Assessing Potential Impacts of a Wastewater Rapid Infiltration Basin System on Groundwater Quality: A Delaware Case Study
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
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.
Data and Graphs of Water Level Summaries for Wells with 20+ Years or 100+ Observations
Ground-water 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 ground-water levels for evaluation of trends. Table contains summary data from wells having 100 or more water level observations.
- aquifer
- Cheswold aquifer
- Cockeysville aquifer
- Columbia aquifer
- Delaware
- Federalsburg aquifer
- Frederica aquifer
- groundwater
- instrumented borehole
- Kent County
- Magothy aquifer
- Manokin aquifer
- Mount Laurel aquifer
- New Castle County
- Piney Point aquifer
- Pocomoke aquifer
- Potomac aquifer
- Rancocas aquifer
- Sussex County
- TAB
- wells
- Wissahickon aquifer
- Interactive
Water Level Summaries for DGS Index Wells
Groundwater levels are basic information needed for evaluating water conditions and for basic and applied research. For these efforts, water levels from various aquifers are being measured statewide. Some wells are measured for specific reasons, such as for the Coastal Aquifers Salinity Project and the Water Conditions Report, while other wells are measured so that staff can maintain long-term records of groundwater levels for evaluation of trends.
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
Delaware Groundwater Monitoring Network - Planning for Sustainable Future Groundwater Supplies
Delaware Groundwater Monitoring Network
- aquifer
- Cheswold aquifer
- Cockeysville aquifer
- Columbia aquifer
- Delaware
- environmental monitoring
- Frederica aquifer
- groundwater
- Magothy aquifer
- Manokin aquifer
- Mount Laurel aquifer
- Piney Point aquifer
- Pocomoke aquifer
- Potomac aquifer
- Rancocas aquifer
- unconfined aquifer
- water resources
- Water Table Aquifer
- wells



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