Mapping was conducted using field maps at a scale of 1:12,000 with 2-ft contours. Stratigraphic boundaries drawn at topographic breaks reflect detailed mapping using contours not shown on this map. Most stratigraphic units mapped in stream valleys are projected from subsurface data. Except for a few erosional bluffs, these units are covered by colluvium. This map supersedes Geology of the Middletown-Odessa Area, Delaware: Delaware Geological Survey Geologic Map Series No. 2 (Pickett and Spoljaric, 1971).
Delaware Geological Survey improving groundwater monitoring efforts with new wells, sampling. Scientists are digging for answers about the amount and quality of water available underground in central Delaware, where ongoing development will put increasing demands on water supplies in the coming decade.
The Delaware Geological Survey (DGS) is installing 7,700 feet of wells at eight sites in southern New Castle and northern Kent counties to improve groundwater-monitoring efforts, supported by a $600,000 grant from the Delaware Department of Natural Resources and Environmental Control (DNREC). Groundwater is the primary source of drinking water south of the Chesapeake and Delaware Canal, and populations there are projected to continue expanding.
The complex geologic history of the surficial units of the Harbeson Quadrangle is one of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition related to sea-level fluctuations during the Pleistocene. The geology is further complicated by periglacial activity that produced dune deposits and Carolina Bays scattered throughout the map area.
In 2000, A. Scott Andres, a senior scientist and hydrologist with the Delaware Geological Survey, released findings that disclosed a unique formation at the swamp.
In geologic time, the swamp isn't that old.
It formed about 22,000 years ago in a fresh-water, cold-climate marsh and boreal forested swamp.
Organic matter started building up and a cold wind blew in silt, clay and sand from nearby dunes and surrounding high ground. More sediment washed in with runoff from streams.
Thin sheets of sand likely spread during times when the land thawed.
Conditions began to change about 10,000 years ago as the climate warmed, forming a temperate-forested swamp, bog and flood plain.
There was more erosion and movement of organic-rich sediment to the fresh-water swamp. Today, it's considered the northernmost Southern forest on the East Coast.
Fluvial sands of the subsurface Cretaceous Potomac Formation form a major aquifer system used by a growing population in the northern Coastal Plain of Delaware. The aquifer is extremely heterogeneous on the megascopic scale and connectivity of permeable fluvial units is poorly constrained. The formation is characterized by alluvial plain facies in the updip section where it contains potable water. While over 50 aquifer tests indicate high permeability, the formation is primarily composed of fine-grained silt and clay in overbank and interfluvial facies.
This study complements Delaware Geological Survey Bulletin No. 17 and deals exclusively with clays and clay-size minerals. The cored section at the location of Je32-04 has been subdivided into 25 clay zones on the basis of major changes in trends and degree of crystallinity of clay minerals. The composition of clay minerals varies from zone to zone. These clay minerals have been identified: kaolinite, berthierine, chlorite, illite, smectite, chlorite/smectite, illite/smectite, glauconite/smectite, and glauconite pellets.
The hydraulic properties of the Piney Point (Eocene) aquifer and overlying basal silt of the Chesapeake Group (Miocene) were determined by a 23-day aquifer test conducted at the Danner Farm Well Field of the City of Dover, Delaware. During the test, head changes were monitored continuously in the Piney Point aquifer, overlying Cheswold (Miocene) aquifer, and the intervening confining bed.
Forty-eight samples of Delaware clays were collected and tested jointly by the Delaware Geological Survey and the U. S. Bureau of Mines. Clays potentially useful for face brick are common. The nonmarine Cretaceous Potomac Formation is a potential economic clay at virtually all locations sampled. Some Miocene and Pleistocene clays are also possibilities for brick clays. Other Potomac clays are potential sources for glazed tile, sewer pipe, refractory brick, and stoneware.