oil tanks, electric transformer oils and other hazardous chemicals and materials.
The surface drainage of New York City is variable through the five boroughs. There are numerous rivers, stream, creeks and brooks as well as ponds, lakes, reservoirs and wetlands in all the boroughs. The topography dictates location and flow of these features on the land surface. Subsurface water throughout the City should be included in the Geologic Site Investigation in order to understand the movement, depth, chemical composition and the physical properties of groundwater. The groundwater in Brooklyn and Queens Counties are part of Long Island Sole Source Aquifer System. In the past, eastern Queens drinking (potable) water supply was groundwater. Today the drinking water is distributed to all boroughs from the Upstate Reservoirs through Aqueducts, Water Tunnels, Trunk Mains and finally the local water mains. Groundwater today in New York City is mostly used for commercial and industrial use. Residential home use is mostly for watering lawns, shrubs and trees.
The urbanization history of New York City has taken more than 400 years and an presently has expanded New York City City's land and water area to approximately 302 square miles. The original City was made up of small towns or neighborhoods with the remaining areas being rural or farmlands. Today most of the original or natural land area are found in parks and cemeteries. As time went by , the recovery of coastal lands under water were built up to expand New York City land area. The water area has decreased from these changes. The harbor and river channels were deepened to allow ships to navigate these coastal waters too. Original topography in these areas are now buried from these activities.
The Role of Geology in Planning. Design and Construction Throughout New York City requires collaboration with Geotechnical Engineers, Architects and Project Managers. The Geologic Site Investigation research of a project site requires one to compile a Geologic Database of historical geology information including maps, boring logs, groundwater data, hydrologic data, environmental data, seismic data, digital reports, digital books, etc.. Today you can acquire most of this information easily from the internet using any number of search engines like Google and Bing. Also, the Geologic Site Investigation research should include GIS Site Maps like DOITT NYC Maps, Oasis NYC Maps, etc., Subsurface Utility Interference Maps, NYC Tax Maps, NYC Fire Insurance Maps like Sanborn Maps, Belcher and Hyde Maps, Beers Maps, etc., USGS 7.5 Topographic Quadrangle Maps (NYC), NYC Aerial Photographs, NYPL Old NYC Digital Pictures and other resources containing data within the area of the site.
All of the above listed data are compiled into a Geological Database to be used in Planning, Design and Construction Throughout New York City of Civil Works Projects.
KEYWORDS: Geologic Database, Geologic Site Investigation, GIS Maps, Subsurface Utility Interference Maps, Tax Maps, Fire Insurance Maps, Aerial Photographs, Digital Pictures, Civil Works Projects
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*Bio: Dennis Askins was employed as a Project Manager\NYS Professional Geologist with Program Administration, Front End Planning – Engineering Support Services, Infrastructure Division for New York City Department of Design and Construction before retiring in January 2020. He has worked as a geologist with city agencies since 1990, and has more than 30 years of experience. He holds a Professional Geologist License in the State of New York. Prior to 1990 he owned an environmental service company. He received a bachelor of science in geology from Brooklyn College, CUNY, in 1980. He specializes in environmental and engineering geology. He has published many papers in the field of geology (2003 to 2019). He is a contributor to USDA NYC Soil Survey, Bronx Watershed, 2008 with NYCDDC Soil Data for this study. He peer reviewed the geology section of NYCDDC 2nd Edition Geothermal Heat Pump Manual, 2013. He has given presentations on the geology of Geothermal Heat Systems to other NYC Agencies. As a Professional Geologist employed by NYCDDC Infrastructure Division he lectured on "Subsurface Interference Investigation In Design and Construction in New York City" to engineers, architects and project managers from various NYC Agencies. Dennis Askins is an Expert on Buried Tracks from past transportation surface street and rail systems throughout the 5 boroughs. He authored the 2011 “NYC DDC Trolley Tracks, Yokes and Elevated Subway Foundation Investigation Book” that are used by engineers with NYCDDC, NYCDOT and NYCSCA. Presently Dennis Askins is doing geologic research for several new school sites for NYCSCA in New York City.
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