DGS Reports of Investigations
Permanent URI for this collection
Browse
Browsing DGS Reports of Investigations by Subject "aquifer"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item High-Capacity Test Well Developed At The Air Force Base, Dover, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1958-06) Rasmussen, W.C.; Groot, J.J.; Depman, A.J.A thick aquifer of Eocene age underlies the Dover area, Delaware at depths ranging from 250 to 400 feet below the land surface. The aquifer is about 250 feet thick beneath the Dover Air Force Base and is composed of fairly uniform medium to fine glauconitic quartz sand. The static water level in a test well at the base was 18 feet below the land surface, or 5.7 feet above sea level, on April 17, 1957. The yield of the test well was about 300 gpm (gallons per minute), and the specific capacity at the end of a 12-hour pumping period was 8.3 gpm per foot of drawdown.Item Kent County Groundwater-Monitoring Project: Results Of Hydrogeological Studies(Newark, DE: Delaware Geological Survey, University of Delaware, 2023-02) Andres, A.S.; McQuiggan, R.W.; He, C.; McKenna, T.E.In 2019, the Delaware Geological Survey, in cooperation with the Delaware Department of Natural Resources and Environmental Control, completed a groundwater-monitoring, infrastructure-construction, and data-collection project in Kent County, Delaware. This work, recommended by the Governor’s Water Supply Coordinating Council and funded by a capital appropriation from the state, addressed data gaps for the shallower aquifers commonly pumped by water-supply wells that serve domestic, public, irrigation, and commercial users and provided additional data to characterize the relationships between the aquifers and streamflow. The aquifers investigated in this study are, from shallowest (closest to the surface) to deepest, the Columbia, Milford, Frederica, Federalsburg, Cheswold, Piney Point, Rancocas, and Mt. Laurel. The groundwater-monitoring infrastructure and data created during this project will facilitate follow-up projects targeted to specific issues for the water resources of Delaware. The Piney Point aquifer has a characteristic uncommon among other aquifers in the Coastal Plain of Delaware, in that it receives recharge only through slow, diffuse leakage through overlying and underlying confining beds. As a result, pumping of the Piney Point aquifer in the Dover area has reduced water levels more than 80 feet over the past 50 years in several wells in the Dover area. Given current rates of decline, static water levels in long-term observation well Id55-01 will reach the top of the aquifer within 30 years. Pumping water levels in two supply wells operated by Dover Water are projected to reach the top of the aquifer within 10 years if current rates of decline continue. Given that the Piney Point aquifer matrix contains glauconite, a compressible clay pellet, there is significant risk for aquifer compaction and reductions in well yield should water levels continue to decline. Water-level and water-quality data from nested wells (e.g., multiple wells at the same site finished at different depths) in the Milford, Frederica, Federalsburg, and Cheswold aquifers are recharged primarily in areas where they are in close hydraulic connection with the overlying water table aquifer. Similarities in hydrographs, potentiometric surface maps from these aquifers, and time series of head differentials between the Frederica, Federalsburg, and Cheswold aquifers indicate that they function as a single, leaky, layered aquifer. Pumping has reduced water levels in the Frederica, Federalsburg, and Cheswold aquifers below sea level over large areas of Kent County, and has caused flow directions to change from a general southeasterly direction in pre-development times to flow directed toward pumping centers. Water quality data that show no significant correlation between dissolved solids and well depth support the interpretation that flow directions have changed in response to pumping. Long-term declines in annual minimum total flow and baseflow at streamflow gaging stations in the Beaverdam Branch and Marshyhope Creek watersheds and associated long-term increases in annual precipitation, number of growing days, irrigated acres, and number of irrigation wells in those basins are consistent with the interpretation that the combined effects of irrigation pumping and climate change are reducing groundwater discharge to those streams. Results of testing major groundwater constituents in the water-table portion of Columbia aquifer are consistent with previous studies in Delaware, with calcium and sodium the major cations, and different mixtures of the anions chloride, nitrate, and bicarbonate depending on land use and composition of the aquifer near each well. Major constituents of groundwater in the Milford, Frederica, Federalsburg, and Cheswold aquifers over most of Kent County are dominated by calcium, bicarbonate and sulfate.Item Simulation of Groundwater Flow and Contaminant Transport in Eastern Sussex County, Delaware With Emphasis on Impacts of Spray Irrigation of Treated Wastewater(Newark, DE: Delaware Geological Survey, University of Delaware, 2015-08) He, C.; Andres, A.S.This report presents a conceptual model of groundwater flow and the effects of nitrate (NO3-) loading and transport on shallow groundwater quality in a portion of the Indian River watershed, eastern Sussex County, Delaware. Three-dimensional, numerical simulations of groundwater flow, particle tracking, and contaminant transport were constructed and tested against data collected in previous hydrogeological and water-quality studies. The simulations show a bimodal distribution of groundwater residence time in the study area, with the largest grouping at less than 10 years, the second largest grouping at more than 100 years, and a median of approximately 29 years. Historically, the principal source of nitrate to the shallow groundwater in the study area has been from the chemical- and manure-based fertilizers used in agriculture. A total mass of NO3- -nitrogen (N) of about 169 kg/day is currently simulated to discharge to surface water. As the result of improved N-management practices, after 45 years a 20 percent decrease in the mass of NO3- -N reaching the water table would result in an approximately 4 percent decrease in the mass of simulated N discharge to streams. The disproportionally smaller decrease in N discharge reflects the large mass of N in the aquifer coupled with long groundwater residence times. Currently, there are two large wastewater spray irrigation facilities located in the study domain: the Mountaire Wastewater Treatment Facility and Inland Bays Wastewater Facility. The effects of wastewater application through spray irrigation were simulated with a two-step process. First, under different operations and soil conditions, evaporation and water flux, NO3- -N uptake by plants, and NO3- -N leaching were simulated using an unsaturated flow model, Hydrus-1D. Next, the range of simulated NO3- -N loads were input into the flow and transport model to study the impacts on groundwater elevation and NO3- -N conditions. Over the long term, the spray irrigation of wastewater may increase water-table elevations up to 2.5m and impact large volumes of groundwater with NO3-. Reducing the concentration of NO3- in effluent and increasing the irrigation rate may reduce the volumes of water impacted by high concentrations of NO3-, but may facilitate the lateral and vertical migration of NO3-. Simulations indicate that NO3- will eventually impact deeper aquifers. An optimal practice of wastewater irrigation can be achieved by adjusting irrigation rate and effluent concentration. Further work is needed to determine these optimum application rates and concentrations.Item Subsurface Geology of the Area Between Wrangle Hill and Delaware City, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2013-03) Jengo, J.W.; McLaughlin, P.P.; Ramsey, K.W.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.Item Wells For The Observation Of Chloride And Water Levels In Aquifers That Cross The Chesapeake And Delaware Canal(Newark, DE: Delaware Geological Survey, University of Delaware, 1958-08) Rasmussen, W.C.; Groot, J.J.; Beamer, N.H.Three test wells were drilled near the banks of the Chesapeake and Delaware Canal, in aquifers formed by sand beds in two geologic units, the nonmarine Cretaceous sediments and the Magothy formation, which crop out along the sides and across the bottom of the canal. The canal carries tidal flow from the Delaware River to and from Chesapeake Bay. The purpose of the wells was to determine whether salt water from the canal has entered the water-bearing beds of these formations, and to determine the head of water in them. It was found that the sands contain fresh water, uncontaminated, and that apparently there was discharge of fresh water from the aquifers to the canal under low head, at least from the winter of late 1955 through early autumn 1957.