Field reconnaissance, geologic mapping, and photogeologic interpretations aided collectively in the identification of 30 potential high-yield well sites in the crystalline rocks of Delaware's western Piedmont. Fracture traces discernable on panchromatic and color infrared photography were identified in the study area. Well locations were selected on individual traces and on fracture trace intersections. Six test wells averaging 468.5 feet in depth were drilled at selected sites. Test analyses indicate that production wells at these sites would have a combined potential estimated at 1.0 to 1.1 million gallons per day of water. A thorough knowledge of the hydrogeologic framework is key to successful ground-water exploration and development. Subsurface fracturing is of prime importance in governing the water-yielding properties in the crystalline rocks. The surface traces of vertical or near-vertical zones of subsurface rock fracture were identified and used as an aid in high-capacity well siting.
Emphasis is placed herein on the years of Dr. Groot's leadership of the Survey. The remarkable work of James C. Booth in the last century is acknowledged but has elsewhere been entered in history. Some continuing activities of the Survey after 1969 are noted together with comments of an experienced observer; this current period may someday receive the attention of a recorder having the enhanced perspective of time.
The results of an intensive ground-water study on University of Delaware lands in the Newark area revealed additional sources of available ground water. Geophysical techniques, air-photo interpretation, studies of existing data, field mapping, test drilling, and pump tests were used as the bases for guiding additional well development. The study, conducted by the Delaware Geological Survey, was a cooperative effort between the University of Delaware and the City of Newark in response to mutual water supply problems. A potential ground-water yield of about 500 gpm was discovered on the University Laird Tract in the Piedmont Province. Ground water available from other locations in the Coastal Plain portion of the study area may total about 175 gpm. However, careful well development and proper well spacing will be necessary to obtain optimum yields.
This report deals with fluctuations in nine observation wells during the period 1960 - 1966. These wells are part of a state-wide ground-water monitoring network and are located in areas of little or no pumping. Eight of the wells respond to water-table conditions; the ninth well appears to reflect artesian conditions.
Although precipitation throughout Delaware was generally below average during the period covered by this report, annual average water levels declined very little in the wells reported on here. There is some evidence, however, for a lowering of water-table levels by three to four feet during the period 1960 - 1962.
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.