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.
- aquifer
- Columbia aquifer
- Columbia Formation
- Cretaceous Period
- cross-sections
- Delaware
- Delaware Bay Group
- Delaware City
- Englishtown Formation
- environmental monitoring
- geology
- groundwater
- hydrogeology
- Lynch Heights Formation
- Magothy Formation
- Marshalltown Formation
- Merchantville Formation
- Mount Laurel Formation
- New Castle County
- Potomac aquifer
- Potomac Formation
- Scotts Corners Formation
- stratigraphy
- subsurface
- unconfined aquifer
- Wrangle Hill
Delaware Geologic Information Resource (DGIR) Map Viewer
- Appalachian Piedmont
- Atlantic Coastal Plain
- Cheswold aquifer
- Columbia aquifer
- elevation
- Englishtown aquifer
- Federalsburg aquifer
- Frederica aquifer
- GIS
- hydrogeology
- Manokin aquifer
- Milford aquifer
- Mount Laurel aquifer
- Piney Point aquifer
- Pocomoke aquifer
- Rancocas aquifer
- subsurface
- surficial geology
- technology
- water table
- watersheds
- wells
Well and Water Level Summary for Wells with 4 or More Observations
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.
Effect of tropical storms Irene and Lee on groundwater levels in well Qb35-08 near Laurel, Delaware
Effect of tropical storms Irene and Lee on groundwater levels in well Qb35-08
IS7 The Delaware Geological Survey
IS7 is a foldout brochure that briefly discusses the background and current activities of the DGS. Specifically, the following major programs are listed: Geology, Hydrology, Cartographic Information, Geologic Hazards, Seismograph Network, Outer Continental Shelf, Mineral Resources, Well Records and Sample Library, Publications, and Joint-funded Programs.
Scientists study flow of groundwater into bays - results may help track pollution
Quantifying Geologic and Temporal Controls on Water and Chemical Exchange between Groundwater and Surface Water in Coastal Estuarine Systems
Presentation on assessing suitability of land for rapid infiltration basin systems
DGS Cooperative and Joint-Funded Programs
The DGS is, by statute, the state agency responsible for entering into agreements with its counterpart federal agencies, including the U.S. Geological Survey, the USGS Office of Minerals Information (formerly the U.S. Bureau of Mines), and the Bureau of Ocean Energy Management, Regulation and Enforcement (formerly the U. S. Minerals Management Service), and for administering all cooperative programs of the State with these agencies. The DGS also works with many in-state and out-of-state partner agencies and organizations.
First Geologic Map (Statewide Generalized Geologic Map)
- Appalachian Piedmont
- Atlantic Coastal Plain
- bedrock
- Cheswold aquifer
- Columbia Formation
- cross-sections
- Delaware
- Frederica aquifer
- geology
- groundwater
- Hornerstown Formation
- hydrogeology
- Magothy Formation
- Manokin aquifer
- mapping
- Matawan Formation
- Monmouth Formation
- Nanjemoy Formation
- Pamunkey Formation
- Piney Point aquifer
- Pocomoke aquifer
- Potomac Formation
- Rancocas Formation
- subsurface
- Vincentown Formation



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