Delaware Geological Survey
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The Delaware Geological Survey (DGS) was first established by the General Assembly in 1837. It was reestablished by that body in 1951 and is a senior natural resources unit in Delaware. The Delaware Geological Survey's mission is, by statute, geologic and hydrologic research and exploration, and dissemination of information through publication and public service.
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Item Ages Of The Bethany, Beaverdam, And Omar Formations Of Southern Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1990-02) Groot, J.J.; Ramsey, K.W.; Wehmiller, John F.The microflora of the Bethany formation and the lower part of the Beaverdam Formation is characterized by a Quercus-Carya assemblage, very few non-arboreal pollen, and Pterocarya and Sciadopitys as exotic constituents. This assemblage has much in common with that of the Brandywine Formation of Maryland and the Eastover Formation of Virginia which are of late Miocene or early Pliocene age. The environment of deposition of the Bethany was probably deltaic, and that of the lower Beaverdam fluviatile.Item Analysis And Summary Of Water-Table Maps For The Delaware Coastal Plain(Newark, DE: Delaware Geological Survey, University of Delaware, 2008) Martin, M.J.; Andres, A.S.A multiple linear regression method was used to estimate water-table elevations under dry, normal, and wet conditions for the Coastal Plain of Delaware. The variables used in the regression are elevation of an initial water table and depth to the initial water table from land surface. The initial water table is computed from a local polynomial regression of elevations of surface-water features. Correlation coefficients from the multiple linear regression estimation account for more than 90 percent of the variability observed in ground-water level data. The estimated water table is presented in raster format as GIS-ready grids with 30-m horizontal (~98 ft) and 0.305-m (1 ft) vertical resolutions. Water-table elevation and depth are key facets in many engineering, hydrogeologic, and environmental management and regulatory decisions. Depth to water is an important factor in risk assessments, site assessments, evaluation of permit compliance data, registration of pesticides, and determining acceptable pesticide application rates. Water-table elevations are used to compute ground-water flow directions and, along with information about aquifer properties (e.g., hydraulic conductivity and porosity), are used to compute ground-water flow velocities. Therefore, obtaining an accurate representation of the water table is also crucial to the success of many hydrologic modeling efforts. Water-table elevations can also be estimated from simple linear regression on elevations of either land surface or initial water table. The goodness-of-fits of elevations estimated from these surfaces are similar to that of multiple linear regression. Visual analysis of the distributions of the differences between observed and estimated water elevations (residuals) shows that the multiple linear regression-derived surfaces better fit observations than do surfaces estimated by simple linear regression.Item Application Of Geophysics To Highway Design In The Piedmont Of Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1971-06) Woodruff, K.D.The feasibility of using geophysical techniques in determining the amount of overburden and the nature of the subsurface along a proposed highway was tested in the Piedmont area of Delaware. The area is underlain by crystalline rocks capped by varying amounts of unconsolidated material or regolith. Seismic refraction and surface resistivity methods were used at selected stations and the interpretations were later compared to results from test holes and to the material exposed in road cuts. In general, interpretation of the seismic refraction results compared quite well with test borings and with field observations made after construction was started. Resistivity data were inconclusive in themselves but provided some additional control points when correlated with seismic refraction data. With proper control, it is concluded that such techniques could be useful in the Piedmont of Delaware for highway planning.Item Aquifers and Groundwater Withdrawals, Kent and Sussex Counties, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2023-08) McLaughlin, P.M.; Tomlinson, J.L.; Lawson, A.K.Groundwater is the sole source of drinking water and the main source of water for agriculture and industry in central and southern Delaware. This study mapped the depth and thickness of thirteen aquifers in Kent and Sussex Counties, used these maps to assign groundwater withdrawals for 2004 to 2008 to the appropriate aquifer, and analyzed withdrawals for each type of water use by geographic area. The geology of the Delaware Coastal Plain is characterized by a broad complex of surficial Quaternary deposits unconformably underlain by Cretaceous to Cenozoic sediments that dip gently to the southeast. Permeable sands within this succession are used as groundwater sources. The hydrogeologic framework of the study area was characterized by maps of the elevation and thickness of thirteen aquifers. The maps were created in a geographical information system by interpolating aquifer depth data extracted from a database encompassing approximately 6,600 boreholes. The unconfined aquifer occurs in surficial Quaternary and Neogene sands. It is generally less than 100 feet thick in Kent County but varies from a few feet to more than 200 feet thick in Sussex County. The confined aquifers mapped include one Cretaceous (Mount Laurel), two Paleogene (Rancocas and Piney Point), and nine Neogene sand units (lower Calvert, Cheswold, Federalsburg, Frederica, Milford, Middle Choptank, Upper Choptank, Manokin, and Pocomoke). These aquifers are typically tens of feet thick and occur at progressively greater depths southeastward from their recharge areas. The study found that annual groundwater withdrawals for all uses in the study area ranged from approximately 89 to 144 million gallons per day annually for 2004 to 2008. Withdrawals were assigned to aquifers using the aquifer maps and well-screen elevation data. For water-use categories where withdrawals could be attributed to specific wells – public, industrial, and golf courses – aquifers were determined by analyzing well-screen elevations relative to aquifer raster surfaces. For categories in which withdrawals could not be assigned to individual wells – irrigation, domestic self-supplied, and livestock – available well depth data in each category were analyzed by census block and compared to the aquifer raster surfaces; for each block, the proportion of wells in each aquifer was used as the basis for apportioning withdrawals to aquifers. The results indicate that the unconfined aquifer accounted for more than half of groundwater withdrawals. Three shallow, confined aquifers primarily used in Sussex County (confined Columbia, Pocomoke, and Manokin) each provided approximately between 8 and 11 percent of total withdrawals. Withdrawals for the three most important confined aquifers in Kent County (Cheswold, Frederica, and Piney Point) each represented 3 to 5 percent of total withdrawals. Estimated withdrawals were also computed by aquifer for each water-use category and each census block.Item Assawoman Bay(2010-01-17) Delaware DataMIL; State of Delaware, Delaware DataMILItem Assawoman Bay(2009-02-01) Delaware DataMIL; State of Delaware, Delaware DataMILItem Assawoman Bay(2011-01-30) Delaware DataMIL; State of Delaware, Delaware DataMILItem Assawoman Bay(2008-01-20) Delaware DataMIL; State of Delaware, Delaware DataMIL (Dover, DE)Item Assawoman Bay(2012-01-29) Delaware DataMIL; State of Delaware, Delaware DataMILItem Basic Data For The Geologic Map Of The Seaford Area, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1995) Andres, A.S.; Ramsey, K.W.; Schenck, W.S.The Seaford area geologic mapping project (Andres and Ramsey, 1995) was conducted by Delaware Geological Survey (DGS) staff and focused on the Seaford East (SEE) and Delaware portion of the Seaford West (SEW) quadrangles (Fig. 1). Data evaluated in support of mapping from these quadrangles and surrounding areas are documented in this report.Item Basic Hydrologic Data For Coastal Sussex County, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1987-01) Talley, J.H.; Andres, A.S.Item Beach Sand Textures From The Atlantic Coast Of Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1999) Ramsey, K.W.The purpose of this report is to characterize Delaware Atlantic Coast beach sand on the basis of sand texture data in order to identify geologic material suitable for beach nourishment.Item 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.Item Bedrock Geologic Map Of The Piedmont OF Delaware And The Adjacent Pennsylvania(Newark, DE: Delaware Geological Survey, University of Delaware, 2000) Schenck, W.S.; Plank, M.O.; Srogi, L.A.Item Bedrock Geology Of The Piedmont Of Delaware And Adjacent Pennsylvania(Newark, DE: Delaware Geological Survey, University of Delaware, 2000) Plank, M.O.; Schenck, W.S.; Srogi, L.A.This report accompanies a new map that revises the original bedrock geologic maps of the Delaware Piedmont compiled by Woodruff and Thompson and published by the Delaware Geological Survey (DGS) in 1972 and 1975. Combined detailed mapping, petrography, geochemistry, and U-Pb geochronology have allowed us to redefine two rock units and formally recognize eleven new units. A section of the Pennsylvania Piedmont is included on the new map to show the entire extent of the Mill Creek Nappe and the Arden Plutonic Supersuite.Item Bennetts Pier(2011-01-30) Delaware DataMIL; State of Delaware, Delaware DataMILItem Bennetts Pier(2009-02-01) Delaware DataMIL; State of Delaware, Delaware DataMILItem Bennetts Pier(2008-01-20) Delaware DataMIL; State of Delaware, Delaware DataMILItem Bennetts Pier(2010-01-17) Delaware DataMIL; State of Delaware, Delaware DataMILItem Bennetts Pier (2012-01-29) Delaware DataMIL; State of Delaware, Delaware DataMIL