Item talk:Q229188
From geokb
{
"@context": "http://schema.org/", "@type": "WebPage", "additionalType": "Project", "url": "https://www.usgs.gov/centers/new-york-water-science-center/science/hydrogeologic-framework-mapping-long-island-new-york", "headline": "Hydrogeologic-Framework Mapping - Long Island, New York", "datePublished": "February 28, 2018", "author": [ { "@type": "Person", "name": "Frederick Stumm", "url": "https://www.usgs.gov/staff-profiles/frederick-stumm", "identifier": { "@type": "PropertyValue", "propertyID": "orcid", "value": "0000-0002-5388-8811" } }, { "@type": "Person", "name": "Michael Como", "url": "https://www.usgs.gov/staff-profiles/michael-como", "identifier": { "@type": "PropertyValue", "propertyID": "orcid", "value": "0000-0002-7911-5390" } }, { "@type": "Person", "name": "Marie A Zuck", "url": "https://www.usgs.gov/staff-profiles/marie-a-zuck", "identifier": { "@type": "PropertyValue", "propertyID": "orcid", "value": "0000-0003-2809-4734" } } ], "description": [ { "@type": "TextObject", "text": "Borehole Geophysics" }, { "@type": "TextObject", "text": "Spontaneous-potential (SP) logs \u2014provide a record of the electrical potential, or voltage, which develops at the contact between clay beds and sand aquifers within a borehole (Keys, 1990). SP logs are used to determine lithology, bed thickness, and salinity of formation water (Keys, 1990)." }, { "@type": "TextObject", "text": "Single-point-resistance (SPR) logs \u2014provide a measure of the resistance, in ohms, between an electrode in the borehole and an electrode at land surface. SPR logs are used to obtain high-resolution lithologic information." }, { "@type": "TextObject", "text": "Core Analysis" }, { "@type": "TextObject", "text": "The time domain electromagnetic (TDEM) method is a surface-geophysical technique that uses a transmitter loop and receiver coil placed on the land surface, from which an electrical current is passed through the transmitter loop creating an electromagnetic field. This field is switched on and off, which induces eddy currents in the subsurface producing a secondary electromagnetic field. The decay of this secondary electromagnetic field is then measured by the receiver coil. The amplitude of the current starts to decay immediately, which induces more current to flow, but now at a greater depth from the transmitter loop. The deeper current flow also decays, which then induces even deeper currents to flow. Data are collected at the receiver coil, with progressively later times representing the electrical properties of the deeper layers in the subsurface. These data are then processed and inverted to produce a one dimensional resistivity curve." }, { "@type": "TextObject", "text": "All borehole geophysical logs collected by the USGS are now available online. The USGS Geolog Locator can be used to obtain information on the logs that have been archived for Long Island." }, { "@type": "TextObject", "text": "Natural-gamma radiation (gamma) logs \u2014provide a record of the total gamma radiation detected in a borehole (Keys, 1990). Clays and fine-grained sediments tend to be more radioactive than the quartz sand that forms the bulk of the deposits on Long Island. Gamma logs commonly are used for lithologic and stratigraphic correlation." }, { "@type": "TextObject", "text": "Borehole-geophysical logs will be collected from new and existing observation wells to provide information that cannot be obtained by drilling and sampling alone. The geophysical-logging systems that will be used in this study provide continuous-digital records that are dependent upon the physical properties of the sediment, the rock matrix, and the interstitial fluids. At each of the drilled boreholes, natural-gamma radiation (gamma), spontaneous potential (SP), single-point-resistance (SPR), and short-and long-normal resistivity (R) logs will be collected in mud-filled open boreholes before the casing is installed, then focused electromagnetic-induction (EM) logs will be obtained after installation of the polyvinyl chloride (PVC) casing. Key existing observation wells will also be logged for EM to determine if saltwater intrusion has changed over time at that location." }, { "@type": "TextObject", "text": "Surface Geophysics (TDEM)" }, { "@type": "TextObject", "text": "Long Island is underlain by unconsolidated Holocene deposits, glacial deposits of Pleistocene age, and coastal-plain deposits of Late Cretaceous age. These sediments consist of gravel, sand, silt, and clay underlain by crystalline bedrock of early Paleozoic age (fig. 1). The bedrock is relatively impermeable, and forms the base of the groundwater-flow system on Long Island. The geologic and hydrologic units underlying Long Island have been studied and characterized by the USGS since the early 1900s. Much of this earlier work has been synthesized by Smolensky and others (1990); however, in this previous work, there continues to be uncertainty in areas of complex hydrogeology especially along the northern parts of Long Island where extensive glacial erosion and deposition has not been adequately mapped." }, { "@type": "TextObject", "text": "Surface Geophysics (H/V Passive Seismic)" }, { "@type": "TextObject", "text": "Drilling" }, { "@type": "TextObject", "text": "A synthesis of all existing lithologic data collected since the last framework compilation (Smolensky and others, 1990) will be augmented with a network of new observation wells that will be drilled in areas of complex hydrogeology to better define and reduce uncertainties in the hydrogeologic framework and to provide additional information for the numerical groundwater-flow model being developed as part of this study. Up to 25 new wells will be drilled over the next three years to collect core samples, borehole-geophysical logs, water-quality samples, and groundwater levels. In addition, surface-geophysical methods will be utilized to fill in data gaps where no wells exist. These methods include passive-seismic and time-domain electromagnetic induction." }, { "@type": "TextObject", "text": "The drilling program will consist of mud-rotary drilling and split-spoon core sampling. Most boreholes will be drilled through the unconsolidated sediments into bedrock, and core samples will be obtained at regular intervals for geologic analysis. Each drilled borehole will be cased with polyvinyl chloride (PVC) to allow for future groundwater sampling, groundwater-level measurements, and borehole-geophysical logging needed to assess long-term changes in aquifer conditions and saltwater-intrusion concerns." }, { "@type": "TextObject", "text": "Core samples obtained during drilling will be analyzed for minerology, grain size, and color (fig. 2). The core samples will be used to correlate borehole-geophysical logs and to determine contacts between hydrogeologic units. The thickness of each hydrogeologic unit will be estimated at each observation well primarily from core data obtained during the drilling, from borehole-geophysical logs, driller\u2019s logs, and through interpolation. Color descriptions of the core samples will be based on the standard Munsell color chart (Natural Resources Conservation Service)." }, { "@type": "TextObject", "text": "The spectral ratio of the horizontal and vertical components of the measured ambient seismic noise is used to determine the fundamental seismic resonance at the site. Using this method depth to bedrock measurements will be collected throughout Long Island to fill in gaps between drilled boreholes." }, { "@type": "TextObject", "text": "Focused electromagnetic-induction (EM) logs \u2014measure formation conductivity using an electromagnetic emitter coil that induces current loops within the surrounding formation to generate a secondary electromagnetic field. The intensity of the secondary field received by the receiver coil is proportional to the formation conductivity (Keys, 1990; Serra, 1984; Keys and MacCary, 1971). EM logs are used in conjunction with gamma logs to distinguish between conductive fluids and conductive clays, and have been used on Long Island to delineate the freshwater-saltwater interface (Chu and Stumm, 1995; Stumm, 1993, 1994, 2001; Stumm and Lange, 1996; Stumm and others, 2002, 2004)." }, { "@type": "TextObject", "text": "The types of geophysical logs being used for this study, and their descriptions and uses are shown below:" }, { "@type": "TextObject", "text": "Approach" }, { "@type": "TextObject", "text": "coastal-plain deposits of Late Cretaceous age" }, { "@type": "TextObject", "text": "Normal-resistivity (R) logs\u2014measure apparent resistivity in ohm-meters using two electrodes typically spaced 16 to 64 in. apart in the borehole, called short and long normal logs, respectively. R logs are used to interpret lithology and water salinity (Keys, 1990)." }, { "@type": "TextObject", "text": "Home" }, { "@type": "TextObject", "text": "The H/V seismic method is considered a \"passive\" seismic method because it does not require an explosive charge or hammer blow to induce seismic noise (fig. 3). The H/V method measures three components of ambient seismic noise, which include micro tremors induced by wind, ocean waves, and anthropogenic (human) activity. The measured data are the vertical and two horizontal (north-south and east-west) components of the seismic noise." } ], "funder": { "@type": "Organization", "name": "New York Water Science Center", "url": "https://www.usgs.gov/centers/new-york-water-science-center" }, "about": [ { "@type": "Thing", "name": "Energy" }, { "@type": "Thing", "name": "Geology" }, { "@type": "Thing", "name": "Hydrogeologic Characterization" }, { "@type": "Thing", "name": "Mapping Application Development" }, { "@type": "Thing", "name": "Science Technology" }, { "@type": "Thing", "name": "Coastal Science" }, { "@type": "Thing", "name": "Environmental Health" }, { "@type": "Thing", "name": "aquifers" }, { "@type": "Thing", "name": "Groundwater Flow Modeling" }, { "@type": "Thing", "name": "Groundwater and Streamflow Information" }, { "@type": "Thing", "name": "Geophysics" }, { "@type": "Thing", "name": "Long Island" }, { "@type": "Thing", "name": "Water" }, { "@type": "Thing", "name": "Information Systems" }, { "@type": "Thing", "name": "Groundwater Monitoring" }, { "@type": "Thing", "name": "Methods and Analysis" } ]
}
