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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Browsing Delaware Geological Survey by Author "Andres, A.S."
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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 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 The Cat Hill Formation And Bethany Formation Of Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2004) Andres, A.S.Because of the rapid development occurring in coastal Delaware and the importance of ground water to the economy of the area, definition of formal lithostratigraphic units hosting aquifers and confining beds serves a useful purpose for resource managers, researchers, and consultants working in the area. The Pocomoke and Manokin are artesian aquifers pumped by hundreds of domestic and dozens of public wells along the Atlantic coast in Delaware and Maryland. These aquifers are being increasingly used for public water supply. Two formal lithostratigraphic units, the Cat Hill Formation and Bethany Formation, are established to supercede the Manokin formation and Bethany formation, respectively. In Delaware, these lithostratigraphic units host important aquifers—the Manokin, which occurs in the Cat Hill Formation, and the Pocomoke, which occurs in the Bethany Formation. Composite stratotypes of these units are identified in five drillholes located near Bethany Beach, Delaware.Item The Cypress Swamp Formation, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2000) Andres, A.S.; Howard, C.S.The Cypress Swamp of Sussex County, Delaware, is underlain by a body of late Pleistocene- to Holocene-age unconsolidated sediments. They form a mappable geologic unit herein named the Cypress Swamp Formation. Deposits of the formation can be found outside the current boundaries of the Cypress Swamp and record the erosion and redistribution of older Pleistocene coastal and Pliocene sedimentary units.Item Digital Watershed And Bay Boundaries For Rehoboth Bay, Indian River Bay, And Indian River(Newark, DE: Delaware Geological Survey, University of Delaware, 2007) McKenna, T.E.; Andres, A.S.; Lepp, K.P.Digital watershed and bay polygons for use in geographic information systems were created for Rehoboth Bay, Indian River, and Indian River Bay in southeastern Delaware. Polygons were created using a hierarchical classification scheme and a consistent, documented methodology that enables unambiguous calculations of watershed and bay surface areas within a geographic information system. The watershed boundaries were delineated on 1:24,000-scale topographic maps. The resultant polygons represent the entire watersheds for these water bodies, with four hierarchical levels based on surface area. Bay boundaries were delineated by adding attributes to existing polygons representing water and marsh in U.S. Geological Survey Digital Line Graphs of 1:24,000-scale topographic maps and by dissolving the boundaries between polygons with similar attributes. The hierarchy of bays incorporates three different definitions of the coastline: the boundary between open water and land, a simplified version of that boundary, and the upland-lowland boundary. The polygon layers are supplied in a geodatabase format.Item Estimate Of Direct Discharge Of Fresh Ground Water To Rehoboth And Indian River Bays(Newark, DE: Delaware Geological Survey, University of Delaware, 1987-06) Andres, A.S.The results of water-budget and flow-net model calculations indicate that the rate of fresh ground-water discharge into Rehoboth and Indian River bays is in the range of 21 to 43 million gallons per day. The estimates should be used only as gross indicators of actual conditions because of data gaps and the simplifying assumptions used in the models. However, the estimated discharge rates are significant and useful studies of the water budget of the Bays.Item Estimate Of Nitrate Flux To Rehoboth And Indian River Bays, Delaware, Through Direct Discharge Of Ground Water(Newark, DE: Delaware Geological Survey, University of Delaware, 1992-05) Andres, A.S.Agricultural fertilizer application, animal (poultry) waste, and wastewater disposal practices of the past 40 years have resulted in widespread nitrate contamination of ground water in coastal Sussex County, Delaware. Discharge of contaminated ground water to Rehoboth and Indian River bays is suspected of being a significant contributor to elevated nutrient concentrations in these surface water bodies, resulting in excessive phytoplankton growth and other related problems.Item Estimating Evapotranspiration for 2016 Growing Season Using Landsat 8 Data and Metric Model in Sussex County, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2023-08) He, C.; Andres, A.S.; Brinson, K.R.; DeLiberty, T.L.Evapotranspiration (ET) is a major part of the water cycle. Reliable measurements or estimates of ET can greatly improve quantitative forecasts and hindcasts of water demand by crops, horticulture, and natural vegetation, and also help to manage and conserve water resources. Direct measurement of ET requires not only specific devices such as eddy covariance instruments, but also well-trained research personnel to collect accurate data. As a result, a variety of indirect methods for estimating ET have been developed in recent decades. Among them, remote sensing methods have proved cost-effective in providing accurate regional and global coverage of ET. In Sussex County, Delaware’s leading county in crop production, the ET distribution for the 2016 growing season was estimated using the Mapping Evapotranspiration at high Resolution with Internalized Calibration method, an energy-balance based ET mapping tool that utilizes satellite images and weather data. The estimated result was compared with field measurements using an eddy covariance instrument. The total estimated ET during Sussex County’s growing season (May-September) in 2016 accounts for 77 to 87 percent of historical-averaged annual ET in this region. The model-simulated seasonal ET for agricultural land is about 33 percent higher than urban/suburban areas and about 22 percent lower than forested areas. This study shows that when forestlands are converted to urban/suburban uses, significant amounts of water are diverted from ET and are then available to run off and/or infiltrate. Given that urban/suburban land has impervious surfaces in the forms of rooftops, roads, driveways, parking lots, sidewalks, etc., much of the water not lost to the atmosphere through ET presumably becomes part of the surface runoff portion of the water budget, thus underscoring the need for adequate storm-water management systems for urban/suburban lands. The results also imply that the practice of ET-based irrigation scheduling could be valuable in Sussex County and throughout the 20 percent of Delaware farmland that is irrigated.Item Estimation Of The Water Table For The Inland Bays Watershed, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2005) Andres, A.S.; Martin, M.J.A geographic information system-based study was used to estimate the elevation of the water table in the Inland Bays watershed of Sussex County, Delaware, under dry, normal, and wet conditions. Evaluation of the results from multiple estimation methods indicates that a multiple linear regression method is the most viable tool to estimate the elevation of the regional water table for the Coastal Plain of Delaware. The variables used in the regression are elevation of a minimum water table and depth to the minimum water table from land surface. Minimum 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 output as a GIS-ready grid with 30-m (98.43 ft) horizontal and 0.305-m (1 ft) vertical resolutions.Item Evaluation Of Remote Sensing And Surface Geophysical Methods For Locating Underground Storage Tanks(Newark, DE: Delaware Geological Survey, University of Delaware, 1986-01) Andres, A.S.Delaware Code, Title 7, Chapter 74, Section 7415 states in part: "The Delaware Geological Survey shall investigate the feasibility of utilizing aerial photographs and other new advanced techniques for locating abandoned tanks." In response to this charge, the Delaware Geological Survey has completed a survey of currently available remote sensing and geophysical tools to determine which methods may be utilized to locate underground storage tanks. Limited preliminary field testing has been performed.Item Evaluation of Wastewater Treatment Options Used in Rapid Infiltration Basin Systems (RIBS)(Newark, DE: Delaware Geological Survey, University of Delaware, 2015-12) Türkmen, M.; Walther, E.F.; Andres, A.S.; Chirnside, A.E.M.; Ritter, W.F.This technical report evaluates several aspects of potential environmental risks, use, and regulation of rapid infiltration basin systems (RIBS) in Delaware. The report reviews and compares regulations regarding RIBS from Delaware, Florida,North Carolina, New Jersey, Maryland, and Massachusetts. Influent and effluent samples from ten advanced wastewater treatment systems that operate in conjunction with RIBS were collected and analyzed. Effluent data obtained from the Non-Hazardous Waste Sites database provided by the Delaware Department of Natural Resources and Environmental Control and other states were assessed. Performance evaluations of the treatment processes that discharge to RIBS were ascertained from the exceedance of concentrations of regulated pollutants in effluent samples. Although RIBS technology has the potential to be a beneficial alternative to surface discharge and a means for groundwater recharge, this technology is appropriate only if the adverse environmental impacts are minimized. Overall operation and maintenance practices play important roles in the performance of treatment plants. The most common and serious problems associated with treatment plants located in Delaware and neighboring states are high nutrient and pathogen concentrations in the effluent. In Delaware, the discharge of poorly treated effluent to RIBS creates a risk of nutrient and pathogen contamination in the receiving water body, the shallow Columbia aquifer. Years of application of treated effluent with high nutrient, pathogen, and organic content to RIBS will result in significant risks for the environment and public health.Item Geohydrology of the Northern Coastal Area(Newark, DE: Delaware Geological Survey, University of Delaware, 1986) Andres, A.S.Item Geohydrology of the Seaford Area, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1994) Andres, A.S.Item Geohydrology Of The Smyrna-Clayton Area, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2001) Andres, A.S.Item Geologic And Hydrologic Studies Of The Oligocene - Pleistocene Section Near Lewes, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1990-10) Andres, A.S.; Benson, R.N.; Ramsey, K.W.; Talley, J.H.Borehole Oh25-02, located about 3 miles southwest of Lewes, Delaware, ends at a total depth of 1,337 ft in a mid-Oligocene glauconitic silt unit. It penetrated 317 ft of glauconitic sands and silts between the base of the Calvert Formation at a depth of 1,020 ft and total depth. A hiatus at 1,218 ft separates an outer neritic lower Miocene interval (Globorotalia kugleri Zone) above it from a deep upper bathyal mid-Oligocene (G. opima opima Zone) section below; the lower section is characterized by abundant large uvigerinid benthic foraminiferal species representing the transition from Uvigerina tumeyensis to Tiptonina nodifera. Similar uvigerinid assemblages identify the mid-Oligocene unit in boreholes near Bridgeville and Milford, Delaware; Cape May, New Jersey; and Ocean City, Maryland. Updip from these boreholes, the Calvert Formation, of latest Oligocene-middle Miocene age in Delaware, unconformably overlies middle Eocene glauconitic sands of the Piney Point Formation. The juxtaposition of the downdip mid-Oligocene rocks against the updip middle Eocene rocks can best be explained by a fault between the two regions.Item Geologic Map of the Frankford and Selbyville Quadrangles, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2013-12) Tomlinson, J.L.; Ramsey, K.W.; Andres, A.S.The geological history of the surficial units of the Frankford and Delaware portion of the Selbyville Quadrangles was the result of deposition of the Beaverdam Formation during the late Pliocene and its subsequent modification by erosion and deposition related to sea-level fluctuations during the Pleistocene. The geology at the land surface was then further modified by periglacial activity that produced dune deposits in the map area. Surficial geologic mapping was conducted using field maps at a scale of 1:12,000 with 2 foot contours. Stratigraphic boundaries drawn at topographic breaks reflect detailed mapping using contours not shown on this map.Item Geologic Map of the Seaford West and Seaford East Quadrangles, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2015-08) Tomlinson, J.L.; Ramsey, K.W.; Andres, A.S.The geological history of the surficial units of the Seaford East Quadrangle and the Delaware portion of the Seaford West Quadrangle was the result of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition related to sea-level fluctuations during the Pleistocene. The geology reflects this complex history by the cut and fill geometry of the middle and late Pleistocene deposits incised into the Beaverdam Formation. The geology is further complicated by periglacial activity that produced dune deposits and the Carolina Bays in the map area, which modified the land surface.Item Geology Of The Seaford Area, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1996) Andres, A.S.; Ramsey, K.W.; Groot, J.J.This report supplements the map "Geology of the Seaford Area, Delaware" (Andres and Ramsey, 1995). The map portrays surficial and shallow subsurface stratigraphy and geology in and around the Seaford East and Delaware portion of the Seaford West quadrangles. The Quaternary Nanticoke deposits and Pliocene Beaverdam Formation are the primary lithostratigraphic units covering upland surfaces in the map area. Recent swamp, alluvial, and marsh deposits cover most of the floodplains of modern streams and creeks. The Miocene Choptank, St. Marys, and Manokin formations occur in the shallow subsurface within 300 ft of land surface. The Choptank, St. Marys, and Manokin formations were deposited in progressively shallower water marine environments. The Beaverdam Formation records incision of underlying units and progradation of a fluvial-deltaic system into the map area. The geologic history of the Quaternary is marked by weathering and erosion of the surface of the Beaverdam and deposition of the Nanticoke deposits by the ancestral Nanticoke River. Depositional environments in the Nanticoke deposits include fresh water streams and ponds, estuarine streams and lagoons, and subaerial dunes.Item Geology Of The Seaford Area, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1995) Andres, A.S.; Ramsey, K.W.
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