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.
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.
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.
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.
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 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 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.
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).