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Site content related to keyword: "unconfined aquifer"

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 Groundwater Monitoring Network

The Delaware Geological Survey (DGS) currently monitors groundwater levels in a network of 68 wells in Delaware. Long time-series of water levels in major aquifers serve as critical baseline data for resource management and analyses of aquifer response to pumping, climatic variability, drought hazards, seawater intrusion, and interaction with streams and their ecosystems.

Groundwater Station: DGS Well Bc43-01

DGS Well Bc43-01

Station Type: 
Groundwater
Period of Record: 
1974 to present
Frequency: 
Quarterly
Map County: 
New Castle County
Map Location: 
39.781700, -75.625099

Groundwater Station: DGS Well Mc51-01a

DGS Well Mc51-01a

Station Type: 
Groundwater
Period of Record: 
1958 to Present
Frequency: 
Monthly
Map County: 
Sussex County
Map Location: 
38.845401,-75.665496

Groundwater Station: DGS Well Hb14-12

DGS Well Hb14-12

Station Type: 
Groundwater
Period of Record: 
1957 to Present
Frequency: 
Monthly
Map County: 
New Castle County
Map Location: 
39.330398,-75.685203

Groundwater Station: DGS Well Db24-18

DGS Well Db24-18

Station Type: 
Groundwater
Period of Record: 
1957 to Present
Frequency: 
Monthly
Map County: 
New Castle County
Map Location: 
39.648700, -75.697502

Thickness, Elevation of the Base, and Transmissivity Grids of the Unconfined Aquifer of Sussex County (Data Product No. 06-01)

Thickness, Elevation of the Base, and Transmissivity Grids of the Unconfined Aquifer of Sussex County (Data Product No. 06-01)

The unconfined portion of the Columbia aquifer is a key hydrologic unit in Delaware, supplying water to many agricultural, domestic, industrial, public, and irrigation wells. The aquifer is recharged through infiltration of precipitation and is the source of fair-weather stream flow and water in deeper confined aquifers. The aquifer occurs in permeable sediments ranging in age from Miocene to Recent. Over most of Delaware, the top of the unconfined or water-table portion of the Columbia aquifer occurs at depths less than 10 feet below land surface. Because of the permeable character of the aquifer and its near-surface location, the unconfined aquifer is highly susceptible to contamination.

Kent and Sussex Water Recharge Data (Digital Data Product No 02-01)

Ground-Water Recharge Potential For Kent and Sussex Counties

Ground-water recharge potential maps show land areas characterized by their abilities to transmit water from land surface to a depth of 20 feet. The basic methods for mapping ground-water recharge potential are presented in Delaware Geological Survey Open File Report No. 34 (Andres, 1991) and were developed specifically for the geohydrologic conditions present in the Coastal Plain of Delaware. The digital data for this layer comes from DGS Digital Data Product DP 02-01, Digital Ground-Water Recharge Potential Map Data For Kent and Sussex Counties, Delaware: A. S. Andres, C. S. Howard, T. A. Keyser, L. T. Wang, 2002.

RI70 Thickness and Transmissivity of the Unconfined Aquifer of Eastern Sussex County, Delaware

RI70 Thickness and Transmissivity of the Unconfined Aquifer of Eastern Sussex County, Delaware

The unconfined portion of the Columbia aquifer is a key hydrologic unit in Delaware, supplying water to many agricultural, domestic, industrial, public, and irrigation wells. The aquifer is recharged through infiltration of precipitation and is the source of fair-weather stream flow and water in deeper confined aquifers. The aquifer occurs in permeable sediments ranging in age from Miocene to Recent. Over most of Delaware, the top of the unconfined or water-table portion of the Columbia aquifer occurs at depths less than 10 feet below land surface. Because of the permeable character of the aquifer and its near-surface location, the unconfined aquifer is highly susceptible to contamination.

RI68 Estimation of the Water Table for the Inland Bays Watershed, Delaware

RI68 Estimation of the Water Table for the Inland Bays Watershed, Delaware

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.

RI41 Hydrogeology and Geochemistry of the Unconfined Aquifer, West-Central and Southwestern Delaware

RI41 Hydrogeology and Geochemistry of the Unconfined Aquifer, West-Central and Southwestern Delaware

The unconfined aquifer is the major source of water supply in west-central and southwestern Delaware. The aquifer, which is composed of quartz sand, gravel, clay, and silt, ranges in thickness from 20 to 200 feet. The water table ranges from land surface to about 20 feet below land surface. Analyses of water from wells distributed throughout the area were used to study processes controlling the chemical quality of the water in the unconfined aquifer.

Groundwater Resources of Sussex County (with an update for Kent County)

Project Contact(s):

This project is an integrated geologic/hydrologic study that will update our knowledge of the unconfined aquifers, confined aquifers, and groundwater resources of Sussex County. In addition, this project will utilize the results of recently completed study of the aquifer geology of Kent County (McLaughlin and Velez, 2005) to better define the groundwater resources of Kent County. The products to be produced by this study include aquifer depth and thickness maps and geologic cross sections for Sussex County. Products will also include a summary of basic hydrologic characteristics of aquifers in Kent and Sussex County and an analysis of water use for each aquifer.

OFR23 Ground-Water Availability in Southern New Castle County, Delaware

OFR23 Ground-Water Availability in Southern New Castle County, Delaware

The purposes of the study described in this report are (1) to determine the total amount of fresh ground water (chloride content less than 150 milligrams/liter) available in New Castle County south of the Chesapeake and Delaware Canal, and (2) to map the geographic distribution of available fresh ground water on the basis of areas delineated by one minute of latitude and one minute of longitude (such areas measure essentially one square mile). The investigation has been based solely on data available in various publications and in the files of the Delaware and United States Geological Surveys.

OFR20 Configuration of the Base and Thickness of the Unconfined Aquifer in Southeastern Sussex County, Delaware

OFR20 Configuration of the Base and Thickness of the Unconfined Aquifer in Southeastern Sussex County, Delaware

The purpose of this study was to map the thickness and the configuration of the base of the unconfined aquifer in southeastern Sussex County, Delaware (figure 1). The unconfined aquifer provides much of the water used in this part of the State and is the first unit to be affected by pollution or waste disposal problems. Contour maps and geologic sections were prepared from available geologic, geophysical, and drillers' logs and previously published reports and maps. Six test holes (figure 1) were drilled to supplement available data. The information in this report will be useful for water-resources planning and for locating water-supply wells in the unconfined aquifer.

OFR48 Results of the Domestic Well Water-Quality Study

OFR48 Results of the Domestic Well Water-Quality Study

The Delaware Geological Survey conducted a review of existing ground-water quality data collected from shallow (less than 100 feet deep) domestic water-supply wells and small public water-supply wells (serving fewer than 100 residents) to determine the extent to which toxic and carcinogenic compounds are present in the shallow ground water serving domestic water supply wells. These data were generated by several agencies including the Delaware Geological Survey, U.S. Geological Survey, Delaware Department of Natural Resources and Environmental Control, Delaware Division of Public Health Office of Drinking Water, and the Delaware Department of Agriculture Pesticide Management Program.

SP27 Water Table in the Inland Bays Watershed, Delaware

SP27 Water Table in the Inland Bays Watershed, Delaware

This poster shows three different map views of the water table as well as information about how the maps were made, how the depth to water table changes with seasons and climate, and how the water table affects use and disposal of water. The map views are of depth to the water table, water-table elevation (similar to topography), and water-table gradient (related to water flow velocity).