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Site content related to keyword: "hydrogeology"

DGS participates in inter-agency meeting on Chesapeake Watershed

DGS staff member A. Scott Andres made a presentation “Results of selected UD nutrient monitoring projects in the Nanticoke River watershed” at the inter-agency meeting Chesapeake basin water quality data, trends, and interpretations held August 11, 2016 at the Delaware Department of Agriculture in Dover.

Journal article "Hydrogeologic controls on groundwater discharge and nitrogen loads in a coastal watershed"

A recently released article “Hydrogeologic controls on groundwater discharge and nitrogen loads in a coastal watershed” by the Journal of Hydrology details the results of a joint groundwater simulation and water quality sampling study that focused on submarine groundwater discharge (SGD) to Indian River and Rehoboth Bays, part of Delaware Inland Bays.

Delaware Geological Survey Issues Report on Groundwater Monitoring and Water-Quality Impacts of Rapid Infiltration Basin Systems

The Delaware Geological Survey released a new technical report entitled “Groundwater Quality and Monitoring of Rapid Infiltration Basin Systems, Theory and Field Experiments at Cape Henlopen State Park, Delaware” which was prepared by A. Scott Andres and Changming He of the Delaware Geological Survey, Edward Walther of the South Water Management District, Florida, Müserref Türkmen of the Izmir Water and Sewerage Administration, Turkey, and Anastasia Chirnside and William Ritter of the University of Delaware. DGS Bulletin 21C documents the results of a detailed study of groundwater quality at a rapid infiltration basin system.

B21C Groundwater Quality and Monitoring of Rapid Infiltration Basin Systems (RIBS), Theory and Field Experiments at Cape Henlopen State Park, Delaware

B21C Groundwater Quality and Monitoring of Rapid Infiltration Basin Systems (RIBS), Theory and Field Experiments at Cape Henlopen State Park, Delaware

A rapid infiltration basin system (RIBS) consists of several simple and relatively standard technologies; collection and conveyance of wastewater, treatment, and discharge to an unlined excavated or constructed basin. By design, the effluent quickly infiltrates through the unsaturated or vadose zone to the water table. During infiltration, some contaminants may be treated by biological and/or geochemical processes and diluted by dispersion and diffusion. The combination of contaminant attenuation and dilution processes that may occur during infiltration and flow through the aquifer are termed soil-aquifer-treatment, or SAT. In the past decade, RIBS have been proposed more frequently for use in Delaware because they stop the direct discharge of treated effluent to surface water, can accommodate significant flow volumes typical of residential subdivisions, yet require much less land than options such as spray irrigation or sub-surface disposal systems.

Decades of research on the shallow Columbia aquifer of the Delmarva Peninsula have clearly identified the high susceptibility of the aquifer from land- and water-use practices, and the processes that control the fate and transport of contaminants from their origin at or near land surface to points of discharge in creeks, estuaries, and wells. The risk of aquifer contamination is great because it is highly permeable, has little organic matter in the aquifer matrix, and the depth to groundwater is very commonly less than 10 ft below land surface. USEPA guidance documents and several engineering texts that cover RIBS design clearly identify these same factors as increasing risk for groundwater contamination but do not provide much information on means to monitor and mitigate those risks. Further, design criteria are based on a small group of experiments conducted in the 1970s prior to development of current understanding of the processes that control groundwater contaminant transport.

Field and laboratory experiments to characterize the physical, chemical, and biological controls and processes associated with the rapid infiltration of treated sewage effluent through infiltration beds and the vadose zone were undertaken at a RIBS located at Cape Henlopen State Park (CHSP), Delaware. Field experiments to understand the geochemical effects of the long-term operation of a RIBS on ground and surface waters, and to evaluate monitoring systems were also conducted at the site. The CHSP RIBS has been in operation since the early 1980s.

Significant concentrations of nitrogen and phosphorus occur in groundwater from the point of effluent entry at the water table to distances greater than 150 ft from the infiltration beds. The high hydraulic, nitrogen (N), phosporus (P), and organic loading rates associated with the operation of RIBS overwhelm natural attenuation (e.g., sorption and precipitation) processes. Data are not sufficient to indicate whether denitrification is occurring. If there is denitrification, the rate is insufficient to remediate RIBS effluent at the site — despite a 25-ft thick vadose zone, an effluent with enough organic carbon to facilitate anaerobic conditions that permit abiotic denitrification and feed microorganism-driven denitrification processes, and hypoxic to anoxic groundwater.

Significant horizontal and vertical variability of contaminant concentrations were observed within the portion of the aquifer most impacted by effluent disposal. Despite the relatively small spatial extent of the disposal area in our study area, identification of the preferential flow zone and characterization of the vertical and temporal variability in the concentrations of contaminants required a multi-phase subsurface investigation program that included an analysis of data from samples collected at bi-monthly intervals from dozens of monitoring points and high frequency temperature monitoring in several wells. A well-designed monitoring system should be based on experimentally determined site specific evidence collected under conditions that duplicate the flow rates that are expected during full-scale operation of the RIBS. Conservative tracers should be used to determine if the monitoring wells are in locations that intercept flow from the infiltration beds.

Delaware Geological Survey Issues Report on Hydrogeologic Impacts of Rapid Infiltration Basin Systems

The Delaware Geological Survey released a new technical report entitled “Hydrogeology of a Rapid Infiltration Basin Systems at Cape Henlopen State Park, Delaware” which was prepared by A. Scott Andres and Changming He of the Delaware Geological Survey, Edward Walther of the South Water Management District, Florida, and Müserref Türkmen of the Izmir Water and Sewerage Administration, Turkey, and DGS Bulletin 21B documents the results of a detailed study of groundwater and hydrogeology at a rapid infiltration basin system.

B21B Hydrogeology of a Rapid Infiltration Basin System (RIBS) at Cape Henlopen State Park, Delaware

B21B Hydrogeology of a Rapid Infiltration Basin System (RIBS) at Cape Henlopen State Park, Delaware

The hydrogeologic framework of Cape Henlopen State Park (CHSP), Delaware was characterized to document the hydrologic effects of treated wastewater disposal on a rapid infiltration basin system (RIBS). Characterization efforts included installation of test borings and monitoring wells; collection of core samples, geophysical logs, hydraulic test data, groundwater levels and temperatures; testing of grain size distribution; and interpretation of stratigraphic lithofacies, hydraulic test data, groundwater levels, and temperature data. This work was part of a larger effort to assess the potential benefits and risks of using RIBS in Delaware.

The infiltration basins at CHSP are constructed on the Great Dune, an aeolian dune feature composed of relatively uniform, medium-grained quartz sand. The age of the dune, determined by carbon-14 dating of woody material in swamp deposits under the dune, is less than 800 years. Underlying the dune deposits are relatively heterogeneous, areally continuous, coarse-grained spit deposits of the proto-Cape Henlopen spit with interbedded and relatively fine-grained, discontinuous swamp and marsh deposits, and beneath, relatively fine-grained, continuous, near-shore marine deposits. The dune deposits can be 45 ft thick under the crest of the dune and nonexistent at the surface. Spit deposits range from 5 to 15 ft thick. Test drilling determined that the near-shore marine deposits are at least 10 ft thick in the vicinity of the infiltration basins. The complete thickness of these deposits was not determined in this study.

Hydraulic testing and grain-size data indicate that the dune and spit deposits are relatively permeable, with average hydraulic conductivities of 140 ft/day and that the swamp and marsh deposits are more than one order of magnitude less permeable, with average hydraulic conductivity of 25 to 10 ft/day. The water-table aquifer is present in the sandier dune and spit deposits. The swamp, marsh, and near-shore marine deposits form a leaky confining unit. The water-table aquifer is 15 to 20 ft thick under the thickest section of the Great Dune and nonexistent where the dune deposits are absent. The vadose zone is greater than 25 ft thick under the infiltration basins.

High-frequency groundwater level and temperature monitoring during periods of maximum wastewater disposal rates indicates that wastewater disposal causes increases in water-table elevations on the order of 1 ft. Groundwater elevations indicate that the water-table elevation is greatest under the infiltration basins and that most flow is directed southward toward a swampy discharge area.

Maximum disposal rates typically occur in summer months when the numbers of park users and water use are greatest. Coincident with greater disposal rates are higher wastewater temperatures. These higher wastewater temperatures are observed in groundwater and provide a means to track the flow of water from beneath the infiltration beds towards a nearby discharge area. Tracking of the warmer groundwater and modeling two-dimensional particle tracking both indicate that wastewater discharged to the infiltration basins reaches the nearby discharge area within 180 days.

Delaware Geological Survey Issues Report on Wastewater Treatment used for Rapid Infiltration Basin Systems

The Delaware Geological Survey released a new technical report entitled “Evaluation Of Wastewater Treatment Options Used In Rapid Infiltration Basin Systems (RIBS)” which was prepared by Müserref Türkmen of the Izmir Water and Sewearge Administration, Turkey, A. Scott Andres of the Delaware Geological Survey, Edward Walther of the South Water Management District, Florida, and William Ritter and Anastasia Chirnside of the University’s College of Agriculture and Natural Resources. DGS Bulletin 21A documents the results of a detailed study of wastewater treatment plant technologies and effectiveness of treatment types that are used to treat wastewater prior to disposal into the ground by rapid infiltration basin systems.

DGS presentation to Delaware River Basin Commission Water Management Advisory Committee on Groundwater Monitoring

Scott Andres presented an invited talk “Update on Groundwater Monitoring in Delaware” at the Groundwater Management Workshop sponsored by the Delaware River Basin Commission (DRBC) in West Trenton, NJ on October 22, 2015.

DGS Presentation on Groundwater to Clean Water Task Force

Presentation on Groundwater to Clean Water Task Force by staff member Scott Andres

Well and Water Level Summary for Wells with 4 or More Observations

Well and Water Level Summary for Wells with 4 or More Observations - Well Cb15-04

Groundwater levels are basic information needed for evaluating water conditions and for basic and applied research. For these efforts, water levels are being measured statewide in wells completed in multiple aquifers. Some wells are measured for specific projects, such as the Coastal Aquifers Salinity Project and the Water Conditions program, while other wells are measured so that staff can maintain long-term records of groundwater levels for evaluation of trends.

Table contains summary data from wells having 4 or more water level observations.

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DGS releases report on subsurface geology of Delaware City area

The Delaware Geological Survey (DGS) has published a report that details new findings on the subsurface geology of the Delaware City area.

Titled Subsurface Geology of the area between Wrangle Hill and Delaware City, Delaware, Report of Investigations Number 78 presents the results of cooperative research between geological consultant John W. Jengo of the firm MWH Americas and DGS researchers Peter P. McLaughlin Jr. and Kelvin W. Ramsey.

RI78 Subsurface Geology of the Area Between Wrangle Hill and Delaware City, Delaware

RI78 Subsurface Geology of the Area Between Wrangle Hill and Delaware City, Delaware

The geology and hydrology of the area between Wrangle Hill and Delaware City, Delaware, have been the focus of numerous studies since the 1950s because of the importance of the local groundwater supply and the potential environmental impact of industrial activity. In this report, 490 boreholes from six decades of drilling provide dense coverage, allowing detailed characterization of the subsurface geologic framework that controls groundwater occurrence and flow.

The region contains a lower section of tabular Cretaceous strata (Potomac, Merchantville, Englishtown, Marshalltown,and Mount Laurel Formations in ascending order) and a more stratigraphically complex upper section of Pleistocene-to-modern units (Columbia, Lynch Heights, and Scotts Corners Formations, latest Pleistocene and Holocene surficial sediments and estuarine deposits). The lowermost Potomac Formation is a mosaic of alluvial facies and includes fluvial channel sands that function as confined aquifer beds; however, the distribution of aquifer-quality sand within the formation is extremely heterogeneous. The Merchantville Formation serves as the most significant confining layer. The Columbia Formation is predominantly sand and functions as an unconfined aquifer over much of the study area.

To delineate the distribution and character of the subsurface formations, densely spaced structural-stratigraphic cross sections were constructed and structural contour maps were created for the top of the Potomac Formation and base of the Columbia Formation. The Cretaceous formations form a series of relatively parallel strata that dip gently (0.4 degrees) to the southeast. These formations are progressively truncated to the north by more flatly dipping Quaternary sediments, except in a narrow north-south oriented belt on the east side of the study area where the deeply incised Reybold paleochannel eroded into the Potomac Formation.

The Reybold paleochannel is one of the most significant geological features in the study area. It is a relatively narrow sandfilled trough defined by deep incision at the base of the Columbia Formation. It reaches depths of more than 110 ft below sea level with a width as narrow as 1,500 ft. It is interpreted to be the result of scour by the sudden release of powerful floodwaters from the north associated with one or more Pleistocene deglaciations. Where the Reybold paleochannel cuts through the Merchantville confining layer, a potential pathway exists for hydrological communication between Columbia and Potomac aquifer sands.

East of the paleochannel, multiple cut-and-fill units within the Pleistocene to Holocene section create a complex geologic framework. The Lynch Heights and Scotts Corners Formations were deposited along the paleo-Delaware River in the late Pleistocene and are commonly eroded into the older Pleistocene Columbia Formation. They are associated with scarps and terraces that represent several generations of sea-level-driven Pleistocene cut-and-fill. They, in turn, have been locally eroded and covered by Holocene marsh and swamp deposits. The Lynch Heights and Scotts Corners Formations include sands that are unconfined aquifers but complicated geometries and short-distance facies changes make their configuration more complex than that of the Columbia Formation.

Delaware Geologic Information Resource (DGIR) Map Viewer

DGIR Map Viewer Screenshot
Project Contact(s):

The Delaware Geologic Information Resource (DGIR) is an online data display tool and map viewer for a variety of geologic and hydrologic information released by the Delaware Geological Survey. It was designed to deliver the most commonly available and requested geologic and hydrologic information that is appropriate for use in hydrologic studies, required by regulation and ordinance, and to support state resource management decisions.

Effect of tropical storms Irene and Lee on groundwater levels in well Qb35-08 near Laurel, Delaware

Rapid, significant groundwater recharge occurred in response to tropical storms Irene and Lee.a

Effect of tropical storms Irene and Lee on groundwater levels in well Qb35-08

Plot of groundwater levels, groundwater temperature, and rainfall near Laurel, Delaware

Tropical storms Irene and Lee caused a 9-1/2 foot rise of the water table in western Sussex County near Laurel. Groundwater levels and temperatures in Qb35-08 were collected with an automated pressure-temperature datalogger system. At the same time, rainfall and soil moisture data were recorded by the DEOS Laurel Airport station located approximately 5 miles from the well.

David R. Wunsch appointed DGS Director

David R. Wunsch appointed DGS Director
Date: Nov 2011

After a nationwide search, David R. Wunsch has been appointed the next Director of the Delaware Geological Survey (DGS) and Delaware State Geologist, effective Nov. 1. He will succeed John H. Talley, who retired on June 30 after more than 38 years of service. Wunsch holds a doctorate in hydrogeology from the University of Kentucky, a master’s degree in geology from the University of Akron, and a bachelor’s degree in geology, with a minor in chemistry, from the State University of New York, Oneonta. In 2011, Wunsch was elected a Fellow of the Geological Society of America. He is an Honorary Member and a past President of the Association of American State Geologists (AASG) and has previously served a term as Secretary of the American Geological Institute.

Wunsch to take helm at DGS

David R. Wunsch, Ph.D.

David R. Wunsch has been appointed the next Director of the Delaware Geological Survey (DGS) and Delaware State Geologist, effective Nov. 1.

Source Water Assessment and Protection Program

Two Delaware Geological Survey staff members attended the Source Water Assessment and Protection Program meeting held Sept. 14 in Dover, Del. Scott Andres made a presentation titled "Results of Field and Lab Experiments on High Rate Land Application of Wastewater" and John Callahan made a presentation titled "Web-Delivered Application for Hydrogeologic Data."

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DGS honors retiring director, state geologist Talley

Talley is retiring after 38 years of service

John Talley joined the Delaware Geological Survey as a project geologist in 1972, became a senior scientist and hydrogeologist by 1986, and rose to director and state geologist by 2004. He’s consulted with dozens of university, state, and federal governments and groups and amassed a list of more than 50 publications and reports.