Open File Reports

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    Bedrock Geologic Map of the Delaware Piedmont
    (Newark, DE: Delaware Geological Survey, University of Delaware, 2021-06) Schenck, W.S.
    The Piedmont rock units in Delaware, and bedrock geologic map of Schenck et al. (2000) are revised in this report based on new rock geochemistry, geochronometric data, petrography, and recent detailed mapping. Major revisions include: • revising the extent of the Christianstead Gneiss and Windy Hills Gneiss • abandoning the Wissahickon Formation as originally mapped in Delaware by Bascom (1902, 1905) and Bascom et al. (1909, 1920, and 1932) and replacing it with the Mt. Cuba Gneiss, a lithodeme of the West Grove Metamorphic Suite (Bosbyshell et al., 2012, 2013, 2014, 2015), and reserving the Wissahickon Schist/Formation for the metasediments on the east side of the Wilmington Complex magmatic arc and referring to them herein as Wissahickon Formation (restricted sense) • extending the Rosemont Shear Zone from Pennsylvania southwest through Delaware to Maryland separating the Mt. Cuba Gneiss and the Wilmington Complex • formally naming and describing two new units in the Wilmington Complex - the Greenville Gabbro and the Thompsons Bridge Gneiss. Additional Notes Plate 1 of OFR54 can also be viewed in a Web Mapping Application. Layers can be turned on and off and manipulated under the "Layers" icon in the upper right hand corner. Cross section is available by clicking on the cross section line. Rock unit descriptions available by clicking on the geologic map. OFR54 Plate 1 (Bedrock Geologic Map of the Delaware Piedmont) Web Mapping Application Plate 1 Summary The vector data set contains the rock unit polygons for the surficial geology for DGS Open File Report 54 - Plate 1. The Piedmont rock units in Delaware, and bedrock geologic map of Schenck et al. (2000) are revised on this map based on new rock geochemistry, geochronometric data, petrography, and recent detailed mapping. Major revisions include: • revising the extent of the Christianstead Gneiss and Windy Hills Gneiss • abandoning the Wissahickon Formation as originally mapped in Delaware by Bascom (1902, 1905) and Bascom et al. (1909, 1920, and 1932) and replacing it with the Mt. Cuba Gneiss, a lithodeme of the West Grove Metamorphic Suite (Bosbyshell et al., 2012, 2013, 2014, 2015), and reserving the Wissahickon Schist/Formation for the metasediments on the east side of the Wilmington Complex magmatic arc and referring to them herein as Wissahickon Formation (restricted sense) • extending the Rosemont Shear Zone from Pennsylvania southwest through Delaware to Maryland separating the Mt. Cuba Gneiss and the Wilmington Complex • formally naming and describing two new units in the Wilmington Complex - the Greenville Gabbro and the Thompsons Bridge Gneiss.
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    Delaware Geological Survey Petrographic Data Viewer
    (Newark, DE: Delaware Geological Survey, University of Delaware, 2021-05) Schenck, W.S.; Wang, L.T.
    Petrography is a branch of geoscience focused on the description and classification of rocks, primarily by microscopic study of optical properties of minerals. A thin sliver of rock is cut from a sample, mounted on a glass slide, ground to approximately 30 microns (0.03mm), and viewed under a microscope that uses polarized light. By observing the colors produced as plain polarized light and crossed (90 degrees) polarized light shines through the minerals, petrologists can determine the minerals that comprise the sampled rock. The data and photomicrographs of thin sections within the Delaware Geological Survey (DGS) Petrographic Data Viewer represent the total collection of the Delaware Geological Survey for the Delaware Piedmont and surrounding areas. The data viewer includes slides from DGS research, slides donated by researchers, and slides culled from class reports, master's theses, and Ph.D. dissertations. Within the application, the “Slide Made For” field identifies the original owner of the thin section. The researchers include: John Branca, A.D. Cohen, Bernard Dirska, Gregory S. Ghon, G. Michael Hager, C. Scott Howard, Guy W. Metz, Margaret O. Plank, LeAnn Srogi, Richard F. Ward, and DGS. Existing data/slide descriptions have been included; however, no attempt was made to change the data/descriptions originally prepared by these researchers other than to correct typographical errors. These data appear as they were originally presented unless noted that modifications were made at a later date. Additional Notes The zoom tool allows one to focus on an area of interest. Click on an outcrop (sample) location to open a popup window containing the data for the selected sample(s). The popup window also includes thumbnail photomicrographs of the thin section in both plain polarized light and crossed polarized light. Click the thumbnail to open a full-size image. If interested in specific outcrops or thin sections, use the search tool to query by DGS outcrop ID, lithology, or address. Launch the Delaware Geological Survey Petrographic Data Viewer References Branca, J., 1979, Petrology and structure of the Glenarm Series and associated rocks in the Mill Creek area, Delaware: Newark, Delaware, University of Delaware, unpublished Master's thesis, 84 p. Cohen, A. D., 1964, Petrologic analysis of the gneisses at Windy Hills Bridge, Delaware: Newark, Delaware, University of Delaware, unpublished Geo402 class paper, DGS Sample/thin section record only. Dirska, B., 1990, Petrology and evolution of the plutonic igneous rocks of the Wilmington Complex, northeastern northeastern Delaware and southeastern Pennsylvania: Newark, Delaware, University of Delaware, unpublished Master's thesis, 227 p. Gohn, G.S., John, C.J., Hager, G.M., Niemann, N.L., Grundl, T.J., Bair, P.L., Dempsey, J.M., Ferris, L.A., and Lazzeri, J.J., 1974, Reconnaissance geology of the Mill Creek uplift, northeastern Delaware and southeastern Pennsylvania Piedmont: Newark, Delaware, University of Delaware, unpublished report, 23 p. Hager, G. M., 1976, Petrologic and structural relations of the crystalline rocks in the Hoopes Reservoir area, Delaware: Newark, Delaware, University of Delaware, unpublished Master's thesis, 79 p. Howard, C. S., 1984, Geological and geophysical investigations in the Wilmington Complex/Wissahickon Formation boundary area, Delaware Piedmont: Newark, Delaware, University of Delaware, unpublished Master's thesis, 258 p. Metz, G. W., 1988, The petrology of the cordierite-bearing gneisses near Montchanin, Delaware: Newark, Delaware, University of Delaware, unpublished senior thesis, 44 p. Plank, M. O., 1989,Metamorphism in the Wissahickon Formation of Delaware and adjacent areas of Maryland and Pennsylvania: Newark, Delaware, University of Delaware, unpublished Master's thesis, 111 p. Srogi, L., 1988, The petrogenesis of the igneous and metamorphic rocks in the Wilmington Complex, Pennsylvania-Delaware Piedmont: Philadelphia, Pennsylvania, University of Pennsylvania, unpublished Ph. D. dissertation, 613 p. Ward, R. F., 1958, Petrology and metamorphism of the Wilmington Complex Delaware adjacent Pennsylvania and Maryland: Philadelphia, Pennsylvania, Bryn Mawr College, unpublished Ph. D. dissertation, 103 p.
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    Kent County Groundwater Monitoring Project: Results of Subsurface Exploration
    (Newark, DE: Delaware Geological Survey, University of Delaware, 2019-09) Andres, A.S.; McQuiggan, R.W.; He, C.
    This report documents the methods and results derived from subsurface exploration, monitoring well installation, and hydraulic testing conducted during the project "Groundwater and Saline Water Intrusion Monitoring Network Infrastructure Improvements: Kent County, Delaware". This project was focused on the aquifers in Kent County that supply water to wells for domestic, public, irrigation, and commercial uses as well as provide base flow to local streams. From shallowest to deepest, they are the Columbia, Milford, Frederica, Federalsburg, Cheswold, Piney Point, Rancocas, and Mt. Laurel aquifers.
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    Results of Groundwater Flow Simulations In the East Dover Area, Delaware
    (Newark, DE: Delaware Geological Survey, University of Delaware, 2018-08) He, C.; Andres, A.S.
    In 2015, staff of the Water Supply Section of the Delaware Department of Natural Resources and Environmental Control (DNREC) informed the DGS of their concerns about overpumping of the unconfined Columbia aquifer in an area east of Dover (Figure 1). In this area, the City of Dover’s Long Point Road Wellfield (LPRW) and numerous irrigation systems pump water from the shallow Columbia aquifer. Overpumping is a cause for concern because it may 1) increase the risk for saltwater intrusion into the aquifer from saline tidal creeks and marshes and, 2) induce extra drawdown that could reduce the transmissivity of the aquifer and decrease well yields. The potential for overpumping will become more significant when an electric generating station served by the LPRW is expected to increase capacity and requires more water. This report summarizes monitoring and modeling that were conducted to investigate the potential impacts of overpumping. Automated water level and salinity sensors were installed and operated in three monitoring wells, and a digital groundwater flow model was constructed. The model was run in both steady-state and transient modes. As is the case with most models, many assumptions and simplifications had to be made because of data limitations. The model was calibrated to a spatially limited set of data. Consequently, model outputs are meant to inform how the aquifers behave given the assumptions and simplifications and will not represent precise predictions of water pressures in the area represented by the model. Additional data are now being collected in the model domain to refine the accuracy and precision of model results.
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    Groundwater Monitoring Procedures Part 1: Equipment and Procedures for Manual and Automated Field Measurement of Groundwater Levels in Dedicated Monitoring Wells
    (Newark, DE: Delaware Geological Survey, University of Delaware, 2018-08) Andres, A.S.; He, C.; McKenna, T.E.
    The Delaware Geological Survey (DGS) has measured, managed, and distributed groundwaterlevel data for several decades using widely accepted procedures and practices, many of which were derived from interactions with staff of the USGS, consulting firms, and other state agencies. Many of the individual methods and procedures have been described in DGS reports, however, written documentation for these tasks have not been assembled in a single published document. The need for such a document has become more apparent with the development of standards for participation in the National Ground-Water Monitoring Network (SOGW, 2009). This document describes methods used by the DGS for routine manual and automated measurement of groundwater levels in dedicated monitoring wells. Alternative methods used for manual measurement of water levels in other types of wells are noted in this document to provide reference for historical measurements but not described in detail. These methods are excerpted and modified from procedures described by federal agencies and national standards organizations (e.g., ASTM, D4750-2007; Drost, 2005; USEPA, 2007). In this document, the term water levels will be used interchangeably with groundwater levels. Please refer to these and other appropriate documents for additional guidance or contact DGS staff with specific questions. Practices pertaining to data processing and management, metadata, and quality assurance procedures for electronic data are rapidly evolving. Additional sections on these topics will be added to this document as time and resources permit.